@article {3745, title = {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.}, journal = {PLoS One}, volume = {10}, year = {2015}, month = {2015}, pages = {e0121642}, 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.

}, issn = {1932-6203}, doi = {10.1371/journal.pone.0121642}, author = {Cascella, K{\'e}vin and Jollivet, Didier and Papot, Claire and Nelly L{\'e}ger and Corre, Erwan and Juliette Ravaux and Clark, Melody S and Toullec, Jean-Yves} } @article {3761, title = {Epsilonproteobacteria as gill epibionts of the hydrothermal vent gastropod Cyathermia naticoides (North East-Pacific Rise)}, journal = {Marine Biology}, volume = {162}, year = {2015}, month = {11 D{\'e}c 2014}, pages = {435-448}, abstract = {

Mollusks, and particularly gastropods, are one of the major taxonomic groups at vents. In these ecosystems, devoid of light, chemoautotrophic bacteria are at the base of the food web and symbiotic association between metazoa and these bacteria is numerous. Nevertheless, apart few {\textquotedblleft}large-size{\textquotedblright} well-known species, the {\textquotedblleft}small-size{\textquotedblright} gastropods (shell \<5\ mm), although very abundant, remain poorly studied regarding symbioses. We investigated here Cyathermia naticoides (War{\'e}n and Bouchet in Zool Scr 18(1), 1989), a small coiled gastropod found in abundance on the East Pacific Rise among Riftia pachyptila tubes, and usually inferred to graze on tubeworm bacterial cover, and/or filter feeding. Among mollusks, symbioses are well known in large species and almost exclusively rely on sulfide or methane-oxidizing proteobacterial endosymbionts, occurring within the host tissues in gill epithelial bacteriocytes. Combining several approaches (molecular biology, microscopy, stable isotopes analyses), we described here an unusual symbiosis, where autotrophic filamentous Epsilonproteobacteria are located extracellularly, at the base of host gill filaments. Numerous endocytotic lysosome-like structures were observed in the gill epithelium of the animal suggesting bacteria may contribute to its nutrition through intracellular digestion by gill cells. Additional food source by non-symbiotic proteobacteria grazed on R. pachyptila tubes could complete the diet. The possible role of temperature in the selection of Epsilon- vs Gammaproteobacterial partners is discussed.

}, url = {http://link.springer.com/article/10.1007/s00227-014-2591-7$\#$}, author = {Magali Zbinden and Marqu{\'e}, Lise and Sylvie M Gaudron and Juliette Ravaux and Nelly L{\'e}ger and S{\'e}bastien Duperron} }