Snakes are ecologically and morphologically plastic organisms that exhibit extensive variations in body size and body condition in response to environmental factors. Documenting inter-population variations is important to describe species comprehensively across their distribution range and to monitor trends over time (e.g. decreasing body condition due to alteration of habitat). Thus, we analyzed the influence of population and sex on body size and body condition in three populations of nose-horned vipers (Vipera ammodytes) in Serbia. In one population, males were larger than females (F1, 39=4.802, p=0.034), but not in the two other populations (F1, 36=0.075, p=0.786; F1, 21=0.018, p=0.893). Females exhibited higher body condition (residual values from the regression of log-body mass against log-body size) than males (F1, 90=10.444, p=0.002); this sex difference was not found in one population when analyzed separately (F1, 35=1.834, p=0.184). Moreover, we found strong inter-population differences in mean body size and mean body condition (F2, 96=8.822, p<0.001 and F2, 90=10.319, p=0.001, respectively). While inter-population difference in body size was driven by males, inter-population difference in body condition was driven by females. These results suggest that, in this species, body size might be an important determinant of mating success in males, while body condition may play a major role in female fecundity.
