Orcinus orca, photo by S. Blanc on www.arkive.org |
What do humans and whales have in common?
Killer
whales (Orcinus orca)
and the short-finned pilot whales (Globicephala
macrorhynchus) have comparable post-reproductive lifespans. Just like human
females, killer whales undergo menopause after they have reached a certain age.
They have the longest post-reproductive lifespan of all non-human animals.
Female orcas usually stop reproducing during their 30’s to their 40’s but can
live until their 90’s, as compared to males that rarely live beyond their 50’s
[1].
Aside from the mortality of the females being higher, their
post-reproductive stage renders a higher survival rate to their pod, especially
to their male progenies. These so called “grandmothers” may serve as teachers,
guides, and keepers of the clans or pods’ traditions [3]. According to a recent
study that was conducted for about 35 years, females that had undergone menopausal
stage exhibit a strong leadership to its pod. During periods wherein food is
scarce, they are most likely to lead the group’s activities, especially when
food source such as salmons are low in supply or extremely difficult to locate
[2]. The mothers are able to share their long experience in the waters which
gives them an advantage in foraging.
Compared to females, males are more likely to follow their mothers as
they conceive the ecological knowledge of their mothers useful. It is known that
once their post-reproductively-aged mother dies, the sons have a higher
probability of dying compared to the females [2]. From this, it can be said
seen that the males highly depend on their mothers for their survival.
Aside from the killer and pilot whales, there has been no evidence or
data in other non-human animals that can suggest similar post-reproductive
behavior [1].
To
know more about whales, visit SeaLifeBase.
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[1] Foster,
E.A., Franks, D.W., Mazzi, S., Darden, S.K., Balcomb, K.C., Ford, J.K.B., and
Croft, D.P. (2012) Adaptive Prolonged Postreproductive Life Span in Killer
Whales. Science. 337:1313
[2] Brent,
L.J.N., Franks, D.W., Foster, E.A., Balcomb, K.C., Cant, M.A., and Croft, D.P.
(2015) Ecological Knowledge, Leadership, and the Evolution of Menopause in
Killer Whales. Current Biology. 25:
746-750
[3] Allen,
S.G., Mortenson, J., and Webb, S. (2011) Field Guide to Marine Mammals of the Pacific Coast . University
of California Press: Berkley , California .
261p.
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