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| Timing of reproduction greatly influences offspring success and resulting
population production. Explaining and predicting species’ dynamics necessitates disentangling
the intrinsic (genotypic) and extrinsic (climatic) factors controlling reproductive timing. Here
we explore temporal and spatial changes in spawning time for 21 populations of Atlantic cod
(Gadus morhua) across the species’ range (408 to 808 N). We estimate spawning time using a
physiologically relevant metric that includes information on fish thermal history (degree-days,
DD). First, we estimate spawning DD among years (within populations) to show how recent
changes in spawning time can be explained by local changes in temperature. Second, we
employ spawning DD to identify temperature-independent trends in spawning time among
populations that are consistent with parallel adaptive evolution and the evolutionary history
of the species. Finally, we use our results to estimate spawning time under future climate
regimes, and discuss the implications for cod ecology across the species’ range. | |
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