Historically the way that many evolutionary biologists thought about mating could be summed up as: males compete for females and females choose who to mate with. This is based on the fact that males, in mammals at least, invest very little in their offspring in terms of sperm and parental care, whereas females produce large eggs and provide large amount of parental care. Many people will disagree with this, but what I have just written is a gross over simplification of a whole field of research. However, recently researchers have begun to investigate male choice and differential investment. A nice paper by Leivers et al, abstract and link below, has just come out in Behavioral Ecology. This work shows that good and poor quality males produce relatively poor quality sperm when looking at pictures of unattractive women. However, the awesome result is that when looking at pictures of attractive women good quality men can produce better sperm, whilst their poorer counterparts don't change. This shows that human men can adjust their investment in sperm based on the quality of their potential mate. Research like this is brilliant, because not only is it very interesting in itself but it also bridges the fields of mate choice and sperm competition.
Leivers et al (2014) Context-dependent relationship between a composite measure of men’s mate value and ejaculate quality. Behavioral Ecology, doi: 10.1093/beheco/aru093
Secondary sexual traits in males are recognized as having arisen in order to gain access to reproductive opportunities, through their effects on the outcome of male–male competition and female choice. The phenotype-linked fertility hypothesis proposes that ejaculate quality is honestly advertised via secondary sexual traits. Alternatively, if males have limited resources to allocate to both pre- and postcopulatory traits, males possessing attractive phenotypic or behavioral traits may produce poorer quality ejaculates. Sperm competition theory also predicts that the female phenotype will influence ejaculate quality, with males increasing investment as female attractiveness increases. However, the extent to which the male and female phenotypes interact in affecting ejaculate quality has not been widely studied. Here, we examine how male and female phenotypes influence ejaculate quality in humans. Eighty-one men, for whom we had a composite measure of overall male mate value, produced a semen sample in response to images of either highly attractive or less attractive women. We found a significant relationship between male mate value and ejaculate quality that was context dependent. Sperm motility and concentration increased with male mate value but only when men viewed images of highly attractive women. Context dependence may contribute, in part, to the often conflicting patterns of variation found in studies that test the phenotype-linked fertility hypothesis.
http://beheco.oxfordjournals.org/content/early/2014/06/03/beheco.aru093.full
Leivers et al (2014) Context-dependent relationship between a composite measure of men’s mate value and ejaculate quality. Behavioral Ecology, doi: 10.1093/beheco/aru093
Secondary sexual traits in males are recognized as having arisen in order to gain access to reproductive opportunities, through their effects on the outcome of male–male competition and female choice. The phenotype-linked fertility hypothesis proposes that ejaculate quality is honestly advertised via secondary sexual traits. Alternatively, if males have limited resources to allocate to both pre- and postcopulatory traits, males possessing attractive phenotypic or behavioral traits may produce poorer quality ejaculates. Sperm competition theory also predicts that the female phenotype will influence ejaculate quality, with males increasing investment as female attractiveness increases. However, the extent to which the male and female phenotypes interact in affecting ejaculate quality has not been widely studied. Here, we examine how male and female phenotypes influence ejaculate quality in humans. Eighty-one men, for whom we had a composite measure of overall male mate value, produced a semen sample in response to images of either highly attractive or less attractive women. We found a significant relationship between male mate value and ejaculate quality that was context dependent. Sperm motility and concentration increased with male mate value but only when men viewed images of highly attractive women. Context dependence may contribute, in part, to the often conflicting patterns of variation found in studies that test the phenotype-linked fertility hypothesis.
http://beheco.oxfordjournals.org/content/early/2014/06/03/beheco.aru093.full
RSS Feed
