The time it takes for snakes to undergo their first shedding event after birth or hatching, known as postnatal ecdysis (PNE), it varies widely across species, ranging from as short as an hour to several weeks. Wagner et al. (2023) examined PNE patterns in 102 snake species, representing about 2.6% of all existing snake species, and correlated these findings with various biological characteristics. Their analysis revealed that the ancestral time for PNE was around 11 days. Since PNE times can deviate from this ancestral norm, we argue that multiple factors influence the timing of PNE.
Wagner et al. (2023) observed that some lineages have evolved to have shorter PNE times, particularly among ambush-foraging viviparous vipers. Conversely, longer PNE times are linked to oviparous species that exhibit maternal care. A crucial factor is the impact of PNE on the scent levels of newborn snakes. This influences the balance between cryptic behavior and mother-offspring recognition. Chemically cryptic species have reduced PNE times to enhance their camouflage, while species relying on scent-based communication tend to retain or extend PNE times. This study highlighted how PNE contributes to chemical camouflage.
The study unveiled that snakes’ shedding cycle affects their life history and ecology. The first PNE, which happens in the initial hours to weeks after birth or hatching, affects behaviors like foraging, thermoregulation, and vulnerability to predators. After their first PNE, neonates exhibit changes in skin properties that aid in water conservation and initiate feeding. Additionally, PNE plays a role in scent recognition and can influence predator avoidance strategies.
An intriguing example is the puff adder (Bitis arietans), which sheds its skin shortly after birth. These viper species use chemical camouflage to evade detection by predators. Although their shed skin is easily detectable, these snakes move to new locations immediately after shedding to maintain camouflage. Such observations suggest that PNE might have evolved as an adaptive response to enhance chemical camouflage in the presence of odor-sensitive predators.
Our research encompassed a diverse array of snake species, examining their PNE times about various factors such as their evolutionary history, ecological preferences, geographic distribution, and life history traits. The authors employed ancestral state reconstruction to estimate the ancestral PNE time and evaluated how different traits influenced the variations in PNE times. Additionally, they tested the hypothesis that PNE affects the scent profiles of puff adders using trained scent-detection dogs.
The diverse selective pressures influencing PNE times have generated hypotheses for further exploration, adding depth to our understanding of snake biology and shedding light on various aspects of their evolution and behavior.
The reconstruction revealed the ancestral time to postnatal ecdysis to be 11 days. Since the time to postnatal ecdysis can be shorter or longer than the ancestral state, Wagner et al. argue that several competing drivers exist for time to postnatal ecdysis. A reduced time to postnatal ecdysis has evolved in several lineages, commonly in ambush-foraging, viviparous vipers. In contrast, 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 reduced time to postnatal ecdysis in chemically cryptic species.
Citation
Wagner C, Miller AK, Engelbrecht HM, Greene HW, Alexander GJ. 2023. When to shed? Patterns and drivers of time to first ecdysis in snakes. Ecology and Evolution. 13(8):e10364.
