Friday, August 26, 2016

A mating like no other and why it matters

Note: This blog contains footage of a mating which recently occurred within Talek West. It is used with the permission of the Mara Hyena Project and for scientific purposes only.

If there is one quality about the Mara ecosystem which can be assured, it is the capacity of the park and its inhabitants to remain unpredictable. A few evenings ago, my fellow RA Amy and I were lucky enough to witness our first hyena mating. This occurrence is rare enough in itself, because hyenas often prefer this to be a more private affair. But what made the session especially interesting from an ecological and behavioral perspective was its participants – Decimeter, one of the most highly ranked females in the clan, and Penne, a natal male.

Penne and his brother Ziti have been special cases within our clan. While most males born within the clan (termed “natal males”) begin to disperse as early as age 2, these brothers have been living comfortably in Talek West for more than 6 years and are showing no signs of wanting to leave any time soon. We fixed both of the boys with GPS collars about 3 years ago when they originally began making long scouting forays into nearby territories, a behavior usually indicating imminent dispersal. However, ultimately not one but both brothers have, at least for the immediate time period, decided that Talek West will remain their home. Now, from what we can deduce from our daily observations, the pair spends the majority of their time hanging out with the high ranking females of the recently split off Main DOC group.
ZITI showing off his GPS collar, which will be used to track him if he disperses
For those unfamiliar with dispersal behavior, especially as it occurs in spotted hyenas, it is a phenomenon which is observed in the vast majority of male hyenas (and indeed in many other males of group-living mammals). Dispersal behavior likely evolved both to prevent inbreeding of closely related individuals and to ensure that the male in question breeds in the clan which gives him the best selection of females which are likely to breed with him. Another important factor which the male must consider when scouting for new clans is the resources which he is likely to gain access to, conditional on the hierarchical climate of the females and males (both natal and immigrant) currently within the clan. Ultimately, he will make his choice based upon the best possible combination of these factors and will gain more and more breeding success in his new clan as he gains seniority over new incoming males.

While it cannot be said for certain what prompted Penne and Ziti to make the unconventional choice to stay, there are certain environmental and social conditions which are fairly rare of the Mara and Talek West itself that could minimize the negative aspects of their decision. Firstly, the park itself, in addition to being one of the prime sites of the migration, is home to a large abundance of other wildlife. In these conditions, carnivores like hyenas, who are extremely versatile in behavior and diet and thus a little less susceptible to human disturbance than species like lions, cheetahs, and leopards, flourish, as even the lowest ranking individuals will likely have regular access to food. However, Talek West is not the only clan living in the Mara, and so even if the clan has an extremely favorable atmosphere in terms of access to food, there are dispersal options which likely have similar conditions as well.
PENE shortly before he was collared
One factor which does play a large role in the success of dispersing males verses natal ones is rank. As natal males, our boys Penne and Ziti are automatically ranked higher than every immigrant male who comes to the clan seeking reproductive success. As such, they have priority access to food and mates over all such males. A study conducted by Davidian et al. on eight separate clans in Tanzania found that, although the number of males which did decide to remain within their natal clan to breed was a small minority, said males had significantly more success with medium to highly ranked females. In their study clans, this led to what was considered equal reproductive success for natal and dispersing males, without the natal males having to dispense the time and energy required to find a new clan.

So if one does consider the role of natal rank not only in its propensity to provide the male with access to higher quality females, but also in its ability to give natal males an additional familiarity with the territory and more time to build good relations with prospective mates, why isn’t this considered to be an optimal breeding strategy in clans which have an equal or higher number of breeding females than their neighbors? Something which must be considered is the willingness of breeding females to take as mating partners males which they have grown up with – in fact, the majority of the time this tends not to happen. This behavior was likely selected for concurrently with that of males to disperse and is one of the key factors which aids in the prevention of inbreeding in what is usually a relatively small clan. But what about clans like Talek West, which while still in the process of fissioning has grown to a size of around 200 individuals? On one hand, this may reduce the possible negative effects of inbreeding. While Penne and Decimeter are both a part of Murphy’s sprawling lineage, dominating nearly half of the clan, there are at least 3 degrees of separation in their relatedness (Penne is the grandson of Decimeter’s cousin once removed to be precise). But of course, there is no way our hyenas could know this to be true. Instead one possibility which could be considered is that, with such a large number of individuals in the clan, the number of regular interactions (and possibly the reluctance of the female to mate) is bound to be reduced.
Decimeter is currently the fifth most highly ranked female in the clan.
While it is still overwhelmingly likely that this natal male will get rejected at the end of the day and find better mating success elsewhere, Penne seems to be doing fine remaining where he is for now. Although we have seen him with at least one high ranking female, it may be impossible to know how many willing breeding partners he and his brother will have in this clan. This may yet lead the boys to disperse to a secondary breeding clan with more willing females. Perhaps we may even see others of his kind arise and find the same kind of success in Talek West – only time will tell.

Footage of the mating between PENE and DECM


Davidian, E., Courtiol, A., Wachter, B., Hofer, H., & Ho Ner, O. P. (2016). Why do some males choose to breed at home when most other males disperse? Science Advances, 2(3). doi:10.1126/sciadv.1501236


Julia said...

What an interesting observation! Thanks for sharing! I remember Pene and Ziti following around their mom, Guci, and Decimeter when she was just a tiny cub. Who are the other hyenas in the video? Is one of them Ziti by any chance? Those two used to be inseparable and it would be interesting if they were learning from each other's reproductive strategies.

Rebecca LaFleur said...

Ziti wasn't there this time, but that certainly would've been interesting as well! If I remember correctly it was El Paso and another immigrant who I haven't ID-ed yet who were present.

dee said...

Great post! Can't wait to see if Decimeter has cubs.Has anyone seen Cyber's cubs? Thanks and keep up the good work.

Rebecca LaFleur said...

We saw Cyber nursing a cub who we think might be Eggplant, but we couldn't confirm the ID. She's being pretty skittish lately unfortunately, so we haven't seen her around the den much.

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