Multivariate Analyses of Shell Morphology of Putative Hybrid Box Turtles

Abstract

Terrapene carolina triunguis (Three-toed Box Turtle) and Terrapene ornata ornata (Ornate Box Turtle) are sympatric in areas of eastern Texas. Usually, these species are easily distinguished by shell shape and pigmentation. However, many turtles from areas of eastern Texas have characteristics of both Three-toed and Ornate Box Turtles, which we presume to be a result of hybridization. We collected, marked, and measured 103 box turtles from Walker County for morphometric analyses. Because of our limited number of Ornate Box Turtles sampled (n = 6), an additional 68 specimens from eastern Texas in the Texas Cooperative Wildlife Collection (TCWC) were examined, and the carapace and plastron measured to characterize species-specific shell morphology for Ornate Box Turtles. Multivariate analyses indicated that all morphometrics of carapace shape (length, width, curvature length, and curvature width) loaded heavily (r = 0.929, 0.897, 0.936, and 0.955, respectively) on the first principle component (Factor 1) and explained 86.41% of the variation in shell morphology and best distinguished observed differences between species and putative hybrids. Putative hybrids demonstrated a shell morphology similar to that of Three-toed Box Turtles and differed significantly from that of Ornate Box Turtles. Of the total 177 turtles examined, we considered 78 to be Three-toed Box Turtles, 74 to be Ornate Box Turtles, and 25 to be hybrids between the two parent species.