7) Natural selection in lizards
A popular evolutionary hypothesis is that behavioural shifts in new environments negate the effects of natural selection. But work by Harvard University’s Jonathan Losos and his colleagues in 2003 lends little support to this theory. The researchers introduced the large ground-dwelling predatory lizard Leiocephalus carinatus to six small islands in the Bahamas, with six other islands serving as controls. They found that the lizard’s prey, a smaller lizard called Anolis sagrei, spent more time higher up in the vegetation on islands occupied by the larger predator than they did on the islands where L. carinatus was absent. But mortality in A. sagrei was still
much higher on the experimental islands than on control islands.
The presence of the larger predator selected for longer-legged male A. sagrei lizards, which can run faster, and also favoured larger females, which are both faster and harder to subdue and ingest. The researchers did not detect any selection on size in males; they suggested that the larger males may have been more vulnerable because of their conspicuous territorial behaviour.
The study shows how the introduction of a predator can cause individuals of a prey species to change their behaviour so as to reduce the risk of predation, but also cause an evolutionary response at the level of the population that differs between the sexes according to their ecology.
Reference
Losos, J. B., Schoener, T. W. & Spiller, D. A. Nature 432, 505–508 (2004).
Additional resources
Butler, M. A., Sawyer, S. A. & Losos, J. B. Nature 447, 202–205 (2007).
Kolbe, J. J. et al. Nature 431, 177–181 (2004).
Calsbeek, R. & Smith, T. B. Nature 426, 552–555 (2003).
Losos, J. B. et al. Nature 424, 542–545 (2003).
Author website
Jonathan Losos: http://www.oeb.harvard.edu/faculty/losos/jblosos
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