New CELS researcher details lizard experiment in Science article
|Hurricanes are notorious for creating havoc but it is a rare wind that does not blow some good as Dr. Jason J. Kolbe, a new faculty member in the CELS Department of Biological Sciences has found out.He and some colleagues recently had a significant paper published in Science in which they detailed an unusual experiment in the Bahamas that weighed in on the long-held controversy of how much influence do random processes such as “founder effects” have on evolutionary divergence.
Kolbe, who just came aboard CELS last summer, has spent several years studying lizards that he considers a great model system for studying evolution that is influenced by global change.
When a hurricane blew through the Bahamas a few years ago it wiped out all the lizards that lived on a small group of very-low-lying islands. The islands are tiny – ranging from 35 to 175 square meters and rise only a couple of feet above mean high tide.
That gave Kolbe and his collaborators a chance to conduct a study – by repopulating those little islands with lizards they could test the relative importance of the founder-effect process versus natural selection.
The five researchers went to a larger forested island in the Bahamas and randomly collected pairs (one male and one female) of brown anole (Anolis sagrei) and placed one pair on each of the seven tiny islands.
The large island where the lizards were originally located had forested vegetation – thick stems and branches. However the small islands that the lizards were relocated to had sparse, small vegetation – mostly shrubs.
|Measurements were taken of the lizards’ hind legs before they were placed on the little islands.
Kolbe explained that lizards growing among thicker vegetation in a forested environment tend to have longer limbs which are more suited for grasping and running in search of prey whereas those living where vegetation is more shrubby will tend to have shorter limbs, more suited for negotiating perches of smaller diameter.
Because all of the islands that were repopulated with the pairs of lizard had shrubby vegetation “we predicted that natural selection would then favor lizards with short hind limbs and so over the course of the next four years that is what we saw – the hind legs on the lizards all decreased over the four-year study period.”
The population growth on the islands was 13-fold over the first couple of years, said Kolbe, as the lizards dined on insects. Lizards can reproduce at six months of age.
At the end of the study, Kolbe said, it was apparent that both founder effects and natural selection contributed to the variations that they measured.
“Our prediction is that if natural selection is the dominant force,” wrote the researchers, “then we would expect all populations to evolve shorter hind limbs as they adapt to using narrower substrates; moreover, vegetation differences among experimental founder islands are expected to produce a relationship between hind limb length and perch diameter.
Conversely, if founder effects are dominant, then we would expect no general trend in limb length evolution, with some populations increasing in limb length and others decreasing with respect to the source population, and limb variation being unrelated to vegetation differences among islands.”
At the end of the study, continued Kolbe, it was shown that “even though the lizards changed and decreased in hind limb length, they maintained their relative differences among the islands” i.e. those that had relatively long limbs at the beginning of the study still had relatively long limbs at the end. Through multiple measurements of the population of each island it was apparent that both the founder effects and natural selection contributed to the variations.
While the first phase of the study is over and reported, the story does not end here. Kolbe and his colleagues plan to revisit the islands this year to see what happened when Hurricane Irene blew nearby to the islands.
Others in the study were Manuel Leal of Duke University, Thomas W. Schoener and David A. Spiller of the University of California at Davis and Jonathan B. Losos of Harvard University.