1. Pilot whales Globicephala spp. are known to display a hierarchical social pattern, but longitudinal data to infer population structure of short-finned pilot whales Globicephala macrorhynchus are rare.2. Using data collected between 2003-2011 in the oceanic archipelago of Madeira, the grouping structure of short-finned pilot whales was studied using photo-identification methods and mtDNA sequences and microsatellite markers to test the hypotheses that (1) there is at least one pelagic and one or more island-associated communities, and (2) groups are made of related individuals, with a matrilineal social structure.3. Pilot whales demonstrated a large degree of variability in site fidelity, including residents (up to 14-year interval), regular visitors and transients. The social and temporal analyses revealed a well-differentiated society with long-lasting relationships (of years). The genetic analyses suggested that individuals of the three residency patterns may not be genetically isolated, and that small groups are made up of related individuals, suggesting some degree of social philopatry, while large groups are probably temporary associations of smaller groups.4. It is proposed that the pilot whales encountered in Madeira belong to a single population encompassing several clans, possibly three clans of island-associated whales and others of transients, each containing two to three matrilineal pods, each with a mean of 15 individuals (SD=9,. We suggest that the clans interact for mating purposes when they meet.5. For management decisions, it is considered that the island-associated whales should not be regarded as demographically independent populations, but instead as stable social entities to be included in governmental management plans and requiring periodic evaluation of their status. The high proportion of marked individuals and low rate of mark change encourages further research in this species.

Despite the openness of the oceanic environment, limited dispersal and tight social structure often induce genetic structuring in marine organisms, even in large animals such as cetaceans. In the bottlenose dolphin, mitochondrial and nuclear DNA analyses have revealed the existence of genetic differentiation between pelagic (or offshore) and coastal (or nearshore) ecotypes in the western North Atlantic, as well as between coastal populations. Because previous studies concentrated on continental margins, we analysed the population structure of bottlenose dolphins in two of the most isolated archipelagos of the North Atlantic: the Azores and Madeira. We analysed 112 samples collected on live animals in the two archipelagos, and nine samples collected on stranded animals in Madeira and mainland Portugal. Genetic analyses consisted in molecular sexing, sequencing of part of the mitochondrial hypervariable region, and screening of ten microsatellite loci. We predicted that: 1/ there is at least one pelagic and one or more coastal populations in each archipelago; 2/ populations are differentiated between and possibly within archipelagos. Contrary to these predictions, results indicated a lack of population structure in the study area. In addition, comparison with published sequences revealed that the samples from the Azores and Madeira were not significantly differentiated from samples of the pelagic population of the western North Atlantic. Thus, bottlenose dolphins occurring in the pelagic waters of the North Atlantic belong to a large oceanic population, which should be regarded as a single conservation unit. Unlike what is known for coastal populations, oceanic bottlenose dolphins are able to maintain high levels of gene flow.

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Mixed‐species associations are temporary associations between individuals of different species that are often observed in birds, primates and cetaceans. They have been interpreted as a strategy to reduce predation risk, enhance foraging success and/or provide a social advantage. In the archipelago of the Azores, four species of dolphins are commonly involved in mixed‐species associations: the common dolphin, Delphinus delphis, the bottlenose dolphin, Tursiops truncatus, the striped dolphin, Stenella coeruleoalba, and the spotted dolphin, Stenella frontalis. In order to understand the reasons why dolphins associate, we analysed field data collected since 1999 by research scientists and trained observers placed onboard fishing vessels. In total, 113 mixed‐species groups were observed out of 5720 sightings. The temporal distribution, habitat (water depth, distance to the coast), behaviour (i.e. feeding, travelling, socializing), size and composition of mixed‐species groups were compared with those of single‐species groups. Results did not support the predation avoidance hypothesis and gave little support to the social advantage hypothesis. The foraging advantage hypothesis was the most convincing. However, the benefits of mixed‐species associations appeared to depend on the species. Associations were likely to be opportunistic in the larger bottlenose dolphin, while there seemed to be some evolutionary constraints favouring associations in the rarer striped dolphin. Comparison with previous studies suggests that the formation of mixed‐species groups depends on several environmental factors, and therefore may constitute an adaptive response.

