Rapid evolution of sperm length in response to increased temperature in an ectothermic fish
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The Intergovernmental Panel on Climate Change predicts an average global temperature increase of 1.8–4.0 °C by 2100. Tropical ectotherms are expected to be particularly sensitive to this temperature increase because they live close to their thermal limits. We investigated the phenotypic plasticity and evolutionary response of sperm traits in guppies (Poecilia reticulata) to increased temperatures after 6, 18, and 24 months. Guppies with evolution temperatures of 25 °C (control) or 28 °C were reared in either 25 or 28 °C in a 2 × 2 common garden design. The plastic response to increased temperature was a decreased sperm length, velocity, and path linearity. The evolutionary response was a subsequent increase in sperm length, resulting in complete compensation after just 6 months (at most four generations) in 28 °C water. Sperm velocity and linearity showed no sign of evolution even after 24 months. This study provides evidence that some reproductive traits can respond via rapid evolution to the temperature increase associated with climate change.
KeywordsPhenotypic plasticity Genetic response Sperm length Sperm velocity Guppy Global warming
We thank J. Hung and M. Lau for their help with conducting sperm video analyses and S. Garner, T. Hain, N. Muñoz, C. Partridge, and three anonymous reviewers for providing comment that improved the manuscript. This research was funded by Natural Sciences and Engineering Research Council of Canada.
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