Of mice and men: Androgen dynamics in dominance and reproduction

In the animal literature, the concept of dominance usually links status in intermale encounters with differential reproductive success. Mazur & Booth effectively review the human literature correlating testosterone with intermale competition, but more profound questions relating this to male–female dynamics have yet to be addressed in research with humans.

Courtship Behavior of the Small-Mouthed Salamander (Ambystoma Texanum): the Effects of Conspecific Males On Male Mating Tactics

Abstract1. The courtship behavior of A. texanum consisted of a rapid nudging period followed by males producing many spermatophores, some of which were picked up by the female. Neither amplexus or leading by the male were integral components of courtship. Consequently, proposed geographic variation in A. texanum courtship remains unsubstantiated. 2. Courtship behavior of A. texanum and A. barbouri (formerly pond and stream form A. texanum, respectively) is very similar; only the location of courtship and perhaps the frequency of sexual interference tactics are different for these two sibling species. 3. A. texanum courtship is rapid, males produce large numbers of spermatophores per courtship and invest little courtship time per spermatophore, and intermale competition is extreme. 4. Male A. texanum promote their sexual success using sexual interference behavior (e.g. covering other spermatophores with their own) and to a lesser degree sexual defense behavior (e.g. forcefully nudging rival males). 5. Male sexual success is primarily enhanced directly - A. texanum males increase the number of spermatophores produced when at least two other males are courting the same female. The temporal allocation of these additional spermatophores is adaptive only if males are maximizing the number of ejaculates per female or breeding typically occurs in polygamous aggregations.

Effects of colour bands on male competition and sexual attractiveness in zebra finches (Poephila guttata)

Recent work suggests that coloured plastic leg bands may alter the sexual attractiveness and reproductive success of zebra finches (Poephila guttata). For example, males wearing red bands are more attractive to females and have enhanced reproductive success compared with males that have light green bands. Colour bands have been widely used in studies of avian behaviour and therefore could introduce bias if they regularly have a significant impact on social interactions among individuals. We carried out an experiment to assess the proximate effects of colour bands on zebra finch behaviour. Male zebra finches maintained in a large indoor aviary were given either red or light green bands and then scored for their ability to compete for a limited number of nest boxes and to attract females. The same males were randomly reassigned either red or light green bands and tested for their ability to regain boxes and attract new females. We found no correlation between band colour and a male's ability to gain either a nest or female. However, there was an association between male activity level and success. Also, those males that attracted a female in the first part of the experiment were more likely to do so in the second part of the experiment. We conclude that any immediate advantages conferred by attractive band colours may be masked under conditions of strong intermale competition for nests and mates.