14 DAY TRIAL // Researchers working with NERC (the Natural Environment Research Council) believe they have figured out why killer whales, otherwise known as orcas, go through menopause.
The specialists explain that, much like humans, these marine mammals go on living for a considerable period after they have lost the ability to reproduce.
Speaking from a strictly biological and evolutionary standpoint, this does not make much sense. However, researchers suspect that it happens due to the fact that orcas live in well-articulated social groups.
Thus, they say that killer whales that can no longer have offspring of their own, i.e. those in their 30s and 40s, stick around for several more years to help the other females in their group look after their calves.
What's more, it appears that older orcas also have to keep tabs on their male offspring.
“Killer whales have a very unusual social system whereby sons and daughters don't disperse from their social group but instead live with their mother her entire life.”
“As a female ages she shares more genes with group members, and theory predicts that older females can benefit more from helping their offspring and grand offspring than reproducing themselves,” says Dr. Darren Croft with the University of Exeter, as cited by PhysOrg.
“When a killer whale couple reproduces, the male will go to another group to mate with a female there. But, unlike the human population, he will later return to the group where his mother is,” Dr. Dan Franks with the University of York further details.
Besides, the researchers suspect that competition also has a say in the matter. More precisely, they theorize that, by not giving birth at the same time as their daughters, older orcas keep conflict for resources from emerging between offspring of different generations.
The researchers wish to confirm these assumptions concerning why killer whales experience menopause by looking at data collected over 30 years. This data is about two different orca populations adding up to 550 such marine mammals.
“One way we will approach the analysis of this data is to use a method similar to insurance companies where they give you a quote on life insurance based on the suspected survival of an individual. If a human smokes, is old, or is a heavy drinker then their insurance premium will go up as their chance of survival is less. We can ask, since this calf's mother or grandmother is alive, how does that affect its chances of survival,” Dr. Darren Croft explains.