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Tropical Ectotherms Avoid Extinction in a Warming Environment

Paper Reviewed
Logan, M.L., Cox, R.M. and Calsbeek, R. 2014. Natural selection on thermal performance in a novel thermal environment. Proceedings of the National Academy of Sciences 111: 14,165-14,169.

Introducing their study, Logan et al. (2014) say that "tropical ectotherms are thought to be especially vulnerable to climate change because they are adapted to relatively stable temperature regimes, such that even small increases in environmental temperature may lead to large decreases in physiological performance." Nevertheless, they offer their opinion that tropical organisms may mitigate the detrimental effects of warming through evolutionary change in thermal physiology. And they go on to describe an experiment they conducted which proves their point.

To determine whether and how thermal physiology is subject to natural selection, the three U.S. researchers say they "measured survival as a function of the thermal sensitivity of sprint speed in two populations of Anolis sagrei lizards from the Bahamas," first quantifying the relationship between thermal performance and survival of 85 males from a non-manipulated population on Kidd Cay, Great Exuma, in order "to test whether a simulated change in thermal environment would increase or otherwise alter selection on thermal performance," which testing they repeated on a population of 80 males from the island of Eleuthera that they transplanted from an interior forested habitat to a warmer, more thermally-variable site. And what did they learn from these manipulations?

Quoting Logan et al., "when we simulated a rapid change in the thermal environment by transplanting a population of lizards to a warmer and more thermally variable habitat, we observed strong natural selection on thermal physiology," which finding, in their words, implies that "rapid climate change may result in directional selection on thermal physiology, even in species whose thermoregulatory behaviors are thought to shelter them from natural selection." They warn, however, that "evolutionary change will not occur unless thermal performance traits are heritable." But in light of other considerations they discuss, Logan et al. ultimately come to the conclusion that "even if the amount of warming expected through the end of the century occurred during a single breeding season, this species could hypothetically compensate for as much as 30% of that environmental change through evolutionary adaptation alone." And assuming that "the standing crop of additive genetic variance in thermal performance traits is sufficient," they further conclude that "many populations may rapidly adapt to changing climates," further citing in this regard the studies of Leal and Gunderson (2012) and Gunderson and Leal (2012).

References
Gunderson, A.R. and Leal, M. 2012. Geographic variation in vulnerability to climate warming in a tropical Caribbean lizard. Functional Ecology 26: 783-793.

Leal, M. and Gunderson, A.R. 2012. Rapid change in the thermal tolerance of a tropical lizard. American Naturalist 180: 815-822.

Posted 27 January 2015