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Only a few studies have estimated fang replacement rate (FRR) in free-ranging snakes. We compared FRR between Crotalinae and Viperinae, two major clades of Viperidae. Crotalinae species differ by having pit organs which allow efficient strike at the prey, while, based on an earlier study, Viperinae species have relatively longer fangs. We hypothesized that FRR is related to the risk of fang damage and predicted that: (1) FRR is related positively to fang length; and (2) the FRR of Viperinae is faster than that of Crotalinae. To test these predictions, we determined the FRR, fang length, body size and hunting strategy of 21 Viperidae species, 7 Viperinae and 14 Crotalinae, controlling for allometric and phylogenetic effects. The average FRR of Viperinae was 2.6 times faster than that of Crotalinae, supporting our second prediction. However, in contradiction to our first prediction, FRR within subfamilies was related negatively to fang length. The phylogenetic analysis indicated that FRR and fang length covaried throughout the lineage, and that the relationship between FRR and fang length persisted beyond phylogenetic relatedness, implying that fang replacement of the two subfamilies followed different evolutionary pathways.

The morphological constraint hypothesis (MCH) states that, in snakes, males typically have relatively longer tails than females to accommodate the hemipenes and retractor muscles. To date, most studies testing the MCH have been interspecific and results have been equivocal. We tested the MCH intraspecifically on Cerastes vipera, a species with a relatively short tail and suitable for testing the MCH. The relative tail length and length of the hemipenes pocket in Cerastes vipera were measured in preserved museum-maintained males (n = 35) and in free-ranging males and females (n = 277). Males exhibited relatively longer tails than females, which was explained fully by the length of the hemipenes pocket. The relatively short tail of C. vipera presents a constraint to the reproductive structures in males, as the length of the hemipenes pocket occupies a greater proportion in shorter- than longer-tailed individuals. This is the first report presenting these intraspecific findings in support of the MCH. Whether these relations are widespread among snake families, within Viperidae, or specifically within C. vipera warrants further studies.

Reproductive success is the ultimate measure of individual quality; however, it is difficult to determine in free-living animals. Therefore, indirect measures that are related to reproduction are generally employed. In snakes, males typically possess longer tails than females and this sexual size dimorphism in tail length (TL) has generally been attributed to the importance of the tail in mating and reproduction. Thus, intra-sexual differences in tail length, specifically within males, were hypothesized to reflect individual quality. We used a body condition index (BCI) as a measure of quality in snakes and predicted that tail length would be correlated with BCI in males. We tested our prediction by determining BCI in the free-ranging adult male and female crowned leafnose snake ( Lytorhynchus diadema ), a colubrid species that inhabits mainly desert sand dunes. The relative TL was correlated positively and significantly to BCI in males (F 1,131  = 11.05; r 2 adj  = 0.07; P  < 0.01) but not in females, thus supporting our prediction. This is the first time that the relationship between TL and body condition was tested in a free-ranging species. In addition, sexual size dimorphism of TL increased intra-specifically with body size, which was also found in interspecific analyses following Rensch’s rule.

Degen et al look at remarkable similarity in pastoral livelihoods at climatic extremes, from the ice of the Himalayas to the Arabian Peninsula and the Sahara. In both contexts, the domestication of yak and camel, and the integration of these exceptional animals in a pastoral system, triggered an evolutionary advantage, enabling the use and occupation of environments that had until then remained out of reach. Extreme climatic conditions were not something that happened to those pastoralists and that they had to cope with. On the contrary, pastoral systems in the Himalayas and in the hot deserts were developed from the new capacity to make use of such extreme environments.