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The place are the beachmasters? Unexpectedly weak polygyny amongst southern elephant seals on a South Shetland Island – Journal of Zoology Weblog


Nichols, H. J., Fuchs, B., Paijmans, A. J., Lewis, G., Bonin, C. A., Goebel, M. E., & Hoffman, J. I. (2022). The place are the beachmasters? Unexpectedly weak polygyny amongst southern elephant seals on a South Shetland Island. Journal of Zoology, vol. 316, pp. 104– 117. https://doi.org/10.1111/jzo.12936

Elephant seals are a textbook instance of a polygynous species. The truth is, monumental male southern elephant seals (“the beachmasters”) combating over their harems on a seashore are the proper image of a mating system the place male competitors achieves its climax amongst mammal societies. On this context, one could ask whether or not it’s even price finding out these animals’ mating programs anymore. Don’t we already know all we have to learn about them? The reply is that we’re removed from having all of it found out, even for a well-studied mammal. Over the previous few many years, behavioural and genetic research have revealed surprising variation within the energy of polygyny in pinniped populations from a number of species, together with elephant seals. We’re studying with every examine that geographical and environmental elements can decide the power of males to monopolize mates.

Southern elephant seals (Mirounga leonina). Picture by Carolina Bonin

On this examine, we investigated the mating success of male elephant seals in a small inhabitants positioned at a wide-open seashore on a distant island. With little competitors on this small inhabitants, males ought to have a simple time monopolizing mates. By the best way, the seashore is on Livingston Island, one of many South Shetland Islands, the place a variable variety of elephant seals (56–158) come ashore to breed each austral summer season. This variation is probably going pushed by seashore entry circumstances: in some years, entry to the seashore is blocked by heavy snow throughout the time when the animals would sometimes arrive. We sampled each pup born along with a lot of the women and men current on the seashore each austral spring (October—December) from 2008 to 2016 and carried out a genetic parentage evaluation. We had been stunned to search out that the beachmasters at our examine seashore solely fathered round 10.7% of the pups born there. Essentially the most profitable male fathered solely seven pups over all the course of the examine. These findings recommend that, even for a species thought-about as a textbook instance of polygyny, essentially the most dominant males needn’t all the time monopolise a lot of the replica.

Elephant seal pup with its mom and a harem holding male. Picture by Carolina Bonin

We recognise that our sampling could have missed some males. Ideally, an observer ought to all the time preserve watch on the seashore and account for each seal coming ashore on on daily basis of each season. However have you ever tried to sit down on an Antarctic seashore holding a pair of binoculars for greater than 2-3h? First, your fingers would seemingly freeze (even with gloves), and relying on the day, the wind may blow you over! Additionally, our examine website is not only a fast stroll from a area station. It’s extra like a area camp, solely occupied by 5 to 6 individuals who have to work practically across the clock to cook dinner, clear, and monitor 5 pinniped species and two penguin species. Nonetheless, we thought-about the potential for lacking a small variety of extremely profitable males by conducting an evaluation of “hypothetical fathers” primarily based on maternal and offspring genotypes. This strategy allowed us to deduce what number of extremely profitable “unsampled” males we’d have missed, and the reply was none.

In the long run, we consider that there’s extra to that seashore than meets the attention. Many females don’t breed yearly, and their breeding behaviour seems to rely on the prevailing environmental circumstances. There may also be different mating ways, like mating within the water with sneaky males that hardly ever if ever come ashore. Regardless, future research will proceed to disclose thrilling patterns of mating and replica in elephant seals and different pinnipeds world wide.

Carolina Bonin

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