Killer Whale Research

Post-reproductive Life

 

Killer whale mothers stop reproducing by the age of 40, but often live into their 70s and 80s. This prolonged period of post-reproductive life is an evolutionary puzzle (Croft et al 2015), because classic evolutionary theory suggests there should be no selection for lifespan beyond the end of reproduction.

 

Post-reproductive life can be explained if older mothers boost the fitness of their offspring or grand-offspring. In resident killer whales, we have shown that mothers are crucial for the survival of their adult sons, particularly the oldest, largest sons (Foster et al 2012 Science). Why sons should grow more dependent on their mother as they age is a facinating puzzle that we are currently investigating. We have recently shown that part of the help provided by older females is in the form of leadership when times are tough (Brent et al 2015). Older females lead the group on foraging trips in period of low salmon abundance. This ‘ecological wisdom’ is something that accumulates rather than deteriorates with age.

 

To see recent press coverage on post reproductive lifespan in killer whales from the BBC http://www.bbc.co.uk/news/science-environment-. and how University of Exeter scientists can use drones to further their understanding of killer whale behaviour http://www.exeter.ac.uk/news/KillerWhalesDrone

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Reproductive Competition

 

We have also confirmed that reproductive competition is a second key driver of menopause in killer whales (Cant, Russell & Johnstone 2009 PNAS; Johnstone & Cant 2010 Proc B). Our recent theory developed for humans suggests that older females cease reproduction to avoid breeding at the same time as the next generation of females. Tests of this ‘reproductive conflict hypothesis’ have yielded mixed results, with some studies supporting the theory but others not. We recently tested this hypothesis in killer whales and found strong evidence of intergenerational reproductive conflict. Moreover, patterns of relatedness within groups almost exactly matched the predictions of our earlier theoretical model (Johnstone & Cant 2010 Proc B).