Ambush foragers use a hunting strategy that places them at risk of predation by both visual and olfaction-oriented predators. Resulting selective pressures have driven the evolution of impressive visual crypsis in many ambushing species, and may have led to the development of chemical crypsis. However, unlike for visual crypsis, few studies have attempted to demonstrate chemical crypsis. Field observations of puff adders (Bitis arietans) going undetected by several scent-orientated predator and prey species led us to investigate chemical crypsis in this ambushing species. We trained dogs (Canis familiaris) and meerkats (Suricata suricatta) to test whether a canid and a herpestid predator could detect B. arietans using olfaction. We also tested for chemical crypsis in five species of active foraging snakes, predicted to be easily detectable. Dogs and meerkats unambiguously indicated active foraging species, but failed to correctly indicate puff adder, confirming that B. arietans employs chemical crypsis. This is the first demonstration of chemical crypsis anti-predatory behaviour, though the phenomenon may be widespread among ambushers, especially those that experience high mortality rates owing to predation. Our study provides additional evidence for the existence of an ongoing chemically mediated arms race between predator and prey species.

No abstract

Stress levels in organisms provide a rapid measure for assessing population health. Handling and capture stress, however, cause error in blood measures, so this method is rapidly being replaced by assessing levels of stress metabolites in faeces. This eliminates the source of error because there is a lag period between stress perception and the resultant stress metabolite accumulation within faeces. This lag period is correlated with specific intestinal passage time, a measure that can vary greatly between taxa, particularly amongst ectotherms. Due to two deleterious consequences associated with extended exposure of the metabolites to the intestinal environment, species that exhibit long and variable intestinal passage times are not good candidates for metabolite studies. We measured gut and intestinal passage times in Trachylepis margaritifer to ascertain whether it would be an appropriate candidate for stress metabolite studies. We first tested if barium sulphate in the meal had an effect on gut passage time at three ambient temperatures (25, 27 and 32 °C). Barium sulphate had no effect; however, temperature had a significant effect with an unexpected pattern: gut passage time was fastest at 32 °C but was slower at 27 °C than at 25 °C. We then used X-ray technology and barium sulphate-loaded meals to measure gut and intestinal passage times at 25 and 27 °C. This allowed us to observe which parts of the digestive process were responsible for increased passage times at 27 °C: the faster passage time at 25 °C was due to faster intestinal passage time; there was no difference in gastric emptying time. We assess the species to be a suitable candidate for studies using faeces to measure stress. It is imperative however, that the effect of temperature on passage rates is known and taken into account in such studies.

Developmental plasticity results from environmental influences on the phenotype of an organism during its development, and its effects are irreversible. The phenomenon of phenotype-genotype uncoupling (plasticity) causes problems in species delineations, and has been suggested as a cause underlying a mismatch between morphology and genetics between the Natal Midlands dwarf chameleon (Bradypodion thamnobates) and the KwaZulu dwarf chameleon (Bradypodion melanocephalum). The two species are morphologically distinct, but are very poorly distinguished genetically. It has been hypothesized that B. melanocephalum and B. thamnobates may be phenotypically plastic populations of the same species, since environmental conditions, the driving force behind developmental plasticity, varies between the distributions of these two allopatric taxa. We raised juveniles of both species under identical controlled laboratory conditions. Two treatments were used. These varied in both habitat structure and temperature, each approximating conditions that one of the species would encounter naturally. Although not specifically controlled or monitored, all other environmental factors (e.g. humidity, light and wind) were standardized since chameleons were raised in the artificial conditions created in environmental chambers. If taxa are developmentally plastic, phenotypes would reflect treatment conditions, irrespective of specific associations. Neither B. thamnobates nor B. melanocephalum were phenotypically plastic over the environmental differences tested; species developed into the expected phenotypes, irrespective of treatment conditions. The low genetic difference between B. thamnobates and B. melanocephalum may indicate their recent divergence from a common ancestor or the mitochondrial gene fragments (ND2 and 16S) used in previously published phylogenetic analyses of the genus may not be representative of divergence for the genome as a whole.

No abstract

No abstract

Time from birth or hatching to the first shed (postnatal ecdysis) in snakes ranges from about an hour to several weeks depending upon the species. We assessed patterns in time to postnatal ecdysis in 102 snake species for which we could source appropriate information, covering 2.6% of all extant snake species, and related measures to various biological traits. Reconstruction revealed ancestral time to postnatal ecdysis to be 11 days. Since time to postnatal ecdysis can be shorter or longer than the ancestral state, we argue that there are several competing drivers for time to postnatal ecdysis. A reduced time to postnatal ecdysis has evolved in several lineages, commonly in ambush‐foraging, viviparous vipers, while extended time to postnatal ecdysis is associated with oviparous species with maternal care. Of central importance is the impact of postnatal ecdysis on the scent levels of neonates, resulting in a reduction of time to postnatal ecdysis in chemically cryptic species, while the pivotal role of scent in mother–neonate recognition has resulted in the retention or extension of time to postnatal ecdysis. We showed that postnatal ecdysis improves chemical crypsis. The patterns revealed in this study suggest that measures of time to postnatal ecdysis can provide insights into the biology of snakes and be used as an indicator of certain life history traits.

No abstract