Killer whales are one of the only three mammals that go through menopause, surviving long after they topped reproducing. The older female killer whales will then be responsible for helping the younger ones to survive and find food. However, in a research study in Current Biology on January 12, the reason why older female killer whales stop reproducing is that it has more to do with a mother and daughter conflicts.
Therefore, it has lesser to do with cooperation. According to the gathered evidence, when females do reproduce along side with their daughters, their younger calves are more likely to die. Because of this circumstance, it is better to stop reproducing and focusing on helping the younger family succeed.
Darren Croft of the University of Exeter said that their study shows how older female help but not why they stop to reproduce. Females in many species usually act as leaders, but do not stop on reproducing. Their new work provides a new mechanism that explains why, they lose out in the reproductive competition to their daughters.
Female killer whales usually start reproducing by age 15. They stop reproducing by their 30s and 40s. However, they are able to live until in its 90s. According to the Science Daily, earlier studies show that the older female killer whales act as a leader and help for the benefit of the entire family. According to the New York Times, the unique demography of killer whale social groups may encourage younger female killer whales to focus on reproduction as the older female lead them to survival and food.
To test the hypothesis of the researchers they analyzed demographic data over 43 years for 200 whales. Scientists found that as younger females aged and had offspring, they had indeed become more related to their pods. And older killer whale offspring has a lower chance of survival than that of the offspring of 15 year old killer whale.