Annual reproduction in females of a viviparous skink (Oligosoma maccanni) in a subalpine environment

摘要

Females of most of New Zealand's endemic reptiles show low rates of annual reproductive output, involving extended gestation and small clutch size. The main purpose of the present study was to investigate the female reproductive cycle and patterns of clutch size in McCann's Skink (Oligosoma maccanni) from a subalpine site in southern New Zealand (Macraes Flat). The results were then compared with those available for the Common Gecko (Hoplodactylus maculatus) from the same site, where females have biennial reproduction with a gestation of up to 14 months. Palpation was used to assess reproductive condition of O. maccanni noninvasively. A subset of females was then dissected to confirm reproductive condition, determine patterns of change in yolk and embryo mass with pregnancy, and determine plasma progesterone profiles. Both species are lecithotrophic with autumn-spring vitellogenesis; however, in contrast to H. maculatus, female O. maccanni are annual breeders with a spring-summer gestation of 4-5 months. Clutch size in O. maccanni decreases (relative to snout-vent length, SVL) between vitellogenesis (mean 3.33, range 2-5) and pregnancy/birth (mean 2.83, range 1-6). Plasma progesterone concentration is elevated during mid-pregnancy, and lowest during early vitellogenesis. More frequent reproduction at Macraes Flat in the diurnal skink O. maccanni than in the primarily nocturnal gecko H. maculatus in part may be a consequence of different thermoregulatory behavior.