Contrasting transcriptome response to thermal stress in two key zooplankton species, Calanus finmarchicus and C. glacialis

Abstract

Climate change has already led to the range expansion of warm-water plankton assemblages in the northeast Atlantic and the corresponding range contraction of colder-water species. The temperate copepod Calanus finmarchicus is predicted to shift farther northward into polar waters traditionally dominated by the arctic copepod C. glacialis. To identify temperaturemediated changes in gene expression that may be critical for the thermal acclimation and resilience of the 2 Calanus spp., we conducted a whole transcriptome profiling using RNA-seq on an Ion Torrent platform. Transcriptome responses of C. finmarchicus and C. glacialis from Disko Bay, west Greenland, were investigated under realistic thermal stresses (at + 5, +10 and +15°C) for 4 h and 6 d. C. finmarchicus showed a strong response to temperature and duration of stress, involving up-regulation of genes related to protein folding, transcription, translation and metabolism. In sharp contrast, C. glacialis displayed only low-magnitude changes in gene expression in response to temperature and duration of stress. Differences in the thermal responses of the 2 species, particularly the lack of thermal stress response in C. glacialis, are in line with laboratory and field observations and suggest a vulnerability of C. glacialis to climate change.

Reduced up-regulation of gene expression in response to elevated temperatures in the mid-Atlantic population of Calanus finmarchicus

“…Fecal pellet production rate was significantly affected by temperature in each experiment. During STC FPR values were significantly higher at 10°C and 15°C than at 0°C and 5°C (P b 0.05) (similar to the previous study; Smolina et al, 2015), while during LTC FPR values were significantly higher at 5°C, 10°C, and 15°C than at 0°C (P b 0.01, Fig. 1A).…”

“…No significant change in the expression of the two hsp genes studied here (hsp70_2 and dnaja1) were observed in the midAtlantic population of C. finmarchicus in contrast to the northern population ( Fig. 2; Smolina et al, 2015). Nevertheless, it is too early to conclude that this population is not stressed at 20°C, particularly given its high mortality and low percent of spawning females after 6 days at this temperature.…”

“…Constitutive expression of these hsps could be explained by multiple homologues within hsp families in Calanus spp. and their differential regulation under various stresses (Aruda et al, 2011;Smolina et al, 2015;Voznesensky et al, 2004). Therefore, additional whole transcriptome profiling would be beneficial and may result in detection of both populationspecific and population-universal molecular processes in response to stress.…”

“…were performed as described in Smolina et al (2015). Expression quantities of the five genes were normalized using geNorm 3.5 (Vandesompele et al, 2002) and two reference genes.…”

“…Experimental manipulation is one way to study a species tolerance to various components of the climate, and to forecast consequences at both the species and ecosystem level. Accordingly, the responses of several Calanus species to various climate stressors such as temperature (Grote et al, 2015;Hildebrandt et al, 2014;Kjellerup et al, 2012;Smolina et al, 2015), ocean acidification (Hildebrandt et al, 2014;Pedersen et al, 2013;Runge et al, 2016;Weydmann et al, 2012), and harmful algal blooms (Lauritano et al, 2012(Lauritano et al, , 2015Roncalli et al, 2016) have already been studied. Within these studies considerable attention has been devoted to temperature, since it affects every aspect of the zooplankton life, from cellular processes to behaviour, development and fitness (Clarke, 2003;Huntley and Lopez, 1992), as well as distributional shifts of Calanus Helaouët et al, 2011;Reygondeau and Beaugrand, 2011a).…”