Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

Ph.D. in Biological Science



First Advisor

William J. Resetarits

Second Advisor

Gregg R. Davidson

Third Advisor

Jason Hoeksema

Relational Format



Phenotypic plasticity is an adaptation to unpredictable environments whereby an organism of a single genotype may express more than one phenotype under differing environmental conditions. Phenotypic plasticity can manifest as polyphenisms, which is an extreme form of phenotypic plasticity that produces two or more discrete, alternative phenotypes. The expression of alternative phenotypes is controlled by biotic and abiotic environmental factors, which variably affect the strength and direction of phenotypic outcomes. Using a model polyphenic salamander, I sought to understand the ecological and hormonal processes that regulate alternative phenotype expression. The mole salamander (Ambystoma talpoideum) and eastern newt (Notophthalmus viridescens) are facultatively paedomorphic, which is a polyphenism with two alternative adult phenotypes: paedomorphs and metamorphs. Paedomorphs retain juvenile characteristics at sexual maturity (i.e., gills and an aquatic morphology), while metamorphs transition to terrestrial environments. The expressed phenotype depends on the environment context in which the larvae develop, with paedomorphosis often occurring under favorable aquatic conditions. I conducted a series of experiments to investigate the roles of population density, predator presence, hydroperiod, and stress hormones in regulating the expression of paedomorphosis. Results indicated the regulation of paedomorphosis through multiple ecological factors may be reducible to density-mediated effects, with a few notable exceptions. I also show that elevated stress hormones play a central role in regulating metamorphosis suggesting that all ecological factors affecting facultative paedomorphosis may funnel through a simple stress physiology framework. In conclusion, environmental factors affecting this polyphenism may share a comthread of inducing a stress response that initiates metamorphosis, thereby regulating phenotype in the population.

Included in

Biology Commons



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