Abstract: The Kerguelen archipelago, isolated in the Southern Ocean, shelters a blue mussel Mytilus metapopulation far from any influence of continental populations or any known hybrid zone. The finely carved coast leads to a highly heterogeneous habitat. We investigated the impact of the environment on the genetic structure in those Kerguelen blue mussels by relating allele frequencies to habitat descriptors. A total sample comprising up to 2248 individuals from 35 locations was characterized using two nuclear markers, mac-1 and Glu-5′, and a mitochondrial marker (COI). The frequency data from 9 allozyme loci in 9 of these locations were also reanalyzed. Two other nuclear markers (EFbis and EFprem's) were monomorphic. Compared to Northern Hemisphere populations, polymorphism in Kerguelen blue mussels was lower for all markers except for the exon Glu-5′. At Glu-5′, genetic differences were observed between samples from distinct regions (FCT = 0.077), as well as within two regions, including between samples separated by <500 m. No significant differentiation was observed in the AMOVA analyses at the two other markers (mac-1 and COI). Like mac-1, all allozyme loci genotyped in a previous publication, displayed lower differentiation (Jost's D) and FST values than Glu-5′. Power simulations and confidence intervals support that Glu-5′ displays significantly higher differentiation than the other loci (except a single allozyme for which confidence intervals overlap). AMOVA analyses revealed significant effects of the giant kelp Macrocystis and wave exposure on this marker. We discuss the influence of hydrological conditions on the genetic differentiation among regions. In marine organisms with high fecundity and high dispersal potential, gene flow tends to erase differentiation, but this study showed significant differentiation at very small distance. This may be explained by the particular hydrology and the carved coastline of the Kerguelen archipelago, together with spatially variable selection at Glu-5′

Abstract: Because glucocorticoid (stress) hormones fundamentally affect various aspects of the behaviour, life history and fitness of free-living vertebrates, there is a need to understand the environmental factors shaping their variation in natural populations. Here, we examined whether spatial heterogeneity in breeding territory quality affected the stress of colonial king penguin (Aptenodytes patagonicus). We assessed the effects of local climate (wind, sun and ambient temperature) and social conditions (number of neighbours, distance to neighbours) on the baseline levels of plasma total corticosterone (CORT) in 77 incubating and 42 chick-brooding birds, breeding on territories of central or peripheral colony location. We also assessed the oxidative stress status of a sub-sample of central vs. peripheral chick-brooders to determine whether chronic stress arose from breeding on specific territories. On average, we found that brooders had 55 % higher CORT levels than incubators. Regardless of breeding status, central birds experienced greater social density (higher number of neighbours, shorter distance between territories) and had higher CORT levels than peripheral birds. Increasing social density positively explained 40 % of the variation in CORT levels of both incubators and brooders, but the effect was more pronounced in brooders. In contrast, climate was similar among breeding territories and did not significantly affect the CORT levels of breeding birds. In brooders, oxidative stress status was not affected by local density or weather conditions. These results highlight that local heterogeneity in breeding (including social) conditions may strongly affect the stress levels of breeding seabirds. The fitness consequences of such variation remain to be investigated.

Abstract: 1. For seabirds that forage at sea but breed fasting on land, successful reproduction depends
on the effective management of energy stores. Additionally, breeding often means
aggregating in dense colonies where social stress may affect energy budgets.
2. King penguin (Aptenodytes patagonicus) males fast for remarkably long periods (up to 1.5
months) while courting and incubating ashore. Although their fasting capacities have been
well investigated in captivity, we still known very little on the energetics of freely
breeding birds.
3. We monitored the heart rate (HR; a proxy to energy expenditure), body temperature, and
physical activity of male king penguins during their courtship and first incubation shift in
a colony of some 24,000 freely breeding pairs. Males were either breeding under low but
increasing colony density (early breeders), or at high and stable density (late breeders).
4. In early breeders, daily mean and resting HR decreased during courtship but increased
again 3 days before egg-laying and during incubation. In late breeders, HR remained
stable throughout this same breeding period. Interestingly, the daily increase in resting HR
we observed in early breeders was strongly associated with a marked increase in colony
density over time. This finding remained significant even after controlling for climate
effects.
5. In both early and late breeders, courtship and incubation were associated with a
progressive decrease in physical activity, whereas core body temperature remained
unchanged.
6. We discuss the roles of decreased physical activity and thermoregulatory strategies in
sustaining the long courtship-incubation fast of male king penguins. We also draw
attention to a potential role for conspecific density in affecting the energetics of breeding
fasting seabirds, i.e. a potential energy cost to coloniality.