Issue #17 - March 2021

Herpetoculturemagazine.com

erpetoculture agazine Issue #17 - March 2021

Creating Living Art With Frank Payne

Breeding Boiga cyanea

How It Works: Temperature -Dependent Sex Determination!

Jewels of the Amazon: The Collared Tree Breaking Down Runner Parthenogenesis

Palmetto Coast

Exotics

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-- On the Cover -Unquestionable Quality Justin Smith Colubrids - Chondros - & More fb.com/ld50photography Herpetoculturemagazine.com

This Issue...

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Copyright © 2021 by Herpetoculture Magazine all rights reserved.

This publication or any portion thereof may not be reproduced or used in any manner whatsoever without the express written permission of the publisher except for the use of brief quotations in a book review.

Seventeenth Edition www.herpetoculturemagazine.com Herpetoculture Magazine

Contributors Justin Smith - Publisher -

Billy Hunt - Publisher -

Phil Wolf - Executive Contributor -

Nipper Read - Executive Contributor -

Josh Hall - Contributor -

Paul Donovan - Contributor -

Jeremy Carroll - Contributor -

Frank Payne - Contributor -

Geoff Obst - Contributor -

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Herpetoculturemagazine.com

From The Publishers’ Desk Spring is upon us (well most of us…) which means it’s herping season! Every year I tell myself I’m going to get out and go herping more but this year I’m making a serious effort to do so. This brings back memories of some of the more interesting encounters and stories while I was out roaming the woods. For a while now I’ve wanted to do a regular piece on funny or even slightly scary herp trips so if you have any send them to herpetoculturemagazine@gmail.com! We hope everyone has a great and safe season both in your rooms and in the field! I have no doubt a lot of folks will be out looking for herps since we’ve all spent so much time stuck inside! With that in mind, enjoy issue 17 of HM! - Justin

Justin Smith & Billy Hunt -Publishers-

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QUALITY BUILT.

FAMILY OWNED.

BLACKBOXCAGES.COM

Do you prefer black or white cages and racks and why?

“I like white because it helps the room feel more open. Though white exterior with black interior would be perfect.” Miguel Villa

“White reflects the light better within the enclosure and brightens the reptile room up a bit” - Justin Milewczik

“White, it displays the snakes better and makes for a brighter, cleaner look. Many folks don't like the discoloration from the protein waste. The black enclosures also are discolored by the urates." - Howard Redding Herpetoculture Magazine

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The Wonderful

Aliens:

Time with Boiga cyanea

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by Justin Smith

It was the fall of 2018. At this point, I had decided to shift my focus back to snakes as I slowly started selling my collection of Crested and Gargoyle geckos. Chondros were a big part of the focus, as well as some other snake species, but I was looking for something different. At the time, several Boiga popped up for sale. As a kid (and even an adult) that genus had always caught my eye. I knew they had, historically, been considered a little tough to acclimate, especially the mangrove snakes due to their importation in large numbers. But one species I saw for sale were Boiga cyanea and captive bred neonates at that. I got a pair and within several days I opened a box with some green headed worms and with them, a new obsession.

I was given a heads up that it was very likely the pair would go off food for a while which meant I’d be assist feeding mouse tails until they decided to take to pinkies again. Sure enough, the seller was right. In dealing with that original pair and the neonates I’ve hatched recently (more on that later), I think it is safe to say that assist feeding should be expected with neonates of this species and some others in the genus. At the time I hadn’t had any experience assist feeding tails but in no time I was getting tails into my pair regularly without any issues. This “trial by fire” has come to be extremely helpful even outside of cyanea neonates.

A few weeks passed and both animals had gone back to eating pinkies with no problems. Unfortunately, the male of the pair started going downhill and eventually passed but the female was doing flawlessly. It wasn’t until June of 2019 that I managed to get my hands on another male. This one was a little bigger, a subadult import that was established and doing great.

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Keeping These Aliens Before I get into pairing, it’s probably wise to give a quick rundown of how I’m keeping the adults. A few years ago I came across these great sterilite brand tubs that are 200 quarts (50 gallons) with nice, snug lids. I outfitted these tubs with a Python Portal from Specialty Enclosure Designs, a hide on the ground, a mounted removable hide (also from S3D), a 28 watt radiant heat panel on the opposite end, and a manzanita perch typically used for birds. I also offer a nice, large water bowl which helps keep humidity high. Under the heat panel I also offer a tub perch from S3D with ½” pvc legs to raise the platform up about mid-height of the tub that gives them a nice spot to bask under the heat. Finally, the tubs are really packed with fake foliage to give them plenty of visual barriers and security.

As neonates they can be a little tricky to get eating regularly.

They come out of the egg incredibly small which I believe is a good indicator that they’re likely to be eating mainly small frogs and lizards in their native range. Once they come around to eating small pinkies, they are usually eager feeders from that point on. But more on getting them there later!

My adult female rarely refuses food unless she is in a shed cycle. As for the males, it isn’t uncommon for them to refuse food for periods of time but I find that if I offer them a cup with 3 or 4 live fuzzies in it, they magically disappear.

Oftentimes I just leave a frozen thawed mouse in the mouth of the mounted hide and they handle the rest.

Pairing We’re now in mid-June of 2020. I noticed my friend, Matt McDowell, had some Boiga producing and that the female was a similar size to my female. After some consideration and doing some research, I came to the conclusion that she was at a healthy weight to be paired. So I put my male in with her but wasn’t really expecting anything to come of it.

Within 15 minutes they were locked! My male went straight to work pursuing her and wasted no time making it happen.

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It should come as no surprise that this species isn’t likely to spend much time in the ground hide. However, they absolutely love the mounted hides and spend a large amount of time in them! A majority of the time I see my female out under the heat panel not long after lightsout. My male is a bit more secretive but does cruise some nights.

Something interesting to note here is when they were locked I noticed the female had some serious swelling right before the cloaca. My first reaction when I saw this was “oh no she’s impacted…” Then I wondered if I was going crazy because I was sure I didn’t see it before he went in since it was so obvious. But did I? I coaxed them into separating, tubed the female and inspected her. Nothing. The mysterious swelling had disappeared. I then gave them the next night or two off to make sure I REALLY wasn’t seeing things.

Humidity isn’t an issue here in the Southeast U.S. but the oversized water bow is a big help in keeping the air thick. The heat panels are hooked up to a thermostat that is set at 85F and they do great.

Occasionally, the panels get unplugged by the snakes causing temps to dip into the upper 70s but, once again, they seem to do fine if things get a little cooler with no problems.

Why this was strange is because I’ve never seen this kind of swelling before in any species when they are locked up. I was very confused and decided to get back on google and see what I could dig up. I ended up finding a post on an old Boiga forum from 2010 or 2011 that showed the same copulatory swelling and breathed a sigh of relief. Upon the second introduction of the pair, there was some interest and a few more locks. After a few days it was obvious they had taken a break so I separated them once more.

A little over a month later (late July) it was clear that the female was gravid and going into a shed cycle. In the beginning of August, she went through her pre-lay shed and 2 weeks later dropped a clutch of 9 pearly white eggs! Her lay box was a standard tupperware container with damp sphagnum moss that I put in with her after her pre-lay shed. Before she dropped the clutch, I noticed she would pace a lot more while also going in and out of the lay box regularly. Personally, I like to put a lay box in earlier rather than later so the females can familiarize themselves with it. I also pulled out her water bowl a few days before I expected eggs just in case she decided that would be a better place for the clutch!

The Long Wait The hardest part of this whole process with breeding cyanea (or Boiga in general) is the long, long wait for incubation! I needed some information on the best way to incubate the clutch so I coupled my google searches with talking to Chris Lgwrd in Europe since Boiga overall has a larger following there than here in the States. He recommended that I use an egg box that is roughly 3 quarts in size on top of light diffuser over a medium like pearlite (I use and love aquatic plant soil) with a bit of damp sphagnum moss to the side. I added a very small hole in each corner of the lid of the tub to offer a little ventilation but still keep humidity high.

