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PLoS One. 2015 Apr 2;10(4):e0121642. doi: 10.1371/journal.pone.0121642. eCollection 2015.

Diversification, evolution and sub-functionalization of 70kDa heat-shock proteins in two sister species of antarctic krill: differences in thermal habitats, responses and implications under climate change.

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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.
Sorbonne Universités, UPMC Université Paris 06, UMR 7208 CNRS, Equipe AMEX, 75005 Paris, France; CNRS 7208, BOREA, UPMC Université Paris 06, 75005 Paris, France.
Sorbonne Universités, UPMC Université Paris 06, FR 2424 CNRS, ABiMS, Analysis and Bioinformatics for Marine Science, Station Biologique de Roscoff, 29680 Roscoff, France; CNRS, FR 2424, Station Biologique de Roscoff, 29680 Roscoff, France.
British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge, CB3 0ET, United Kingdom.



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.


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.

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