Variation in thermal courtship activity curves across individuals exceeds variation across populations and sexes.

Abstract

The dynamics of mating interactions can vary in response to a wide variety of environmental factors. Here, we investigate the potential for individuals to vary consistently in the environmental conditions under which they actively engage in courtship. Specifically, we quantify variation in how courtship activity changes with environmental temperature across levels of biological organization in Enchenopa binotata treehoppers. Male E. binotata produce vibrational courtship signals and receptive females respond with their own sex-specific vibrational courtship signal. We tested each individual twice for the production of courtship signals across a range of ecologically-relevant temperatures (18 - 36 °C). Then, we measured repeatability and variability in the resulting thermal courtship activity curves, including the temperature of peak activity and tolerance to thermal extremes. We also looked at patterns of variation across populations and sexes. We found minimal variation across populations, but significant variation across individuals. Specifically, we found prevalent repeatability in how thermally generalized or specialized individuals are. However, repeatability was limited to females only. We also found higher variability in female traits than in male traits, although patterns of variability did not always predict patterns of repeatability. These results suggest that thermal variation could alter the dynamics of mate competition, and that-due to potentially different selective optima for males and females-the sexes may respond to changes in temperature in different ways. Specifically, females show a higher potential to adapt but males show a higher potential to be more robust to changes in temperature due to overall higher courtship activity across temperatures.