Abstract: Sperm quality determines offspring fitness. However, investment into sperm being costly, it depends on the health or condition of males. According to the differential allocation hypothesis, males should decrease their investment into sperm when mated with a low-quality female. In this study, we show that, in the black-legged kittiwake, a monogamous seabird, sperm quality affects chick performance and that good-quality males produce a sperm of good quality. In addition, males mated with more genetically compatible females produce better quality sperm. This study suggests that the effects of sperm quality on offspring fitness may act as a natural selective pressure on males' differential allocation strategies.

Abstract: Our understanding of how microbiome signatures are modulated in wild fish populations remains poorly developed and has, until now, mostly been inferred from studies in commercial and farmed fish populations. Here, for the first time, we have studied changes in the skin and blood microbiomes of the Salmo trutta population of the volcanic Kerguelen archipelago located at the northern limit of the Antarctic Ocean. The Kerguelen Islands present a natural framework of population expansion and reveal a likely situation representing further climate change in distribution areas. Our results showed that S. trutta of the Kerguelen Islands has a microbiome signature distinct from those of salmonids of the Northern Hemisphere. Our study also revealed that the skin and blood microbiomes differ between sedentary and migratory S. trutta. While 18 phyla were shared between both groups of trout, independent of the compartment, 6 phyla were unique to migratory trout. Further analyses showed that microbiome signatures undergo significant site-specific variations that correlate, in some cases, with the peculiarity of specific ecosystems. Our study also revealed the presence of potential pathogens at particular sites and the impact of abiotic factors on the microbiome, most notably due to the volcanic nature of the environment. This study contributes to a better understanding of the factors that modulate the microbiome signatures of migratory and sedentary fish populations. It will also help to better monitor the impacts of climate change on the colonization process in the sub-Antarctic region.

Abstract:

Les milieux polaires et subpolaires ne sont pas dépourvus de parasites. Chez les manchots royaux, les ectoparasites tels que les tiques (Ixodes uriae) sont suspectés d’avoir des effets marqués sur la santé et le succès reproducteur des adultes. En utilisant un traitement expérimental réduisant drastiquement l’abondance d’ectoparasites chez des adultes reproducteurs, nous avons pu démontrer que l’infestation par les ectoparasites induit une augmentation du stress physiologique caractérisé par des taux élevés de corticostérone (glucocorticoïde) et une situation de stress oxydant. Bien que l’éradication des ectoparasites n’ait pas d’influence notable sur le succès d’éclosion des œufs ou la survie des poussins durant l’élevage, le traitement améliore visiblement la croissance des poussins jusqu’à l’émancipation, avec des effets positifs probables sur leur survie future. Il semble donc que les ectoparasites exercent une pression de sélection naturelle non-négligeable chez le manchot royal.

Abstract: The ability of marine mammals to accumulate sufficient lipid energy reserves is vital for mammals' survival and successful reproduction. However, long-term monitoring of at-sea changes in body condition, specifically lipid stores, has only been possible in elephant seals performing prolonged drift dives (low-density lipids alter the rates of depth change while drifting). This approach has limited applicability to other species. Using hydrodynamic performance analysis during transit glides, we developed and validated a novel satellite-linked data logger that calculates real-time changes in body density (?lipid stores). As gliding is ubiquitous amongst divers, the system can assess body condition in a broad array of diving animals. The tag processes high sampling rate depth and three-axis acceleration data to identify 5 s high pitch angle glide segments at depths >100 m. Body density is estimated for each glide using gliding speed and pitch to quantify drag versus buoyancy forces acting on the gliding animal. We used tag data from 24 elephant seals (Mirounga spp.) to validate the onboard calculation of body density relative to drift rate. The new tags relayed body density estimates over 200 days and documented lipid store accumulation during migration with good correspondence between changes in body density and drift rate. Our study provided updated drag coefficient values for gliding (Cd,f = 0.03) and drifting (Cd,s = 0.12) elephant seals, both substantially lower than previous estimates. We also demonstrated post-hoc estimation of the gliding drag coefficient and body density using transmitted data, which is especially useful when drag parameters cannot be estimated with sufficient accuracy before tag deployment. Our method has the potential to advance the field of marine biology by switching the research paradigm from indirectly inferring animal body condition from foraging effort to directly measuring changes in body condition relative to foraging effort, habitat, ecological factors and anthropogenic stressors in the changing oceans. Expanding the method to account for diving air volumes will expand the system's applicability to shallower-diving (<100 m) species, facilitating real-time monitoring of body condition in a broad range of breath-hold divers.