Background: Identifying genes of adaptive significance in a changing environment is a major focus of ecological genomics. Such efforts were restricted, until recently, to researchers studying a small group of model organisms or closely related taxa. With the advent of next generation sequencing (NGS), genomes and transcriptomes of virtually any species are now available for studies of adaptive evolution. We experimentally manipulated temperature conditions for two groups of crimson spotted rainbowfish (Melanotaenia duboulayi) and measured differences in RNA transcription between them. This non-migratory species is found across a latitudinal thermal gradient in eastern Australia and is predicted to be negatively impacted by ongoing environmental and climatic change. Results: Using next generation RNA-seq technologies on an Illumina HiSeq2000 platform, we assembled a de novo transcriptome and tested for differential expression across the treatment groups. Quality of the assembly was high with a N50 length of 1856 bases. Of the 107,749 assembled contigs, we identified 4251 that were differentially expressed according to a consensus of four different mapping and significance testing approaches. Once duplicate isoforms were removed, we were able to annotate 614 up-regulated transfrags and 349 that showed reduced expression in the higher temperature group. Conclusions: Annotated blast matches reveal that differentially expressed genes correspond to critical metabolic pathways previously shown to be important for temperature tolerance in other fish species. Our results indicate that rainbowfish exhibit predictable plastic regulatory responses to temperature stress and the genes we identified provide excellent candidates for further investigations of population adaptation to increasing temperatures.

We studied the impact of hibernation and food supply on relative telomere length (RTL), an indicator for aging and somatic maintenance, in free-living edible dormice. Small hibernators such as dormice have ∼50% higher maximum longevity than non-hibernators. Increased longevity could theoretically be due to prolonged torpor directly slowing cellular damage and RTL shortening. However, although mitosis is arrested in mammals at low body temperatures, recent evidence points to accelerated RTL shortening during periodic re-warming (arousal) from torpor. Therefore, we hypothesized that these arousals during hibernation should have a negative effect on RTL. Here, we show that RTL was shortened in all animals over the course of ∼1 year, during which dormice hibernated for 7.5–11.4 months. The rate of periodic arousals, rather than the time spent euthermic during the hibernation season, was the best predictor of RTL shortening. This finding points to negative effects on RTL of the transition from low torpor to high euthermic body temperature and metabolic rate during arousals, possibly because of increased oxidative stress. The animals were, however, able to elongate their telomeres during the active season, when food availability was increased by supplemental feeding in a year of low natural food abundance. We conclude that in addition to their energetic costs, periodic arousals also lead to accelerated cellular damage in terms of RTL shortening. Although dormice are able to counteract and even over-compensate for the negative effects of hibernation, restoration of RTL appears to be energetically costly.

Significance: Adaptation to climate change is expected to be influenced by thermal conditions experienced by species during their evolutionary history. We studied plastic capacity as a target of climatic selection, hypothesizing that populations that evolved under warmer climates have greater plastic adaptive resilience to climate change. This was tested experimentally by comparing upper thermal tolerance and gene expression in fish populations from desert, temperate, and subtropical regions of Australia. Divergent adaptive plastic responses to future climates were found across different bioregions, including in key heat stress genes. The greatest adaptive resilience was shown by the subtropical ecotype, followed by the desert and temperate ecotypes. These results have implications for large-scale assessments of climate impacts and for predictions of species distribution changes.