Abstract
To better understand the effects of transient thermal stress in an aquatic insect, we first identified static temperatures associated with fitness deficits, and then reared larvae from egg hatch to adulthood under diurnally variable regimens including daily forays into deleterious temperatures. We sampled mature larvae at the coolest and warmest portions of their respective regimens for RNA-seq analysis. Few transcripts (28) were differentially expressed when larvae oscillated between favorable temperatures, while 614 transcripts were differentially expressed when experiencing daily transient thermal stress. Transcripts associated with N-glycan processing were downregulated while those associated with lipid catabolism and chitin turnover were significantly upregulated in heat stressed larvae. An across-regimen comparison of differentially expressed transcripts among organisms sampled at comparable temperatures demonstrated that the effects of daily thermal stress persisted even when larvae were sampled at a more optimal temperature (806 differentially expressed transcripts). The chronically stressed population had reduced expression of transcripts related to ATP synthesis, mitochondrial electron chain functions, gluconeogenesis and glycolytic processes while transcripts associated with cell adhesion, synaptic vesicle transport, regulation of membrane potential and lipid biosynthesis increased. Comparisons of constant vs. variable temperatures revealed that the negative consequences of time spent at stressful temperatures were not offset by more time spent at optimal temperatures.
Highlights
To better understand the effects of transient thermal stress in an aquatic insect, we first identified static temperatures associated with fitness deficits, and reared larvae from egg hatch to adulthood under diurnally variable regimens including daily forays into deleterious temperatures
As the global climate changes and human activities alter the thermal regimes of freshwater ecosystems[13,14,15,16], it is increasingly likely that organisms are subjected to stressful temperatures on different temporal scales17(e.g. hourly, daily, seasonally, annually) that differentially affect physiological processes, developmental trajectories, life history outcomes, and species distributions[18]
We have developed a better understanding of both short-term[36,37] and long-term[38] thermal challenge in N. triangulifer, but the more ecologically relevant situation of long-term development in a diel thermal regime with daily excursions out of the acclimation zone and into stressful temperatures has remained unstudied
Summary
To better understand the effects of transient thermal stress in an aquatic insect, we first identified static temperatures associated with fitness deficits, and reared larvae from egg hatch to adulthood under diurnally variable regimens including daily forays into deleterious temperatures. An across-regimen comparison of differentially expressed transcripts among organisms sampled at comparable temperatures demonstrated that the effects of daily thermal stress persisted even when larvae were sampled at a more optimal temperature (806 differentially expressed transcripts). As the global climate changes and human activities alter the thermal regimes of freshwater ecosystems[13,14,15,16], it is increasingly likely that organisms are subjected to stressful temperatures on different temporal scales17(e.g. hourly, daily, seasonally, annually) that differentially affect physiological processes, developmental trajectories, life history outcomes, and species distributions[18]. Understanding the physiological processes that occur under repeated, transient thermal stress are especially important because this situation is likely common as conditions warm
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