Male mate preference for female eyespan and fecundity in the stalk-eyed fly, Teleopsis dalmanni

Traditional views of sexual selection view males as the indiscriminate sex, competing for access to choosy females. It is increasingly recognized that mating can also be costly for males and they are therefore likely to exhibit choice in order to maximize their reproductive success. Stalk-eyed flies are model species in sexual selection studies. Males are sperm limited and constrained in the number of matings they are able to partake in. In addition, variation in female fecundity has been shown to correlate positively with female eyespan, so eyespan size could provide males with a reliable signal of female reproductive value. We examined male mate preference in the wild in the stalk-eyed fly, Teleopsis dalmanni. In addition, we set up experiments in the laboratory allowing males a choice between females that varied in 1) eyespan (a proxy for fecundity) and/or 2) fecundity (manipulated through diet). We found that males exhibited preference for large eyespan females, both in the wild and laboratory studies. As well as using female eyespan as a mating cue, males were also able to assess female fecundity directly. Changes in fecundity among large eyespan females caused corresponding changes in male mate preference, whereas changes in the fecundity of small eyespan females had limited effect on their attractiveness. These results show that male mate preferences are a prevalent feature of a canonical example of female mate choice sexual selection and that males use multiple cues when they assess females as potential mates.