As for temps, Chris recommended day temps of 82F with a night drop to 78F. Whether the insulation of my former wine cooler turned incubator actually dropped down to that 78 for any extended period of time at night, I’m not sure, but the eggs looked healthy throughout incubation. I really loved this method of incubation because it kept the egg box humid but the eggs themselves were dry which is ideal.

It wasn’t until December 1st that the eggs hatched, a total of 114 days! I noticed the first neonate had pipped which I then gently cut the rest of the clutch. One thing that I found very interesting was just how thick the egg shells were. Compared to other species I have bred previously, these shells seemed abnormally tough. However, after talking to some other people who have produced Boiga, this seems to be a normal thing.

It took 4 or 5 days for most of the neonates to make their way out of the egg. Unfortunately, there were a few that were full term but either died before they were to hatch or simply drowned in the albumin after cutting. I lost 3 this way and then lost 3 more after they had come out for reasons unknown. Where I think I went wrong was the egg box I used for this clutch. It had an opaque lid which meant to check on the eggs, I had to open the box and the main chamber of the incubator. My female laid a second clutch about a month after the first batch hatched.

With that clutch I switched to a small gasket box with the same set up inside as the first. The difference here is I can use a flashlight to check

The mystery swelling that is common when breeding Boiga

The first egg box (above) and the improved one (below)

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on things, see the level of condensation, and not have to open the incubator as often, keeping things more stable.

Whether this will make a difference or not? Time will tell as that clutch is still incubating.

I set up the neonates in a 6 quart tub in a rack with some perches from S3D, water, and a hide on paper towel. Since I’m not in and out of my room constantly I opted not to add some fake foliage. One of the most important parts when it comes to neonates is keeping them hydrated and humidity high so their first shed is easy on them. I mist mine and let the tub dry out until I mist it again. Since they are colubrids, they can be messy so making sure the paper towel is changed regularly will help prevent mold from growing and causing problems.

Neonates are the hardest part of breeding this species. As mentioned before, they don’t always take to pinkies from the start so expect to either be scenting or assist feeding mouse tails. I offered food before their first shed and had no takers. With this second clutch I’ll be waiting until after their first shed to offer anything since they seem to have no interest in food in that time anyway. Assist feeding tails, in my opinion, is the simplest and less stressful option if you have neonates refusing their first or second meal. While tails may not be as nutrient filled as assist feeding whole day-old pinkies or pinkie heads, I think it’s better to get a tail in them in under 30 seconds than to tease feed for several minutes. I still offer pinkies and if they don’t eat them via drop feeding then they get a tail and I repeat this process until they decide to start eating whole pinkies on their own. This process usually only takes a few weeks.

Conclusion This piece is by no means an expert guide on breeding Boiga cyanea but simply my experience with my first clutch.

Overall I found this species to be extremely easy to breed with the challenges coming once neonates are out. The Boiga genus really is a great and interesting group of snakes that I wish had a bit more of a following here in the U.S. but at the same time they aren’t a group that is for everyone. I very much look forward to breeding my cyanea again later this year and getting more species of the genus!

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Book Review: Anaconda The Secret Life of the World's Largest Snake

by Jesus A. Rivas Review by Geoff Obst Jesus Rivas, a South American herpetologist and leading expert on all things anaconda, gives us a second book on these giant snakes. Through a tremendous amount of dedication he spent years wading, barefoot, through murky swamps riddled with leeches. As he was looking for and tracking these giants, playing a very scary game of what did I just step on?

A caiman? An Anaconda? or maybe something else? So not only is this book informative on the natural history of Anacondas in Los Llanos but it's also an entertaining story of Jesus' time spent there.

Jesus covers many Anaconda focused topics such as biology, behavior, demography, their reproductive habits, and diet. A few interesting points that stood out to me were when he explained the variance in the diet among male and female Anacondas or how they deal with injuries and infection by basking in the sun.

This is definitely more than just a book on Anaconda natural history; it's a personal account of his time spent in Los Llanos. From befriending a wild dog, all the way to having his hands full of breeder male anacondas while having a journalist catch the feces of one of the males that was actively defecating and shoving it in his pocket so as to not miss the opportunity to collect the data! It’s safe to say this man is dedicated. If the brave, and often humorous, stories that Jesus tells you along the way don't get you to love this book then the stunning photos definitely will.

I absolutely loved this book, partly because it read like one big herping trip journey filled with tons of scientific information. Overall, Jesus does a fantastic job of educating you and keeping you engaged throughout the ride. I can't recommend this book enough whether you work with these stunning creatures on a professional level or you're just an avid hobbyist.

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Creating

Living

Art

An Interview 11

With Frank Payne

This issue, we talk to Frank Payne of Living Art

by Frank Payne about his endeavors into some of the less popular and lesser known species of lizards he currently works with!

HM: What was your initial draw to lizards that drove you to primarily focus on them?

FP: I’m originally from Texas and I spent the early part of my childhood and every summer there. I think my interest in reptiles began with the fact that there were so many anoles and geckos in my backyard for me to watch and catch. My dad was also a big aquarium enthusiast and the one shop we went into regularly in Houston also occasionally had reptiles. The first time I saw a large planted terrarium full of chameleons in that shop, I was hooked forever. It’s cliche, but that day is literally ingrained in my mind forever, even though it was nearly thirty years ago. It had that much of an impact on me.

I love snakes and other reptiles, but the diversity of features and behaviors in lizards cannot be matched in my mind.

HM: How many species are you working with currently?

FP: I am breeding or working on breeding around ten species at the moment. My main projects are the electric blue gecko (Lygodactylus williamsi), carpet chameleons (Furcifer lateralis), lesser chameleons (Furcifer minor), Northern blue tongue skinks (Tiliqua scincoides intermedia), and jeweled lacertas (Timon lepidus). I am also working with spotted flying lizards (Draco maculatus), spearpoint leaf tail geckos (Uroplatus ebenaui), Peter’s banded skinks (Scincopus fasciatus), rough knob tailed geckos (Nephrurus amyae), and gargoyle geckos (Rhacodactylus auriculatus). I do have a few other odds and ends, but I try to limit that these days and only keep that which I plan to breed over multiple generations.

babies often fail to thrive. Based on my conversations with the one other breeder of Draco in the states, my problem may be as simple as diet. His babies do not readily accept fruit flies, but do well on pinhead crickets. His survival rate of captive bred babies is much better than mine. I will make that adjustment for future clutches. At the time of this article, I have two gravid females.

I have not produced any of the Peter’s banded skinks yet, although I still feel as if I’m in early stages with them. As far as I’m aware, no one has produced them in the USA and only two people have done so worldwide. I find sexing these animals to be extremely problematic and I think that people generally can’t sex them accurately despite claims to the contrary. I have a feeling they will become more straightforward to breed once accurate sexing is more common and seasonal cycling is provided. We’ll see. I could be eating those words five years from now.

HM: Which species has proven to be the most challenging?

FP: I have produced hundreds of carpet and minor chameleons, but they still throw curveballs in the breeding process. Females, especially of Furcifer minor, can be very delicate when gravid and going through the egg laying process.

The flying lizards have proven surprisingly easy to keep and breed, but raising the babies has been a real challenge. I do have babies that I produced nearing half grown, but my success rate at raising babies is still very low. On the other hand, my success rate with wild caught adults has been very high. The adults mate, lay eggs, and the babies hatch without difficulty; but the

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HM: How did you come to get into the flying lizards?

FP: I have always been attracted to working with species that haven’t been figured out yet, at least not on a large scale. Keeping the Draco was pretty coincidental. I was at a reptile show outside Baltimore and saw a large group of them that actually looked to be in decent shape. It seemed like a good opportunity to give that genus a real shot. Since I am a long time chameleon keeper, I feel very comfortable acclimating wild caught, delicate, arboreal lizards.

HM: Do you see those getting easier to keep as more captive bred generations come about?

FP: That’s definitely hard to say, but I do think they will.

