Drivers of interspecific variation in thermal developmental plasticity
Developmental plasticity refers to the modification of phenotypes based on conditions experienced in early life, and can have potentially lifelong consequences for organismal fitness. Temperature elicits plastic responses in embryos in many reptile species, however, little is known about how patterns of thermal developmental plasticity evolve across species. I experimentally determined patterns of developmental plasticity in seven species of Anolis lizards inhabiting South Florida by incubating embryos of each species at two different temperature treatments. I tested whether distributions of reaction norms describing plasticity best supported hypotheses of adaptive, maladaptive, and neutral plasticity. I used Bayesian mixed models to analyze reaction norm variation determine how much variation in reaction norm slopes was attributable to phylogeny, species identity, and local versus historic temperatures. These results use evidence from a macroevolutionary scale to assess how plasticity evolves, as well the potential role of plasticity invasion success.
A) Phylogeny of seven anole species introduced to South Florida and thermal heterogeneity of their native environments. Letters correspond to the native area for that species, while shared shapes show a shared ecomorph class (diamond = crown giant, square = trunk-crown, circle = trunk-ground, triangle = trunk). B) Expected reaction norm distributions under three hypotheses of plasticity evolution.
Local adaptation of thermal developmental plasticity
A) Map of study localities. States sharing a color are expected to have similar thermal environments. Shapes indicate study populations – shared shapes indicate latitudinal replicates. B) Expected reaction norm distributions under three hypotheses of plasticity evolution in heat tolerance. C) Expected reaction norm distributions under three hypotheses of plasticity evolution in cold tolerance.
Patterns of developmental plasticity in organisms are predicted to be driven by levels of environmental heterogeneity in occupied habitat. Green anoles (Anolis carolinensis) occupy a relatively broad climatic cline across the southeast United States, potentially facilitating intraspecific differences in patterns of thermal plasticity on the basis of environmental heterogeneity. I measured patterns of thermal developmental plasticity in a suite of thermal physiology and life history traits among green anole populations spanning their native geographic range in southeast USA. I analyzed how reaction norms in each trait covaried across space as developmental thermal environments shifted, as well as the ability of local climate data to predict reaction norms. This study will determine whether geographic variation (or lack thereof) in fitness-related phenotypes points toward adaptive, maladaptive, or neutral evolution of plasticity.
Developmental plasticity in tropical lizards
Click here to read the blog post I wrote about this project for the American Philosophical Society!
Plasticity should evolve in response to increasing environmental heterogeneity, producing more plastic phenotypes in response to more heterogeneous environments. Most studies of plasticity in ectotherms are conducted on species from temperate environments, where temperatures. are heterogeneous annually. However, the vast majority of ectotherm biodiversity is concentrated in the tropics, where temperatures are relatively homogeneous and seasons are marked by stark changes in moisture. I measured patterns of reproduction and developmental plasticity among four species of Anolis lizards at La Selva Biological Station in Costa Rica to assess whether patterns of developmental plasticity match expected trends based on annual environmental heterogeneity. These results will provide information about the relative importance of macroclimatic variables in driving plasticity evolution and describe the reproductive ecology for several species of anoles not previously bred in a laboratory environment.
A) Experimental design. 20 females from each species produce 160 eggs total – 40 eggs will be allocated to each combination of temperature moisture treatments and reared until hatching. B) Expected reaction norm distributions under the hypothesis that homogeneous tropical temperatures lead to an average reaction norm of 0. C) Expected reaction norm distributions under the hypothesis that highly seasonal (i.e. heterogeneous) moisture environments in the tropics lead to selection for moisture developmental plasticity, resulting in non-zero average reaction norms for species.