Phylogeographyj kinship and molecular ecology of sperm whales (Physeter macrocephalus)

Abstract

The molecular ecology for sperm whales (Physeter macrocephalus) in the northern Gulf of Mexico was investigated in detail using a suite of molecular markers. In addition, several genetic related aspects for the Mediterranean Sea, North Sea and the North Atlantic Ocean putative sperm whale populations were described. These analyses have provided new insights requiring proper management to ensure the survival of the northern Gulf of Mexico sperm whale stock m an area of increasing industrial activity. The majority of surface behavioural reactions witnessed after biopsy darting were mild and short-term. No significant differences were determined between males and females and repeat sampling events on the same individual did not lead to an increase in the response level. Population structuring between the four putative populations, with respect to mtDNA, was highly significant and warrants the classification of each putative population as a unique stock for management purposes. The majority of Gulf of Mexico samples were from females and young males believed to be sexually immature based on rough size estimates. Incidental resampling of a few individuals over periods of days, months and years adds support for site-fidelity to the northern Gulf of Mexico exhibited by at least some whales. Although our sample set compares a more restricted geographic area than previous studies, the lack of significant nuclear differentiation between neighbouring populations suggests that sexually mature males disperse from their natal populations and spread their genes to the more philopatric females. The genetic composition of Gulf of Mexico sperm whale groups fits the mixed sex and bachelor group type so common in other areas of the world, while the two all-male North Sea stranding groups fit the bachelor group scenario. Relatedness within the Gulf of Mexico female-dominated groups was significantly greater than that found between groups, but still surprisingly low and composed of both single and multiple matrilines. Highly related whales (i.e. parent-offspring) were present within groups, but infrequent. The most common relationship found was that of half- siblings. The all-male bachelor groups were comprised of multiple matrilines and members were generally unrelated, although cases for half-sibling pairs were present.