Phenotypic plasticity related to temperature induces song variation in the field cricket Gryllus rubens

Mating songs and preferences for these songs have to match for communication to function. Since this match restricts variation, understanding how phenotypic variation is introduced in communication systems is essential for understanding their evolution. The environment, through phenotypic plasticity or parental effects, is an important catalyst for phenotypic variation. In Kentucky, the cricket Gryllus rubens has one reproductive generation in the spring and one in the fall and the mating songs differ substantially between generations. I tested whether these differences in songs are the result of intergenerational (i.e., parental effects) or intragenerational phenotypic plasticity. To test for the role of parental effects on songs, I reared offspring of field-collected spring and fall females in a common garden environment and recorded their songs. None of the analyzed song characters differed between the sons of fall and spring parents, suggesting that parental effects do not play a role in song development. To test for the effect of phenotypic plasticity on songs, I reared juvenile and adult males in two separate sets of experiments at two different levels of temperature and daylength. Rearing temperature affected every analyzed song character: The higher adult rearing temperature (32°C) induced significantly faster pulse rates, shorter pulse durations, and higher dominant frequency compared with the lower rearing temperature (24°C). The higher juvenile temperature induced significantly shorter pulse durations, longer interval durations, and lower pulse duty cycles than the lower rearing temperature. Rearing photoperiod did not affect male song development. The changes induced by the temperature treatments paralleled those observed in the wild, suggesting that the seasonally different songs in Kentucky are primarily the result of seasonal temperatures. Possible evolutionary consequences of the temperature-related phenotypic plasticity are discussed.