Biologists since Aristotle have puzzled over the reasons for mass strandings of whales and dolphins, in which groups of up to several hundred individuals drive themselves up onto a beach, apparently intentionally. Recent genetic research has shed some light on whether family relationships play a role in these enigmatic and often fatal beachings of otherwise healthy whales.
One hypothesis regarding the reason for strandings is that "care-giving behavior," mediated largely by family relationships, plays a critical role. In this scenario, the stranding of one or a few whales, because of sickness or disorientation, triggers a chain reaction in which healthy individuals are drawn into the shallows in an effort to support their family members.
A recent study published in the Journal of Heredity (DOI:10.1093/jhered/est007) questions this explanation, using genetic data to describe the kinship of individual long-finned pilot whales involved in mass strandings in New Zealand and Tasmania. The largest of these strandings included more than 150 whales, all of which died.
The study found that stranded groups are not necessarily members of one extended family, evidence that contradicts the hypothesis that stranding groups all descend from a single ancestral mother. Further, many stranded calves were found with no mother in evidence.
Long-finned pilot whales are the most common species to strand en masse and it has long been assumed this tendency was related to the species' social organization. Previous studies have shown that pilot whales have a matrilineal social organization, in which neither males nor females disperse from the group into which they were born. This group structure is also found in killer whales, but is otherwise thought to be rare in mammals.
"If kinship-based social dynamics were playing a critical role in these pilot whale strandings
|Contact: Nancy Steinberg|
American Genetic Association