Social competitiveness associated with rapid fluctuations in sperm quality in male fowl.

When females copulate with multiple males, paternity is determined by the competitive ability of a male to access females and by the ability of its ejaculates to out-compete those of other males over fertilization. The relationship between the social competitiveness of a male and the fertilizing quality of its sperm has therefore crucial implications for the evolution of male reproductive strategies in response to sexual selection. Here, we present a longitudinal experimental study of the relationship between social status and sperm quality.

Male mounting alone reduces female promiscuity in the fowl.

The fertilization success of an insemination is at risk when a female has the possibility to copulate with multiple males, generating sperm competition and sexual conflict over remating. Female propensity to remate is often reduced after copulation, and a staggering diversity of highly derived male traits that discourage female promiscuity have been investigated. However, it is difficult to separate the effect of such specialized traits and insemination products from the more basic effect that the act of mounting per se may have on female remating.

Sex-specific, counteracting responses to inbreeding in a bird.

Inbreeding often depresses offspring fitness. Because females invest more than males in a reproductive event, inbreeding is expected to be more costly to mothers than fathers, creating a divergence between the reproductive interests of each sex and promoting sex-specific inbreeding strategies. Males and females may bias the probability of inbreeding by selecting copulation partners, and, in sexually promiscuous species, through male strategic sperm investment in different females and female selection of the sperm of different males.

Chicken genomics: feather-pecking and victim pigmentation.

Feather-pecking in domestic birds is associated with cannibalism and severe welfare problems. It is a dramatic example of a spiteful behaviour in which the victim's fitness is reduced for no immediate direct benefit to the perpetrator and its evolution is unexplained. Here we show that the plumage pigmentation of a chicken may predispose it to become a victim: birds suffer more drastic feather-pecking when the colour of their plumage is due to the expression of a wild recessive allele at PMEL17, a gene that controls plumage melanization, and when these birds are relatively common in a flock.

A novel test of the phenotype-linked fertility hypothesis reveals independent components of fertility.

The phenotype-linked fertility hypothesis predicts that male sexual ornaments signal fertilizing efficiency and that the coevolution of male ornaments and female preference for such ornaments is driven by female pursuit of fertility benefits. In addition, directional testicular asymmetry frequently observed in birds has been suggested to reflect fertilizing efficiency and to covary with ornament expression. However, the idea of a phenotypic relationship between male ornaments and fertilizing efficiency is often tested in populations where environmental effects mask the underlying genetic associations between ornaments and fertilizing efficiency implied by this idea.

Sophisticated sperm allocation in male fowl.

When a female is sexually promiscuous, the ejaculates of different males compete for the fertilization of her eggs; the more sperm a male inseminates into a female, the more likely he is to fertilize her eggs. Because sperm production is limited and costly, theory predicts that males will strategically allocate sperm (1) according to female promiscuity, (2) saving some for copulations with new females, and (3) to females producing more and/or better offspring. Whether males allocate sperm in all of these ways is not known, particularly in birds where the collection of natural ejaculates only recently became possible.