Don’t Be a Big Baby: Phenotypic Novelty in the Facultative Paedomorph Ambystoma Talpoideum.

This thesis explores the relationship between heterokairy and the skin microbiota of amphibians, specifically focusing on the facultatively paedomorphic salamander, Ambystoma talpoideum. Heterokairy refers to variations in developmental timing that generate phenotypic novelty within life stages. The first chapter investigates how reordering metamorphosis relative to sexual maturation affects the skin microbiota in this species. By sampling different life stages—larval, paedomorphic, and metamorphic—results show the emergence of novel microbial combinations, resulting from both microbial gain and loss in the heterokairic paedomorphic stage. These findings suggest that changes in microbial communities may lead to phenotypic novelty and have broader eco-evolutionary implications. The second chapter further examines ecological drivers of phenotypic novelty in the skin microbiota. It isolates metamorphosis and sexual maturation as independent processes, assessing how environmental factors influence the microbiota and the diversity of antifungal microbes. I find that habitat associations and the process of sexual maturation affect microbiota diversity, with the metamorphic stage showing the greatest diversity and potentially reduced susceptibility to chytridiomycosis and other diseases. These results highlight the role of ontogenetic changes in shaping skin microbiota and suggest important ecological and conservation implications, particularly in understanding the pressures faced by amphibians like A. talpoideum.