Friday, June 19, 2009

Orca Fathers - They Often Raise Each Other's Offspring

Among our southern resident whales, the dads don't participate directly in raising their offspring…but they help raise the calves sired by other males instead!


K26 travels tight with new sibling K42 on the west side of San Juan Island, July 6, 2008 (Photo by Holly Fernbach)

Killer whales are polygamous, so they mate with more than one partner, and in this case the males do not have any known defined role to play in raising the calves they produce.

Instead, the adult males stay with their own mothers and help care for their siblings, nieces and nephews, who were sired by a different male. Similarly, their own calves are raised in a different maternal group, and any males in that family will help with raising the calves sired by the other males.

By all accounts, mating is a free-for-all between different pods, yet it is extremely rare for two members of the same family to mate together. Periodically the different pods hang out together, and occasionally all three of the southern resident pods - J,K,and L - meet in what the researchers call a "super pod". Vigorous interaction and mating can occur at these gatherings, but apparently the females only select males from outside of their own family group.


Young males from three pods traveling together: L78, J27 and K26 (Photo by Ken Balcomb)




It all sounds like a pretty sweet deal for the males - they live with their moms and frolic freely, not responsible for outcomes. 15 to 17 months later when the calves are born, the females are living with their own families. And it is - but it is a sweet deal for the whole clan, and may be key to why the orcas coexist so peacefully.

In this situation, male rivalry is minimized, plus they would seem to have a vested interest in insuring the well being of all calves since most likely they don't know which ones they might have fathered.

Young male J26 (Photo by Katie Jones)

The members of J,K, and L pods are closely tied genetically, and as I looked through the Center's archived photos for this post, there was something that really struck me (not an original observation I am sure!) - which reminded me of my sixth grade biology class and introduction to genetics. Something about wrinkled versus smooth peas...


Creative Commons Photo

L73, also wavy. (Photo by Dave Ellifrit)

J1, known for his wavy dorsal fin. (Photo by Emma Foster)








The bottom line is that although the males don't mate within their birth families, they must wind up breeding with their own offspring at some point, and the population shows the expected low genetic diversity. Yet that appears to be true throughout their range, even among populations that are healthy.

To account for this, scientists speculate that the orca's low genetic diversity might be the result of having gone through a genetic "bottleneck" about 130,000 years ago, during which time their population was drastically reduced, and is not just do to their tendency to mate with related individuals.

It may turn out that the orcas' reproductive strategy - though it creates or maintains a limited gene pool - enhances the success of the population as a whole. Their population is controlled by factors we don't quite understand, but it is closely tied to food abundance, and it may turn out that birth defects as a result of close inbreeding are naturally weeded out.

However indirectly, the dads play a key role in ensuring the success of the whole southern resident clan of orcas. And although orcas are deemed apex predators and appear to have no natural enemies, what that really means is that there are no successful natural predators. I imagine that the males are active and vigilant in protecting their families along with their involvement in the rearing of other males' offspring.

In the big picture, it works beautifully.


L41 traveling north through Haro Strait, August 10, 2008 (Photo by Dave Ellifrit)

From: January 2008 II-124 NMFS

" Resident killer whales display some of the most advanced social behavior of any nonhuman mammal, as evidenced by their highly stable social groupings, complex vocalization patterns, the presence of long-lived post-reproductive females, and behaviors such as cooperative foraging, food sharing, alloparental care, matriarchal leadership, and innovative learning. Maintenance of minimal group sizes is therefore probably necessary in preserving beneficial social interactions and in raising young."

5 comments:

  1. I happened to be on a whale watch boat this past Sunday and was fortunate enough to observe the orcas mating. It was something I will never forget for as long as I live. I never thought I'd be lucky enough to see it, let alone photograph it. Absolutely awesome!

    Carole May

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  2. Very interesting post, I have always wondered about the genetic diversity in orcas populations.

    So, I have a question.

    I understand that resident orcas do not mate with the other two kinds of killer whales even if they meet with them. So, they will always breed with relatives. Wouldn't that cause in the future a great reduction of their numbers?

    I mean, shouldn't this lack of mixture of genes cause diseases, failures and mutations at some point?
    So, even though they are very sucessful animals and apex predators, wouldn't this cause a natural extinction of them in a farther future?

    I hope you can understand my doubt(English is not my first language) and I would appreciate very much if you could answer me.

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  3. This comment has been removed by the author.

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  4. Not sure youll see this Liz since its been 9 years since your comment...
    But I was investigating things for another reason, when I came across baffling info and was sure I had misunderstood what I interpreted...
    Sadly I was right... - It was SeaWorld using a father's sperm on his daughter... which had me look into incest in orcas...

    I can provide you the info if you respond to this...

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  5. Guess Ill provide some info for you or others regardless of if you respond
    Any copied material is between = signs - = like this =
    References and more depth of detail can be provided to any who ask if they want.

    My Concern and thoughts about SeaWorld's practice's, - and your own thoughts about inbreeding have now been proven to have occurred....
    * So things may have changed a bit for the pods in the years since
    this was published and you commented...
    * Or it actually might have been the case during that time as well... they are uncertain how long it's been this way..

    = While orcas in J, K and L pods avoid mating with siblings or offspring, a significant number of young whales in recent years have been born to parents that are members of the same pod... =

    Maybe population and Necessity caused this to have to occur...because
    = The potential for polygyny, and the extent to which it is realized, depends on the degree to which receptive females are aggregated in space and time. =

    = It’s also not clear whether the southern residents have always bred this way or have somehow been forced to change mating patterns over time as the population declined. =

    There is concern over this as there should be...
    It shows a lack of potential mates for the females who will actively search and choose the BEST partner for mating..

    = Female marine mammals enhance their reproductive success by engaging in mate choice, mating with multiple partners, and selecting genetic partners separately from social partners. =

    And the inbreeding negatives are well known.

    = “In terms of how bad it is … that depends on how long the population size stays small,” said Ford, a scientist with the National Marine Fisheries Service’s Northwest Fisheries Science Center in Seattle. =

    But there is some hope knowing that the females will definitely choose a mate outside the pod at any opportunity I'd think....which could do a significant impact in recovery and repairing negatives from what I have found out...

    There is an article about this info with much much more details about inbreeding and pods histories and what they know, and what they don't... and more...

    Google new-worry-for-orcas-in-puget-sound-inbreeding

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Candace Calloway Whiting