Spatial and temporal variation in three call traits and preferences of the tree cricket Oecanthus forbesi

摘要

Multiple selective forces act on the evolution of mating preferences. While mating preferences are central to pre-zygotic isolation, certain preferences and traits may make greater contributions. For some traits, females may exhibit preferences, but accept heterospecifics trait values when preferred values are scarce. For other traits, females may fail to reproduce before accepting heterospecifics trait values. Understanding patterns of variation and divergence in this later class of traits is particularly relevant to understanding divergence and speciation. Here, I focus on three call traits of Forbes' Tree Cricket (Oecanthus forbesi) to quantify their capacity to produce reproductive isolation and to compare patterns of variation and divergence in these traits. By generating female preference functions and measuring male call parameters, I test two hypotheses: (1) traits and preferences vary in their capacity to contribute to reproductive isolation and (2) traits that are important to reproductive isolation have lower intrapopulation, interpopulation, and interannual variation and weaker correlation with male body size. I find that female response to one trait (pulse rate) decreased sharply when trait values fell within the heterospecific range. This trait had low variation and no correlation with male morphology. For two other traits (pulse duration and dominant frequency), females responded to many values, including values characteristics of co-occurring heterospecifics. Trait variation was higher and pulse duration correlated with male leg length. These results indicate that the evolutionary dynamics of a low-variation trait (pulse rate) may be more important to speciation than changes in more conspicuously variable sexually selected traits.