Morphological and functional consequences of the land-to-water transition in the salamander families Ambystomatidae and Plethodontidae

Land-to-water transitions are major evolutionary events and introduce new constraints to tetrapod morphology. Two North American salamander groups have recolonized aquatic habitats: mole salamanders (Ambystomatidae) and lungless salamanders (Spelerpini; Plethodontidae). I examined the morphological and biomechanical consequences of this transition using a comparative approach. First, I tested the hypothesis that aquatic species have convergent skull morphologies, given the different developmental pathways followed by the two groups. Using 3D microCT scan data from online repositories and museum specimens, I performed a geometric morphometric analysis on skull shape and applied a phylomorphospace to the morphometric data to determine whether morphological variation was due to phylogeny or ecology. Second, I performed nanoindentation tests on cartilage and bone from dissected Ambystoma to determine if Young’s modulus differed significantly between aquatic and terrestrial taxa, and to determine the difference in magnitude between cartilage and bone. Finally, to focus more closely on a structure primarily involved in feeding, I examined the mandibular morphology and functional performance in the two families. I tested the importance of morphology and Young’s modulus values in the mandible in resisting forces that simulated prey-capture by holding shape volume and applied loads constant in a Finite Element Model. While there are statistically significant differences in the jaw proportions in aquatic and terrestrial salamanders in both families, the mechanical models did not support that terrestrial morphologies are better suited for applying bite forces. The results of these four studies will guide future work investigating the functional demands on salamander skulls and what structural changes occur when terrestrial species recolonize aquatic habitats.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Darcy, Hannah Elizabeth

Contributors dc:contributor

• Anderson, Philip SL
• Kawano, Sandy
• Roseman, Charles
• Suarez, Andrew

• Morphology
• Salamanders
• Secondarily Aquatic
• Morphometrics
• Nanoindentation
• Finite Element Analysis

Statement dc:rights

• Copyright 2023 Hannah Darcy

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/120565

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F120565