Morphological variation of the European Pond Turtle, Emys orbicularis (Linnaeus 1758), on the island of Menorca

Abstract

The European Pond Turtle (Emys orbicularis) is a widely distributed species in Menorca (Balearic Islands, western Mediterranean) and it likely was introduced in historical times. In this study, we evaluated sexual dimorphism and morphological variation of E. orbicularis on the island from a sample of 455 individuals captured at ten survey sites. In these individuals, we measured seven linear traits related to body size. In addition, we measured two shape descriptors (carapace and plastron shape) and iris and plastral coloration. The results showed very pronounced sexual dimorphism, with females being larger than males and also having longer and broader plastra with higher carapaces. The site of capture had significant effects on carapace, plastral shape, and coloration. Both males and females had darkor light-colored plastra, but some males had almost completely dark plastra (to 99% dark), whereas in females, the maximum extent of black plastra was lower (79%). The sexes also differed in iridal chromatic attributes, with females more frequently having yellow and males having red or orange irises. However, this was not diagnostic of sexual identity, as 13% of females had red irises and 15% of males had yellow irises