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Abstract Under climate change, ectotherms will likely face pressure to adapt to novel thermal environments by increasing their upper thermal tolerance and its plasticity, a measure of thermal acclimation. Ectotherm populations with high thermal tolerance are often less thermally plastic, a trade‐off hypothesized to result from (i) a phenotypic limit on thermal tolerance above which plasticity cannot further increase the trait, (ii) negative genetic correlation or (iii) fitness trade‐offs between the two traits. Whether each hypothesis causes negative associations between thermal tolerance and plasticity has implications for the evolution of each trait.We empirically tested the limit and trade‐off hypotheses by leveraging the experimental tractability and thermal biology of the intertidal copepodTigriopus californicus. Using populations from four latitudinally distributed sites in coastal California, six lines per population were reared under a laboratory common garden for two generations. Ninety‐six full sibling replicates (n = 4–5 per line) from a third generation were developmentally conditioned to 21.5 and 16.5°C until adulthood. We then measured the upper thermal tolerance and fecundity of sibships at each temperature.We detected a significant trade‐off in fecundity, a fitness corollary, between baseline thermal tolerance and its plasticity.Tigriopus californicuspopulations and genotypes with higher thermal tolerance were less thermally plastic. We detected negative directional selection on thermal plasticity under ambient temperature evidenced by reduced fecundity. These fitness costs of plasticity were significantly higher among thermally tolerant genotypes, consistent with the trade‐off hypothesis. This trade‐off was evident under ambient conditions, but not high temperature.Observed thermal plasticity and fecundity were best explained by a model incorporating both the limit and trade‐off hypotheses rather than models with parameters associated with one hypothesis. Effects of population and family on tolerance and plasticity negatively covaried, suggesting that a negative genetic correlation could not be ruled as contributing to negative associations between the traits. Our study provides a novel empirical test of the fitness trade‐off hypothesis that leverages a strong inference approach. We discuss our results' insights into how thermal adaptation may be constrained by physiological limits, genetic correlations, and fitness trade‐offs between thermal tolerance and its plasticity. Read the freePlain Language Summaryfor this article on the Journal blog.
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The Potential for Experimental Evolution to Uncover Trade‐Offs Associated With Anthropogenic and Climate Change Adaptation
ABSTRACT Evolutionary responses to climate change may incur trade‐offs due to energetic constraints and mechanistic limitations, which are both influenced by environmental context. Adaptation to one stressor may result in life history trade‐offs, canalization of phenotypic plasticity, and the inability to tolerate other stressors, among other potential costs. While trade‐offs incurred during adaptation are difficult to detect in natural populations, experimental evolution can provide important insights by measuring correlated responses to selection as populations adapt to changing environments. However, studies testing for trade‐offs have generally lagged behind the growth in the use of experimental evolution in climate change studies. We argue that the important insights generated by the few studies that have tested for trade‐offs make a strong case for including these types of measurements in future studies of climate adaptation. For example, there is emerging consensus from experimental evolution studies that tolerance and tolerance plasticity trade‐offs are an often‐observed outcome of adaptation to anthropogenic change. In recent years, these types of studies have been strengthened by the use of sequencing of experimental populations, which provides promising new avenues for understanding the molecular mechanisms underlying observed phenotypic trade‐offs.
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- PAR ID:
- 10582485
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 30
- Issue:
- 11
- ISSN:
- 1354-1013
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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