Testosterone concentration coincides with distance travelled in the free-ranging male Saharan sand-viper, Cerastes vipera

Testosterone levels have been linked to reproduction and locomotor activities in vertebrates and even to some invertebrates. However, the relationship between testosterone concentration and daily distance travelled (DDT) in a free-ranging reptile has not been tested. The aim of this study was to fill this gap. Seasonal plasma testosterone concentration in the free-ranging male Saharan sand viper, Cerastes vipera, was reported to be bimodal: a large peak in spring during spermatogenesis and mating, and a small peak in autumn, during spermatogenesis but without mating prior to hibernation. We hypothesized that DDT would be bimodal as well, the pattern coinciding with testosterone concentration. To test this hypothesis, we measured monthly DDT in free-ranging C. vipera of the same population at the same site, and compared the pattern with that of plasma testosterone concentrations reported earlier. A bimodal pattern in DDT was observed that coincided with testosterone concentration, and, therefore, our hypothesis was supported. This is the first study demonstrating a link between plasma testosterone concentration and DDT in a free-ranging animal; however, the link is correlational as there was no manipulation and cannot be attributed to a casual effect. Further studies are warranted to clarify the relationship between testosterone level and DDT.