| Summary: | The social structure of sperm whales (Physeter macrocephalus ) in the eastern tropical Pacific Ocean was investigated by using photo-identification data (1985--1997) and molecular analysis of sloughed skin samples, to examine patterns of association and genetic relatedness between individuals. These analyses have revealed new levels of complexity and variability in sperm whale social structure. Analysis of the temporal stability of associations between individuals confirmed the unstable nature of groups of female and juvenile whales. These groups were found to be temporary aggregations of separate, and more temporally-stable, social units. Social unit size was highly variable (3--24 members, mean 12.3). Instances of splitting and merging of units, and of transfers of individuals between units, indicated that unit membership was not necessarily entirely stable over periods of years. Molecular analyses (sexing, mitochondrial DNA sequencing, multi-locus microsatellite profiling) revealed the genetic structure of social units. In conjunction with simulation modeling, these results demonstrated that the units analysed were not strictly matrilineal, but included some unrelated individuals. Thus patterns of long-term association and genetic relatedness are indicative of some female dispersal from social units. Analyses of association patterns within groups revealed that individuals were more likely to be in spatio-temporal proximity to members of their own unit, rather than to other group members. However, there were no clear indications of preferred companionships within units, and unit members did not appear to associate preferentially with respect to genetic relatedness. Large male sperm whales have increased in abundance in the Galipagos Islands area in recent years. Aggregations of large males have been observed, within which individuals may associate closely. In conjunction with anecdotal indications of long-term or repeated associations between individuals, these findings indicate greater complexity in the social structure of large males than had been recognised previously. Thesis (Ph.D.)--Dalhousie University (Canada), 1999.
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