Rare breed of car­ing dads

Moun­tain go­ril­las dis­play­ing this be­hav­iour sire more off­spring than peers that don’t

Cape Argus - - METRO - STACEY ROSENBAUM The Con­ver­sa­tion Stacy Rosenbaum is a Post­doc­toral Fel­low, Univer­sity of Cal­i­for­nia, Los An­ge­les.

PA­TER­NAL care – where fa­thers care for their chil­dren – is rare among mam­mals (that is, an­i­mals which give birth to live young). Sci­en­tists have iden­ti­fied more than 6 000 mam­mal species, but pa­ter­nal care only oc­curs in 5 to 10% of them.

Hu­mans fall into that cat­e­gory, along with species such as mice and lions. There are also a num­ber of South Amer­i­can mon­key species where males take on equal or greater child­care bur­dens than fe­males. But these species are the ex­cep­tions, not the rule.

Sci­en­tists be­lieve the rea­son so many male mam­mals don’t get in­volved in car­ing for their young is that they get higher “re­turns on in­vest­ment” if their en­ergy is spent seek­ing out more mat­ing op­por­tu­ni­ties rather than ac­tively par­ent­ing.

Sim­ply put, male mam­mals that spend their time pro­duc­ing more in­fants rather than tak­ing care of the ones they have will leave be­hind more off­spring.

Over time, nat­u­ral se­lec­tion favours males who use this strat­egy, so fa­ther­ing be­hav­iour rarely gains an evo­lu­tion­ary foothold.

But moun­tain go­ril­las, found in the moun­tains of Rwanda, Uganda and the Demo­cratic Re­pub­lic of Congo, are among the ex­cep­tions to the rule.

Though moun­tain go­rilla groups are full of com­plex so­cial dy­nam­ics, just as hu­man fam­i­lies are, in many groups some of the strong­est so­cial bonds we ob­serve are be­tween adult males and in­fants – even when the in­fants aren’t the males’ own off­spring.

From the time that young go­ril­las are old enough to move away from their moth­ers, they fol­low males ev­ery­where. Males, in turn, are ex­tremely tol­er­ant. Some reg­u­larly hold, play with, groom, and let in­fants sleep in their nests with them.

In a re­cent study, my col­leagues and I set out to de­ter­mine why this might be the case, since this be­hav­iour didn’t seem to only ben­e­fit their own in­fants. We found that the go­ril­las who spent the most time with any young, not just their own, also sired the most in­fants.

This is a no­table find­ing, since moun­tain go­ril­las are not a species in which sci­en­tific the­ory pre­dicts this sort of be­hav­iour, much less a con­nec­tion to the males’ even­tual re­pro­duc­tive suc­cess. They have the be­havioural and phys­i­cal char­ac­ter­is­tics of a species where males are ex­pected to in­vest their en­ergy in find­ing mat­ing op­por­tu­ni­ties, not bond­ing with in­fants.

For our study we used 30 years of ge­netic pa­ter­nity data to de­ter­mine which males sired which in­fant, and com­pared that to hun­dreds of hours of data on their be­hav­iour. We recorded what per­cent­age of each male’s time he spent groom­ing and rest­ing with in­fants. We used data from 23 males, who col­lec­tively sired 109 in­fants.

Our mod­els show that, across the course of their lives, males that do the most groom­ing and rest­ing with in­fants are ex­pected to sire about five times as many in­fants as the males that do the least. This is true even after con­trol­ling for other very im­por­tant fac­tors, such as how long the male lived and his dom­i­nance in rank.

This is a sur­pris­ing find­ing. When we ob­serve pa­ter­nal care among mam­mals, the vast ma­jor­ity of the time it is in species that are monog­a­mous – that is, males only mate with a sin­gle fe­male, and vice versa. Go­ril­las are not monog­a­mous, and the males’ very well-de­vel­oped char­ac­ter­is­tics for fight­ing (like large mus­cles and teeth) sug­gest that their pri­mary strat­egy is to fight for new mat­ing op­por­tu­ni­ties, not to care for in­fants.

Though we can­not be sure ex­actly why the males that care more for in­fants fare bet­ter than their peers that don’t, our best guess is that fe­male go­ril­las pre­fer to mate with males that are nicest to in­fants.

Other pos­si­bil­i­ties need to be ex­plored, how­ever – for ex­am­ple, maybe the males that have per­son­al­i­ties that fe­males like are also more in­clined to in­ter­act with in­fants.

Re­gard­less of ex­actly how the con­nec­tion be­tween males’ re­la­tion­ships with in­fants and their re­pro­duc­tive suc­cess oc­curs, if males that have the strong­est so­cial bonds with in­fants are also leav­ing be­hind the most in­fants, then we would ex­pect that over time a larger and larger pro­por­tion of male go­ril­las would en­gage in this kind of be­hav­iour.

Pre­sum­ably, some­thing sim­i­lar could have hap­pened among the now-ex­tinct species that led to mod­ern hu­mans. Our an­ces­tors, like the go­ril­las, were prob­a­bly not monog­a­mous. And yet at some point males in these species must have also started in­ter­act­ing with, and car­ing for, in­fants.

The kind of care-tak­ing that male go­ril­las do is ex­tremely rudi­men­tary in com­par­i­son to what hu­mans do. None­the­less, it is no­table be­cause of the in­sights it can pro­vide into how male care-tak­ing in the lin­eage that led to hu­mans might have over­come the usual evo­lu­tion­ary pay-offs that kept it from evolv­ing in most liv­ing mam­mal species. |

The males are ex­tremely tol­er­ant. Some reg­u­larly hold, play with, groom, and let in­fants sleep in their nests

AP African News Agency (ANA)

A SILVERBACK go­rilla plays with ju­ve­niles at Vol­ca­noes Na­tional Park in Ruhen­geri, Rwanda. Moun­tain go­ril­las are an ex­cep­tion to the rule of mam­mals car­ing for their off­spring.|

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