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 eleven 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.

Records of time to PNE were collected for snakes through data mining of the scientific literature and consultation with herpetologists and snake breeders. Records were mostly reported as a range of days to PNE observed within and across clutches or litters from one or more sources. The average number of days to PNE was calculated by averaging the time to PNE for each record for each species.

Records of time to PNE for 102 Afrophidia species (92 Caenophidia and ten Henophidia species, Harrington & Reeder, 2017) were gathered, of which 17 were collected through personal communication or unpublished data and 85 based on available literature (S1 Table). A frequency histogram showing the distribution of records of time to PNE was trimodal (Figure 1). However, a high proportion of species were reported to shed almost immediately after birth and this subset was considered to be a different category to those that shed during subsequent days. Thus, the species were assigned to four categories: immediate PNE (≤1 day); early PNE (2–4 days); standard PNE (5–17 days); and extended PNE (>17 days).

Information related to several life history traits was collected from the literature and online resources (S2 Table). These included (categories defined below): foraging mode, body pattern, parity mode, maternal care, biogeographic region, and subfamily. Foraging mode was categorised as either ambush or active foraging.

Microsoft Excel, Microsoft Word.