Patterns of song and preference variation in Laupala cerasina and their evolutionary implications
Grace, Jaime Leigh
Shaw, Kerry L
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Closely related species often differ conspicuously in secondary sexual characters, many of which may be shaped by sexual selection. Changes in these characters may directly influence speciation, since females use them to assess males and to choose a mate. I investigate the hypothesis that in closely related populations, divergence in preference for sexually selected characters may promote sexual isolation through assortative mating. Ultimately, if reproductive isolation is complete, this process of divergent sexual selection through preference divergence may result in the formation of new species. I have investigated the relationship between divergence in the pulse rate of male song and female preference for pulse rates in a group of Hawaiian crickets, Laupala cerasina. Within a population, males sing at a characteristic pulse rate, but males from different populations sing with significantly different pulse rates. The degree of population divergence is almost an order of magnitude less than that which distinguishes closely related species of Laupala. Using phonotaxis trials, I found that females show acoustic preferences for males whose pulse rates fall nearest to the population mean. Across populations, male pulse rates and female preferences are significantly correlated, suggesting that they are coevolving. I have demonstrated that females discriminate among songs whose pulse rates vary within the range of pulse rates found among neighboring populations. Furthermore, in choice trials, females prefer the songs of males from the same population to those from neighboring populations. These females also exhibit significant assortative mating based on their acoustic preferences. Divergence in female acoustic preference among populations thus provides a mechanism for generating and maintaining biodiversity through divergence in sexually selected characters used in mate choice.