Social structure in migrating humpback whales (Megaptera novaeangliae)

Abstract

Although largely solitary, humpback whales exhibit a number of behaviours where individuals co-operate with one another, for example during bubble net feeding. Such cases could be due to reciprocal altruism brought on by exceptional circumstances, for example the presence of abundant shoaling fish. An alternative explanation is that these behaviours have evolved through kin selection. With little restriction to either communication or movement, diffuse groups of relatives could maintain some form of social organization without the need to travel in tight-nit units. To try to distinguish between these hypotheses, we took advantage of the fact that migrating humpback whales often swim together in small groups. If kin selection is important in humpback whale biology, these groups should be enriched for relatives. Consequently, we analysed biopsy samples from 57 groups of humpback whales migrating off Eastern Australia in 1992. A total of 142 whales were screened for eight microsatellite markers. Mitochondrial DNA sequences (371 bp) were also used to verify and assist kinship identification. Our data add support to the notion that mothers travel with their offspring for the first year of the calf's life. However, beyond the presence of mother-calf/yearling pairs, no obvious relatedness pattern was found among whales sampled either in the same pod or on the same day. Levels of relatedness did not vary between migratory phases (towards or away from the breeding ground), nor between the two sexes considered either overall or in the north or south migrations separately. These findings suggest that, if any social organization does exist, it is formed transiently when needed rather than being a constant feature of the population, and hence is more likely based on reciprocal altruism than kin selection.

Dolphin-Inspired Target Detection for Sonar and Radar

“…the wall of bubbles, and so are trapped within the 'bubble net', making an easy meal for the whales when they swim up from the base of the net, mouths agape (Sharpe, Dill, 1997;Valsecchi et al, 2002). The reason why fish and other prey do not cross the bubble wall was not clear.…”

Genetic evidence for sex-specific migratory behaviour in western South Pacific humpback whales

“…These individuals include a sub-sample of the whales previously analysed at the nDNA level by Valsecchi et al 2002. Here we integrated also singletons or whales which were the only sampled member in pods of 2 or more individuals: these individuals, for the purpose of the research, were excluded in the previous study (Valsecchi et al 2002).…”

“…In some populations, males comprise the majority of migrating animals , Craig & Herman 1997, indicating that females do not migrate every year. Analyses of nuclear DNA variation in migrating ani-mals indicate that whales do not migrate in kin-based social units (Valsecchi et al 2002, Pomilla & Rosenbaum 2006.…”

Population genetics and social organization of the sperm whale (Physeter macrocephalus) in the Azores inferred by microsatellite analyses

“…However, the non significant F IS -value and the high genetic variability existing within social groups indicated that the population did not suffer from inbreeding. This might be explained by the fact that sperm whales have evolved complex social behaviours, including behavioural mechanisms that minimize inbreeding amongst individuals (Valsecchi et al 2002;Whitehead 2003). One of these mechanisms is the selective dispersal of males associated to female philopatry (Pusey and Wolf 1996).…”