Killer whale grandmothers that have passed reproductive age help improve the survival rates of their grandoffspring, a study suggests. Killer whales and humans share a trait rare among mammals: females survive long past their reproductive period. In humans, grandmothers can help increase the survival of their grandoffspring and, in turn, their own evolutionary fitness. Stuart Nattrass and colleagues investigated whether such a grandmother effect also exists in killer whales, which have a close-knit family-based society. The authors examined more than 40 years of census data on 2 killer whale groups off the coast of Washington state in the United States as well as British Columbia. The authors analyzed the survival rate of 378 grandoffspring with known maternal grandmothers. Controlling for annual salmon abundance, the authors found that in the 2 years following a grandmother whale's death the survival of grandoffspring was reduced. The impact was highest in years of low-to-moderate salmon abundance. The grandmother effect was also relatively high for postreproductive females, a result the authors attribute to postreproductive grandmothers being better able to provide help when they are not trying to reproduce themselves. According to the authors, the findings suggest that the grandmother effect in killer whales, combined with the known costs of late reproduction, could help explain their long postreproductive lifespan.
Article # 19-03844: "Postreproductive killer whale grandmothers improve the survival of their grandoffspring," by Stuart Nattrass et al.
MEDIA CONTACT: Daniel W. Franks, University of York, UNITED KINGDOM; tel: 44-1904-325342; e-mail: email@example.com
Proceedings of the National Academy of Sciences