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International audience; Describing patterns of connectivity throughout a species range is critical to conservation management. In common with other mammals, pinnipeds typically display male-biased dispersal. Earlier studies using mitochondrial DNA showed that the endangered Australian sea lion (Neophoca cinerea) exhibits extreme matrilineal structure throughout its range. If male dispersal were similarly restricted, most breeding colonies may not receive sufficient levels of new genetic variation to buffer against risks associated with inbreeding and environmental change. To address these concerns we used 16 microsatellite loci to obtain a more highly resolving measure of genetic structure among colonies and determine whether dispersal is male-biased. We found that both male and female Australian sea lions are highly philopatric with limited dispersal. Within those constraints, when animals disperse between close colonies (

International audience; 1. The degree of individual specialization in resource use differs widely among wild populationswhere individuals range from fully generalized to highly specialized. This interindividualvariation has profound implications in many ecological and evolutionary processes. A recentreview proposed four main ecological causes of individual specialization: interspecific andintraspecific competition, ecological opportunity and predation.2. Using the isotopic signature of subsampled whiskers, we investigated to what degree threeof these factors (interspecific and intraspecific competition and ecological opportunity) affectthe population niche width and the level of individual foraging specialization in two fur sealspecies, the Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalustropicalis), over several years.3. Population niche width was greater when the two seal species bred in allopatry (low interspecificcompetition) than in sympatry or when seals bred in high-density stabilized colonies (highintraspecific competition). In agreement with the niche variation hypothesis (NVH), higherpopulation niche width was associated with higher interindividual niche variation. However, incontrast to the NVH, all Antarctic females increased their niche width during the interbreedingperiod when they had potential access to a wider diversity of foraging grounds and associatedprey (high ecological opportunities), suggesting they all dispersed to a similar productive area.4. The degree of individual specialization varied among populations and within the annualcycle. Highest levels of interindividual variation were found in a context of lower interspecificor higher intraspecific competition. Contrasted results were found concerning the effect ofecological opportunity. Depending on seal species, females exhibited either a greater or lowerdegree of individual specialization during the interbreeding period, reflecting species-specificbiological constraints during that period.5. These results suggest a significant impact of ecological interactions on the population nichewidth and degree of individual specialization. Such variation at the individual level may bean important factor in the species plasticity with significant consequences on how it mayrespond to environmental variability.

International audience; Highlights• We assessed the extent of geographical variation in male Australian sea lion calls.• We found significant variation in male vocalization across breeding colonies.• The acoustic structure does not fully reflect either genetic or geographical patterns.• Concordance between acoustic and genetic structures is found at large scale only.• Environmental or morphological factors may refine differences in vocal characteristics.Vocalizing by males plays an important role in the reproductive activities of many species. Geographical variation in the characteristics of male vocalization is well studied in birds, but largely unexplored in mammals. This study quantified the extent of geographical variation in male Australian sea lion, Neophoca cinerea, barking calls and examined what drives vocal differences in this species. We recorded male barking calls from seven breeding colonies separated by ca. 5–2700 km enabling us to investigate acoustic differences on both micro- and macrogeographical scales. Our results revealed significant nonuniform geographical variation across colonies. Neither genetic nor geographical distances between colonies fully explained the observed acoustic variation. We suggest that environmental or morphological factors are likely to further contribute to differences in vocal characteristics.

International audience; The estimation of milk consumption in free-ranging seals using tritium dilution techniques makes the key assumption that the animals drink no pre-formed water during the experimental period. However, frequent observations of unweaned Antarctic fur seal pups drinking water at Iles Kerguelen necessitated the testing of this assumption. We estimated water flux rates of 30 pups (10.7"0.3 kg) in four experimental groups by isotopic dilution over 4 days. The groups were: (1) pups held in an open air enclosure without access to water to estimate fasting metabolic water production (MWP); (2) free-ranging pups not administered additional water; (3) pups held in an open air enclosure and given a total of 300 ml of fresh water to verify technique accuracy; and (4) free-ranging pups given 200 ml of fresh water. Pups without access to water exhibited water flux rates (20.5"0.8 ml kgy1dy1), which were significantly lower than those observed for the free-ranging group (33.0"1.7 ml kgy1 dy1). Mean estimated pre-formed water intake for the free-ranging experimental groups was 12.6 ml kgy1 dy1. Thus, MWP, measured as total water intake during fasting, may be significantly overestimated in free-ranging Antarctic fur seal pups at Iles Kerguelen and at other sites and subsequently milk intake rates may be underestimated.