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Biological Sciences


Ben Sadd

Mentor Department

Biological Sciences


Sexual selection arises from differences in reproductive success that are a product of variation in mating success. Sexual selection has shaped a variety of male-specific sexual traits, such as bird song and elaborate male courtship rituals, but the relative importance of sexual selection should vary across environments. In particular, the ratio of reproductively mature males to females, known as the operational sex-ratio (OSR), determines the intensity of competition for mates. The decorated cricket, Gryllodes sigillatus, is an ideal model system to study the effects OSRs on male sexually selective traits. Male decorated crickets have several traits that are associated with increased mating success, including acoustic signaling and the manufacture of nuptial food gifts that are presented to females at mating. Previous research has shown that increased mass of nuptial gifts leads to increased mating success, suggesting that gift size is critical to reproductive success. Using an experimental evolution approach, we explored the effect of varying OSRs on the evolution of investment in this important male reproductive trait. Male crickets were taken from replicate populations that had been kept for 20 generations under male-biased or female-biased OSRs, and were screened every other day for 21 days for the production of a nuptial gift. Gifts were extracted and weighed to obtain wet mass, and then dried to obtain a dry mass. Results are currently being analyzed, but we predict that the crickets from the male biased OSR lines will produce larger gifts than those from the female biased lines due to a greater intensity of sexual selection. This work is important because it furthers our knowledge about the evolutionary ecology of sexual selection using an accessible system with readily measurable sexual traits.

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