(Non)parallel evolution in extant threespine stickleback

Background and Findings: Convergence onto similar phenotypes in similar environments by independent species or populations is strong evidence for evolution by natural selection. Often, evolutionary ecologists focus on those traits that are evolving most in parallel. Multi-trait, quantitative approaches to parallel evolution that ask how much parallelism there is, and why, are more rare. In collaboration with Dan Bolnick, Catherine Peichel and Andrew Hendry, I have studied populations of threespine stickleback adapting to lake and stream environments replicated across 16 different watersheds on Vancouver Island, BC, Canada. We found that the extent of parallel evolution depended strongly on which trait was being investigated. Deviations from parallel evolution of lake-stream divergence, and depended on watershed specific differences in environment and lake-stream gene flow. This suggests that evolution is not parallel, but can still be predictable if we know enough about the system.

Ongoing Work: I am currently experimentally investigating (non)parallelism in natural selection, to see if that helps explain non-parallel evolution in morphology. Concurrently, I am collaborating with Marius Roesti,  Dan Bolnick, and Catherine Peichel to investigate habitat choice and its genetic basis in lake and stream fish.

Evolutionary Ecology of Novel Interactions in Anolis lizards


Background and Findings: Stuart’s graduate work tested whether and how the native lizard Anolis carolinensis is responding evolutionarily to the recent invasion of A. sagrei to small spoil islands in Mosquito Lagoon, Florida. Anolis carolinensis naturally occurs on every island in the lagoon. A. sagrei has reached nearly every island. Stuart compared A. carolinensis perch height and toepad morphology on five islands where A. carolinensis was the only anole (the controls) to six islands where A. sagrei had invaded sometime since 1995 (the treatments). Anolis carolinensis perched higher in the presence of A. sagrei and also had larger toepads with more clingy lamellae. This is consistent with toepad morphology across myriad arboreal anole species. A common garden experiment suggests that these toepad differences are evolved. Stuart et al. also also ruled out alternative explanations like chance or environmental differences among treatments.

Ongoing work: With colleagues Ambika Kamath, Nick Herrmann, and Kiyoko Gotanda, we re-started this work in 2019, after finding that one of the five control islands had been invaded by A. sagrei sometime between 2011 and 2018. We are now able to compare pre-invasion data directly to post-invasion data to confirm that habitat use change and toepad evolution does indeed happen in situ on these islands. We are also collaborating with Adam Freedman and Thomas Sanger (Loyola University Chicago) to better understand the developmental and genetic basis of toepad variation in these lizards.

                       Anolis carolinensis                                                 Anolis sagrei
(Lizard photos by C. Gilman)

Microevolution and Macroevolution in a Fossil Stickleback Lineage

DSC03700Background and Ongoing Work: A diatomite mine in Fernley Nevada hosts a fossil threespine stickleback lineage the is probably one of the best examples of gradual Darwinian evolution in the fossil record. Stickleback were fossilized in annual varves and this deposit spans more than 100,000 years. We have recently started collaborating with Dr. Michael A. Bell, who developed this system (e.g., Bell 1985; Bell et al. 2006; Hunt et al. 2008; Bell 2009). We are currently comparing Dr. Bell’s fossil data to patterns observed in extant stickleback to infer the genetic basis of fossil change (ms in review) and the potential for gradual phyletic evolution to generate new species (data currently being collected).

(Last updated, 9 October 2019)

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