Metabolism and water loss are not related to environmental heterogeneity in two mygalomorph spiders

The reproductive period of tarantulas is constrained by their thermal preferences (Araneae, Theraphosidae)

Locomotor and physiological performance of ectotherms are affected by temperature. Thermoregulation is achieved by changes in behavior and the selection of micro-habitats with adequate temperatures to maintain the body temperature (T_b) within a range of preference. Apart from this temperature dependence at spatial scales, ectotherms are also affected by temperature at temporal scale. For instance, ectotherms can only be active some months of the year, particularly in temperate environments. Tarantulas are ectotherms that live in burrows most of their life. Nevertheless, after the sexual maturation molt, males leave their refugia and start a wandering life searching for females to mate. The reproductive period varies among species. In some species walking males are seen in late spring or early summer, while in other species males are only seen during fall or winter. Apart from the differences in lifestyles after maturation, tarantulas exhibit sexual dimorphisms in longevity and body mass, having smaller, shorter-lived males. Thus, to optimize energetic budgets, decreasing thermoregulation costs, we hypothesize and examine a putative correlation between an individual's preferred body temperature (T_pref) and the environmental temperature during the reproductive period. Hence, we characterize T_pref in seven tarantula species and analyze which factors (i.e., time of day, body mass, and sex) correlated with it. Furthermore, we assess putative correlated evolution of T_pref with ambient temperature (minima, mean, and maxima) during the reproductive period by means of phylogenetic independent contrasts. We did not find differences in thermal preferences between sexes; and only one species, Acanthoscurria suina, exhibited diel differences in T_pref. We found evidence of correlated evolution between T_pref and minimum temperature during the reproductive period among all seven species studied herein. Our results show that the reproductive period is constrained by thermal preferences, dictating when males can start their wandering life to mate.