Abstract
Anthropogenic global warming has become a major geological and environmental force driving drastic changes in natural ecosystems. Due to the high thermal conductivity of water and the effects of temperature on metabolic processes, freshwater ecosystems are among the most impacted by these changes. The ability to tolerate changes in temperature may determine species long‐term survival and fitness. Therefore, it is critical to identify coping mechanisms to thermal and hyper‐thermal stress in aquatic organisms. A central regulatory element compensating for changes in oxygen supply and ambient temperature is the respiratory protein haemoglobin (Hb). Here, we quantify Hb plastic and evolutionary response in Daphnia magna subpopulations resurrected from the sedimentary archive of a lake with known history of increase in average temperature and recurrence of heat waves. By measuring constitutive changes in crude Hb protein content among subpopulations, we assessed evolution of the Hb gene family in response to temperature increase. To quantify the contribution of plasticity in the response of this gene family to hyper‐thermal stress, we quantified changes in Hb content in all subpopulations under hyper‐thermal stress as compared to nonstressful temperature. Further, we tested competitive abilities of genotypes as a function of their Hb content, constitutive and induced. We found that Hb‐rich genotypes have superior competitive abilities as compared to Hb‐poor genotypes under hyper‐thermal stress after a period of acclimation. These findings suggest that whereas long‐term adjustment to higher occurrence of heat waves may require a combination of plasticity and genetic adaptation, plasticity is most likely the coping mechanism to hyper‐thermal stress in the short term. Our study suggests that with higher occurrence of heat waves, Hb‐rich genotypes may be favoured with potential long‐term impact on population genetic diversity.
Highlights
Variation in temperature has occurred throughout Earth’s history, anthropogenic climate change has become a major geological and environmental force (Corlett, 2015; Parmesan, 2007; Parmesan & Yohe, 2003) driving drastic changes in natural ecosystems (Hoffmann & Sgro, 2011; Hoffmann et al, 2015; McGill, Dornelas, Gotelli, & Magurran, 2015)
These findings suggest that whereas long-term adjustment to higher occurrence of heat waves may require a combination of plasticity and genetic adaptation, plasticity is most likely the coping mechanism to hyper-thermal stress in the short term
Our results show that plasticity in Hb expression is a coping mechanism to hyper-thermal stress in the studied population
Summary
Variation in temperature has occurred throughout Earth’s history, anthropogenic climate change has become a major geological and environmental force (Corlett, 2015; Parmesan, 2007; Parmesan & Yohe, 2003) driving drastic changes in natural ecosystems (Hoffmann & Sgro, 2011; Hoffmann et al, 2015; McGill, Dornelas, Gotelli, & Magurran, 2015). Previous studies on Daphnia magna provide strong evidence of evolution of temperature tolerance across few decades (Geerts et al, 2015) This evolution is mediated by both plastic and evolutionary changes in gene expression at a number of candidate genes, including some heat shock proteins (Jansen et al, 2017; Klumpen et al, 2017). We measured constitutive (evolutionary) differences in Hb protein content among the subpopulations resurrected across these major environmental transitions, and linked these evolutionary differences to competitive abilities of genotypes under hyper-thermal stress. By measuring constitutive differences in Hb protein content among subpopulations, we assessed whether evolution in this candidate gene family occurred in coincidence with an increase in average temperature and a higher occurrence of heat waves. We assessed whether Hb- rich genotypes had superior competitive abilities under hyper-thermal stress in presence (microcosms) and absence (mesocosms) of prior acclimation to this stress
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