Reproduction in Australian elapid snakes II. Female reproductive cycles

Abstract

Female reproductive cycles were studied in seven species of Australian elapid snakes, and the results compared with published information on snake faunas of other continents. Of the species studied, five are live-bearing (Austrelaps superbus, Hemiaspis signata, Notechis scutatus, Pseudechis porphyriacus and Unechis gouldii) and two egg-laying (Pseudonaja nuchalis and P. textilis). The live-bearing species usually produce one clutch per year, a higher reproductive frequency than has been found in most previously studied venomous snakes. All live-bearing species show similar seasonal timing of ovulation and parturition. Gestation occupies about 14 weeks. The egg-laying species ovulate at about the same time as sympatric live-bearers, but oviposit shortly thereafter and may produce a second clutch of eggs in late summer. P. porphyriacus shows true 'viviparity', including placental transfer of nutrients (ash content of oocytes increases during gestation, energy content decreases only slightly). The live (wet) weight of the oocytes increases up to fourfold during gestation in live-bearing species, but dry weights change very little. Extra-uterine transfer of oocytes is common. Infertility is rare in A. superbus and P. porphyriacus, but frequent in N. scutatus. Clutch size is correlated with maternal body size in all species. The ratio of clutch weight to body weight decreased slightly with increasing maternal size in N. scutatus and P. porphyriacus. Published data on reptilian 'reproductive effort' are reviewed.