About Saiphos equalis (Gray, 1825)
Saiphos equalis grows to a length of 18 cm (7.1 in) including the tail. It has a brown back and an orange belly. This nocturnal skink feeds on insects. It is common in New South Wales and Queensland in eastern Australia. This species displays three main reproductive modes across different populations: oviparity (egg-laying) with long 15-day incubation periods, viviparity (live birth) with no 0-day incubation period, and intermediate oviparity with short ~5-day incubation periods. No populations of this skink show the typical scincid oviparity with incubation periods longer than 30 days, a pattern that has been suggested to indicate the species is undergoing a transition to exclusively viviparity. Along Australian coastal lowlands, individuals of this species are oviparous (lay eggs), while mountain populations to the north are almost exclusively viviparous (give birth to live young). In a 2001 study of coastal Saiphos equalis populations, researchers used mitochondrial nucleotide sequences (ND2 and cytochrome b) to examine relationships between different populations. Smith et al.'s analysis found that the long incubation period oviparous lineage is the sister group to all other short-period oviparous and viviparous populations. These clades are consistent, and correspond to variation in reproductive mode as well as geographic location by latitude and altitude. Lizards from high elevation sites (over 1,000 m / 3,300 ft) in north-eastern New South Wales are viviparous, while low-elevation populations across northern and southern New South Wales show short-period oviparity, an intermediate between viviparity and typical oviparity. Viviparous populations give birth to fully developed offspring inside transparent membranes. Short-incubation oviparous populations lay partly shelled eggs that contain mostly developed embryos, which continue to develop inside the egg before hatching. In the northernmost coastal region of New South Wales, the lizards have relatively long incubation periods (approximately 15 days) and thicker eggshells. In April 2019, Saiphos equalis received media attention when University of Sydney researchers reported observing a single female producing both eggs and live young from one pregnancy, marking the first recorded observation of this ability in a vertebrate.
