Osteological Comparisons of the Eastern Newt (Notophthalmus viridescens) Between the Terrestrial Eft and Adult Stage.

Eastern Newts (Notophthalmus viridescens) are a ubiquitous member of eastern North America’s caudate fauna. Unlike the typical amphibian, their life cycle is split into three phases instead of two, commonly called a triphasic life cycle. The larvae of N. viridescens are fully aquatic, eventually metamorphosing to become terrestrial juveniles, called efts. Upon sexual maturity, the eft will metamorphose into a semi-aquatic adult where its external morphology is typical of an aquatic salamander. Since there are apparent differences in their ecological niche, there are different forces acting on their skeletons. We hypothesize that due to differences in buoyancy, torsion, and locomotion, differences are expected in the morphology of the axial skeleton. Using image data generated on a SkyScan 1273 micro-computed tomography (µCT) scanner, 3D shape analyses will be used to quantify shape differences between vertebrae and test the hypothesis. Three dimensional digital models of each vertebrae of interest will be rendered from the scans in Dragonfly (Object Research Systems). Each 3D model is then loaded into SlicerMorph (3D Slicer), where landmarks are placed upon homologous structures on each vertebra. A Generalized Procrustes Analysis (GPA) followed by a Principal Component Analysis (PCA) is conducted for each vertebra to test for potential shape differences between each life stage. GPA and PCA analysis will be conducted on 10 terrestrial juveniles, 10 semi-aquatic adults, 5 aquatic juveniles, and 5 paedomorphic adults. The 5 aquatic juveniles and 5 paedomorphic adults, eastern newts that remain in the water through their entire lives, will validate if the semi-aquatic adult is truly adapting towards an aquatic lifestyle. If GPA and PCA indicate statistical shape differences between certain vertebrae, those vertebrae will be run through the Automated Landmarking through Pointcloud Alignment and Correspondence Analysis (ALPACA) module of SlicerMorph to produce heatmap data on the 3D models showing where exactly the shape changes are occurring in the vertebra