Introduced species can become invasive, damaging ecosystems and disrupting economies through explosive population growth. One mechanism underlying population expansion in invasive populations is ‘enemy release’, whereby the invader experiences relaxation of agonistic interactions with other species, including parasites. However, direct observational evidence of release from parasitism during invasion is rare. We mimicked the early stages of invasion by experimentally translocating populations of mite-parasitized slender anole lizards ( Anolis apletophallus ) to islands that varied in the number of native anoles. Two islands were anole-free prior to the introduction, whereas a third island had a resident population of Gaige's anole ( Anolis gaigei ). We then characterized changes in trombiculid mite parasitism over multiple generations post-introduction. We found that mites rapidly went extinct on one-species islands, but that lizards introduced to the two-species island retained mites. After three generations, the two-species island had the highest total density and biomass of lizards, but the lowest density of the introduced species, implying that the ‘invasion’ had been less successful. This field-transplant study suggests that native species can be ‘enemy reservoirs’ that facilitate co-colonization of ectoparasites with the invasive host. Broadly, these results indicate that the presence of intact and diverse native communities may help to curb invasiveness.

If fitness optima for a given trait differ between males and females in a population, sexual dimorphism may evolve. Sex-biased trait variation may affect patterns of habitat use, and if the microhabitats used by each sex have dissimilar microclimates, this can drive sex-specific selection on thermal physiology. Nevertheless, tests of differences between the sexes in thermal physiology are uncommon, and studies linking these differences to microhabitat use or behavior are even rarer. We examined microhabitat use and thermal physiology in two ectothermic congeners that are ecologically similar but differ in their degree of sexual size dimorphism. Brown anoles (Anolis sagrei) exhibit male-biased sexual size dimorphism and live in thermally heterogeneous habitats, whereas slender anoles (Anolis apletophallus) are sexually monomorphic in body size and live in thermally homogeneous habitats. We hypothesized that differences in habitat use between the sexes would drive sexual divergence in thermal physiology in brown anoles, but not slender anoles, because male and female brown anoles may be exposed to divergent microclimates. We found that male and female brown anoles, but not slender anoles, used perches with different thermal characteristics and were sexually dimorphic in thermal tolerance traits. However, field-active body temperatures and behavior in a laboratory thermal arena did not differ between females and males in either species. Our results suggest that sexual dimorphism in thermal physiology can arise from phenotypic plasticity or sex-specific selection on traits that are linked to thermal tolerance, rather than from direct effects of thermal environments experienced by males and females.

Temperature affects the mating displays of many ectothermic animals, yet almost no information exists on the temperature preferences of ectotherms while they are displaying for mates. This study investigated the preferences of displaying male field crickets ( Gryllus integer) for microhabitats of different temperatures. G. integer males attract sexually receptive females by calling from cracks in the ground. We collected data from the field on the temperature of male calling sites (cracks in the ground), on the amount of herbaceous cover (which affects crack temperature) surrounding calling sites, and on the temporal properties of male calls at different temperatures. Laboratory experiments demonstrated that males prefer warmer sites and confirmed that temperature influences mating calls. We conclude that males of this ectothermic species prefer to call for mates from warmer sites, and that microhabitat choice on the basis of temperature affects their mating calls, and potentially their reproductive success.

Physiologists have primarily focused on two potential explanations for heat stress in animals—the classic model of molecular stability and an alternative model of oxygen limitation. Although the classic model has widespread support, the oxygen-supply model applies to many aquatic animals and some terrestrial ones. In particular, the embryonic stage of terrestrial animals seems most susceptible to oxygen limitation because embryos acquire oxygen from the atmosphere by diffusion rather than ventilation. We report experiments confirming the two conditions of the oxygen-supply model in Japanese quail embryos, Coturnix coturnix . Hypoxia (12% O 2 ) greatly reduced the chance of survival at 47.5°C, and hyperoxia greatly improved the chance of survival at 48.5°C. This finding expands the scope of the oxygen-supply model to a terrestrial, endothermic species, suggesting that oxygen supply generally limits the heat tolerance of embryos.

Theoretical models predict that lizards adjust their body temperature through behavioral thermoregulation as a function of food availability. However, behavioral thermoregulation is also governed by interactions among physiological and ecological factors other than food availability, such as hydration state, and sometimes it can even conflict with the locomotor activity of animals. Here, we aimed to investigate the role of food intake and hydration state on behavioral thermoregulation and voluntary locomotor activity in the lizard Tropidurus catalanensis. We hypothesized that food intake can influence behavioral thermoregulation via an interaction with hydration state. We also hypothesized that lizards should endeavor to spend as little time as possible to reach their preferred body temperature to defend other physiological and/or ecological functions. We collected lizards in the field and brought them to the laboratory to measure the preferred temperature selected in a thermal gradient and the total distance traveled by them in fed and unfed conditions and with variable hydration state. Our results showed that food consumption was the most important predictor of preferred temperature. In contrast, either the hydration state alone or its interaction with food consumption did not have important effects on the lizards’ thermal preference. Also, we found that the total distance traveled by lizards was not affected by food intake and was barely affected by the hydration state. We provide an experimental approach and a robust analysis of the factors that influence behavioral thermoregulation and locomotor activity in a tropical lizard.