Biphasic Geographic Variation in Sexual Size Dimorphism of Turtle (Mauremys leprosa) Populations Along an Environmental Gradient in Morocco

Abstract

Abstract The varying influences of selective forces throughout a species' range can result in geographic variation in sexual size dimorphism (SSD). The Moroccan turtle, Mauremys leprosa, occupies an extremely wide variety of ecoregions and habitats, including coastal rivers, mountain streams, oases, and intermittent rivers in the northern fringe of the Sahara Desert. To assess geographic variation in SSD, we collected specimens along an environmental gradient in central Morocco, including Oued (River) Ksob on the Atlantic coast, Oued Zat in the High Atlas Mountain foothills, and Oued Drâa in the Sahara Desert. Only turtles with conspicuous secondary sexual characteristics were included in our analysis. We calculated a sexual dimorphism index (SDI) using the mean size of the larger sex divided by the mean size of the smaller sex and subtracted one from that ratio. The direction of SSD was biphasic: in one population males and females exhibited the same body size, whereas, in two other populations, females ...