Convergent evolution of pain-inducing defensive venom components in spitting cobras.

Convergent evolution provides insights into the selective drivers underlying evolutionary change. Snake venoms, with a direct genetic basis and clearly defined functional phenotype, provide a model system for exploring the repeated evolution of adaptations. While snakes use venom primarily for predation, and venom composition often reflects diet specificity, three lineages of cobras have independently evolved the ability to spit venom at adversaries. Using gene, protein, and functional analyses, we show that the three spitting lineages possess venoms characterized by an up-regulation of phospholipase A2 (PLA2) toxins, which potentiate the action of preexisting venom cytotoxins to activate mammalian sensory neurons and cause enhanced pain. These repeated independent changes provide a fascinating example of convergent evolution across multiple phenotypic levels driven by selection for defense.

Patterns of philopatry and longevity contribute to the evolution of post-reproductive lifespan in mammals.

While menopause has long been known as a characteristic trait of human reproduction, evidence for post-reproductive lifespan (PRLS) has recently been found in other mammals. Adaptive and non-adaptive hypotheses have been proposed to explain the evolution of PRLS, but formal tests of these are rare. We use a phylogenetic approach to evaluate hypotheses for the evolution of PRLS among mammals. In contrast to theoretical models predicting that PRLS may be promoted by male philopatry (which increases relatedness between a female and her group in old age), we find little evidence that male philopatry led to the evolution of a post-reproductive period. However, the proportion of life spent post-reproductive was related to lifespan and patterns of philopatry, suggesting that the duration of PRLS may be impacted by both non-adaptive and adaptive processes. Finally, the proportion of females experiencing PRLS was higher in species with male philopaty and larger groups, in accordance with adaptive models of PRLS. We suggest that the origin of PRLS primarily follows the non-adaptive 'mismatch' scenario, but that patterns of philopatry may subsequently confer adaptive benefits of late-life helping.

Suitability of day-old chicks as food for captive snakes.

Snakes are increasingly kept by private hobbyists and their numbers in the pet trade are increasing. Since suitable diets are essential for the health, welfare and maintenance of captive animals, objective research is required to improve and evaluate current feeding practices. Unfortunately, the husbandry of reptiles is frequently led by tradition, resulting in methods which are not evidence based. One such occurrence is the widespread belief that day-old chicks (DOCs) are unsuitable as food for captive snakes. Since this assumption has not been systematically assessed, herein I review the evidence in order to provide a more informed basis from which to evaluate the suitability of chicks in relation to rodent prey. Commonly expressed nutritional, ecological and husbandry-related concerns are examined using compilations of previously published data, new data, prior experience and nutrient compositions obtained from the Zootrition™ database. Day-old chicks were compared with two rodent species (mice and rats) since these are the most commonly used alternative prey item. Rodents were clearly the better option only in their 'naturalness', in that mammalian prey species are more frequently represented in natural diets than birds. I conclude that DOCs are a suitable prey item for snakes in captive collections since the available data provide no firm evidence for their avoidance, contrary to popular belief. Many gaps in our knowledge remain that would assist further discussion of this issue, and these are highlighted within. It is pertinent that although these data indicate that DOCs are a viable alternative to rodent prey for captive snakes, they do not necessarily indicate its superiority. In most instances, rodents and DOCs may be regarded as practically equivalent and interchangeable. It is therefore the individual keeper's preference as to which to use, informed in particular circumstances by the information presented herein.