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Human activities on the shoreline generate a growing pollution, creating deleterious habitats in coastal zones. Some species nevertheless succeed in such harsh milieus, raising the question of their tolerance to environmental stress. The annelid Hediste diversicolor lives buried in the sediments, directly exposed to contaminants trapped in the mud. After verifying the similarity of their genetic contexts, we compared reproductive output and individual immune resistance measures of populations living in polluted vs. 'clean' sediments, and related these assessments with measures of phthalates and metal pollution, and associated toxicity indices. Chemical analyses predicted no toxicity to the local infauna, and phenological studies evidenced no direct cost of living in noxious habitats. However, populations exposed to pollutants showed a significantly reduced survival upon infection with a local pathogen. Surprisingly, physiological studies evidenced a basal overinflammatory state in the most exposed populations. This over-activated baseline immune phenotype likely generates self-damage leading to enhanced immune cell death rate and immune failure. Monitoring the immune status of individual worms living in anthropic areas could thus be used as a reliable source of information regarding the actual health of wild populations., (Copyright © 2017 Elsevier B.V. All rights reserved.)

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Evolution of antimicrobial peptides (AMPs) has been shown to be driven by recurrent duplications and balancing/positive selection in response to new or altered bacterial pathogens. We use Alvinella pompejana, the most eurythermal animal known on Earth, to decipher the selection patterns acting on AMP in an ecological rather than controlled infection approach. The preproalvinellacin multigenic family presents the uniqueness to encode a molecular chaperone (BRICHOS) together with an AMP (alvinellacin) that controls the vital ectosymbiosis of Alvinella. In stark contrast to what is observed in the context of the Red queen paradigm, we demonstrate that exhibiting a vital and highly conserved ecto-symbiosis in the face of thermal fluctuations has led to a peculiar selective trend promoting the adaptive diversification of the molecular chaperone of the AMP, but not of the AMP itself. Because BRICHOS stabilizes beta-stranded peptides, this polymorphism likely represents an eurythermal adaptation to stabilize the structure of alvinellacin, thus hinting at its efficiency to select and control the epibiosis across the range of temperatures experienced by the worm; Our results fill some knowledge gaps concerning the function of BRICHOS in invertebrates and offer perspectives for studying immune genes in an evolutionary ecological framework.

The Arctic and the Antarctic Peninsula are currently experiencing some of the most rapid rates of ocean warming on the planet. This raises the question of how the initial adaptation to extreme cold temperatures was put in place and whether or not directional selection has led to the loss of genetic variation at key adaptive systems, and thus polar species' (re)adaptability to higher temperatures. In the Southern Ocean, krill represents the most abundant fauna and is a critical member at the base of the Antarctic food web. To better understand the role of selection in shaping current patterns of polymorphisms, we examined genetic diversity of the cox-1 and hsp70 genes by comparing two closely related species of Euphausiid that differ in ecology. Results on mtcox-1 agreed with previous studies, indicating high and similar effective population sizes. However, a coalescent-based approach on hsp70 genes highlighted the role of positive selection and past demographic changes in their recent evolution. Firstly, some form of balancing selection was acting on the inducible isoform C, which reflected the maintenance of an ancestral adaptive polymorphism in both species. Secondly, E. crystallorophias seems to have lost most of its hsp70 diversity because of a population crash and/or directional selection to cold. Nonsynonymous diversities were always greater in E. superba, suggesting that it might have evolved under more heterogeneous conditions. This can be linked to species' ecology with E. superba living in more variable pelagic conditions, while E. crystallorophias is strictly associated with continental shelves and sea ice.

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.