Costs of female odour in males of the parasitic wasp Lariophagus distinguendus (Hymenoptera: Pteromalidae)
The display of female traits by males is widespread in the animal kingdom. In several species, this phenomenon has been shown to function adaptively as a male mating strategy to deceive sexual rivals (female mimicry). Freshly emerged males of the parasitic wasp Lariophagus distinguendus (Hymenoptera: Pteromalidae) are perceived by other males as if they were females because of a very similar composition of cuticular hydrocarbons which function as a sex pheromone in this species inducing courtship behaviour in males. Within 32 h, however, males deactivate the pheromone and are no longer courted by other males. In this paper, behavioural experiments were performed to test hypotheses on potential costs and benefits associated with the female odour in young males. We did not find any benefits, but demonstrated that young males were significantly more often outrivaled in male–male contests when competing with two older males for a female. Also, young males were significantly more often mounted in homosexual courtship events during these contests. Thus, display of female traits by males is not necessarily beneficial, and in fact, can be disadvantageous. We suggest that these costs have favoured the evolution of the pheromone deactivation mechanism in L. distinguendus males. The function of cuticular hydrocarbons as a female courtship pheromone in L. distinguendus might have evolved secondarily from a primary function relevant for both genders, and the deactivation of the signal in males might have caused a shift of specificity of the chemical signal from the species level to the sex level.
KeywordsCourtship pheromone Cuticular hydrocarbons Lariophagus distinguendus Parasitic wasps Pheromone evolution Pteromalidae
S1 T he movie shows a typical L. distinguendus male–male contest (1:2 constellation). One young male (with the courtship pheromone) and two old males compete for a virgin female. Initially, the young male engages in courtship towards the female as indicated by wing fanning. Subsequently, the young male is detected by one of the old males which immediately displays courtship behaviour. Whilst the two males are neutralised by the homosexual interaction, the second old male courts the female undisturbed and gains the copulation (WMV 3.01 MB).