The Dorado or Plateado (Gilded catfish) Brachyplatystoma rousseauxii (Pimelodidae, Siluriformes) is a commercially valuable migratory catfish performing the largest migration in freshwaters: from the Amazonian headwaters in the Andean foothills (breeding area) to the Amazon estuary (nursery area). In spite of its importance to inform management and conservation efforts, the genetic variability of this species has only recently begun to be studied. The aim of the present work was to determine the population genetic structure of B. rousseauxii in two regions: the Upper Madera Basin (five locations in the Bolivian Amazon) and the Western Amazon Basin (one regional sample from the Uyucalí-Napo-Marañon-Amazon basin, Peru). Length polymorphism at nine microsatellite loci (284 individuals) was used to determine genetic variability and to identify the most probable panmictic units (using a Bayesian approach), after a significant departure from Hardy-Weinberg equilibrium was observed in the overall dataset (Western Amazon + Upper Madera). Bayesian analyses revealed at least three clusters in admixture in the five locations sampled in the Bolivian Amazon, whereas only two of these clusters were observed in the Western Amazon. Considering the migratory behaviour of B. rousseauxii, different life history strategies, including homing, are proposed to explain the cluster distribution. Our results are discussed in the light of the numerous threats to the species survival in the Madera basin, in particular dam and reservoir construction.

(English)In the Northeast Atlantic Ocean, the archipelago of the Azores is frequented by female-offspring groups of sperm whales (Physeter macrocephalus L., 1758), as well as large males. Little is known on their population and group structure, even though the Azores apparently constitute both a feeding ground and a reproduction site. We analysed 151 sloughed skin and biopsy samples by genetic tagging with 11 microsatellite loci and molecular sexing, in order to: determine the population genetic structure, compare relatedness within and between social groups, estimate kinship and the age of males at dispersal. Results suggest that individuals visiting the archipelago of the Azores belong to a single population. High genetic diversity and absence of inbreeding suggest that the population is recovering from whaling. Individuals sampled in close association are highly related, as well as those observed in the same area on the same day, suggesting that secondary social groups (corresponding to the union of primary social units) are composed of relatives. Probable mother-offspring and fullsibling pairs were identified. We obtained an estimated value of 16.6 years for the age of males at dispersal, which was well above previous estimates for this species. Abstract (French)Dans l'Atlantique Nord-Est, l'archipel des Açores est fréquenté par des groupes de cachalots (Physeter macrocephalus L., 1758) femelles avec leurs petits et par des grands mâles. Il semble que les Açores constituent à la fois un site d'alimentation et un site de reproduction, mais la structure des populations et la composition des groupes sociaux sont peu connues pour cette région. Nous avons analysé 151 échantillons de peau de cachalot (peau desquamée et biopsies) par "genetic tagging", en utilisant 11 marqueurs microsatellites, et par sexage moléculaire. Nos objectifs étaient de déterminer la structure génétique des populations, de comparer le degré d'apparentement au sein des groupes et entre groupes, et d'estimer les relations de parenté entre individus. Nous avons aussi estimé l'âge des mâles à la dispersion. La valeur obtenue de 16,6 ans représente un âge très avancé par rapport aux estimations disponibles pour cette espèce. Les résultats suggèrent que les individus fréquentant les Açores appartiennent à une seule et même population. La diversité génétique élevée et l'absence de consanguinité suggèrent que la population est en phase de récupération suite à l'arrêt de la chasse "à la baleine". Les individus échantillonnés ensemble sont fortement apparentés, de même que ceux observés dans une même zone géographique au cours d'une même journée. Les groupes sociaux secondaires regroupant plusieurs unités primaires seraient donc composés d'individus apparentés. Plusieurs paires probables de mères et enfants et de frères et soeurs véritables ont été identifiées. Des preuves indirectes de fidélité au site confortent l'hypothèse que les Açores constituent un site d'alimentation. Par ailleurs, l'observation de mâles adultes étaye l'hypothèse qu...