Date of Award
Doctor of Philosophy
Ecology, Evolution, and Organismal Biology
Ecology and Evolutionary Biology
Dean C Adams
Biologists have long sought to understand how ecological selective pressures drive evolutionary responses. Defining how morphology, life history, and abiotic conditions interact across deep time can reveal the selective pressures responsible for shaping various axes of biodiversity. I used this three-pronged framework to investigate the macroevolution of the family of lungless salamanders (Plethodontidae), well-known for its impressive ecological and geographic diversity while exhibiting little apparent morphological diversity. Employing ancestral state estimation methods, geometric morphometrics, and various phylogenetic comparative approaches, I first investigated the macroevolutionary responses of functional morphology to microhabitat-use across the clade's history. From these analyses, I estimated at least five independent transitions towards arboreality and over 60 transitions away from arboreality across the plethodontid tree of life. This suggests that arboreality may represent an evolutionarily transitory state for lungless salamanders, with a high tendency to abandon arboreal habitats to return to the ancestral terrestrial habitat. I also found no evidence of morphologically distinct body shapes or foot shapes in arboreal species, suggesting that it is unlikely that the tendency to occupy or abandon arboreal microhabitats is driven by biomechanical constraints. I next explored the relationship between microhabitat use and abiotic conditions, revealing that arboreal species occupy warmer, wetter climates than terrestrial species as measured by coarse environmental data summarized across entire species' ranges. This pattern was explicated using phylogenetic comparative methods and corroborated with a novel implementation of ecological niche modeling. From this analysis, I concluded that the availability of arboreal microhabitats is largely determined by the abiotic conditions of the species range. Finally, following our discovery of the importance of climate in determining these species' ecological patterns, I investigated the macroevolution of the morphological trait, surface area to volume ratios (SA:V), across the family with respect to climatic variation. SA:V is particularly relevant for climatic conditions as lungless salamanders display little cutaneous resistance to water-loss and are thus prone to environmentally-induced desiccation. I developed a method to estimate SA:V which strongly outperformed traditional estimates of SA:V and revealed that salamanders in less-desiccation prone climates exhibit higher and more disparate SA:Vs. This is consistent with our hypothesis that drier climates restrict the evolution of body forms conferring high SA:Vs. Altogether, these results reveal that broad climatic patterns may be the most important ecological selective pressure in shaping the macroevolution of morphology and microhabitat use for plethodontids.
Erica Karin Baken
Baken, Erica Karin, "Macroevolution of microhabitat, climate, and morphology in lungless salamanders (Family: Plethodontidae)." (2020). Graduate Theses and Dissertations. 17970.