Keeping Mum: Grandmother effects in Asian elephants

Why is it that some animals, including ourselves, live on after they have stopped having babies? This is a question that has puzzled evolutionary biologists and life history scientists for decades. We hope that our new paper in Scientific Reports by Mirkka, investigating how the presence of grandmothers in the Asian elephant maternal environment influences survival in both grandchildren and daughters, sheds some light on how post-reproductive survival may occur. Grandmas turn out to be pretty important for calf survival and reproduction in timber elephants.

It’s easy to envisage a scenario in which grandmothers benefit their daughters and grandchildren when they are close at hand. A grandmother can provide additional parental support, as well as sharing her knowledge and experience to ensure that both mother and baby survive and reproduce to their full potential.

Asian elephant calves have help from their grans as well as their mums

Because grandmothers share a greater amount of genetic information with their daughters and grandchildren than most of the population, investment in to their offspring’s reproduction and survival rather than their own will actually increase their own inclusive fitness. It is hypothesised therefore that this fitness benefit can result in selection for increased post-reproductive survival and menopause, allowing individuals to live decades after their last offspring are born. This is known as the grandmother hypothesis. Evolutionary theory suggests that this phenomenon is expected to have occurred in species that are menopausal such as humans, but positive grandmother effects have also been documented in non-menopausal species.

We found that mortality of calves in the timber elephants was decreased when the grandmother was present in the maternal environment, compared to when the grandmother was absent. Furthermore, the presence of grandmothers decreased mother inter-birthing intervals. Perhaps most interestingly, the grandmothers own reproductive status did not influence these benefits to survival and reproduction, challenging the idea that grandmother effects alone can result in post-reproductive survival.

However these effects may have arisen, what is clear is that grandmothers play a crucial role in the survival and reproduction of their offspring in elephants, and a maintenance of this cooperative maternal environment is crucial for the management of this species in captivity. So, let’s keep our mums around, you never know how much they may help…