Geographic Variation In Body Size Among French Populations Of The European Pond Turtle

The processes underlying macroecological gradients in body size are widely debated, in part because their intraspecific variability remains poorly described even in well-studied taxa such as vertebrates. In this study, we investigated how climate, habitat, genetic lineage and sex explain body size variations in French populations of the European pond turtle (Emys orbicularis). We measured 7016 adult individuals captured in 41 populations, covering most of the species' distribution in metropolitan France, including Corsica. Body size variation in our sample was wide and comparable to that found across the species' worldwide range. Variation was similar in magnitude at regional and local levels, suggesting that body size is influenced by local factors as much as by regional factors such as climate or genetic lineage. Smaller sizes were associated with Mediterranean or altered oceanic climates, and with two lineages (E. o. galloitalica and E. o. galloitalica/E. o. orbicularis), while larger sizes were associated with northern environments and the orbicularis lineage. Body size variations recorded at local level reflect an adaptive response to environmental constraints, suggesting that habitat is also an important factor in understanding size variation.