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

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

Abstract

Background: 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.

Conclusions: 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological / genetics*
  • Amino Acid Sequence
  • Animals
  • Antarctic Regions
  • Arthropod Proteins / genetics*
  • Arthropod Proteins / metabolism
  • Biological Evolution
  • Climate Change
  • Ecosystem
  • Euphausiacea / classification
  • Euphausiacea / genetics*
  • Euphausiacea / metabolism
  • Gene Expression
  • HSP70 Heat-Shock Proteins / genetics*
  • HSP70 Heat-Shock Proteins / metabolism
  • Molecular Sequence Data
  • Multigene Family
  • Phylogeny
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Species Specificity
  • Temperature

Substances

  • Arthropod Proteins
  • HSP70 Heat-Shock Proteins

Grant support

KC received a PhD grant by the Emergence-UPMC 2011 research program and the “Région Bretagne”. JYT benefited from funding provided by Institut Paul Emile Victor (IPEV) (KREVET program) and also by the “Région Bretagne” (SAD-1 - DRAKAR program). MSC was funded by the Polar Sciences for Planet Earth programme, by the British Antarctic Survey and the Natural Environment Research Council. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.