Menopause in Female Killer Whales

Menopause in Female Killer Whales

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      The issue of menopause is a mystery for scientists and it cannot be fully explained. Why would a female of a given species stop to reproduce at a certain point through her life? Menopause is a special trait mostly found among short finned pilot whales, humans and killer whales (Gregg, 2013). This article focuses on why female killer whales experience menopause.

      Female killer whales are among the species who outlive their productiveness. Though they can live for more than 90 years, female whales roughly spend two-thirds of their lifetime without reproducing since reproduction begins at the age of 15 and stops in their 30s or40s. Initially, it was suggested that the females underwent the change in order to focus on their extended families. However, a recent study on the female whales suggests that they reach menopause once their daughters become fertile. The middle-aged orca females, (mothers approaching menopause) suffer higher costs when competing with younger mothers to reproduce (Kellar, N. M et al 2013). The study discovered that if the mothers and daughters breed at the same time, the mother’s calves have very minimal chances of survival while those of the daughters survive well. But, if older females have calves when a reproducing daughter is absent, the calves survive; this reproductive conflict among daughters and mothers may have contributed to evolution of menopause. Once older mothers get into this competition with their daughters, they lose and their calves die.

      The grandmother hypothesis is also used to explain the evolution of menopause among female whales. It argues that menopause is a developed trait driven by cooperation and the conflict among family groups. The distinctive demography of killer whales social groups may also influence young females to devote more competitive efforts into reproduction. Females in killer whales usually mate with males who are from other groups and later rejoin their families with other groups which they are not related to. As the female grows older and begins having calves, she develops kinship ties to those surrounding her but if she continues bearing off springs it would bring harm to survival of the entire pod group. Resources used in reproduction are highly limited within the groups and there is only a definite amount of food to go round. Therefore, there evolves a tug-of-war over accessing these resources. The younger females normally pull harder and compete to ensure they get those resources (Brent, Lauren JN, et al 2015). Older females are likely to share their food, compared to the young females, and thus play an important role in the survival of not only their calves but also that of the family members. Young females, however, reach a tipping point where they advance from competing to reproduce to being helpful later in life once they become older. The orcas also have a ‘grandmother’ responsibility of pinpointing the best places to get salmon, which is the main source of food, within the pod. Menopause in killer whales therefore results from this odd family structure which results to both reproductive and cooperative competition among generations.

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