Purpose of Post Reproductive Whales

Source: Current Biology

Summary:

In the article titled Ecological Knowledge, Leadership and the Evolution of Menopause in Killer Whales, the major thesis of the research is that post-reproductively aged females are more likely to lead a group. Post reproductive females are those who are unable to further reproduce because they have gone through menopause. The study further describes that these same females are even more likely to lead a movement when the supply of food is low. The last aspect of this study also expresses the hypothesis that male offspring are more likely to follow a post reproductive female rather than a female offspring.

            The article essentially illustrates the correlation between female humans and their ability to reproduce and then go through menopause and killer whales same ability. In the natural habitat it is often assumed that a female organism’s ability to reproduce is what makes them attractive to the opposite sex. So naturally when a female is going through menopause there survival rates decrease because of no selection. Humans and killer whales are two of the only species known that do end up living and average of 30 years after they stop reproducing. The big question is that why do those individuals who are unable to further reproduce, usually end up leading their families and other members of the species. The article highlights a hypothesis that states how post reproductive members are known to have knowledge on how the hardships of the environment and therefore take on the role to protect the others in their group.

            All the data that was collected for this experiment was done over a long term period of time where 751 hours of footage was screened to gather the results. This footage was taken from the coastal waters of British Columbia. 102 individuals were recorded for observation all ranging in age so that the testing group was random. The classification for leaders was that the member that was at the front or head of the group was considered the leader and every other member was considered a follower.

            The results all showed that females were most often known to be the leaders and rarely ever were the men. The hypothesis was proven and post-menopausal whales were almost always the leaders of the groups. When there was fewer salmon available in an area, a post-menopausal whale often was the leader where if there was an abundance of salmon available the leader could be another female or even a male. This further proves that women who were post reproductive usually chose to be leader and in charge of a situation when a crisis was evident. However the last hypothesis of the sex of the followers was disproved simply for the reason that most of the offspring remained close to their mother and therefore there was no correlation on who followed the mother.

            The major discussion on what “use” post reproductive individuals have was answered by this study. They do play a necessary role in assisting their offspring and other members of the species. Their wisdom makes them a better protector in the end and therefore they do promote an aspect of selection.

Brent L., Franks D., Foster A. E., Balcomb K., Cant M., Croft D.,2015. Ecological Knowledge, Leadership and Evolution of Menopause in Killer Whales. Current Biology.