Ecology and Reproductive Characteristics of the Skink Sphenomorphus Incognitus on an East Asian Island, with Comments on Variati
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Zoological Studies 49(6): 779-788 (2010) Ecology and Reproductive Characteristics of the Skink Sphenomorphus incognitus on an East Asian Island, with Comments on Variations in Clutch Size with Reproductive Modes in Sphenomorphus Wen-San Huang* Department of Zoology, National Museum of Natural Science, 1 Kuan-Chien Rd., Taichung 404, Taiwan (Accepted May 7, 2010) Wen-San Huang (2010) Ecology and reproductive characteristics of the skink Sphenomorphus incognitus on an East Asian island, with comments on variations in clutch size with reproductive modes in Sphenomorphus. Zoological Studies 49(6): 779-788. I describe the diet, and male and female reproductive cycles of Sphenomorphus incognitus, an oviparous skink in Taiwan. Most individuals of S. incognitus were first observed in a leaf litter microhabitat or at the edge of a forest. The diet of S. incognitus consists mostly of orthopteran insects. Two prey categories, crickets and ants, numerically dominated the diet. The stomachs of 2 lizards contained spiders, 2 lizards had eaten insect larvae, and 2 had eaten the blind snake, Ramphotyphlops braminus. The mean snout-vent length (SVL) of adult males was 87.6 mm (n = 45), and that of females was 79.8 mm (n = 43). Males had a significantly larger SVL than females. Females exhibited spring and summer vitellogenesis, with parturition occurring from Mar. to July. The onset of vitellogenesis was not correlated with the female liver mass. Females produced 3-6 eggs per clutch, and clutch size was not correlated with the SVL. Male testis mass showed significant monthly variations, with an increase commencing in Dec. and a peak maintained from Jan. to Apr. Female and male liver masses did not coincide with the period of reproductive activity. Clutch size variations in other Sphenomorphus groups were compared to those in S. incognitus. Clutch sizes of oviparous skinks were not larger than those of viviparous ones, and clutch size relative to female SVL showed a positive correlation in oviparous skinks but not in viviparous ones. Similarities of the reproductive cycle found in this study and other congeneric Sphenomorphus inhabiting temperate and subtropical areas of Taiwan might be explained by phylogenetic constraints. http://zoolstud.sinica.edu.tw/Journals/49.6/779.pdf Key words: Reproductive cycle, Clutch size, Lizard, Food habits. Many ecological studies (i.e., examining The genus Sphenomorphus (Squamata: spatial, temporal, feeding, and reproductive Scincidae) is an extremely heterogeneous and patterns) of lizards were carried out in the past diverse group distributed in South and Southeast 3 decades (Vitt and de Carvalho 1995, Vitt and Asia, on islands of the West Pacific, and in Zani 1996a b). However, most studies on tropical Australia (Greer 1974, Ota 1991, Zhao and Adler lizards focused on the Amazon region (Vrcibradic 1993, Huang 1997a). In Australia, the surface- and Rocha 1996, Vitt et al. 1997 2000) and Mexico dwelling Sphenomorphus group is divided into 5 (Ramirez-Bautista and Vitt 1998, Jimenez-Cruz et genera: Eulamprus, Gnypetoscincus, Ctenotus, al. 2005, Ramirez-Sandoval et al. 2006, Ramirez- Notoscincus, and Eremiascincus (Greer 1989). Bautista et al. 2006 2008), and little is known about Sphenomorphus incognitus (Thompson 1912), a other lowland rainforest lizards (but see Benabib surface-dwelling skink, was long known under the 1994, Ramirez-Bautista et al. 2006), especially on name S. boulengeri by VanDenburgh (1912), but tropical islands of East Asia. Thompson’s description was apparently published *To whom correspondence and reprint requests should be addressed. Tel: 886-4-23226940 ext. 510. Fax: 886-4-23232146. E-mail:[email protected] 779 780 Zoological Studies 49(6): 779-788 (2010) 1 mo earlier than VanDenburgh’s. This species including its morphology, clutch sizes, liver mass is a poorly known species ranging from southern as an energy source, and reproductive cycles of China to Taiwan, including tropical Orchid I. (Zhao males and females. I also compared its clutch size and Adler 1993), off the southeastern coast of to those of other species of Sphenomorphus for Taiwan. which data are available. For most tropical oviparous lizards, both males and females seem to exhibit year-round gonadogenesis, with subsequent courtship, MATERIALS AND METHODS mating, and oviposition (Fitch 1970, Huang 2006a b), but some in the seasonal tropics are This study was conducted on tropical known to show seasonal cyclicity in reproduction Orchid I. (Lanyu in Chinese) (22°02'N, 121°33'E) (e.g., Auffenberg and Auffenberg 1989). Although situated 60 km off the coast of Taitung County, Taiwan is generally categorized as a subtropical southeastern Taiwan, from Apr. 1997 to July area, it does have tropical areas in the southern 2001, at about 100 m in elevation. The mean part of the main island, as well as on