Reproductive output in a small Mediterranean lizard, the western three-toed skinks Chalcides striatus

The Western Three-toed Skink (Chalcides striatus) is a viviparous species found in arid Mediterranean climates. Using artificial shelters, we captured five pregnant females (snout vent length = 139.2 ± 7.9 mm [SD], 131 to 150 mm; total length = 286.0 ± 9.6 mm, 275 to 292 mm [N = 3, two females with damaged tails]); body mass 15.72 ± 3.89 g, 11.55 to 19.88) and kept them in captivity until parturition. Mean litter size and litter mass were 6.2 ± 1.3 (5 to 8 neonates) and 3.85 ± 0.88g (2.99 to 5.13g), respectively. Mean neonatal size and mass were 81.2 ± 4.1 mm (total length = 70 to 90 mm, N = 26) and 0.62 ± 0.07 g (0.49 to 0.82 g, N = 31), respectively. On average, the relative litter mass represented 32 ± 3% (29% to 36%) of the postpartum female body mass. The estimated mass of water lost at birth (total mass loss at parturition minus litter mass) was 0.37± 0.39 g (0.00 to 0.98 g), representing 10 ± 8% (0 to 26%) of the individual neonate mass. This low value is in line with that expected for viviparous squamates from arid climates, which is much lower than that observed in oviparous or in viviparous squamates from temperate climates. These results help to fill a gap, as the reproductive output of Chalcides striatus has been poorly documented, but mostly because the importance of extraembryonic water mass has been neglected.