Cold temperature represses daily rhythms in the liver transcriptome of a stenothermal teleost under decreasing day length

Abstract

The climate-change-driven increase in temperature is occurring rapidly and decreasing the predictability of seasonal rhythms at high latitudes. It is therefore urgent to understand how a change in the relationship between photoperiod and temperature can affect ectotherms in these environments. We tested whether temperature affects daily rhythms of transcription in a cold-adapted salmonid using high-throughput RNA sequencing. Arctic char () from a subarctic population were reared at a high and a low temperature (15 and 8°C) for 1 month under natural, decreasing day length during late summer. Liver transcriptomes were compared between samples collected in the middle and towards the end of the light period and in the middle of the dark period. Daily variation in transcription was lower in fish from the low temperature compared with strong daily variation in warm-acclimated fish, suggesting that cold temperatures dampen the cycling of transcriptional rhythms under a simultaneously decreasing day length. Different circadian clock genes had divergent expression patterns, responding either by decreased expression or by increased rhythmicity at 15°C compared with 8°C. The results point out mechanisms that can affect the ability of fish to adapt to increasing temperatures caused by climate change.

Sex-specific co-expression networks and sex-biased gene expression in the salmonid Brook Charr Salvelinus fontinalis

“…Published male Arctic Charr liver transcriptome data was then compared to the network to evaluate cross-species module preservation (Prokkola et al 2018). Even with caveats regarding sample size (see Methods), several female Brook Charr modules were highly preserved in Arctic Charr males, including blue2 (Zsummary = 34), green (Zsummary = 24), and salmon (Zsummary = 17), also the most conserved in male Brook Charr (Table 1).…”

“…The broodstock of this population was reared in hatchery conditions for three generations after being collected from a subarctic, land-locked population in Finland (Lake Kuolimo, 61°16′ N; 27°32′ E). The data were collected from nine male liver samples (fish relatedness not known) from each of 8 o C and 15 o C (total = 18 samples), but due to a large effect of temperature on the transcriptome, and differences between sampling times in the 15 o C group, only the nine samples from the 8 o C, group were used here (normal rearing temperature during summer at the fish hatchery; Figure S2) (Prokkola et al 2018). Fish body mass at 8°C was on average 24.2 g ± standard deviation (S.D.)…”

“…Sample processing was explained fully by Prokkola et al (2018) and briefly described here. In August 2013, fish were euthanized using 200 ppm sodium bicarbonate-buffered tricaine methanesulfonate (MS-222), after which liver samples were collected and flash frozen in liquid nitrogen (Prokkola et al . 2018).…”

“…However, a network was not constructed for these samples. Using samples from both temperatures, modules were previously identified (Prokkola et al 2018). Once normalized and input to WGCNA, read counts in Arctic Charr 8°C samples were used to build a gene adjacency matrix, which was then compared against modules generated for female and male Brook Charr samples using the modulePreservation function as described above.…”

Circadian rhythms and environmental disturbances – underexplored interactions

“…Accordingly, it has recently been shown that the daily variation of transcription in a polar salmonid, the Arctic char (Salvelinus alpinus), is much reduced after a 1 month acclimation to 8°C in comparison with acclimation to 15°C (Fig. 2) (Prokkola et al, 2018).…”