Dusky dolphins in New Zealand: group structure by sex and relatedness
MetadataShow full item record
The sex of and genetic relatedness among interacting individuals are known to be biologically fundamental features that characterize the composition of animal groups. Current work continues to illuminate reasons for the variety of animal social patterns, including patterns in group membership. I investigated the composition of dusky dolphin groups relative to sex and relatedness at two locations in New Zealand. In Kaikoura, dusky dolphins are found year-round, foraging nocturnally on verticallymigrating prey and socializing in distinct group types (mating, nursery, and adult) during the day. By contrast, dusky dolphins use Admiralty Bay, where they feed diurnally on small schooling fishes, primarily in the winter. Molecular sexing revealed the sex of 107 dusky dolphins. The Kaikoura data support previous findings that small mating groups consist mostly of males and indicate that small adult groups can consist of either or both sexes. In Admiralty Bay, the percentage of female dolphins present during the study was estimated to be only 7.4%Ã¢ÂÂ22.2% (95% confidence interval, n=88). A randomization test further indicates that dusky dolphins in Admiralty Bay grouped preferentially with same-sex individuals. Nuclear and mitochondrial markers were used to investigate patterns of relatedness. Dusky dolphins sampled in Kaikoura (n=17) and Admiralty Bay (n=47) were genotyped at seven microsatellite loci, and genetic relatedness among all genotyped pairs was estimated. A randomization test indicates that dusky dolphins did not group preferentially by relatedness in Admiralty Bay. Grouping history for 13 genotyped samples was also known from a multi-year photographic record of individually distinctive dusky dolphins. No relationship was found between these longer-term grouping patterns and genetic relatedness. The d-loop region of the mitochondrial DNA (mtDNA) was sequenced for 197 dusky dolphins. The pattern of grouping among dolphins with different haplotypes indicates that dusky dolphin groups are not strongly structured by maternal lineages. However, data from eight individual dusky dolphins hint that nursery groups in Kaikoura tend to consist of dolphins that share a maternal ancestor. This investigation raises many questions about the nature of dusky dolphin social organization and suggests promising avenues for finer-grained investigations into the causes and consequences of dusky dolphin group structure.
Shelton, Deborah Ellen (2006). Dusky dolphins in New Zealand: group structure by sex and relatedness. Master's thesis, Texas A&M University. Texas A&M University. Available electronically from