Abstract
Elevated temperatures resulting from climate change are expected to disproportionately affect ectotherms given their biological function has a direct link to environmental temperature. Thus, as climate change leads to rapid increases in water temperatures in rivers, aquatic ectotherms such as fish may be highly impacted. Organisms can respond to these stressors through flexible and rapid phenotypic change induced via developmental and/or transgenerational plasticity. In oviparous species, gravid females may translate environmental stress across generations via increased exposure of eggs to maternally-derived glucocorticoids (i.e., maternal stress), which has been shown to result in diverse phenotypic effects in offspring. Recent studies suggest these phenotypic changes from maternal glucocorticoids may elicit predictive adaptive responses, where offspring exposed to maternal stress may be better prepared for the stressful environment they will encounter (i.e., environmental match hypothesis). We applied the environmental match hypothesis to examine whether a prenatal exogenous increase in egg cortisol may prepare Chinook salmon offspring (Oncorhynchus tshawytscha) to cope with thermal challenges after being reared in chronically elevated temperatures. Specifically, we exposed eggs to aqueous bath of cortisol-dosed (1000ng/mL) or control (0ng/ml) solutions, and then raised both treatments at current (+0°C—contemporary ambient river temperature) or elevated (+3°C—projected future river temperature) thermal regimes. We quantified thermal performance in fish 7-9 month post fertilization using two methods: via critical thermal maximum (CTMax), and energetic responses (in plasma cortisol, glucose, and lactate) to environmentally relevant, but challenging thermal spikes over 3 days. Overall, we found that exposure to elevated rearing temperatures had a large impact on thermal tolerance, where elevated-temperature reared offspring had significantly higher CTMax. In comparison, egg cortisol treatment had little to no clear effects on CTMax and blood energetic response. Our study demonstrates the importance of elevated water temperatures as an inducer of offspring phenotypes (via early developmental cues), and highlights the significance of examining offspring performance in environments with ecologically relevant stressors.
Highlights
Climate change is a major contributor to rapid global changes, whether via increasing average temperatures (Solomon et al, 2012), or increasing frequency of extreme weather events
We already appreciate that elevated temperatures can lead to altered offspring phenotypes across generations (Burt et al, 2011; Jonsson and Jonsson, 2016; Le Roy et al, 2017), it is unclear whether phenotypes induced by maternal stress signals enable offspring to optimally respond to chronic elevated rearing temperature as well as rapid, extreme changes in water temperature, especially in at-risk species (Love et al, unpublished; Sopinka et al, 2017)
For Critical Thermal Maximum (CTMax), we examined the interactive effects of rearing temperature and prenatal cortisol using a model that included the fixed effects of rearing temperature × cortisol treatment interaction, and their main effects and marginal and conditional R2 values of significant interactions against model without interaction, as a method of estimating the interaction effect size
Summary
Climate change is a major contributor to rapid global changes, whether via increasing average temperatures (Solomon et al, 2012), or increasing frequency of extreme weather events (e.g., droughts: Rahmstorf and Coumou, 2011). Exposure to increased maternal GCs has been shown to result in phenotypes expected to have lowered energetic demand (i.e., slower growth: Hayward and Wingfield, 2004, smaller body size: Love et al, 2005; Burton et al, 2011, and lower baseline energetics: Capelle, 2017), allowing offspring to outcompete individuals with faster growth or larger size in energetically demanding warmer waters (Messmer et al, 2017) This expected increase in performance of offspring exposed to increased maternal GCs within a harsher environment requires further testing (Sopinka et al, 2017). We already appreciate that elevated temperatures can lead to altered offspring phenotypes across generations (Burt et al, 2011; Jonsson and Jonsson, 2016; Le Roy et al, 2017), it is unclear whether phenotypes induced by maternal stress signals (via GCs) enable offspring to optimally respond to chronic elevated rearing temperature as well as rapid, extreme changes in water temperature, especially in at-risk species (Love et al, unpublished; Sopinka et al, 2017)
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