Speaking with the one other current breeder in the states it seems that, when done correctly, captive bred babies are very hardy. In my experience, once wild caught and captive bred babies are well established they are very hardy and straightforward to keep. They will never be a beginner species, but I don’t find them to be any more difficult than chameleons.

HM: Out of all the chameleon species out there, why carpet chameleons?

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FP: Carpet chameleons are easily my favorite species of chameleon. I could go on about them for pages, but I will try to contain myself. They tick so many boxes that I think they should be the most popular pet chameleon species bar none. First, they’re extremely colorful- easily one of the most variable and beautiful of all animal species. Their small size makes them perfect terrarium inhabitants. An adult animal can live its whole life comfortably in an eighteen inch cube glass terrarium, which can be beautifully planted. That small size equates to less space needed, and therefore less money spent on enclosures, lighting, and feeders. As captive bred, they are just as hardy as any other chameleon species out there. They are extremely prolific and make for a very rewarding breeding project. Carpets can be sexually mature in as little as three to six months! Males can breed without problem as soon as ready, but I never breed females before six months. People often cite the short lifespan of carpets (3 years) as being a draw back to the species, but my good friend and fellow carpet chameleon breeder Tim Marks, pointed out that this is how long hamsters live and they are one of the most popular pets in the world!

Also, based on conversations with other keepers around the world, it seems their lifespan can be significantly prolonged (5 years or more) if they are kept cooler, fed less, and not bred too often. Basically keep them more like crested geckos and as a pet (not breeding) and they will live longer!

HM: Were those ever popular? I don’t recall seeing many for sale on a regular basis.

FP: I think they’ve always been popular as far as chameleons go, but only as wild caught. Thousands have been imported into the states. Unfortunately, pretty much only one person, my good friend Kevin Stanford, took them seriously and put the effort into breeding them over multiple generations. Kevin was very successful breeding them, producing up to two hundred a year for a while, but he was basically the only one doing it. After getting captive bred carpets from Kevin as well as some wild caught lines of my own, I recognized their untapped potential in the hobby and made a point to get as much exposure on them as possible. It seems that I’ve been at least somewhat successful doing that and I hope to push their popularity even further.

HM: What advice would you give to someone who has an interest in a species that doesn’t have a lot of info or other people working with it?

FP: First, I would say to make sure that you have enough experience to take on something like that. I think it’s very important that keepers first become proficient at keeping and breeding more commonly kept species before attempting something that is more of an unknown quantity. I’ve found that the experience gained and the best practices learned from keeping more commonly kept species translates surprisingly well to less common species. After gaining experience with more common species, researching the species’ natural habitat and niche as much as possible is extremely important when taking on something less common. So much of the animal’s health and ability to thrive depends on the keeper imitating its natural habitat as closely as possible. There’s tons of weather data out there, and Google scholar can be your friend finding papers on similar species or genera.

"It seemed like a good opportunity to give that genus a real shot. Since I am a long time chameleon keeper, I feel very comfortable acclimating wild caught, delicate, arboreal lizards."

HM: Last question, what do you wish there was more of in the hobby? Whether it’s a species, a mentality, a way of keeping, what would it be?

FP: There’s definitely a lot I would like to see changed, but I think the thing that is most personal to me is to see people focus more. I have been as guilty as anyone of wanting two of everything, but I have found the most fulfillment from working with at least ten individuals of a species and breeding them generation after generation. The more individuals you have of a species and the more generations that you have produced, the more you will know about them. I have been keeping and breeding chameleons for most of my life, but I still learn more every single year. The reason I keep learning more each year is because I am seeing their entire life cycle play out time and time again. If I was simply keeping two at a time, I wouldn’t know a fraction of what I do. I really can’t emphasize enough how rewarding that is. It doesn’t even have to be a rare species, it can be leopard geckos or ball pythons, but pick one species that you are truly passionate about and stick with them.

HM: Do you think more people should pursue some of these species that haven’t had a lot of attention in collections?

FP: I definitely do. Reptilia is an extremely diverse class of life, and as keepers we still have access to a large diversity of species. I don’t think that’s going to last. We have seen it in the trade many times already that once commonly imported species become restricted, they disappear from the trade. This will only increase as time goes on. If it does, the diversity of captive collections and the knowledge gained from that diversity will bottleneck.

It only takes one or two devoted individuals to keep a niche species going in the trade. I can speak from experience that the knowledge and even reputation gained from doing this is invaluable.

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Specializing in Morelia & Old World Ratsnakes.

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uwabamireptiles.com @uwabamireptiles Herpetoculturemagazine.com

Herpetoculture Magazine

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Unlocking the Mystery of

Parthenogenesis

Over the past few issues, I have covered reproduction in scorpions, spiders and insects. This month I want to look at a rather unusual mode of reproduction; so-called ‘virgin births’. This is where a female can give birth to offspring without the intervention, or genetic contribution of a male. This we call asexual reproduction, or parthenogenesis.

With Paul Donovan

Parthenogenesis was first discovered by the naturalist and philosopher, Charles Bonnet, in 1740. Bonnet was studying aphids and observed how females could give birth without being mated, giving it the name virgin birth. Further observations discovered the trait in drone bees, silkworm moths and bagworm moths. It was not until the 1840s that the phenomena was given the name ‘parthenogenesis’.

In simple terms, parthenogenesis is defined as ‘the ability of an unfertilised ovum to produce a fully functional adult’. In other words, at cellular level, the difference between parthenogenesis and sexuals, is that in the latter, meiosis (cell division) is followed by fusion of a male and female gamete. In parthenogenesis, meiosis is changed so that only one particular set of chromosomes is transferred in a non-random fashion. This can lead to one hypothesising that unisex populations are literally producing virgin clones of themselves, but this is not the case; I will come back to this in a moment. A species can be obligate parthenogenic (reproduce exclusively through asexual reproduction) or, facultative (can switch between asexual, and sexual [requiring a male] reproduction).

Parthenogenesis has only ever been reported in several species of fish, amphibians, some species of reptiles, but it is widespread in the invertebrate world. Interestingly, in the order Hymenoptera (wasps, bees, sawflies and ants), a male is born from unfertilised eggs, and females from fertilised eggs, a process called arrhenotoky.

As hobbyists, the one group of insects which display high levels of parthenogenesis, are the stick insects (Phasmatodea). Although phasmids are often regarded as being obligately parthenogenic, the greater majority show high levels of facultative reproduction.

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How did parthenogenesis evolve?

Although little is known of the origins of parthenogenesis, the ancestors of parthenogenetic species were unquestionably sexual ones, and must have come about as a result of genetic instabilities which accompanied the interference of foreign chromosomes. According to one study “all vertebrate parthenogens appear to have arisen from interspecific hybridisation, as shown by studies of chromosomes, protein variation, and DNA sequences''.

That being said, there is a chain of thought that parthenogenesis can occur without hybridisation. One of these is induced thelytoky (unfertilised eggs develop into females).

Intracellular bacteria in the genera Rickettsia, Wolbachia and Cardinium, can induce thelytoky in a number of insect species.

In other words, some bacteria can influence parthenogenesis, and every year strains are being found which can cause this.

Geographical distribution

ZW sex-determination system, the offspring will be male. As a consequence, some parthenogenetic species may be able to regulate the ratio of males to females in the group.

The question now arises, are asexually produced offspring, weaker than sexually produced offspring due to the lack of genetic variability? Much would seem to depend on the species. If a facultative species breeds sexually in the wild, subsequent offspring, due to variable genetic input, will be strong over several generations. If that same species were to be then be restricted to asexual reproduction, theoretically, due to the lack of genetic input, this would influence the strength of the offspring over a similar period, or the eggs viability during development.

A classic example which illustrates this, is the Giant Prickly Stick Insect, or Macleay's Spectre, Extatosoma tiaratum.

Females produced over several generations will result in smaller, weaker individuals. Whereas if a male mates with a female, the offspring show higher levels of strength and size.

