Abstract
Social relationships in female mammals are usually determined by an interplay among genetic, endogenous, social and ecological factors that ultimately affect their lifetime reproductive success. However, few studies have attempted to control for, and integrate these factors, hampering our understanding of drivers underlying female sociality. Here, we used generalized affiliation indices, combined with social networks, reproductive condition, and genetic data to investigate drivers of associations in female southern Australian bottlenose dolphins. Our analysis is based on photo-identification and genetic data collected through systematic boat surveys over a two-year study period. Female dolphins formed preferred associations and social clusters which ranged from overlapping to discrete home ranges. Furthermore, matrilineal kinship and biparental relatedness, as well as reproductive condition, correlated with the strength of female affiliations. In addition, relatedness for both genetic markers was also higher within than between social clusters. The predictability of resources in their embayment environment, and the availability of same-sex relatives in the population, may have favoured the formation of social bonds between genetically related females and those in similar reproductive condition. This study highlights the importance of genetic, endogenous, social and ecological factors in determining female sociality in coastal dolphins.
Highlights
Social relationships in female mammals are usually determined by an interplay among genetic, endogenous, social and ecological factors that affect their lifetime reproductive success
We found a significant correlation between home range overlap, gregariousness and the association indices; these structural variables were controlled for when estimating female generalized affiliation indices (GAIs)
We showed that female southern Australian bottlenose dolphins in Coffin Bay form moderate to strong affiliations and social clusters in which kinship generally correlated positively with their associations
Summary
Social relationships in female mammals are usually determined by an interplay among genetic, endogenous, social and ecological factors that affect their lifetime reproductive success. The predictability of resources in their embayment environment, and the availability of same-sex relatives in the population, may have favoured the formation of social bonds between genetically related females and those in similar reproductive condition. Cantor and Farine[35] demonstrated, using agent-based models, that simple foraging interactions in competitive environments may give rise to the formation of stable social groups consisting of relatives They showed that a process by which ‘individuals keep foraging with the same individuals if they were successful together in the past’ can lead to a stable social community structure and the emergence of kin-structure via fitness benefits or philopatry[35]. In Sarasota Bay, USA, and Port Stephens, Australia, female common bottlenose dolphins (T. truncatus) and Indo-Pacific bottlenose dolphins (T. aduncus), respectively, form clusters or stable subsets of frequent associates that share similar core areas within their home ranges[37,39,42]
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