Orchid I. maximum air temperature from June to Aug. (Huang 2004). Climatic patterns on this island are ranged 25.75-26.11°C, and the minimum ranged similar to those of tropical regions. Previously, I 18.58-19.69°C during Dec. to Feb. The mean demonstrated that annual reproductive patterns of maximum monthly precipitation for 11 yr of data in 3 high-elevation Taiwanese lizards, Takydromus the study area was about 408 mm in Sept., most hsuehshanensis, Eumeces elegans (the genus of which was brought by typhoons in that month has since been changed to Plestiodon), and (Fig. 1). Sphenomorphus taiwanensis, resemble those of temperate lizards (Huang 1996b 1997a b 1998); and patterns of 3 tropical lizards, T. sauteri, Sunshine duration Temperature 200 30 Japalura swinhonis, and Mabuya longicaudata 180 also resemble those of temperate lizards (Huang 25 2006a b 2007). Although the reproductive biology 160 140 of low-elevation subtropical lizards of Taiwan was 20 C) examined (Cheng 1987), that of lizards of tropical 120 ° areas such as those on Orchid I. has not been well 100 15 studied (Huang 2006a b 2007). 80 10 Comparisons of clutch sizes in lizard species 60 Temperature ( suggest that in addition to local adaptations (Ota 40 5 1994), plasticity in response to environmental Sunshine duration (h) 20 variations (Huang 2004), physiological constraints, 0 0 and phylogenetic constraints (James and Shine Precipitation Relative humidity 1985, Vitt 1986) all play important roles in 450 93 determining aspects of clutch size. Likewise, 400 92 comparative studies of clutch size in animal 350 91 species have often identified underlying causes 300 90 responsible for observed reproductive patterns 250 89 (Huang 2006b 2007). Most such studies suggest that clutch size variations are attributable to 200 88 latitude, in that lower clutch sizes are found at 150 87 100 86 lower latitudes (Lack 1947, Cody 1966, MacArthur Relative humidity (%) 1972). However, the clutch size of the temperate Precipitation (mm) 50 85 S. taiwanensis (X = 5.2) is smaller than that of the 0 84 subtropical S. indicus (X = 7.3) in Taiwan (Huang Jan. Feb. Mar. Apr.May June July Aug.Sept. Oct.Nov.Dec. 1996a 1997a). Presently, no such attempts have Month been made for Taiwanese tropical lizards (i.e., Fig. 1. Annual variation in sunshine duration, temperature, S. incognitus), although a number of species have precipitation, and relative humidity during 1992-2002 (monthly been studied (Okada et al. 1992, Huang 1998 average) on Orchid I., Taitung County, Taiwan (22°03'N, 2004) . 121°33'E) (Orchid I. Weather Station, Central Weather Bureau, I studied the ecology of the lizard S. incognitus, Taipei, Taiwan). Huang – Ecology of a Tropical Skink 781 Lizards were hand-collected each month. differences were body mass (BM), waist diameter For each sampling, I attempted to collect 5 males (WD, diameter of the waist between the hind limb and 5 females, but some monthly samples were and abdomen), head length (HL), head width (HW), smaller due to difficulty in finding lizards in rainy head depth (HD), tail length (TL), forelimb length weather (total males, n = 45; total females, n = 43). (FLL), hind limb length (HLL), 3rd toe length (TTL), After capture, 1) each specimen was weighed to and 4th toe length (FTL). Because the organ the nearest 0.01 g; 2) its snout-vent length (SVL) variables usually varied with SVL, I calculated a was measured to the nearest 0.1 mm; and 3) it regression of all log10-transformed masses against was dissected to remove the liver, gonads, and log10 SVL. Data on monthly differences in the associated organs; all organs were weighed wet log10-transformed liver mass (LM) in each sex, to the nearest 0.01 g. The stage of maturity for and testis mass (TM) in males were assessed males was assessed by spermatogenic activity; the by analysis of covariance (ANCOVA) using log10 appearance of sperm bundles and/or free sperm in SVL as the covariate (SAS 8.2, SAS Institute, the seminiferous tubules in a given specimen was Cary, NC, USA). I also used ANCOVA (with regarded as indicative of maturity. SVL as the covariate) to determine differences The reproductive state of adult females between oviparous and viviparous species, and was determined on the basis of the presence examined whether the slope of the SVL and clutch or absence of vitellogenic ovarian follicles of size regression differed between the 2 groups. I > 3 mm and oviductal eggs (Huang 2006a b accepted the analyses if interactions between 2007). Females with large vitellogenic follicles or log10 SVL and test variables were non-significant eggs were defined as being reproductively active, (homogeneity of slopes). The Mann-Whitney test and those with neither of these were defined as was used to examine differences in clutch sizes being inactive. Clutch size was estimated on the in temperate, subtropical, and tropical lizards. I basis of the number of larger vitellogenic follicles adopted a type I error level of 0.05 for all statistical or oviductal eggs (Huang 2006a b 2007).