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is sharing meat once enough to increase mating success?

Posted by avjaeggi on 17 Apr 2009 at 12:57 GMT

we journal-clubbed your article today and while we liked the approach of testing exchange over long periods of time while controlling for other variables, we were all puzzled about one thing: in your model, only the binary variable for meat sharing (did a male ever share meat with a female yes/no) had a significant influence whereas neither the amount of meat shared nor the frequency of sharing did. wouldn't these two measures better reflect the impact on female fitness? do you have an explanation why only the binary factor turned out to be significant?

thanks for your reply

No competing interests declared.

RE: is sharing meat once enough to increase mating success?

cristinagomes replied to avjaeggi on 17 Apr 2009 at 14:15 GMT

That's a good point and I have thought a lot about it myself.

I have come up with three possible explanations:

1. Although our data set is large (90 successful hunts) it’s possible that in order to pick up on a more precise and detailed relationship, as a linear one between meat and sex, we would require a larger and more detailed data set. If this were the case, it’s possible that such a relationship exists but we were only able to pick up on the more robust binary effect. Therefore, larger long term data sets of perhaps many more hunts would be required. This would not be surprising for a long lived species that has such complex relationships, as do chimpanzees.

2. Its also possible that females prefer males who share meat with them over those who don't (binary response) but then other factors, such as rank (which has a linear effect), override the linear effect of meat sharing.

3. Finally, it’s possible that small quantities of meat are so important to an individuals health that it’s more important if a male shares meat or not with a female rather than how much meat he actually shares. The meat scrap hypothesis proposes that small quantities of meat (meat scraps) provide individuals with important micronutrients (vit A, vit K, calcium, sodium, potassium) necessary to remain healthy. A recent publication suggests that group hunting in chimpanzees is driven by the increased probability of acquiring meat scraps and therefore micronutrients, rather than by the increased probability of maximizing caloric intake (Tennie et al. 2009,BES). This explanation would also support the previous one, resulting in that once a female has acquired some meat from a particular male, other factors would have a stronger influence on her choice of mates.

I hope I have manged to address your comment to some extent, however, if you have any other idea as to why this might be the case I would be happy to hear it and discuss some more. I appreciate your interest.

No competing interests declared.

RE: RE: is sharing meat once enough to increase mating success?

avjaeggi replied to cristinagomes on 17 Apr 2009 at 14:44 GMT

thanks for your response!

i think the meat-scrap hypothesis is a good point, in that case a female's needs would be quickly satisfied and larger amounts of meat don't significantly improve her fitness anymore, right? so her "fitness improvement curve" has a very steep early ascent and then flattens out, and she then wouldn't respond anymore with conceding more matings.
but does the tennie et al paper say something about how often these micronutrients would be needed? maybe then you could still find an influence of sharing frequency on mating success if you could divide your study period into time periods of that length, "micronutrient-need-intervals" so to speak. would that make sense?

thanks again for the response

No competing interests declared.