Sperm whale social structure: kith and kin. Implications for behavior, culture and conservation SARAH MESNICK, SOUTHWEST FISHERIES SCIENCE CENTER, NOAA FISHERIES SERVICE Knowledge of the genetic structure of social groupings provides the
Sperm whale social structure: kith and kin. Implications for behavior, culture and conservation
SARAH MESNICK, SOUTHWEST FISHERIES SCIENCE CENTER, NOAA FISHERIES SERVICE
Knowledge of the genetic structure of social groupings provides the basis for understanding the relative influences of kin selection and reciprocity in the evolution of individual behavior and for understanding the basis of population structure, which is important for conservation. Sperm whale, Physeter macrocephalus, groups comprised of females and dependent young were once thought to be strictly matrilineal, with a social structure similar to that of African elephants. We investigated this hypothesis using samples from 3 completely sampled mass strandings in Tasmania (n = 11, 37, 64 individuals respectively) and 55 partially sampled groups from the eastern North Pacific. We used mitochondrial (400 bp of the hypervariable control region) and nuclear (six microsatellites and 36 single nucleotide polymorphisms) markers and the sex of individual sperm whales to estimate genetic relatedness within and among groups. The preliminary results indicate that sperm whale groups were not purely matrilineal in structure. Rather, groups were comprised both of individuals that had no close relations and of individuals accompanied by potential first and second order relations, some potentially related through their fathers and others through their mothers. Groups were composed of mixed matrilines, as evidenced by the presence of 1 – 5 mtDNA haplotypes (maternally inherited) per group. The mean coefficient of relatedness for the completely sampled groups ranged from 0.15-0.27. The groups were comprised of small clusters of related individuals although in all groups there were several individuals with no relations closer than those expected by chance. Pairs of individuals with high coefficients of relatedness, but different mtDNA haplotypes, were consistent with patterns of paternal half sibs. Three subadult males with unique mtDNA haplotypes were found among a group of adult females indicating that their mothers were not present, an unexpected finding. Some old (and very old) females, some of whom were accompanied by close relatives and others not, were lactating. These results cause us to rethink the relative influences of kin selection and reciprocity in the evolution of individual behavior (e.g., babysitting, communal defense). We suggest that for the sperm whale, and other cetacean species that live, raise young and contend with predators in the open ocean, the integrity of the bonds developed through association, cooperation and lactation, are as strong as blood relations.
For this presentation, I will summarize what is known about sperm whale social and population structure from recent genetic work in our laboratory and observations of social interactions at sea. Additional insights from the acoustic research of colleagues provide the background for cross disciplinary, cross- taxa discussion on three topics: (a) social structure within females groups and observations during an attack by killer whales; (b) social transmission of a novel foraging behavior (depredation on demersal long lines) among adult males in Alaska; and (c) population structure – geographically defined stocks and culturally defined clans – for conservation and management.
(Monday) 12:00 pm - 1:30 pm
Haines Hall 352