Thermal Fluctuation Correlates with Sex-Specific Effectiveness of Behavioral Thermoregulation in Melanoplus differentialis
Environmental drivers of the evolution of behavioural thermoregulation are still being elucidated. Much attention has been given to mean temperatures in this respect, but less has been given to thermal heterogeneity. Here, we tested in situ effectiveness of thermoregulation of a generalist grasshopper at five sites that vary in temporal thermal heterogeneity to see if individuals from more heterogeneous sites thermo regulated more effectively. We sampled 1) operative temperatures, 2) preferred temperatures, 3) deviations between preferred and field body temperatures, 4) deviations between preferred and operative temperatures, and 5) effectiveness of thermoregulation (E). We found that: 1) operative temperatures did not differ among sites; 2) preferred temperatures did not differ among sites; 3) environmental thermal quality and accuracy of thermoregulation differed among sites, but there was not a clear correlation between these and temporal thermal heterogeneity; and 4) E differed among sites and partially followed our hypothesized pattern, but patterns differed between the sexes. We concluded that temporal thermal heterogeneity affects some organismal thermal properties, and may be a factor in differences in E among populations. However, spatial heterogeneity in thermal resources, which we did not measure, may be affecting the evolution of thermal properties in the populations we examined.
Devin B. Preston, Steven G Johnson