The Reproductive Cycle and the Size at Maturity of Tupinambis rufescens (Sauria: Teiidae) in the Dry Chaco of Argentina

Abstract

The reproductive patterns of Tupinambis rufescens have not been described. The present study had three objectives: (1) to describe the reproductive and fat body cycles of T. rufescens from our study site in the dry chaco of Argentina; (2) to elucidate and analyze the distribution of sizes at which female T. rufescens reach sexual maturity; and (3) to discuss the conservation implications of the repro- ductive cycle of T. rufescens. Oviductal width increased significantly after females reached 320 mm SVL, and we presumed the increase was due to stretching of the oviducts in females that had been gravid. Seventy-eight percent of the females >319 mm snout-vent length (SVL) and 84.3% > 349 mm SVL possessed oviducts > 3.5 mm wide, our criterion for indicating a female had reproduced, while only 6.9% of the females 3.5 mm wide were convoluted, while all the narrower oviducts were straight or striated. The reproductive and fat body cycles of T. rufescens at our study site were characteristic of lizards from seasonal environments, and appeared closely tied to the onset of the rainy season and increasing spring temperatures. Mature females exhibited significantly longer ovaries in No- vember than in other months, and nesting was observed in November and December. The average clutch size was 21.4, and the smallest female we found with eggs was 330 mm SVL. Testis mass was significantly greater in November than in other months, and declined slightly throughout the activity season. Some gonadal development in males presumably occurred while the lizards were inactive during winter. Fat body volume was tightly linked to the gonadal cycle of both males and females. Females apparently allocated fat stores to developing eggs, while males probably used fat stores for spermatogenesis or for meeting the energetic demands of mate seeking. Large numbers of Tupinambis are exploited for their skins, and this study provides life history infor- mation needed to develop scientifically-based management plans, for example, the size distribution of reproductive females, the timing of reproduction, and clutch size. Based on our analyses, management strategies aimed at harvesting adults and subadults could be evaluated because the proportions of the harvest comprised of adults can be reliably determined. We recommend that strategies aimed at classifying harvests according to adults and subadults use 350 mm SVL as a cut-off point for mature females.