A lot of parthenogenetic species are island forms, and that a single female, or an egg from a female that finds its way onto an island, may give rise to an entirely new colony. A good example of this is a species of New Zealand stick insect which found its way on the Isles of Scilly, where they are now thriving as an all-female colony. Parthenogenesis may also have allowed some species to have expanded their range, and become dominant over other forms, simply because males are not required for reproduction.

Is it like cloning?

One could be forgiven for thinking that as a female is giving birth to young without the intervention of a male, she is effectively producing clones of herself. But that is not the case.

Parthenogenesis is a true form of reproduction, giving rise to genetically variable young based on the genetic material contained within the egg. Furthermore, as the genetic coding comes from a single individual, and not the combination of two parents, the offspring show genetic stability. It is this genetic stability which has allowed species to optimise the environment in which they live, by not introducing genes which would not be optimally suited to it.

The inheritance and subsequent duplication of the genes, involves only a single sex chromosome, meaning the unfertilised egg can be either male or female depending on the chromosome arrangement of that species; XY sexdetermination system, the offspring will be female, and in

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Genetic input can influence the strength of the offspring

"One could be forgiven for thinking that as a female is giving birth to young without the intervention of a male, she is effectively producing clones of herself. But that is not the case. "

Why in some species and not in others?

Parthenogenesis can be inherently important in populations of animals which are isolated from one another, or where sexes are isolated. It reduces the females need to rely on a male for reproduction, and limits the amount of time she expends in energy searching for one. It also ensures in isolated species, that they will not suffer as a consequence of low male numbers, or weak males, as producing only females (except in lizards and snakes where parthenogenesis produces only males) bolsters population numbers. Each female is capable of contributing to the next generation ensuring population numbers remain stable or at higher levels than species whose reproduction produces both males and females. Such females are also better placed to recover from natural disasters more quickly. In this respect, parthenogenetic reproduction offers distinct advantages.

Phasmids are often regarded as being obligate parthenogenic, but the greater majority show high levels of facultative reproduction

Parthenogenesis was discovered in aphids in the mideighteenth century.

Of course parthenogenesis is not without its faults. We can see from the limited number of species which practice it, that it is not a desirable mode of reproduction. One of the biggest disadvantages, is that it limits genetic diversity that would otherwise occur from the input of a female mating with different males. This allows a species to strengthen individual traits in the long term, which are advantageous to adapting to specific biological changes.

Are males ever needed?

As I have mentioned, some parthenogenic species have the ability to switch between asexual and sexual reproduction.

Although many species of stick insects, for example, have negated the need for males entirely, (males have never been found in some species), others do produce males, albeit on a limited scale. What is interesting, is how some species can exhibit asexual or sexual reproduction depending on whether they are in the wild, or in captivity. From the few studies which have been undertaken, those species which are obligate parthenogenic reproduce sexually, producing both males and females; if kept in captivity they show high levels of facultative asexual reproduction.

So-called virgin births are observed in bagworm moths \

It is difficult to say why this should be, but having worked in zoological collections, and now work with invertebrates and reptiles in their natural habitats, I am of the strong opinion, that many of the behaviours exhibited by captive individuals are borne from the constraints of being kept in captivity, and are not a true representation of how they function in the wild. In other words, those behaviours we see in captivity are artificial.

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Parthogenesis in Reptiles Parthenogenesis is widespread through the insect order, but reproduction solely through obligate parthenogenesis is only limited to a few species of reptiles - predominantly lizards.

That being said, in the absence of males, it is uncertain how many reptilian species are capable of facultative reproduction.

It may be more widespread than we are currently aware of.

Amongst the most notable reptiles to exhibit parthenogenesis are the Caucasian rock lizards of the genus Lacerta, and Whiptail lizards in Cnemidophorus. There are between 13 and 15 species in this genus which are considered truly parthenogenetic.

Given that these lizards do not require the services of a male to produce young, they do show the need to engage in some sort of courtship to stimulate ovulation. And this is achieved in female-female stimulation. Two females will come together, where one assumes the role of the male. Although no penetration of any type will take place, the behaviour is necessary to induce ovulation.

be used as an advantage in island colonisation. A theory has been put forward, that this could enable a single female to have male offspring asexually, and then switch to sexual reproduction to maintain a higher level of genetic diversity than asexual reproduction alone could produce.

This could be an indication that these lizards are still evolving asexuality, but have yet to lose the courtship behaviour element, which is not present in fully fledged parthenogenetic species?

Two cases of parthenogenesis were reported in captive Komodo dragons in 2006. One was from Chester Zoo, and the other London zoo. Tests revealed their eggs had developed without being fertilised by sperm.

Quite a few gecko species have been reported to be parthenogenetic, including representatives of Heteronotia, Rhacodactylus, Lepidodactylus, Lepidophyma, Hemidactylus, Nactus and Hemiphyllodactylus. In a number of these species, as with Cnemidophorus, female-female courtship takes place.

The case of Komodos Watts, in 2006, reported a case of a Komodo dragon, Varanus komodoensis, showing asexual behavior. Unlike in other parthenogenetic species, where the offspring are females, this Komodos’ offspring were male. This is because Komodo dragons use the W and Z chromosomes; females have one W and one Z, males have two Zs. The egg from the female carries one chromosome, either a W or Z, and when parthenogenesis takes place, either the W or Z is duplicated. This means the eggs are WW or ZZ. WW eggs are not viable, but ZZ eggs are, meaning only males are born.

There is an intriguing hypothesis behind why only males are born as a result of asexual reproduction, and that is, it may

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Partho in other groups Parthenogenesis has been reported in the Brahminy Blind snake Ramphotyphlops braminus from Africa, Asia and other regions.

While this is the only known obligate parthenogenetic snake species, I personally believe there is a lot of scope for other burrowing species to exhibit this trait as well. When one thinks, these snakes live in a rather alien environment, where the chances of finding one another to mate with are rather hit-or-miss.

Although pheromones must play a part in locating one another, there are strong reasons to assume parthenogenesis must be practiced more widely.

The only other snake, that I am aware of which has shown Parthenogenesis, is a Burmese python, Python bivittatus, from Artis Zoo in Amsterdam. Over a period of five consecutive years from 1997 up to 2002, this individual produced viable eggs containing embryos, despite having no interaction with a male. As with the Komodo dragon, because of the W and Z chromosome relationship, all offspring were male.

Parthenogenesis has been recorded in a number of amphibians, including, frogs, caecilians and salamanders. In fact, when we

begin to trace back the origins of vertebrate parthenogenesis, using molecular analysis, it was first seen in salamanders dating to the Pliocene 3.9-5 million years ago, making them the oldest known parthenogenetic animals.

Evidence points towards parthenogenesis occurring in amphibians as a result of hybridisation between two closely related species. For example, Ambystoma jeffersonianum, Ambystoma tigrinum, and Ambystoma texanum are recognised as the hybridisation pool from which all unisexual salamanders within the genus originated. Although many amphibian species may reproduce parthenogenetically, in response to environmental cues they may then begin to produce both male and female offspring which reproduce sexually.

Parthenogenesis has been witnessed in a number of spider species, including Theotima, Steatoda, Heteroonops and Triaeris, and scorpion species. In those species where parthenogenesis is practiced, the presence of males may be non-existent, as is the case with Tityus serrulatus. However, this is not the case with all parthenogenetic species. What's more, parthenogenesis can even vary depending on an individual species’ range. Throughout the Asian distribution range of Liocheles australasiae males are not evident, but through their Australian range, males can be encountered, albeit infrequently. Furthermore, it has been discovered that some populations of this scorpion produce only females when a male is not present. This may be an indication that the male is beginning to evolve or, is in the final stages of becoming totally redundant.

Although reproduction via parthenogenesis is known in a number of scorpion species, its true extent has still not been fully investigated. It may turn out to be more widespread than we first thought.

