Research

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.

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Current Findings:

In this publication, we 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.

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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

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