Let’s pull up their genes: are multiple climatic events affecting the genetic diversity of coral-dwelling fishes?

ACRS Research Award

Genetic diversity | Cyclones and heatwaves | Coral gobies

Let’s pull up their genes: are multiple climatic events affecting the genetic diversity of coral-dwelling fishes?

By Catheline Froehlich University of Wollongong

In this new era where cyclones and mass bleaching events are happening consecutively, marine life has been experiencing population stressors unlike ever before. It is possible that some animals underwent such intense stress that only a few individuals within a population survived multiple disturbances. This is called a population bottleneck. Think of cheetahs and how their populations were reduced to the brink of extinction. When population bottlenecks occur, the DNA of the remaining survivors dictates the diversity of future generations. If survivors have very similar DNA, then inbreeding is likely prevalent and the populations may not recover. This means the remaining populations have low genetic diversity. However, if survivors have different and varied DNA, then populations should recover as genetic diversity is high.

What is happening to the genetic diversity of marine animals following consecutive disturbances? I will shed some light to this question by studying coral-dwelling gobies, an adorable fish that lives exclusively in corals. Gobies protect corals from predators, algal growth, and stagnant water. Corals in return provide food, shelter, and breeding sites. Yet, after four back-to-back cyclones and bleaching events at Lizard Island, few goby species remained and most corals were empty, which is making us wonder: what happened to the genetic diversity of gobies? If we find that their diversity has changed, then we can predict which goby species are likely to recover, and which corals may suffer if their goby inhabitants disappear. For my goby project and with the ACRS research funding, I plan to unzip their genes and get to the heart of the question. We first collected fish tissue from different coral goby species before and after multiple disturbances at Lizard Island, QLD, by cutting off a small piece of their tail. Don’t worry, the fish grow it back quickly. Martin Hing collected tissue in 2014 before any disturbances, and then I returned to collect tissue of the same species in 2020 after 4 backto-back extreme disturbances (2 category four cyclones, and 2 long heatwaves that caused mass coral bleaching). Back at the lab, I recently extracted all the DNA, which basically just meant washing the tissue many times with different fancy soaps to get rid of unnecessary parts of the cells and only leave behind DNA. These samples are now at a different facility that will provide me with the genetic code of each DNA sample. I will then spend several months playing on the computer to analyse the DNA sequences from 2014 vs 2020 to figure out whether the catastrophic disturbances have affected the

Above: If you look closely, you can see that we cut a tiny piece of tail. Luckily they grow it back quickly. That’s all we need to know their DNA secrets. © Catheline Froehlich

Left: This adorable goby lives in a coral with algae growing on the edges. That’s a lot of algae maintenance for the goby, especially since algae grows faster with warming temperatures. © Catheline Froehlich

Right: These gobies have excellent camo game and the only way to see them is to shine a fashlight in their corals. © Jemma Smith

populations of coral gobies on a genetic level.

Right now, the work is still ongoing, so as the true scientist that I am, I can’t give anything away. However, from annual surveys I have been completing as a different part of my PhD, I can tell you that coral gobies declined more than corals after the consecutive cyclones and prolonged heatwaves. Now, three years after the last disturbance, coral goby populations are still lower than before disturbances and several gobies are no longer found. I realize this sounds a bit depressing, but in reality these adorable little fish may be more resilient than we think! Tune in later to find out what I have discovered about their genetic diversity.

“After four back-toback cyclones and bleaching events at Lizard Island, few goby species remained and most corals were empty, which is making us wonder: what happened to the genetic diversity of gobies?”

Acknowledgements

I am grateful to the Australian Coral Reef Society and the Centre for Sustainable Ecosystem Solutions at the University of Wollongong for funding the genetic analyses for my project. I thank the Zoltan Florian Marine Biology Fellowship as a part of the Lizard Island Doctoral Fellowship program and the Hermon Slade Foundation for funding the field trips to collect fish tissue. I am grateful for the support from my PhD supervisors Dr. Marian Wong, Dr. Selma Klanten, and Dr. Mark Dowton.

Above: The author is getting squeaky clean in the lab to extract the mitochondrial DNA, a.k.a. use fancy soaps to breakdown tissues and cell walls and leave behind just the DNA. © Renae Kirby