Developmental plasticity of thermal ecology traits in reptiles: Trends, potential benefits, and research needs.

A variety of phenotypic traits in reptiles are affected by conditions during embryonic development, a phenomenon known as developmental plasticity. In particular, many traits in which expression changes with temperature, such as locomotor performance or growth rates, are also developmentally plastic. However, much less is known about the extent to which traits associated with thermal ecology, such as thermal tolerance and behavioral thermoregulation, are developmentally plastic. Here, we review the literature on developmental plasticity in physiological and behavioral traits associated with thermal ecology in reptiles. Most studies on developmental plasticity of thermal traits have assessed plasticity in behavioral traits, such as selected temperature or time spent basking, and these studies have found mixed support for the presence of developmental plasticity in behavioral thermal traits. In contrast, very few studies have assessed developmental plasticity in physiological traits, yet these studies generally support a developmentally plastic basis for thermal tolerance. Most studies have only tested for developmental plasticity in thermal ecology traits at the hatchling stage, which limits our understanding of the benefits of developmental plasticity to individuals, or the adaptive significance of developmental plasticity in populations. We recommend that research on developmental plasticity in reptile thermal ecology be expanded to include incubation conditions other than mean temperature, consider traits associated with cold-tolerance, and endeavor to understand how developmental plasticity in thermal ecology traits is beneficial. In particular, determining how long differences persist over ontogeny, and testing for benefits of developmental plasticity across multiple life stages, are crucial first steps towards understanding the adaptive significance of developmental plasticity in thermal ecology traits.

Cellular and whole-organism effects of prolonged versus acute heat stress in a montane, desert lizard.

Global climate change involves both prolonged periods of higher-than-normal temperatures and short but extreme heat waves. Both types of temperature increases are likely to be detrimental to ectotherms, and even if such temperature increases do not cause mortality directly, compensating for such temperature increases will likely entail costs to organisms. We tested the effects of prolonged periods of higher-than-average temperatures and short-term, acute heat stress in wild populations of greater short-horned lizards (Phrynosoma hernandesi), a temperate, montane lizard of the Colorado Plateau, UT, USA. We transplanted one group of lizards from a high- to a low-elevation site, exposing them to a prolonged period of warmer temperatures. These lizards, exposed to prolonged periods of higher-than-average temperatures, experienced no change in sprint speed, endurance, or heat shock protein (HSP) production after treatment compared to baseline levels; however, they had lower water content after the transplant to a warmer climate compared to before the transplant. We exposed a second group of lizards to acute heat stress by exposing them to thermally stressful temperatures for 4 h. These lizards, exposed to a short period of acute heat stress, had no change in endurance, water content, or HSP production following acute heat stress; however, lizards exposed to acute heat stress had slower sprint speeds than control lizards. Our results demonstrate that both prolonged temperature increases and acute heat stress, each of which are predicted to occur with climate change, had different cellular and/or whole organismal-level effects on lizards.