Abstract
Thermal stress response is an essential physiological trait that determines occurrence and temporal succession in nature, including response to climate change. We compared temperature-related demography in closely related heat-tolerant and heat-sensitive Brachionus rotifer species. We found significant differences in heat response, with the heat-sensitive species adopting a strategy of long survival and low population growth, while the heat-tolerant followed the opposite strategy. In both species, we examined the genetic basis of physiological variation by comparing gene expression across increasing temperatures. Comparative transcriptomic analyses identified shared and opposing responses to heat. Interestingly, expression of heat shock proteins (hsps) was strikingly different in the two species and mirrored differences in population growth rates, showing that hsp genes are likely a key component of a species’ adaptation to different temperatures. Temperature induction caused opposing patterns of expression in further functional categories including energy, carbohydrate and lipid metabolism, and in genes related to ribosomal proteins. In the heat-sensitive species, elevated temperatures caused up-regulation of genes related to meiosis induction and post-translational histone modifications. This work demonstrates the sweeping reorganizations of biological functions that accompany temperature adaptation in these two species and reveals potential molecular mechanisms that might be activated for adaptation to global warming.
Highlights
Thermal stress response is an essential physiological trait that determines occurrence and temporal succession in nature, including response to climate change
Fecundity and the resulting population growth rate of both species were strongly affected by temperature
Transcriptomic responses were found to correlate with differences in fitness and especially differences in population growth, indicating underlying mechanisms of phenotypes’ responses to environmental change
Summary
Thermal stress response is an essential physiological trait that determines occurrence and temporal succession in nature, including response to climate change. We found significant differences in heat response, with the heat-sensitive species adopting a strategy of long survival and low population growth, while the heat-tolerant followed the opposite strategy In both species, we examined the genetic basis of physiological variation by comparing gene expression across increasing temperatures. The best studied freshwater monogonont rotifer is the Brachionus calyciflorus species complex that has recently been resolved to four different species using integrative taxonomy: Brachionus calyciflorus sensu stricto (s.s.), Brachionus fernandoi, Brachionus dorcas, and Brachionus elevatus[20,21] The species of this complex exhibit temporal succession, and their occurrences have been related to temperature in several studies[7,8,17,22]. We confirmed that temperature tolerance likely plays a role in their temporal distribution[23]
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