Sexual Size Dimorphism and Female Reproductive and Fat Body Cycles of the Viviparous Chalcides ocellatus and Sphenops sepsoides (Squamata: Scincidae) from Southern Egypt

Abstract

Chalcides ocellatus (Ocellated Skink) and Sphenops sepsoides (Wedge-snouted Skink) give birth and co-occur in many areas of Egypt. This study examined the intra- and interspecific morphological variables and seasonal changes in the masses of oviducts and fat bodies and reproductive traits of females of both species to evaluate the extent of their relationship. Both species were highly divergent morphologically. Females and males of Ocellated Skinks showed larger morphological variables for all measured characteristics than the corresponding sexes of Wedge-snouted Skinks. They were sexually dimorphic, with females having larger body and abdomen sizes than males. Relative head size (length and width) was significantly larger in males than females of Ocellated Skinks, unlike Wedge-snouted Skinks where females possessed wider heads. Males mature at a larger size in Ocellated Skinks than in females, but females and males of Wedge-snouted Skinks mature at comparable sizes. Based on the simultaneous occurrence of yolked ovarian follicles and ova or embryos in the oviduct, some females in both species produced two clutches per reproductive season. In Ocellated Skinks, the average number and relative mass of late-stage embryos were 4.18 (range 2–7) and 0.25 (range 0.09–0.63), respectively, and were positively and significantly associated with female body size; in Wedge-snouted Skinks, the average number and relative mass of late-stage embryos were 2.75 (range 2–6) and 0.24 (range 0.07–0.43), respectively, and were not correlated with female body size. Postbreeding, females of both species stored fat in their fat bodies. Females had a marked seasonality in reproduction (spring–summer), which was correlated with ambient temperature and day length. This seasonality simultaneously negatively impacted the fat body and positively impacted the oviduct referring to the utilization of storage material during embryonic development.