Meeting Abstract
The presence of intraspecific variation in skeletal morphology is problematic for morphological analyses with low sample sizes. To assess the validity of utilizing low sample sizes within species in interspecific morphological analyses, we analyzed the size of the morphospace occupied by a sample of Diamondback Terrapin (Malaclemys terrapin) crania versus that occupied by a broad sample of extant testudine species. Ten Male and 10 female M. terrapin specimens and 22 testudine species representing extant diversity were CT-scanned and subsequently reconstructed as 3D digital models. These models were landmarked with the R-package auto3DGM. The generated pseudolandmarks were then subjected to a Generalized Procrustes Alignment and further analyzed within the R-package geomorph. The Procrustes-fit points were used in a disparity analysis which compared the morphospace sizes of groups of specimens. We hypothesized that interspecific disparity values would be much greater than intraspecific disparity values. The disparity within the interspecific sample was 0.043 while the disparity within the intraspecific sample was 0.016. The nearly three-fold increase in interspecific disparity suggests that the overall pattern of testudine species in morphospace is unlikely to be affected by the small changes in position that individuals within a species may cause. Indeed, a Principal Components Analysis of these points reveals a tightly clustered intraspecific sample along all PC axes. Notably, although Malaclemys terrapin is quite sexually dimorphic among testudines, this did not greatly affect the position of the species relative to others in tangent space. Nevertheless, caution is warranted when sampling species that have demonstrated extreme sexual dimorphism.
