Abstract
The adaptive value of phenotypic plasticity for performance under single stressors is well documented. However, plasticity may only truly be adaptive in the natural multifactorial environment if it confers resilience to stressors of a different nature, a phenomenon known as cross‐tolerance. An understanding of the mechanistic basis of cross‐tolerance is essential to aid prediction of species resilience to future environmental change. Here, we identified mechanisms underpinning cross‐tolerance between two stressors predicted to increasingly challenge aquatic ecosystems under climate change, chronic warming and hypoxia, in an ecologically‐important aquatic invertebrate. Warm acclimation improved hypoxic performance through an adaptive hypometabolic strategy and changes in the expression of hundreds of genes that are important in the response to hypoxia. These ‘frontloaded’ genes showed a reduced reaction to hypoxia in the warm acclimated compared to the cold acclimated group. Frontloaded genes included stress indicators, immune response and protein synthesis genes that are protective at the cellular level. We conclude that increased constitutive gene expression as a result of warm acclimation reduced the requirement for inducible stress responses to hypoxia. We propose that transcriptional frontloading contributes to cross‐tolerance between stressors and may promote fitness of organisms in environments increasingly challenged by multiple anthropogenic threats.
Highlights
Animals in the wild naturally encounter changes to multiple environmental drivers (Boyd et al, 2018)
In addition to natural environmental fluctuations, free-living wild animals across ecosystems are being increasingly pressured by greater intensities of stressor combinations under climate change, driving reductions in performance and fitness (Deutsch et al, 2015; Gunderson et al, 2016) plasticity displayed upon exposure to one environmental driver may only be adaptive if it does not come at the cost of impaired performance under another, a phenomenon referred to as “cross-susceptibility” (Todgham & Stillman, 2013)
This study aimed to investigate whether transcriptional frontloading generates cross-tolerance between stressors
Summary
Animals in the wild naturally encounter changes to multiple environmental drivers (Boyd et al, 2018). Trade-offs between competing physiological demands from multiple stressors constrain fitness (Kelly et al, 2016) Transcriptional frontloading of protective groups of genes such as cellular defences or metabolic genes has been demonstrated between populations along environmental gradients with consequences for whole-organism thermal tolerance (Barshis et al, 2013; Dong et al, 2008; Kenkel et al, 2013). Thermal acclimation could be predicted to alter hypoxic performance if it induces mechanisms to either increase oxygen supply or reduce oxygen demand, i.e. hypometabolism (Anttila et al, 2015; McBryan et al, 2013). The molecular mechanisms underpinning responses to these treatments were evaluated using RNA-Seq
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