Abstract
Thermal tolerance range, based on temperatures that result in incapacitating effects, influences species’ distributions and has been used to predict species’ response to increasing temperature. Reproductive performance may also be negatively affected at less extreme temperatures, but such sublethal heat-induced sterility has been relatively ignored in studies addressing the potential effects of, and ability of species’ to respond to, predicted climate warming. The few studies examining the link between increased temperature and reproductive performance typically focus on adults, although effects can vary between life history stages. Here we assessed how sublethal heat stress during development impacted subsequent adult fertility and its plasticity, both of which can provide the raw material for evolutionary responses to increased temperature. We quantified phenotypic and genetic variation in fertility of Drosophila melanogaster reared at standardized densities in three temperatures (25, 27, and 29°C) from a set of lines of the Drosophila Genetic Reference Panel (DGRP). We found little phenotypic variation at the two lower temperatures with more variation at the highest temperature and for plasticity. Males were more affected than females. Despite reasonably large broad-sense heritabilities, a genome-wide association study found little evidence for additive genetic variance and no genetic variants were robustly linked with reproductive performance at specific temperatures or for phenotypic plasticity. We compared results on heat-induced male sterility with other DGRP results on relevant fitness traits measured after abiotic stress and found an association between male susceptibility to sterility and male lifespan reduction following oxidative stress. Our results suggest that sublethal stress during development has profound negative consequences on male adult reproduction, but despite phenotypic variation in a population for this response, there is limited evolutionary potential, either through adaptation to a specific developmental temperature or plasticity in response to developmental heat-induced sterility.
Highlights
An increase in mean temperatures and temperature variation associated with ongoing climate change threatens biodiversity (Pachauri et al, 2015)
Males Reproductive performance was significantly negatively affected as developmental temperature increased, with 25◦C as the least affected, 27◦C intermediate, and 29◦C the most affected (Figure 1A and Table 1)
Block effect explained about 0.26 of variance of the model (σ2Block divided by σ2Block + σ2Line + σ2Residual) and Drosophila Genetic Reference Panel (DGRP) line explained about 0.20 of variance (σ2Line divided by σ2Block + σ2Line + σ2Residual, Table 1)
Summary
An increase in mean temperatures and temperature variation associated with ongoing climate change threatens biodiversity (Pachauri et al, 2015). Climate change risk assessments are frequently based on quantification of thermal parameters (Deutsch et al, 2008; Sinclair et al, 2016; Kellermann and van Heerwaarden, 2019), such as thermal tolerance (e.g., either critical tolerance or lethal temperatures, such as lower temperatures (CTmin) and higher temperatures (CTmax), representing a species lower and upper operational temperature), and thermal performance curves, e.g., reaction norms in which individuals are exposed to different temperatures until performance fails at CTmin and CTmax These parameters are associated with latitudinal species’ range distributions (AddoBediako et al, 2000; Kellermann et al, 2012; Overgaard et al, 2014). Because the capacity for adaptation to climate warming will depend on the underlying genetic architecture and the extent to which adaptation and plasticity contributes to responses to climate warming, these patterns indicate much concern about the consequences of a warming climate on ectotherm species’ distributions and persistence
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