Extended Adolescence: The Ecology and Endocrinology of Facultative Paedomorphosis

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 (<em>Ambystoma talpoideum</em>) and eastern newt (<em>Notophthalmus viridescens</em>) 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.

Name thesis:degree_name

Ph.D. in Biological Science

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biology

Year dc:date.available

2019

Author dc:creator

• Bohenek, Jason R.

Contributors dc:contributor

• William J. Resetarits
• Gregg R. Davidson
• Jason Hoeksema

• amphibian
• mesocosm
• paedomorphosis
• phenotype
• plasticity
• predators
• Biology

Repository record dc:identifier

https://egrove.olemiss.edu/etd/1554

OAI identifier oai:identifier

oai:egrove.olemiss.edu:etd-2553