Development in heterogenous landscapes: Linking embryonic environments to juvenile fitness in a lizard model.

Abstract

Developmental plasticity is the capacity of a single genotype to express multiple phenotypes in response to different early-life environments. Because developmental environments differ across space and time, they create heterogenous conditions that induce phenotypic differences among offspring. Embryonic and early-life environments can generate nongenetic variation in traits through developmental plasticity, which can strongly influence fitness outcomes. Theory predicts that developmental plasticity should produce phenotypes that are adaptively matched to a given environment, especially when an environmental cue reliably predicts the conditions in which the fitness consequences are realized (i.e., environmental matching hypothesis; EMH). On the other hand, developmental plasticity could generate phenotypes that are universally beneficial across all environments if offspring develop in high-quality conditions (i.e., silver spoon hypothesis; SSH). Developmentally plastic responses are often measured as a reaction norm, a mathematical function, which may vary among individuals or populations. Reaction norms are a useful tool when evaluating developmental plasticity. In this dissertation we use a lizard (Anoles sagrei) to create developmental family-level reaction norms to compare between populations, assess the EMH and SSH, and evaluate fitness in early life traits subject to developmental genetic by environment interactions. In Chapter 1, we quantified variation in embryonic developmental plasticity within and between populations using the brown anole lizard. We captured lizards from two islands in the Matanzas River (Florida, USA) and incubated their eggs under one of two multivariate treatments that mimicked the temperature, moisture and substrates of nest sites in either a shaded or open habitat. We measured hatchling morphology, performance, and physiology to quantify variation in family-level reaction norms. We observed evidence of family-level variation in reaction norms for morphology but not for performance or physiology, indicating an opportunity for natural selection to shape plasticity in hatchling body size. Overall, the results indicate that multiple abiotic conditions in natural nests combine to increase or reduce phenotypic variation, and that family-level variation in reaction norms provides a potential for natural selection to shape plasticity. In Chapter 2, we tested the EMH and the SSH by incubating eggs under conditions that simulated spatial variation in natural nest sites (open and shaded environments) and temporal variation (shaded environments in the mid versus early season). After hatching, juvenile lizards were raised in outdoor cages that mimicked either an open or shaded environment. Based on measurements of offspring growth and survival, we found no support for the EMH across any of our experiments. Although egg incubation conditions induced variation in offspring phenotypes, those conditions did not differentially affect growth or survival in either post-hatch environment. However, we found strong support for the SSH in the temporal test, but not the spatial test, whereby offspring exposed to mid-season developmental environments had greater growth and survival in both post-hatch environments. Our results suggest that developmental plasticity may be shaped more by silver spoon effects rather than by environmental matching of phenotypes to post-hatch conditions. In Chapter 3, we tested the EHM by incubating eggs under ecologically relevant conditions simulating open or shaded nest environments. Hatchlings were released on islands that either matched or mismatched their developmental environments, and survival was monitored through mark–recapture surveys. This experiment was replicated in 2022 and 2024. We found no evidence supporting the EMH; hatchlings in matched environments did not survive at higher rates than those in mismatched environments. However, families exhibiting greater plasticity in body size showed higher survival, and both hatchling mass and hatching date were under directional selection. These findings suggest that, rather than environmental matching, selection may favor early hatching and greater developmental plasticity in body size.