Final Thoughts Understanding parthenogenesis can give us a great insight into the adaptive laws of genetics, detailing where they may be postponed or overthrown. As insects have short life cycles, any changes in gene activity will become evident within a few generations. This is why they are great study tools for many areas of research. Given that the role parthenogenesis has played in certain island species establishing themselves, it is obvious that it has played an important role is evolution. It has also enabled species to adapt their reproductive habits to certain environmental conditions.

Further Reading Further reading.

Bogart, J.P.; Licht, L.E. (1986). "Reproduction and the origins of polyploids in hybrid salamanders of the genus Ambystoma".

Canadian Journal of Genetics and Cytology. 28 (4): 605–617.

Highfield, R. 2006. No sex please, we’re lizards. Daily Telegraph. Retrieved July 28, 2007.

Judson, O. 2002. Dr. Tatiana’s Sex Advice to All Creation: The Definitive Guide to the Evolutionary Biology of Sex. New York: Metropolitan Books. ISBN 0805063315.

Purves, W., D. Sadava, G. Orians, and C. Heller. 2004. Life: The Science of Biology, 7th edition. Sunderland, MA: Sinauer. ISBN 0716766728.

Vitt, L. J. and J. P. Caldwell. 2008. Herpetology: An Introductory Biology of Amphibians and Reptiles, 3rd Ed. Academic Press, Burlington, Massachusetts Watts, P. C., et al. 2006. Parthenogenesis in Komodo dragons.

Nature 444: 1021.

Parthenogenesis may be more widespread in burrowing species than we are aware of.

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Photo >> Renato Gaiga

The Collared Tree Runner: The Jewel of the Amazon by Jeremy Carroll 21

If you take a walk in the rainforest of the Amazon for any given period of time while surveying the trees around you, you may find a jewel of the forest running along the bark catching insects and chasing each other around. This little lizard is known as the Collard Tree Runner (Plica plica). Plica are a member of a family of South American lizards known as Tropidurids. They are a little lizard with a lot of personality and are very intelligent. They are not seen much in the hobby and some zoos do keep them in their collections but they are often an overlooked species. Years ago, you could find these little lizards for about 25 dollars a pop and they bred just as easily.

They can be compared in appearance to the Collared Lizard (Crotaphytus sp.) from the American Southwest and the Blue Spiny Lizard (Sceloporus cyanogenys).

These lizards are in the genus Plica which is composed of 8 recognized species none of them not getting much bigger than a foot in length. The most common one that is seen in captivity is Plica plica. This species is differentiated from others in the group by the number of spines on the head and body (Harding). They are found in South America including the countries of Brazil, Ecuador, Peru, Venezuela, and Suriname.

They spend most of their time running up and down trees chasing each other and their insect prey. This species is sexually dimorphic in size with males getting about a foot long from head to tail and females about 8 inches give or take.

Males also have noticeable femoral pores. In the terrarium, they are fun to watch run around and interact with one another though males can be territorial to the point that the larger of the group will injure the others.

Plica In the Home Plica plica are a species that you do not often see in herp circles. My pair was one that I came across online from the late Ken Foose. A week later they were in the herp room. A small group of 1.2 in a large, zoo med type enclosure will be ok but go bigger and taller if possible. Bigger groups of 2.3 in a large enclosure would be something to see and will work as long as they have plenty of places to hide. The males can get aggressive to other males during territorial disputes and to females during the breeding season, sometimes stressing them to the point of death. If you do go this route, make sure each animal has enough space to get away if needed.

These animals are fast so be prepared to get a workout if one escapes on you! Make sure to give them lots of tree limbs and pieces of bark to climb around on. Give them a lizard highway that has branches going both vertically and horizontally.

Most of the time the animals will likely be hanging out on the horizontal branches. Try to stay away from thinner branches because they can be hard on the animals’ feet and might not give as much grip as larger branches would. These are not chameleons or geckos therefore their feet and legs are more geared towards running than gripping so they seem to have a hard time on smaller, more slender branches.. They also like to hide under bark so give them some hides on the ground and hides that are suspended off the ground if possible. They don’t spend much time on the ground but these, like all animals, should be given options to decide what they want to do and where.

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Photo >> Bernard Dupont

The only time you may see Plica grounded is when they are chasing food or if the females are laying eggs. You may also notice them on the ground if the temperatures are not to their liking. I put a layer of leaves and any cuttings from the plants on the ground because they not only provide a good egg laying medium for the females, but they also decompose and nourish the plants that are growing in the enclosure. Right now there are just Areca palms that seem to be thriving in my enclosure despite being jumped on and trampled upon by the animals.

The look of the leaves that have fallen from the plants looks natural as well and returns nourishment to the soil. When they are feeding, the Plica may grab some of the leaves and swallow them. If husbandry parameters are good these should be passed without a problem.

These lizards like a nice warm basking spot of about 100 degrees. Anything warmer than that and they try to avoid it.

They do like some sun so use a bulb like a 5.0 UV bulb to make sure these animals get their adequate amounts of UV. With that being said, they do like to have some shade since they live on the trunks of trees where they might not receive a lot of UV penetration so making sure they have a spot to go to get away is important. They will thermoregulate as they please if adequate places are given for them to do so.

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I feed the adults three times a week with adequate size crickets, mealworms, and superworms and dust every other feeding with a calcium supplement and once a month with herptivite.

They are eating machines and will eat as many insects that wander in front of them as they can. Pinkies have been offered but they showed no interest and just held onto them for a second before spitting them out.

After the female lays eggs, I up the supplementation a bit just to make sure the females don’t get hypocalcemia. It has been noticed that hatchlings are prone to deficiency so make sure they get adequate amounts of calcium. Usually it happens soon after they come out of the egg and are just starting to eat. As far as water goes a dish is provided but, for these guys, it is a learned behavior and most of the time they drink when being misted right before the lights go out. I try to keep the humidity levels at about 70% with misting and keep them hydrated.

Reproduction Breeding these animals is a fairly easy endeavour. There is not a big demand for Plica but they can sometimes be found for sale on classifieds around the herp community. They are a fun and interesting little lizard. They reach sexual maturity at about 2 years old but one should wait for the females to be a little bigger just to make sure they can handle egg laying. Egg laying is stressful to the female and can even shorten the life of the animal so making sure the female is ready before attempting this is vital with all reptiles and amphibians.

The males can be relentless in pursuing the females and as soon as she drops one clutch he will go and try to breed with her again. The females lay about 2 clutches of eggs a season which typically starts in the spring. Females lay about 3, maybe 4, eggs in a clutch and usually in the substrate usually under a log or piece of bark. They sometimes dig some false holes before digging the actual one but once she starts she will be laying them for a good part of the day.

Conclusion These little jewels of the amazon are cool little lizards that are rewarding to watch and a joy to keep. If you are looking for something that is not as commonly kept, you may want to look into these guys. They are intelligent as well, learning who their keeper is and running to them during feeding time. Watching them run along the branches of the enclosures and live their lives is not a bad way to spend the day. Some other keepers out there are keeping these as well so you may have a good chance of finding some captive bred animals which is the better way to go to avoid health issues. Thanks to Robert Mendyk for giving this a once over and the folks at Herpetoculture Magazine for the opportunity.

When the female does lay, you will notice that she will have a collapsed midsection which is usually a good sign that a gravid female has laid her eggs. Gestation period for the eggs is about 30 days and after laying the eggs take roughly 100 days for them to hatch at a temperature of 82 degrees Fahrenheit in an incubation medium of vermiculite at a ratio of 1:2 (vermiculite to water). Towards the end of incubation try not to bother the eggs much because when the eggs are disturbed the hatchlings tend to burst out of the egg. When this happens as opposed to hatching on their own the hatchlings are weaker and do not do as well. When they hatch they are about 4 inches and start off well on small crickets, mealworms, and fruit flies. Be ready to have lots of small bugs available for them. They grow fast so feed them daily. When they are about a year old you can cut back on how often you are offering food.

