Temporal variation in natural and sexual selection of male calling behavior in the field cricket Gryllus rubens

A primary goal of sexual selection theory is to understand how natural and sexual selection interact to favor variation in sexually-selected traits. The goal of this dissertation is to examine variation in male calling behavior of the field cricket Gryllus rubens and how temporal changes in natural and sexual selection may favor this variation. The results of this dissertation are important because they show that temporal variation in natural and sexual selection may favor variation in male sexually-selected traits.; Male calling song in G. rubens attracts females. It also attracts gravid females of the parasitoid fly Ormia ochracea . These female flies deposit larvae on and around calling males, killing infected crickets within 7--10 days. In northern Florida, O. ochracea is abundant in the fall and rare in the spring, and fly parasitism rates are higher in the fall than in the spring. This temporal variation in natural selection could favor different male songs in the fall than in the spring. I evaluated this possibility by examining seasonal variation in male calling behavior. I found that fewer males sing each night in the fall than in the spring and that fewer males sing at times when parasitoid flies are most active.; Because seasonal changes in parasitoid fly abundance may change the costs and benefit of choice, fall and spring females may behave differently towards calling males. I evaluated this hypothesis by observing the phonotactic behavior of fall and spring females. I found that fall females are less attracted to male songs than spring females at times when flies are most active.; Seasonal changes in sexual selection may change the seasonal benefits males derive from singing. I explored this hypothesis by examining whether the benefits of singing change seasonally and whether such changes are correlated with seasonal differences in male calling duration. The results of a playback experiment show that long duration calls attract more females in the fall, where call durations are long, than in the spring, where call durations are short.; Temporal changes in natural and sexual selection may favor seasonal variation in male G. rubens calling behavior. To evaluate how such fluctuating selection may affect seasonal patterns in calling duration, I developed a model evaluating the fitness of different calling strategies in the fall and spring given seasonal changes in natural and sexual selection. By varying these selective forces independently and comparing the fitness of calling strategies to observed calling durations, I found that temporal changes in sexual selection may have a greater effect on calling duration than changes in natural selection.