Does Female Mate Choice Confer Direct Fitness Benefits? Results From a Tephritid Fruit Fly

The melon fly, Bactrocera cucurbitae (Coquillett), exhibits a lek mating system in which males aggregate on plants, weakly defend leaf territories that lack any resources vital to females, and produce pheromone to attract potential mates. Males are attracted to and feed on the plant-borne compound raspberry ketone (RK) as well as its synthetic analogue, cue lure (CL), and studies have demonstrated that females mate preferentially with males fed these chemicals over males denied them. The objective of the present study was to investigate whether females gained direct fitness benefits by mating with CL-fed males, potentially via CL-mediated modifications in male ejaculate composition and quantity that act to enhance female longevity and reproduction. Mating trials were first performed to re-confirm that CL-feeding conferred a mating advantage to males. Then, having detected an advantage, female survival, fecundity, and fertility were compared between females mated to CL-fed males versus nonfed males. In addition, the incidence and duration of successful egg-to-pupa development were compared between the two groups of females. None of the comparisons suggested that fitness was enhanced by mating with a CL-fed male, and one parameter—fertility or egg hatch rate—showed a potential cost to mating with CL-fed males. Thus, mating with CL-fed males does not appear to confer direct fitness benefits to females. Factors potentially confounding interpretation of this finding are noted, and the possible role of a runaway selection process, mediated via RK or CL consumption, in shaping female mate choice in this species is proposed.