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Temperature-Dependent Sex Determination in Reptiles

By Josh Hall

In the 1960s, Madeline Charnier started incubating eggs of the African Rainbow Agama (Agama agama) at different temperatures in her lab at the University of Dakar, Senegal. She noticed the sex ratio of the hatchlings was altered by the incubation temperature and in 1966 published the first report of temperature-dependent sex determination (henceforth “TSD”) in a vertebrate.

This novel finding demonstrated that genetic sex determination (henceforth “GSD”) via chromosomes was not the only sex-determining mechanism in vertebrates. Subsequent study revealed that some fish and many reptiles have TSD including many lizards and turtles (but no snakes), the tuatara, and all crocodilians.

More than half a century has passed, and scientists across the globe are still working to understand the evolutionary and ecological importance of TSD as 25

well as the molecular mechanisms that regulate this fascinating trait. In this article, I aim to summarize some of what we have learned about TSD over the past 50 years with a focus on aspects that should be interesting and useful to herpetoculturists. I will explain some important terminology which is necessary to understand the scientific literature and facilitate conversations among hobbyists, professionals, and scientists. I will then describe how a TSD pattern can vary across populations and individuals within a species. This is important to consider when selectively breeding. I will describe how fluctuating (vs constant) temperatures can alter a TSD pattern and how TSD patterns result from the combination of multiple factors. Ultimately, my goal is to make it easier for hobbyists and professional herpetoculturists to read and evaluate the scientific literature concerning TSD in reptiles.

Some important terms First, we need to establish some basic definitions that come from the scientific literature. There are three currently recognized TSD patterns in reptiles (birds are technically reptiles, but when I say “reptiles” in this article, I am excluding birds).

- Pattern Ia TSD (also called MF for “Male-Female”) occurs when cool temperatures produce mostly males and warm temperatures produce mostly females.

- Pattern Ib TSD (also called FM for “Female-Male”) is the opposite of pattern Ia and cool temperatures produce females while warm temperatures produce males.

- Finally, pattern II TSD (also called FMF for “FemaleMale-Female”) occurs when relatively cool and warm temperatures produce females but intermediate temperatures produce males.

Figure 1 shows an example of a FMF pattern using data from the landmark experiment that described the full TSD pattern in leopard geckos (Eublepharis macularius) (Viets et al. 1993). The authors incubated eggs at a range of constant temperatures and examined the sex ratios of hatchlings. I will refer to this figure to explain some of the remaining definitions. The y-axis at left shows the percentage of hatchings that are male. The x-axis on the bottom shows the incubation temperatures. The black circles show the sex ratios from the temperatures used in the study, and the solid black line that connects the circles can be considered an estimate of the entire TSD pattern.

The temperatures that produce males and females differ among species (and within species). As such, we have several terms that refer to incubation temperatures. Some temperatures are called female-producing temperatures (or male-producing temperatures). These terms describe incubation temperatures that produce 100% females (or 100% males). In Figure 1, incubation temperatures of 26 - 28 °C are female-producing temperatures. Note that 35 °C is also a female-producing temperature and that, in this study, no male-producing temperature was discovered (i.e. no one temperature produced 100% males).

Indeed, many species that exhibit a FMF pattern have no male-producing temperatures. We may, however, refer to female-biased temperatures (or male-biased temperatures) which produce mostly (i.e. greater than 50%) females (or

Figure 1. The FMF (type II) TSD pattern of leopard geckos (Eublepharis macularius). This figure was produced using data from Viets et al. 1993.

The black circles show results from the incubation temperatures used in the study, the black line shows an estimate of the TSD pattern based on those data, and the horizontal gray line denotes a 50:50 sex ratio which can be used to define the pivitol temperatures.

mostly males) but not 100%. In Figure 1, temperatures between 28 and 30 °C are examples of female-biased temperatures and those between about 31 and 33 °C are examples of male-biased temperatures. Note that there are additional female-biased temperatures above 33 °C because this is a FMF pattern.

Finally, scientists often study and refer to pivotal temperatures (abbreviated “Tpiv”) which is the temperature that produces a balanced sex ratio (50% males and 50% females). In Figure 1, the gray broken line demonstrates a 50:50 sex ratio. The temperatures at which this line crosses the solid black line are the two Tpivs in this TSD pattern (~30.5 and 33.5 °C). Importantly, species with MF or FM TSD patterns will only have one Tpiv while those with a FMF, like leopard geckos, will have two Tpivs. The cooler Tpiv (30.5 °C) is the one that herpetoculturists usually think about because most eggs are incubated from 28-32 °C. There are two final terms that do not describe a temperature in the TSD pattern but are very important. The thermosensitive period is the time during embryonic development when temperature is able to determine sex. This is often the middle third of development; however, there is a lot of variation across reptiles with respect to the length of the thermosensitive period and how advanced the embryos are at the time that eggs are laid (Figure 2). We will compare turtles, crocodilians, and lizards to illustrate. Most lizards complete the first third of development inside the oviducts of the mother (i.e. before egg-laying; Figure 2).

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TSD Variation in a Species Population

Figure 2. The timing of egg-laying (black arrows) and the thermosensitive period (blue-shaded regions) for turtles, crocodilians, and lizards. For lizards, the thermosensitive period is shown for a skink (Bassiana duperreyi) and a gecko (Eublepharis macularius) to demonstrate variation within a major reptile group.

The gray-shaded regions indicate the percent of development that occurs inside the female before eggs are laid. This figure is adapted from Shine et al. 2007.

Therefore, the thermosensitive period usually starts at or very close to the time of oviposition (i.e. egg-laying).

Turtles and crocodilians, conversely, lay eggs when the embryo is at a very early developmental stage; therefore, the thermosensitive period for these groups does not start until several weeks after the eggs are laid. Therefore, to produce desired sex-ratios you must know both the TSD pattern and the thermosensitive period. Because temperature influences a diversity of traits in reptiles (e.g. coloration), many breeders take advantage of the thermosensitive period. For example, gecko breeders may incubate eggs at cooler temperatures initially to get females, but later move the eggs to a warmer incubator to brighten coloration.

Finally, you may see experimental studies refer to a splitclutch design. This is when researchers equally divide eggs from one clutch into different experimental treatments, like two temperature treatments. For a species that produces two eggs at a time, like most geckos, that would mean separating the two eggs from each clutch into the two treatments. This prevents confounding the effect of the treatment with maternal or genetic effects. As you will see in this article, the shape of the TSD pattern can differ among mating pairs for many reasons, so it is important to divide the eggs of each mating pair among treatments so that no one mating pair can heavily influence the results of a particular treatment.

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Biologists focus much of their research attention on variation (i.e. differences among species, among populations, and among individuals). The overall TSD pattern (i.e. MF vs FM vs FMF) is consistent within a species, but the exact temperatures that produce male- or female-biased sex ratios can differ between populations. Figure 3 shows an example of how the TSD pattern might differ among two populations. In this experiment (Ewert et al. 2005), the researchers incubated common snapping turtle eggs (Chelydra serpentina) at various temperatures.

The eggs came from six different populations across the species range in the USA. In Figure 3, the green line shows results for a population from Indiana and the pink line shows results from a population in Florida. Notice that the overall TSD pattern is consistent between the populations (FMF pattern), but the maleand female-biased temperatures and Tpivs differ significantly.

These population-level differences in the TSD pattern probably represent local adaptation via natural selection, but the evolutionary and ecological importance of such differences is still under investigation.

Figure 3. Differences in the TSD pattern of two snapping turtle (Chelydra serpentina) populations. The green line shows results from a population in Indiana and the pink line shows results for a population in Florida. Data were adapted from Ewert et al. 2005.

TSD Variation in Individuals in a Population The population-level differences in Figure 3 are intriguing, but they ultimately emerge from differences in the TSD pattern among individuals (i.e. among mating pairs). The TSD patterns shown in Figure 1 and Figure 3 result from incubating eggs from lots of male:female pairs at various temperatures and recording the resulting sex ratios.

