Sexual dimorphism in size and shell shape, and dichromatism of Spotted Turtles (Clemmys guttata) in Southwestern Michigan

Abstract

Differences in pigmentation, morphometry, and body size between sexes within populations can imply intersexual differences in reproductive biology. We assessed variation in body size, morphometries, and pigmentation in Spotted Turtles (Clemmys guttata) in a southwestern Michigan population. Clemmys guttata was not sexually dimorphic in body size but when compared to males, positive allometric increases in shell height resulted in relatively domed shells in females. Integumental reflectance was mostly limited to the visual spectrum 400-700 nm with little to no reflectance in the UV spectrum (340-700 nm). We found no intersexual differences in the intensity (brightness) of yellow spots or black ground color of the head and carapace, perhaps suggesting that such markings are involved in cryptic coloration. The orange-red stripes of the head and forelimbs, that were similar in intensity between the sexes, would look conspicuous in the full spectrum light of the shallow aquatic habitats of C. guttata and thus could be involved in mate recognition. Chins of males were darker than those of females suggesting that chin color is a sexually selected trait. © Koninklijke Brill NV, Leiden, 2012.