Female bisexual kinship ties maintain social cohesion in a dolphin network

Social assortativity, where individuals preferentially mix with certain conspecifics, is widespread among a diverse range of taxa. Animals may assort by a variety of characteristics and receive substantial benefits from these interactions, such as a reduction in predation risk, increased foraging efficiency or greater access to resources. We investigated the social network structure of an embayment population of Indo-Pacific bottlenose dolphins, Tursiops aduncus, using a long-term photoidentification data set, and examined the impact of sex and kinship in maintaining the cohesion of the social network. We applied recently developed social network techniques that incorporate uncertainty into statistical measures to delineate four smaller social groups within two previously defined communities. Temporal stability of associations within social groups was substantially greater than among individuals from different groups. We also found that the dolphin population was not strongly segregated by sex and both males and females had similar degrees of social connectivity in the network. Moreover, genetic analyses showed that relatedness had a greater influence on female than on male social relationships, as association strength was positively correlated with genetic relatedness between females and between female and male pairs, but not between males. These results suggest that females and males may target kin interactions with females and that kinship appears to be important for maintaining the cohesiveness of this dolphin social network.