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Rapid Evolution of Reproductive Traits in Response to Warming
Reference
Breckels, R.D. and Neff, B.D. 2014. Rapid evolution of sperm length in response to increased temperature in an ectothermic fish. Evolution and Ecology 28: 521-533.

Background
The authors write that "genetic adaptations to temperature can occur via natural selection acting on either phenological mechanisms or thermal physiology," citing Angilletta (2009). But they say that "relatively little is known about rapid evolutionary adaptations of thermal physiology (Leal and Gunderson, 2012), especially in vertebrates," although they remark that "Hendry et al. (1998, 2000) provide one of the few empirical examples of a vertebrate, the newly diverged Lake Washington sockeye salmon (Oncorhynchus nerka), showing rapid adaptation in thermal tolerance and body shape after only 9-14 generations," which clearly indicates that "vertebrate species can adapt rapidly via evolutionary responses to increased temperature."

What was done
In further exploring this intriguing subject, Breckels and Neff studied the phenotypic plasticity and evolutionary responses of sperm traits in guppies (Poecilia reticulata) that they maintained for either 6, 18 or 24 months at temperatures of either 25 or 28°C in a 2 x 2 common garden design.

What was learned
In the words of the two Canadian researchers, "the plastic response to increased temperature was a decreased sperm length, velocity and path linearity," the last two of which characteristics "showed no sign of evolution even after 24 months." However, in the case of the first of the three characteristics they studied, they found there was an evolutionary response, and that it was an increase in sperm length that completely compensated for the plastic decrease in sperm length after just six months (at most four generations) in 28°C water.

What it means
As a result of the above findings, Breckels and Neff concluded that "guppies can respond to climate warming via rapid evolution, at least for some reproductive traits," which reasoning poses the possibility that longer time periods may have revealed evolutionary responses to the other two reproductive traits they investigated," as well as the possibility that still other traits might likewise exhibit evolutionary responses in both guppies as well as other forms of life, which further suggests that similar types of experiments should be conducted with other life forms and over still longer time periods.

References
Angilletta, M.J. 2009. Thermal Adaptation: A Theoretical and Empirical Synthesis. Oxford University Press, Oxford, United Kingdom.

Hendry, A.P., Hensleigh, J.E. and Reisenbichler, R.R. 1998. Incubation temperature, developmental biology, and the divergence of sockeye salmon (Oncorhynchus nerka) within Lake Washington. Canadian Journal of Fisheries and Aquatic Sciences 55: 1387-1394.

Hendry, A.P., Wenburg, J.K., Bentzen, P., Volk, E.C. and Quinn, T.P. 2000. Rapid evolution of reproductive isolation in the wild: evidence from introduced salmon. Science 290: 515-518.

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

Reviewed 3 September 2014