Immobile and Mobile Life-History Stages Have Different Thermal Physiologies in a Lizard

Abstract

Temperature affects multiple aspects of an organism's biology and thus defines a major axis of the fundamental niche. For ectotherms, variation in the thermal environment is particularly important because most of these taxa have a limited capacity to thermoregulate via metabolic heat production. While temperature affects all life-history stages, stages can differ in their ability to respond to the thermal environment. For example, in oviparous organisms, free-living adults can behaviorally thermoregulate, whereas developing embryos are at the mercy of the nest environment. These differences in the realized thermal environment should select for life-history stages to have different thermal tolerances, although this has been rarely examined. I tested the hypothesis that stage-specific thermal reaction norms can evolve independently by using southern alligator lizards (Elgaria multicarinata, Anguidae). Using incubation experiments (five temperatures: 24°, 26°, 28°, 30°, and 32°C), I described the thermal reaction norm for embryonic development and compared these results to previous studies on the thermal ecology of adults. Offspring survivorship and morphology were similarly affected by incubation temperature. While developing embryos had the same optimum temperature as adults (approximately 28°C), the breadth of their thermal reaction norms differed. My results suggest that developing embryos of E. multicarinata are more sensitive to variation in the average thermal environment than are adults. Variation in the thermal sensitivity of life-history stages might be common and has implications for how organisms respond to variation in the thermal environment. Identifying those life-history stages that are most sensitive/limiting will be important for developing models that best predict species' responses to impending environmental change.

Evolution of phenotypic plasticity in extreme environments

“…Another important temporal component is the agedependency of reaction norms. The environment influences phenotypes during development for most morphological traits, so reaction norms often have an ontogenic component [34,109], and more generally plasticity is likely to change with life stages, as shown in many studies [110]. A reaction norm might be constructed for each life stage, but the challenge is then to integrate them into an overall response in temporally changing environments, accounting for the fact that conditions at one life stage might influence reaction norms at a subsequent life stage.…”

Physiology at near‐critical temperatures, but not critical limits, varies between two lizard species that partition the thermal environment

“…Thus, despite living in different thermal habitats, classic descriptors of thermal preference, performance and tolerance fail to distinguish NAL and SAL (summarized in Table ). Notably, these animals differ in reproductive mode (NAL is viviparous and SAL is oviparous), which may explain NAL occurring in cold habitats unsuitable for SAL (Blackburn, ; Shine, ; Stewart, ; Telemeco, ). Nonetheless, both SAL and NAL can successfully reproduce in warm environments.…”

Stage-specific heat effects: timing and duration of heat waves alter demographic rates of a global insect pest

“…For example, adult amphibians and reptiles are able to tolerate higher temperatures for a longer time than those at earlier life-stages (e.g. eggs or larvae) (Sherman 1980;Xu and Ji 2006;Telemeco 2014), while in invertebrates, juvenile stages often have a higher tolerance (Krebs and Loeschcke 1995;Klok and Chown 2001;Ma et al 2004a;Lyons et al 2012;Zhang et al 2015). It is also possible that the effects of temperatures experienced during early life-stages could also be carried over to alter adult traits.…”