Social structure of Lahille’s bottlenose dolphin Tursiops truncatus gephyreus (Cetacea: Delphinidae) off the uruguayan marine coast

Information about the social relations among individuals is essential to de ne and developmanagement plans for a socially structured population. Association data for 25 adult Lahille’s bottlenosedolphins were obtained from 189 photo-identi cation surveys that took place between January 2007 and May2009 in La Coronilla-Cerro Verde and Cabo Polonio, Rocha, Uruguay. Group size averaged 5.22 individuals(SD= 3.77, n= 255). Coe cients of association were calculated using the Half-Weight Index. Most of theassociations were weak (79.7%) and variation of real association indices was greater than would be expected bychance. Thus, the null hypothesis that individuals associated randomly was rejected. Standardized LaggedAssociation Rate analysis also indicated that nonrandom associations between individuals persisted over thestudy period. The exponential decay model that ts best to the data suggested the existence of constantcompanions and casual acquaintances. This study is the rst report about the social structure of the populationof Lahille’s bottlenose dolphin inhabiting the Uruguayan marine coasts. Cerro Verde and Cabo Polonio werethe rst marine protected areas selected by the government of Uruguay. However, information about theecology and behavior of the species in these areas is still insu cient. It is recommended that the results of thisstudy be taken as baseline information to assess the conservation status of this population, as well as for thedevelopment of adequate conservation and management plans.Para una población socialmente estructurada, disponer de información sobre las relaciones sociales entre individuos es esencial para definir y desarrollar planes de manejo. Se obtuvieron datos de asociación para 25 toninas adultas a partir de 189 salidas de foto-identificación, realizadas entre enero 2007 y mayo 2009, en La Coronilla-Cerro Verde y Cabo Polonio, Rocha, Uruguay. El tamaño grupal promedió 5.22 individuos (DS = 3.77, n = 255). Los coeficientes de asociación se calcularon utilizando el Índice de Peso Medio. Las asociaciones fueron mayormente débiles (79.7%) y la variación de los índices de asociación fue mayor que lo esperado por azar. Por tanto, se rechazó la hipótesis nula de que los individuos se asociaron aleatoriamente. El análisis utilizando la Tasa de Asociación con Retardo Estandarizada también indicó que asociaciones no aleatorias persistieron durante el período de estudio. El modelo exponencial que mejor ajusta a los datos sugiere la existencia de compañeros constantes y compañeros casuales. Este estudio reporta por primera vez información sobre la estructura social de la población de toninas que habita la costa marina uruguaya. Cerro Verde y Cabo Polonio fueron las primeras áreas marinas protegidas por el gobierno de Uruguay. Sin embargo, aún es insuficiente la información sobre la ecología y el comportamiento de la especie en estas áreas. Se recomienda que los resultados de este estudio se tomen como información de base para evaluar el estado de conservación de esta población, así como para el desarrollo de planes adecuados de manejo y conservación

Dispersal and population structure at different spatial scales in the subterranean rodent Ctenomys australis

<p>Abstract</p> <p><b>Background</b></p> <p>The population genetic structure of subterranean rodent species is strongly affected by demographic (e.g. rates of dispersal and social structure) and stochastic factors (e.g. random genetic drift among subpopulations and habitat fragmentation). In particular, gene flow estimates at different spatial scales are essential to understand genetic differentiation among populations of a species living in a highly fragmented landscape. <it>Ctenomys australis </it>(the sand dune tuco-tuco) is a territorial subterranean rodent that inhabits a relatively secure, permanently sealed burrow system, occurring in sand dune habitats on the coastal landscape in the south-east of Buenos Aires province, Argentina. Currently, this habitat is threatened by urban development and forestry and, therefore, the survival of this endemic species is at risk. Here, we assess population genetic structure and patterns of dispersal among individuals of this species at different spatial scales using 8 polymorphic microsatellite loci. Furthermore, we evaluate the relative importance of sex and habitat configuration in modulating the dispersal patterns at these geographical scales.</p> <p>Results</p> <p>Our results show that dispersal in <it>C. australis </it>is not restricted at regional spatial scales (~ 4 km). Assignment tests revealed significant population substructure within the study area, providing support for the presence of two subpopulations from three original sampling sites. Finally, male-biased dispersal was found in the Western side of our study area, but in the Eastern side no apparent philopatric pattern was found, suggesting that in a more continuous habitat males might move longer distances than females.</p> <p>Conclusions</p> <p>Overall, the assignment-based approaches were able to detect population substructure at fine geographical scales. Additionally, the maintenance of a significant genetic structure at regional (~ 4 km) and small (less than 1 km) spatial scales despite apparently moderate to high levels of gene flow between local sampling sites could not be explained simply by the linear distance among them. On the whole, our results support the hypothesis that males disperse more frequently than females; however they do not provide support for strict philopatry within females.</p