Importantly, these patterns represent the average TSD pattern across all of the mating pairs. Each mating pair, however, results in a unique combination of factors, including genes, which may influence TSD, creating slight differences in the TSD pattern among pairs. To illustrate, we will consider how the lower Tpiv of leopard geckos (~ 30.5 °C) might differ among mating pairs. Figure 4 shows results from an experiment that incubated eggs from several leopard gecko pairs at two temperatures: 29.5 and 31.5 °C. These data are based on a real study (Rhen et al. 2011), but I have simplified the data for the sake of explanation.

Figure 4 shows the sex ratios from 6 mating pairs. Eggs from each pair were divided among the two temperature treatments (i.e. a split-clutch design). Each line connects the results from a single pair (6 lines = 6 mating pairs), and 3 pairs are identified with the letters A, B, C to illustrate some important points. The thick blue line represents the average of all the lines. In this example, the average sex ratios across all mating pairs is 20% male for eggs incubated at 29.5 °C and 80% male for eggs incubated at 31.5 °C. Moreover, the average Tpiv for these geckos (where the blue line crosses the dotted gray line) is about 30.5 °C. Those averages are similar to what is expected from the overall TSD pattern shown in Figure 1. However, notice that there is some variation among mating pairs.

For example, mating pair A produced male-biased results at both temperatures while mating pair C produced femalebiased results at both temperatures. Mating pair B produced all females at 29.5 °C and all males at 31.5 °C. If we estimate a Tpiv (i.e. where the black line for a mating pair crosses the dotted gray line) for each mating pair, we would end up with some variation in Tpivs. The Tpiv for pair A would be lower than 29.5 °C. The Tpiv for pair C would be greater than 31.5 °C. The Tpiv for pair B would be about 30.5 which is the average Tpiv for all pairs. You can also see that the other lines don’t always cross the dotted line at exactly 30.5 °C.

Figure 4. Results of an incubation experiment with six mating pairs of leopard geckos (adapted from Rhen et al. 2011). The black dots show the sex ratios from each breeding pair at both 29.5 and 31.5 °C. The lines connecting the dots can be used to estimate a pivotal temperature (i.e. where the black lines cross the gray dotted line). The heavy blue line shows the average slope of all six lines from the breeding pairs. Letters A, B, and C are references for discussion in the text.

Let’s imagine that we collected data from 10,000 male:female pairs of leopard geckos. We then could estimate a Tpiv for all 10,000 pairs and plot the percentage of Tpivs across temperatures. Figure 5 shows what such a graph might look like (this is hypothetical and not from a real study). The x-axis on the bottom shows all the potential Tpivs from the mating pairs. The y-axis at left shows the percentage of the mating pairs that have each Tpiv. Note that I have placed the Tpivs of pairs A, B, and C from Figure 4 on this graph. For now, ignore the area at right that is shaded in dark gray. I will explain that later. This graph is what we call a normal distribution or sometimes a “bell curve”. It shows that most mating pairs would have a Tpiv very close to the average Tpiv of 30.5 °C (like pair B).

However, some mating pairs will have a Tpiv that is below or above the average like pairs A and C. A small percentage of mating pairs will have a Tpiv that is far away from the average. The purpose of this graph is to demonstrate that the TSD pattern is like many biological traits - there is variation among individuals.

You could measure other traits in leopard geckos, like tail length, and plot a similar graph. Most geckos would have a tail length that is close to the average but some geckos would have tails that are much shorter or much longer than average. Due to variation among individuals in the TSD pattern, it is important to remember that some breeding pairs will produce sex ratios that differ from what is expected based on information reported in care guides and books.

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of morphological abnormalities, it will ensure that desirable sex ratios are always attainable.

Figure 5. A hypothetical normal distribution of pivotal temperatures for leopard geckos. The vertical dotted lines (A, B, C) correspond to estimated pivotal temperatures of breeding pairs from Figure 4.

The Influence of Selective Breeding and TSD Patterns Scientists have only recently started to rigorously study the mechanisms that cause variation in the TSD pattern among individuals. We do know, however, that some of this variation results from genetic differences among mating pairs (Rhen et al 2011). Such genetic variation may explain how TSD patterns evolve, and this is an exciting avenue of current research.

Regardless, the genetic underpinnings of TSD should force us to consider potential unintended consequences of selective breeding.

Imagine, for example, that by chance you only have mating pairs in your collection that have Tpivs above 31.5 °C (illustrated by the dark gray shading in Figure 5). This may not be very likely but it is possible, especially if you only have a few pairs in your collection. If you breed those pairs and incubate eggs at 31 °C, you would get mostly females even though you would expect to get mostly males at that temperature based on the overall TSD pattern (shown in Figure 1). Perhaps you conduct several generations of line-breeding (i.e. breeding only your collection to itself - no outcrossing) to try and enhance a particular trait (e.g. body color).

Your entire collection might have an unusually high Tpiv which could make it difficult to produce desired sex ratios.

Herpetoculturists have long been familiar with potential problems that result from line-breeding and extensive inbreeding (e.g. short tails, underbites, odd behaviors), but we should remember that TSD is an important trait that may also be altered by inbreeding.

Therefore, occasional outcrossing will not only reduce the chances

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Many species probably exhibit a lot of genetic variation in captivity due to collection at multiple times and from multiple points across their native range. For such species, it isn’t likely that selective breeding will drastically alter the TSD pattern in some harmful way. However, for captive populations that originate from a few individuals collected in a single or few localities, this could be a problem. The East Indian Leopard Gecko (Eublepharis hardwickii) may be an example because many breeders have trouble producing males in this species. No study has formally characterized their TSD pattern; however, my suspicion is that some breeding pairs/colonies have unusually high Tpivs (i.e. the dark shaded region in Figure 5). This makes sense given that some breeders report difficulty producing males but others have no trouble at all. As such, increasing the genetic diversity of breeding colonies may be the solution. Another option would be to experiment with fluctuating temperatures (see below); however, if the true cause is genetic, fluctuating incubation temperatures will only treat the symptom and not the cause.

The Influence of Temperature Fluctuations and TSD Patterns Most herpetoculturists incubate eggs at constant temperatures. For decades, this was true of scientists conducting TSD research as well. Indeed, TSD patterns, like those in Figures 1 and 3, are typically characterized using constant temperatures. However, in the wild, nest temperatures often fluctuate. As the sun rises and falls each day, nest temperatures rise and fall, too. Moreover, most eggs take many weeks or months to incubate, and nest temperatures can change dramatically over this time period due to weekly and monthly changes in weather. Over the last three decades, scientists have been trying to understand how such temperature changes influence all kinds of traits in reptiles, including sex-ratios.

One simple example of how daily fluctuations in temperature can alter sex-ratios comes from the painted turtle (Chrysemys picta), which has been used extensively in TSD research. This species has a MF pattern with a Tpiv of about 28 °C. Figure 6 shows the sex-ratios that result from incubating eggs at a constant 28.5 °C (solid gray line) and a treatment that fluctuates around 28.5 °C by 3°C on a daily basis (solid black line). Even though the fluctuating treatment had a mean temperature of 28.5 °C, which is close to the Tpiv

and the same as the constant temperature treatment, this resulted in 100% females (Les et al. 2007) vs 55% females in the constant temperature treatment.

warmer constant temperatures. Indeed, a constant 30 °C usually results in 100% females for C. picta. For this reason, scientists have developed statistical models that can be used to convert fluctuating temperatures, like those measured from nests in the wild, to what we call “constant temperature equivalents” (abbreviated as CTEs). These models attempt to reconcile the way that TSD patterns are characterized (i.e. by using constant incubation temperatures in the lab) with how nest temperatures fluctuate in the wild.

The TSD pattern may result from a combination of several factors Figure 6. Results from incubating painted turtle (Chrysemys picta) eggs at constant (solid gray line) and fluctuating (solid black line) incubation temperatures. The fluctuating temperature was repeated every day during incubation. The mean temperature of the fluctuating treatment was identical to the constant temperature treatment: 28.5 °C. Data were taken from Les et al. 2007.

