The Rock Pocket Mouse Adaption by Natural Selection by Lauren Doyle Hugh Hulse Rob Rix
Table of Contents pg.2 What is Natural Selection? pg.3 Rock Pocket Mouse pg.4 New Mexico Geography pg.5 White Sands/ Valley of Fire pg.6 Rock Pocket Mouse Coloration pg.7 Mutation and the Mc1r gene pg.8 Has There Been Enough Time? pg.9 Further Exploration‌ pg.10 Bibliography
What is Natural Selection? Natural selection is the process by which heritable traits that increase an organism’s chances of survival and reproduction are favored more than less beneficial traits. These traits are encoded in the organism’s genes, and as such are passed on to subsequent generations. If the trait is beneficial to the organism, it will be selected for by factors in the environment or the population. Natural selection is the process that drives adaptation and results in the evolution of organism.
For Example...
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Rock Pocket Mouse The rock pocket mouse, or Chaetodipus intermedius, is a species of mouse found exclusively in the rocky habitats of the southwestern states. Due to historic lava flows, the original brown habitat of these mice has been interrupted with dark lava flow areas. Through natural selection, various external factors have lead to a wide range of coat coloring, depending on whether the mice inhabit the light or dark substrate. These factors may largely be due to predation. When the dark lava interrupted the original light habitat, mice with lighter coat coloration contrasted the new substrate more dramatically, making it easier for predators such as hawks to spot and capture them. Over time, the coat color of mice on dark substrate gradually began to darken as the light coat color was selected against. While this is easy to understand on a large scale, these seemingly simple alterations have a genetic basis underlying them.
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New Mexico Geography The Tularosa Basin, located in the south central portion of New Mexico, is a geographicly diverse region which is inhabited by the rock pocket mouse. This reqions drastic shifts in appearence from white sands to black lava flows offers a unique circumstance for the rock pocket mouse to adapt to.
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White Sands
Valley of Fire Valley of Fires recreation area is located immediately adjacent to the Malpais Lava Flow. Approximately 5,000 years ago, Little Black Peak erupted and flowed 44 miles into the Tularosa Basin, filling the basin with molten rock. The resulting lava flow is four to six miles wide, 160 feet thick and covers 125 square miles. The lava flow is considered to be one of the youngest lava flows in the continental United States.
The largest gypsum dune field in the world is located at White Sands National Monument in south-central New Mexico. This region of glistening white dunes is in the northern end of the Chihuahuan Desert within an "internally drained valley" called the Tularosa Basin. The monument ranges in elevation from 3890' to 4116' above sea level. There are approximately 275 total square miles of dune fields here, with 115 square miles (about 40%) located within White Sands National Monument. ground water.
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Rock Pocket Mouse Coloration as Predation Defense Strategy
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Mutation and the Mc1r gene Scientists have narrowed this alteration in coat color down to one gene: the Mc1r gene. This gene has two alleles: D and d. When a mouse possesses two D alleles, it is said to be homozygous dominant and is typified as DD. When a mouse possesses one D and one d allele, it is said to be heterozygous dominant and is typified as Dd. Finally, if a mouse has two d alleles, it is said to be homozygous recessive and is typified as dd. If a mouse has one D, its coat color will appear dark, as D is the dominant allele. Conversely, if a mouse does not have a D allele, its coat color will appear light. One would predict mice occupying dark substrate to show either DD or Dd genotype, whereas mice inhabiting light substrate to show dd genotype. Scientists have found nature reflects this prediction. Therefore, over the course of evolution, as predators made their selections upon mice populations, the genotypes of mice on dark substrate was modified. Slowly, those mice with the DD or Dd genotype were more successful at surviving and reproducing than those of genotype dd. With enough time, natural selection was able to alter the genotype of mice populations to reflect the most successful traits: dark color on dark substrate and light color on light substrate.reproducing than those of genotype dd. With enough time, natural selection was able to alter the genotype of mice populations to reflect the most successful traits: dark color on dark substrate and light color on light substrate.
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Has There Been Enough Time? Many question if there has been enough time for this adaptation to occur. It has been approximately 1,000 years since the tectonic activity in this region caused the dark colored lava flows which changed the environment for the Rock Pocket Mouse. According to Hoekstra, mutation rates are likely to occur at a rate of approximately 10-5 per locus per generation (which is once per year), which gives approximately 10-8 nucleotide sites per generation. If it is assumed that there are 100 sites in the genome at which mutations produce dark coloration, there would be a rate of 10-6 dark color mutations per generation. If the Rock Pocket Mouse population is approximately 10,000 and that there have been 1000 generations, we can safely say that the dark color mutation has had time to mutate ten times (Hoekstra, 2005).
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Further Exploration‌
Choose a species from the options below or find your own that models the rock pocket mouse in phenotypic variation. Given the framework provided in this e-book, research and apply the various aspects of genotypic and phenotypic variation to that species. Most importantly, have fun!
Holbrookia maculata (lesser earless lizard)
Sceloporus undulates (eastern fence lizard)
Cnemidophorus inornatus (little striped whiptail)
Others?
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Bibliography Bureau of Land Management. U.S. Department of the Interior. 5-12-2011. 4-30-2012 <http://www.blm.gov/nm/st/en/prog/ recreation/roswell/valley_of_fires.html>. “Finches Chart.” Digital Image. 30 April 2012. <http://bizzymicbizness. com/blog/uploads/2010/02/Adaptive-radiation-in-Galapagosfinches.jpg>. Hoekstra, H.E., Drumm, K.E., and Nachman, M.W. 2004. Ecological genetics of adaptive color polymorphism in pocket mice: geographic variation in selected and neutral genes. Evolution. 58 (6): 1329- 1341. Hoekstra, H.E., Krenz, J.G., and Nachman, M.W. 2005. Local adaptation in the rock pocket mouse (Chaetodipus intermedius): natural selection and phylogenetic history of populations. Heredity. 94: 217-228. “Map of New Mexico.” Map. lib.utexas.edu 15 April 2012. <http:// www.lib.utexas.edu/maps/us_2001/new_mexico_ref_2001.jpg>. Nachman, M.W., Hoekstra, H.E., and D’Agostino, S.L. 2003. The genetic basis of adaptive melanism in pocket mice. PNAS. 100 (9): 52685273. National Park Services. U.S. Department of the Interior. 4-21-2012. 4/30/2012 <http://www.nps.gov/whsa/naturescience/index. htm>. “Rock Pocket Mouse.” Video. You Tube 1 May 2012. < http://www. youtube.com/watch?v=us1Yy9-zTL8>. “Satellite Photo.” Photo. 15 April 2012. <http://4.bp.blogspot.com/6nBm-6Ixffg/TxwaJl-vA9I/AAAAAAAAAwA/hDqx5cDBn6c/ s1600/White+Sands+NM+-+Carrizozo.jpg>. “Science Data.” Digital Image. 30 April 2012. <http://student.biology. arizona.edu/honors2004/group12/mice.html>. Weckerly, F.W., and Best, T.L. 1985. Morphologic variation among rock pocket mice (Chaetodipus intermedius) from New Mexico lava fields. The Southwestern Naturalist. 30 (4): 491-501.
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