Body size and seasonal body condition in two small coexisting desert snake species, the Saharan sand viper (Cerastes vipera) and the crowned leafnose (Lytorhynchus diadema)

Background/Question/Methods

: The Saharan sand viper, Cerastes vipera, and the crowned leafnose, Lytorhynchus diadema, co-exist and consume primarily lizards. Cerastes vipera is ovoviparous, uses sidewinding movement and is a sit-and-wait ambusher, while L. diadema is oviparous, uses serpentine movement and is an active hunter. Active hunters are usually lighter than sit-and-wait ambushers to reduce locomotory costs and ovoviparous snake species are generally heavier than oviparous species to allow for more abdominal space for developing embryos. Therefore, we hypothesized that C. vipera would be heavier than L. diadema per unit of snout-vent-length (SVL). In addition, viviparity and ovoviparity have been associated with a tendency of females to be larger than males. We, therefore, hypothesized sexual size dimorphism in C. vipera with a bias towards larger females, and that there would be seasonal changes in body condition within the two species and between the two species. Females require more energy than males at the time of mating and, therefore, we hypothesized that females would demonstrate larger seasonal fluctuations than males. In addition, ovoviparous females require more energy than oviparous females and, therefore, we hypothesized that C. vipera females would show larger fluctuations than L. diadema females.

Results/Conclusions

: Cerastes vipera was heavier than L. diadema per unit snout-vent length and therefore, our first hypothesis was supported. We concluded that this was related to foraging, as L. diadema had to move quicker than C. vipera, and to reproduction, as C. vipera needed more abdominal space for embryos than L. diadema. Sexual size dimorphism was found in adults in both species. The relatively small size, ovoviparity, sandy habitat with sidewinding, for C. vipera whereas oviparity and sandy habitat for L. diadema may explain partly sexual size dimorphism in these species. Females showed seasonal fluctuations in BCI in both species, but males did not and C. vipera females showed greater fluctuations than L. diadema females. We concluded that the former resulted from higher energy costs of females than males and the latter because ovoviparity is costlier than oviparity. In addition, neither of these species display male-to-male combat; consequently, there is less need for an increase in body condition at a time of mating.