Why did the fluctuating treatment produce all females when the average temperature was 28.5 °C, which is close to the Tpiv? To understand this, you have to think about embryos with respect to two different clocks. One clock is the one you might wear on your wrist (i.e. time measured in seconds, minutes, and hours). According to that clock, the eggs in the fluctuating treatment spent the same amount of time at temperatures below 28.5 °C as they spent at temperatures above 28.5 °C. That might lead you to think that the average temperature during development was 28.5 °C. The other clock, which is a bit metaphorical, is the developmental clock.

This is not measured in minutes and hours but rather by how much development occurs in a unit time. This clock is heavily influenced by temperature: it runs faster at warmer temperatures and slower at cooler temperatures because the chemical reactions that regulate development speed up and slow down with temperature.

Therefore, even though the clock on your wrist says that the eggs spent the same amount of time at temperatures warmer than 28.5 °C (i.e. female-producing temperatures) as cooler than 28.5 °C (i.e. male-producing temperatures), the embryo actually spent a greater portion of development at temperatures above 28.5 °C, because development proceeds at a faster rate at warmer temperatures. That means that when temperatures fluctuate, the sex ratios will not be predicted by the average temperature of the fluctuation (in this example, 28.5 °C) but will be more similar to sex-ratios produced by

The final point I wish to illustrate is that TSD isn’t always simple or easy to describe because factors other than temperature can influence the TSD pattern. Bearded dragons (Pogona vitticeps) are a fine example of how TSD can be rather complicated. A few relatively recent studies have demonstrated that bearded dragons have both GSD and TSD. Like birds and many other reptiles, they have ZW/ZZ sex chromosomes and the heterogametic sex (i.e. the sex with different chromosomes - ZW) is female while the homogametic sex (ZZ) is male. This differs from mammals which have XY/XX chromosomes and the heterogametic sex (XY) is male. Figure 7 illustrates how sex-determination works for bearded dragons.

An embryo with ZW chromosomes will always be female regardless of incubation temperature (shown on the right side of Figure 7). An embryo with ZZ chromosomes, however, will be male at most all incubation temperatures but will be female at really hot temperatures (shown on the left side of Figure 7).

These females are called “sex-reversed” females, and they are found both in captive and wild populations. If a ZZ male mates with a typical ZW female, then the offspring can have ZZ or ZW chromosomes and sex-determination will follow typical GSD across most incubation temperatures: ZW will be female and ZZ will be male. This would cause anyone to assume they don’t have TSD so long as they didn’t incubate at really high temperatures. If, however, a ZZ male and a ZZ female (i.e. “sexreversed” female) mate (as shown bottom left), all offspring will have ZZ chromosomes. Offspring sex ratios will follow a classic MF TSD pattern with a Tpiv = ~ 33 °C. Importantly, researchers found that “sex-reversed’ females were capable of producing viable eggs, and their offspring had no noticeable signs of abnormalities. Bearded dragons are now being used as a model species to help scientists understand how TSD evolves (Holleley et al. 2015).

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Another species for which sex is determined both by chromosomes and temperature is the Australian three-lined skink (Bassiana duperreyi). This species is not commonly kept and bred in captivity but has been used extensively in research. In this species, sex is typically determined by an XX/XY chromosome system. In 2002, researchers discovered that the sex chromosome system could be overidden by incubating eggs at relatively cool, fluctuating temperatures (Shine et al. 2002). These researchers mimicked fluctuations that characterize nests in the wild and found that fluctuating treatments with cooler mean temperatures resulted in a much greater percentage of males than expected. Intriguingly, regardless of temperature, larger eggs were more likely to be female and smaller eggs were more likely to be male, so the size of the egg at oviposition also partly determines sex!

Finally, much research demonstrates that yolk steroids, like estrogen, can influence offspring sex. Females may differ in how they allocate these steroids to egg yolk, and this can further influence how TSD patterns differ among mating pairs. This is called a “maternal effect”. Considering both maternal and genetic effects is probably necessary to understand why a TSD pattern varies across populations and between individual mating pairs. These are just a few examples of how TSD patterns are not always simple to describe, but many other examples have been discovered and certainly more are yet to be found.

Some final thoughts...

Hopefully, I’ve presented a clear explanation of some of the important factors related to TSD in reptiles. From these concepts, I think some practical advice emerges for breeders who work with species that exhibit TSD. 1. Be sure to outcross and maintain genetic diversity - not just to prevent morphological and behavioral abnormalities but because TSD likely has a genetic basis. This is particularly important if you are having trouble producing desired sex ratios or work with a species that is relatively rare in captivity.

2. Keep careful records of sex ratios for each mating pair and use a split-clutch design when possible. This is the only way to determine if any individuals in your breeding colony consistently produce unusual sex ratios. Such individuals should probably not be bred for the same reasons that you wouldn’t breed individuals with other types of abnormalities.

3. Be cautious (and forgiving) when purchasing or advertising “temp-sexed” individuals. This is a general rule people follow, but hopefully knowing that the TSD pattern can vary among populations and mating pairs further emphasizes this point.

Moreover, Tpivs have been shown to change slightly through a breeding season and as males/females age. I didn’t have space to explain that, but it should further emphasize that there are many factors that influence the TSD pattern.

Figure 7. A diagram of how TSD and GSD work in bearded dragons.

Embryos with ZW chromosomes are always female and those with ZZ are male across most temperatures. At temperatures greater than 32 °C; however, ZZ embryos will be female. If a ZZ male and ZZ female mate, their offspring will exhibit a classic MF TSD pattern.

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4. Rely on the scientific literature to understand TSD. Herpetoculturists have provided the world with excellent information about the captive husbandry and breeding of all sorts of species, but unless a species’ TSD pattern has been subjected to scientific investigation, it isn’t wise to make assumptions based on limited data. Crested geckos (Correlophus ciliatus) are a fine example. Early reports indicated these geckos have TSD, but we now know they actually have a ZZ/ZW sex chromosome system.

5. Be sure to read the scientific literature! Use scholar.google. com to find original research articles about TSD in the species that you keep and breed. Sometimes, you won’t be able to access the articles if you don’t have a subscription to the journal. You can usually still get the article in one of two ways. First, most scientists have a personal website where they make pdfs of their papers available for download. Second, try sending an email to the corresponding author (their contact information is nearlyalways available). Most likely, they will be thrilled to send you a copy of their manuscript, and many will even be happy to answer questions for you.

- Refferences Ewert, M. A., Lang, J. W., & Nelson, C. E. (2005). Geographic variation in the pattern of temperature‐dependent sex determination in the American snapping turtle (Chelydra serpentina). Journal of Zoology, 265(1), 81-95.

Holleley, C. E., O'Meally, D., Sarre, S. D., Graves, J. A. M., Ezaz, T., Matsubara, K., ... & Georges, A. (2015). Sex reversal triggers the rapid transition from genetic to temperature-dependent sex.

Nature, 523(7558), 79-82.

Les, H. L., Paitz, R. T., & Bowden, R. M. (2007). Experimental test of the effects of fluctuating incubation temperatures on hatchling phenotype. Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 307(5), 274-280.

Rhen, T., Schroeder, A., Sakata, J. T., Huang, V., & Crews, D. (2011). Segregating variation for temperature-dependent sex determination in a lizard. Heredity, 106(4), 649-660.

Shine, R., Elphick, M. J., & Donnellan, S. (2002). Co‐ occurrence of multiple, supposedly incompatible modes of sex determination in a lizard population. Ecology Letters, 5(4), 486-489.

Shine, R., Warner, D. A., & Radder, R. (2007). Windows of embryonic sexual lability in two lizard species with environmental sex determination. Ecology, 88(7), 1781-1788.

Viets, B. E., Tousignant, A., Ewert, M. A., Nelson, C. E., & Crews, D. (1993). Temperature‐dependent sex determination in the leopard gecko, Eublepharis macularius. Journal of Experimental Zoology, 265(6), 679-683.

Joshua M Hall, PhD www.devoeco.weebly.com

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