Upper Thermal Tolerances of Different Life Stages, Sexes, and Species of Widow Spiders (Araneae, Theridiidae).

Temperature strongly influences the physiology and behavior of ectotherms. Persistence within different environments can be limited by thermal tolerances. These thermal tolerances can also shift through life stages and differ between sexes. The critical thermal maximum (CTMax ) defines the temperature at which animals experience unorganized locomotion or spasms. In this study, we tested if CTMax varied between a native and an invasive widow species. We separately tested if CTMax varied by widow life stage and sex. We predicted that the invasive species would have higher CTMax due to originally inhabiting warmer climates. We also predicted that juveniles and male widows would possess higher CTMax because they are more mobile and could experience a greater scope of thermal extremes throughout landscapes. We did not find a difference in CTMax between the species, but we did find differences across development stages. Temperature of spasms and death decreased with developmental stages, which corresponds with previous studies in spiders. Future studies of ontogenic and interspecific comparisons will be crucial for more broadly understanding how upper tolerances shapes species persistence in changing climates or ability to invade new habitats.