Cascella Kévin, Jollivet Didier, Papot Claire, Léger Nelly, Corre Erwan, Ravaux Juliette, Clark Melody S, Toullec Jean-Yves
Sorbonne Universités, UPMC Université Paris 06, UMR 7144 CNRS, Equipe ABICE, Station Biologique de Roscoff, 29680 Roscoff, France; CNRS, UMR 7144, Adaptation et Diversité en Milieu Marin, Station Biologique de Roscoff, 29680 Roscoff, France.
Université de Lille1, CNRS UMR8198, Ecoimmunology of Marine Annelids, 59655 Villeneuve d'Ascq, France.
PLoS One. 2015 Apr 2;10(4):e0121642. doi: 10.1371/journal.pone.0121642. eCollection 2015.
A comparative thermal tolerance study was undertaken on two sister species of Euphausiids (Antarctic krills) Euphausia superba and Euphausia crystallorophias. Both are essential components of the Southern Ocean ecosystem, but occupy distinct environmental geographical locations with slightly different temperature regimes. They therefore provide a useful model system for the investigation of adaptations to thermal tolerance.
METHODOLOGY/PRINCIPAL FINDING: Initial CTmax studies showed that E. superba was slightly more thermotolerant than E. crystallorophias. Five Hsp70 mRNAs were characterized from the RNAseq data of both species and subsequent expression kinetics studies revealed notable differences in induction of each of the 5 orthologues between the two species, with E. crystallorophias reacting more rapidly than E. superba. Furthermore, analyses conducted to estimate the evolutionary rates and selection strengths acting on each gene tended to support the hypothesis that diversifying selection has contributed to the diversification of this gene family, and led to the selective relaxation on the inducible C form with its possible loss of function in the two krill species.
The sensitivity of the epipelagic species E. crystallorophias to temperature variations and/or its adaptation to cold is enhanced when compared with its sister species, E. superba. These results indicate that ice krill could be the first of the two species to be impacted by the warming of coastal waters of the Austral ocean in the coming years due to climate change.
对磷虾科的两个姊妹物种（南极磷虾）——南极大磷虾和晶磷虾进行了比较耐热性研究。它们都是南大洋生态系统的重要组成部分，但占据着不同的环境地理位置，温度状况略有不同。因此，它们为研究耐热性适应提供了一个有用的模型系统。
方法/主要发现：最初的最高临界温度（CTmax）研究表明，南极大磷虾比晶磷虾的耐热性略强。从这两个物种的RNA测序数据中鉴定出了5种热休克蛋白70（Hsp70）mRNA，随后的表达动力学研究揭示了这两个物种中5种直系同源物的诱导存在显著差异，晶磷虾的反应比南极大磷虾更快。此外，为估计作用于每个基因的进化速率和选择强度而进行的分析倾向于支持这样一种假设，即多样化选择促成了这个基因家族的多样化，并导致了诱导型C形式的选择性松弛，其在这两种磷虾物种中可能失去功能。
与姊妹物种南极大磷虾相比，上层物种晶磷虾对温度变化的敏感性和/或其对寒冷的适应性增强。这些结果表明，由于气候变化，冰磷虾可能是未来几年这两个物种中第一个受到南大洋沿海水域变暖影响的物种。
