Image credit: Wikimedia Commons
Ryan Calsbeek and Robert Cox, evolutionary biologists at Dartmouth University, are not mad scientists bent in the image of H.G. Wells' Doctor Moreau, but they have commandeered a string of islands in the Bahamas to act as a real-world laboratory.The two scientists set sail in the Caribbean in an effort to better understand the ways in which pressure—from predators, population, and the environment—influences natural selection. In doing so, they are helping to demonstrate that evolutionary biology—not known for its use of live organisms in research—can benefit from hard experimental science. Calsbeek explained:
Many people are skeptical of evolutionary biology because they perceive it as a purely historical science that can't be tested experimentally.
For anoles in the Bahamas, competition with other lizards is more significant than pressure from predators. Image credit: Wikimedia Commons
To combat this misconception, Calsbeek and Cox built an experiment that allowed them to control the selection process.
Tinkering with Nature
The researchers found a group of islands—each barely large enough for a game of catch—and began building their experiment. First, they removed all of the native Anolis sagrei and replaced them with natives of a nearby island that had been measured, tested for stamina, and individually marked.
One of the research islands, covered in netting to keep birds away. Image credit: R. Calsbeek/R. Cox
On some of the islands, they removed the influence of bird predation by covering the entire area with nets. On other islands, they did not alter the environment. On a final group of islands, the researchers introduced a second predator—lizard-eating snakes.
This represents one of the first large-scale experimental manipulations of a process that is central to evolution...this really is a hard experimental science. You can manipulate agents of selection and test hypotheses about how the process works.
Indeed, their results confirm a long-held hypothesis: That competition between lizards in the Caribbean was a greater driver of change than pressure from predators.
We found repeated evidence that death by predators occurred at random with respect to traits like body size and running ability...but we also found that increasing the density of lizards on an island consistently created strong natural selection favoring larger size and better running ability.
Though the experiment only speaks to populations of anoles on some Caribbean islands, it showed that increases in population density led to increased competition over food, space, and other resources, which favored larger, stronger, individuals.
For Edward Prendick, the protagonist of Wells' The Island of Doctor Moreau, the shocking discoveries he made while shipwrecked on the island laboratory drove him to an isolated life searching for solace in the stars. For Calsbeek and Cox, their discovery will lead them back into the field, where the lab space is as expansive as the turquoise-blue waters.
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