Sexual dichromatism is common in many animal taxa, but little quantitative information on sexual dichromatism is available for turtles. We quantified sexual dichromatism in the postorbital spots of northern map turtles (Graptemys geographica) using reflectance spectrometry and examined the relationship between postorbital spot coloration and circulating testosterone among males. We found that the coloration of postorbital spots differs between the sexes, with adult males exhibiting brighter spots than adult females. However, adult males and juvenile females did not exibit siginficant differences in coloration, and testosterone levels did not explain the variation in postorbital spot coloration among males.

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