London: Scientists have cracked one of the most enduring marine mysteries - why adult male killer whales pretty much stay momma`s boys all their lives.
Researchers at the Universities of Exeter and York found that for a male over 30 years, the death of his mother meant an almost 14-fold-increase in likelihood of death the following year.
The female killer whale has the longest menopause in the mammalian species. The reason for the menopause remains one of nature`s enduring mysteries.
According to a paper in the journal "Science," which quoted a statement from Exeter and York, female killer whales stop reproducing in their 30s-40s, but can survive into their 90s.
Emma Foster, doctoral student from Exeter, who led the study, said: "Killer whales are extraordinary animals and their social groups are really unusual in that mothers and sons are lifelong companions. Our research suggests that they have developed the longest menopause of any non-human species so that they can offer this level of commitment to their older offspring."
The research team, which also includes the Centre for Whale Research (US) and Pacific Biological Station (Canada) analysed records spanning 36 years of the members of two populations of killer whales (Orcinus orca) in the North Pacific ocean, off the coast of the USA and Canada.
Females also stay within their mother`s group, but for daughters of the same age, the difference is just under three-fold. For females under the age of 30, the death of their mothers had no effect on their survival rates.
Killer whales live in unusual social groups, with sons and daughters staying with their mothers in a single group throughout their lives. With this close association, older mothers have the opportunity to increase the transmission of their genes by helping adult offspring survive and reproduce.
When sons mate, their offspring are cared for by females in another group, whereas when daughters reproduce, the offspring stay in the group, which increases local competition for resources within the group.
Dan Franks, biologist at the University of York, said: "Our analysis shows that male killer whales are pretty much mommy`s boys and struggle to survive without their mother`s help. The need for mothers to care for their sons into adulthood explains why killer whales have evolved the longest post-reproductive lifespan of any non-human animal."