Tuesday, April 29, 2008

Everyone gets excited about rapid evolution

No discoveries in evolution attract more attention than examples of rapid phenotypic change via natural selection. When we observe impressive evolutionary changes happening over an interval of time that's shorter than a typical human life-span, the abstract power of natural selection becomes tangible. Excitement about rapid evolution often leads to publication in top tier journals, in some cases before other alternatives have been adequately considered.

In 1997 my PhD supervisor - Jonathan Losos - published a paper in Nature that suggested rapid evolution via natural selection in a population of lizards introduced to a Bahamian island only a few decades ago. It was more than ten years before follow-up experiments demonstrated that this observation could be the result of phenotypic plasticity. In spite of this finding, the work continue to be cited as an example of rapid evolution via natural selection.

I was surprised, however, to see it cited in this context by another paper purporting to have observed rapid evolution in another island lizard population. In the pages PNAS, Herrel et al. report dramatic phenotypic changes in a lizard population introduced to a Croatian island in the Adriatic Sea. They observe significant changes in both morphology and performance; perhaps the most striking of these is the appearance of cecal valves, which are thought to increase efficiency of digestion in herbivorous lizards (the introduced population appears to be more herbivorous than the population from which it was derived). Although one could reasonably argue that the types of changes seen in this population are unlikely to represent a plastic response, this possibility cannot, and should not, be brushed under the table too rapidly.

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