Kinship in Sperm Whale Society: Effects on Association, Alloparental Care and Vocalizations
The overarching goal of my thesis is to characterize the relationship between kinship and social behaviour in a species with a cooperative, multilevel social structure – the sperm whale. To do so, I use a combination of genetic, behavioural and acoustic data collected during a longitudinal study of sperm whale social units, in the eastern Caribbean. Social units are a stable and basal component of sperm whale social structure. Associations between social units occur within large cultural groups, called vocal clans. To deal with degraded DNA from non-invasive sampling, I develop a protocol that maximizes genotyping success with degraded DNA, while quantifying and minimizing error rates. Using microsatellite loci and mitochondrial DNA haplotypes, I evaluate kinship among sperm whales, and I examine its relationship to social association, alloparental care and vocal repertoires. First, I characterize the extent and pattern of kinship in and among sperm whale social units, and test whether association is predicted by kinship. I document that social units have a clear matrilineal basis, but do not appear to be strictly matrilineal. My findings also indicate paternal relatedness between social units. Within units, I find individuals associate more with their closer relatives, but this is not the case among units. Second, I investigate calf care in relation to kinship. I demonstrate that behavioural observations are not always sufficient for assigning maternity, and that alloparental care is considerable in some cases and correlates positively with maternal kinship. Exceptions to the general pattern, however, demonstrate that, in addition to kin-selection, other factors influence alloparental care, perhaps including reciprocity, group augmentation or gaining maternal experience. Lastly, I examine acoustic repertoires of individuals and social units, in the context of kinship and social association. Variation in vocal repertoires was not explained by close kinship or social bonds. This supports the prevailing hypothesis that these vocalizations are culturally transmitted, and not determined genetically. Further, this suggests that vocal learning occurs broadly within clans, rather than preferentially from close kin or close social associates, or that biases in vocal learning at lower levels of social structure are diffused by clan-level processes. Also, by observing an absence of signals of kinship in vocalizations, my results suggest that a different mechanism, perhaps familiarity, regulates kin-selection among sperm whales. In conclusion, kinship clearly influences social unit composition, association preferences and alloparental care among sperm whales. However, I also reveal variability in social behaviour that is unexplained by kinship, which highlights the complexity of drivers behind social structure, cooperation and communication in this cultural, highly social and large-brained species.