Genetic Diversity, Population Structure and Morphology in New Zealand's Beaked Whales

Abstract

The study of rare or cryptic species in inaccessible habitats presents a particular challenge to biologists. To address this difficulty in cetaceans, tissue samples from beach-cast animals have been collected over the past 20 years. The New Zealand Cetacean Tissue Archive (NZCeTA) now holds samples from 1,983 individuals. Using this archive I show that there are at least 36 species of cetaceans in New Zealand waters, of which 12 are beaked whales (Family Ziphiidae). In this study I report the distribution of stranded beaked whales around New Zealand between 1991 and 2011. Samples from the three most commonly found species: Gray’s (Mesoplodon grayi); straptoothed (M. layardii) and Cuvier’s beaked whale (Ziphius cavirostris) represent 83% of all ziphiid specimens in the NZCeTA. I have used the spatial and temporal records to provide new evidence of a key habitat for beaked whales and for seasonal and sex-biased patterns of strandings. A 530 bp fragment of the mitochondrial control region was sequenced from 123 Gray’s beaked whales. Genetic diversity was high in these animals, (h = 0.97 ± 0.01, π = 0.92% ± 0.50) and no evidence of population structure was found (FST = 0.0001, p = 0.45; ΦST = -0.004, p = 0.82). Gray’s beaked whales are unique amongst ziphiids in that they regularly strand in groups. An analysis of both group composition and patterns of haplotypes revealed no evidence of matrilinearity in this species. Whilst no clear sexual dimorphism in the external morphology of Gray’s beaked whale was evident, cranial morphology between sexes is markedly different. Females have longer skulls with longer more slender rostra (beaks) in comparison to males. This may indicate that either intra-specific aggression between males is regular, as is thought to be the case in other mesoplodonts, or that there are sexual differences in vocal communication. This research has used archival records, molecular data and morphological characters to provide critical baseline information to contribute to the better understanding of these enigmatic animals.