Causes and consequences of maleemale courtship in fruit flies

Keywords: courtship Drosophila melanogaster fruit fly homosexual behaviour learning The mechanisms maintaining homosexual behaviour in animals are not well understood. In fruit flies, where maleemale courtship is prevalent, it has been suggested that young males gain from being courted by mature males, perhaps through learning. I conducted two series of experiments to critically examine why mature males court immature males and what immature males may gain from such courtship. The results indicate that mature males do not identify the sex of the sexually ambiguous immature males and find them attractive even after substantial experience. These findings agree with recent research indicating that males initially court a broad range of potential mating targets and then narrow their courtship focus based on their experience of being rejected by classes of flies such as recently mated females or heterospecific females, which are clearly identified by their distinct phero-monal profiles. Compared to inexperienced males, males that either had received courtship when immature or had been housed with mature males when young did not have either higher mating frequencies or shorter mating latencies but spent more time courting females. Such higher courtship intensities may translate into a mating advantage in some settings. It appears that young males that interact with mature males develop into a sexually aggressive phenotype, which could better prepare them to compete for females. Homosexual behaviour is widespread among animals including humans, but the proximate and ultimate mechanisms that have maintained it in spite of its probable costs are not well understood suggested that immature male fruit flies that elicit courtship from mature males subsequently gain increased mating success owing to mechanisms 'reminiscent of the song learning process that occurs in some bird species' (McRobert & Tompkins 1988, page 1096). This tantalizing claim, however, has not been subjected to the necessary critical research. Learning in the context of sexual behaviour is well known in fruit flies as well as other insects (Siegel & Hall 1979; Dukas 2006). In fruit flies, males initially court a broad range of receptive and unreceptive conspecific and heterospecific females. The males then learn to selectively reduce courtship of the female categories that persistently reject them, thus allowing them to maximize the time they devote to courting sexually receptive females (Dukas 2004b, 2005, 2009; Dukas et al. 2006). The phenomenon of males courting immature males readily fits within the above generalization: immature males do not yet produce the …