Abstract: Understanding the factors that sculpt fish gut microbiome is challenging, especially in natural populations characterized by high environmental and host genomic complexity. Yet, closely related hosts are valuable models for deciphering the contribution of host evolutionary history to microbiome assembly, through the underscoring of phylosymbiosis and co-phylogeny patterns. Here, we hypothesized that the recent allopatric speciation of Harpagifer across the Southern Ocean (1.2–0.8 Myr) will promote the detection of robust phylogenetic congruence between the host and its microbiome. We characterized the gut mucosa microbiome of 77 individuals from four field-collected species of the plunderfish Harpagifer (Teleostei, Notothenioidei), distributed across three biogeographic regions of the Southern Ocean. We found that seawater physicochemical properties, host phylogeny and geography collectively explained 35% of the variation in bacterial community composition in Harpagifer gut mucosa. The core microbiome of Harpagifer spp. gut mucosa was characterized by a low diversity, mostly driven by selective processes, and dominated by a single Aliivibrio taxon detected in more than 80% of the individuals. Almost half of the core microbiome taxa, including Aliivibrio, harbored co-phylogeny signal at microdiversity resolution with Harpagifer phylogeny. This suggests an intimate symbiotic relationship and a shared evolutionary history with Harpagifer. The robust phylosymbiosis signal emphasizes the relevance of the Harpagifer model to understanding the contribution of fish evolutionary history to the gut microbiome assembly. We propose that the recent allopatric speciation of Harpagifer across the Southern Ocean may have generated the diversification of Aliivibrio into patterns recapitulating the host phylogeny. Importance Although challenging to detect in wild populations, phylogenetic congruence between marine fish and its microbiome is critical, as it allows highlighting potential intimate associations between the hosts and ecologically relevant microbial symbionts.Through a natural system consisting of closely related fish species of the Southern Ocean, our study provides foundational information about the contribution of host evolutionary trajectory on gut microbiome assembly, that represents an important yet underappreciated driver of the global marine fish holobiont. Notably, we unveiled striking evidence of co-diversification between Harpagifer and its microbiome, demonstrating both phylosymbiosis of gut bacterial communities, and co-phylogeny of specific bacterial symbionts, in patterns that mirror the host diversification. Considering the increasing threats that fish species are facing in the Southern Ocean, understanding how the host evolutionary history could drive its microbial symbiont diversification represents a major challenge to better predict the consequences of environmental disturbances on microbiome and host fitness.

Abstract: Les îles subantarctiques de Kerguelen sont soumises à un changement climatique rapide et intense. Ces îles abritent des espèces végétales endémiques de grand intérêt dans l’hémisphère sud. La flore comporte peu d’espèces et leurs interactions sont mal connues. De tels systèmes pourraient être particulièrement fragiles, et a contrario leur résilience dépendre plus fortement des interactions biotiques entre espèces. Le projet PlantADAPT vise à évaluer et suivre la réponse des espèces de plantes endémiques des îles Kerguelen au changement climatique, en prenant en compte le système plante-sol intégré et les interactions biotiques (plante holobionte). Dans l’objectif d’évaluer les parts respectives de la plasticité phénotypique et de l’adaptation locale dans la variation phénotypique, l’expérience en Jardins Communs est un dispositif déterminant. Nous développons aussi des approches d’écologie fonctionnelle des communautés microbiennes et du système sol associé.

Abstract: Central place foragers such as pelagic seabirds often travel large distances to reach profitable foraging areas. King penguins (Aptenodytes patagonicus) are well known for their large-scale foraging movements to the productive Antarctic Polar Front, though their fine-scale travelling and foraging characteristics remain unclear. Here, we investigated the horizontal movements and foraging patterns of king penguins to understand their fine-scale movement decisions during distant foraging trips. We attached multi-channel data loggers that can record depth, speed, tri-axis acceleration, tri-axis magnetism, and environmental temperature of the penguins and obtained data (n = 8 birds) on their horizontal movement rates from reconstructed dive paths and their feeding attempts estimated from rapid changes in swim speed. During transit toward main foraging areas, penguins increased the time spent on shallow travelling dives (< 50 m) at night and around midday, and increased the time spent on deep foraging dives (≥ 50 m) during crepuscular hours. The horizontal movement rates during deep dives were negatively correlated with maximum dive depths, suggesting that foraging at greater depths is associated with a decreased horizontal travelling speed. Penguins concentrated their foraging efforts (more deep dives and higher rates of feeding attempts) at twilight during transit, when prey may be more accessible due to diel vertical migration, while they travelled rapidly at night and midday when prey may be difficult to detect and access. Such behavioural adjustments correspond to a movement strategy adopted by avian deep divers to travel long distances while feeding on prey exhibiting diel vertical migration.

Abstract: Compared to other animal movements, prospecting by adult individuals for a future breeding site is commonly overlooked. Prospecting influences the decision of where to breed and has consequences on fitness and lifetime reproductive success. By analysing movements of 31 satellite- and GPS-tracked gull and tern populations belonging to 14 species in Europe and North America, we examined the occurrence and factors explaining prospecting by actively breeding birds. Prospecting in active breeders occurred in 85.7% of studied species, across 61.3% of sampled populations. Prospecting was more common in populations with frequent inter-annual changes of breeding sites and among females. These results contradict theoretical models which predict that prospecting is expected to evolve in relatively predictable and stable environments. More long-term tracking studies are needed to identify factors affecting patterns of prospecting in different environments and understand the consequences of prospecting on fitness at the individual and population level.

Abstract: Southern elephant seals (Mirounga leonina) play a pivotal role in the Southern Ocean as wide-ranging marine predators and major prey consumers within Southern Ocean marine ecosystems. Due to their circumpolar distribution and the remoteness of their habitat, large uncertainties remain about their total population sizes. This is especially true for elephant seal populations in the French Southern Territories in the southern Indian Ocean (i.e. Crozet and Kerguelen Archipelagos) as many breeding sites are inaccessible for ground censuses. Here, we present a simple and efficient approach for estimating the total elephant seal populations of the Kerguelen and Crozet Archipelagos by using very high-resolution satellite imagery (<1m resolution). Twenty-eight satellite images taken during the breeding season to count female elephant seals in inaccessible areas were used and complemented the traditional annual ground counts in accessible areas. For Kerguelen Island sectors likely to host colonies and where no satellite images were available for the breeding season, a statistical predictive model was built to estimate the most likely number of breeding females to be present on a given beach according to its physiographic characteristics. Our results show the reliability of using very high-resolution satellite images, a relatively low-cost platform, to count pinniped populations and provide the first estimation of the total southern elephant seal population for both the Kerguelen 347,995 (s e = 4,950) and Crozet 13,065 (s e = 169) Archipelagos. The combined total represents over 35% of the global elephant seal population with the Kerguelen stock being numerically equivalent to the South Georgia stock. In addition, we re-examined the population trends since the last mid-century for Kerguelen and over the last five decades for Crozet. The demographic trends of the southern Indian Ocean populations show marked growth over the last decade (5.1% and 1.6% annual growth rate for Crozet and Kerguelen respectively), particularly on Crozet where the elephant seal population has more than tripled.