Edited Image 2016-05-17 00-59-54

Project: Repeated Evolution of Small Body Size in Island Reptiles
Genetics, Physiology and Life History

The "Island Rule" is a worldwide phenomenon of rapid body size evolution on islands where smaller taxa show a tendency towards dwarfism, and larger taxa show a tendency towards gigantism. On the Channel Islands off the coast of California three species of reptiles have evolved to be dwarf relative to the mainland populations. We are using the repeated evolution of dwarfism to understand  how molecular networks (genes, hormone regulation, etc) underlying complex traits, such as body size, can evolve. These molecular data are integrated with estimates of reproductive output obtained through advanced field-portable ultrasound technology which can inform us about the life history evolution of these species as well that allows us to extend our understanding of the process of convergent evolution on correlated life-history traits.

Previous Findings

We have demonstrate the differences between the mainland and island populations for three reptile species: the gopher snake, the yellow-bellied racer, and the southern alligator lizard. We presented 6 years of body size, relative head size, and blood glucose measurements from two mainland California populations and two California Channel Islands. Our data indicates that the three reptiles have independently obtained lower blood glucose levels and smaller body sizes on islands relative to the mainland populations, which is consistent with lower resource availability in island habitats.

Sparkman, AM, AD ClarkG, LJ BrummettU, KR ChismU, LL CombrinkU, NM KabeyU, TS Schwartz. 2018. Convergence in reduced body size, head size, and blood glucose in three island reptiles. Ecology and Evolution. 8(12):6169-6182. doi: 10.1002/ece3.4171​

Related Media Links

National Parks Service, 2017: Channel Islands Serve As Reptile Evolution Laboratory

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Current Work

We are now diving in deep with the molecular work to understand how these animals have become so small on the islands. We have sequenced reference genomes for the gopher snake and the alligator lizard. We are doing whole genome population sequencing across mainland and island populations the gopher snake to understand the history of these populations and to identify which genes have become most different, that may explain how the animal's body size and physiology have changed.

Our Collaborators and Funders


Principal Investigators:

  • Tonia Schwartz, Auburn University

  • Amanda Sparkman, Westmont College

Graduate Students:

  • Amanda Clark, Auburn University

Undergraduate Students:​

  • Milica Courtenay

Channel Islands: https://www.nps.gov/chis/index.htm; https://www.nature.org/en-us/get-involved/how-to-help/places-we-protect/santa-cruz-island-california/

Sedgwick preserve:  https://sedgwick.nrs.ucsb.edu/

We are grateful for funding from the following sources that have supported this research.

  • National Science Foundation, Graduate Research Fellowship to Ms. Amanda Clark