The first is one that looks at extrapair mating and it's prevalence. This research is a meta analysis of studies related to looking at how genetically similar mated bird pairs are and how high the rates of extrapair paternity are. Unsurprisingly they find that when genetic relatedness is high then extrapair paternity is high. The novelty of this review is that is shines some light on why some previous work has failed to show this pattern, principally because they were looking at the wrong markers for genetic relatedness. Microsatellite markers were the best predictors. The females who are closely related to their behavioural mate is not surprising, it avoids inbreeding depression and has the potential for her offspring to have higher fitness. The part of this field that is truly interesting is how the female, or the male for that matter, knows they are closely related. Kin recognition is useful not only in cooperative breeding societies but also to avoid inbreeding, and birds presumably (from these results) are able to do this. A study on meerkats showed that relatives will and do mate with each other if they were not present in their natal group at the same time, but when this happens their offspring don't do as well as more outbred offspring. So there is a long-term fitness cost to sleeping with your relatives!
The second paper I saw looked at response and reward to seeing cute babies. The interesting finding of this work was that although there was no difference in how the women rated the cuteness of the babies faces, women who had higher 'maternal tendencies' got a higher reward from seeing the cuter babies.The language of the paper is not the easiest to read, this might be because Biology Letters papers are very short and so they've tried to cram everything in. It would be interesting to note if women's response change through their reproductive cycle or as they get older and are more likely to want to have children. There might be some sort of evolutionary adaptation to getting a higher reward when you actually want children rather than when you don't want them.... who knows, more research is needed!
Arct et al. (2015) Genetic similarity between mates predicts extrapair paternity—a meta-analysis of bird studies. Behavioral Ecology doi: 10.1093/beheco/arv004
Extrapair mating has been recorded in approximately 90% of investigated avian monogamous species. However, factors triggering female mating decisions and potential fitness benefits from extrapair matings still remain poorly understood. Some studies suggest that females mate socially with low-quality males but seek extrapair mates offering superior genes for their progeny. This mating strategy may also help in mitigating the potential negative effects of pairing with a genetically similar mate. Here, we investigate whether genetic similarity within a social pair may predict the occurrence of extrapair paternity (EPP) in birds. Using a meta-analytical approach to a number of studies performed on birds, we found a positive relationship between the occurrence of EPP and the relatedness of social mates. Moreover, we found that the type of molecular markers used to estimate relatedness significantly affected the observed effect size. Specifically, we showed that only microsatellite markers were associated with significantly positive effect sizes. Thus, failure of some of the previous studies to detect the relationship between occurrence of EPP and the relatedness of social mates may at least partly arise due to methodological reasons.
Hahn et al. (2015) Reported maternal tendencies predict the reward value of infant facial cuteness, but not cuteness detection. Biology Letters, DOI: 10.1098/rsbl.2014.0978
The factors that contribute to individual differences in the reward value of cute infant facial characteristics are poorly understood. Here we show that the effect of cuteness on a behavioural measure of the reward value of infant faces is greater among women reporting strong maternal tendencies. By contrast, maternal tendencies did not predict women's subjective ratings of the cuteness of these infant faces. These results show, for the first time, that the reward value of infant facial cuteness is greater among women who report being more interested in interacting with infants, implicating maternal tendencies in individual differences in the reward value of infant cuteness. Moreover, our results indicate that the relationship between maternal tendencies and the reward value of infant facial cuteness is not due to individual differences in women's ability to detect infant cuteness. This latter result suggests that individual differences in the reward value of infant cuteness are not simply a by-product of low-cost, functionless biases in the visual system.