Atypical Reproduction and Sexual Dimorphism of the Tropical Bonaire Island Whiptail Lizard, Cnemidophorus murinus

Abstract

We investigated reproduction, sexual dimorphism in color, and sexual dimorphism in body size of Cnemidophorus murinus, the endemic whiptail lizard of Bonaire, Netherlands Antilles, during a year-long study and two later recapture periods. Growth rate declines as C. murinus increases in size. Males reach reproductive maturity at smaller snout-vent lengths (SVL) than do females (73 vs 85 mm) but continue to grow to larger final SVL (151 vs 116 mm maximum SVL). Bonaire whiptails can live at least four years. Reproduction was aseasonal; enlarged ovarian follicles and/or oviductal eggs in females and enlarged testes in males were observed in every month with no peak period of reproduction. Fat body growth, however, was strongly seasonal, and fat body mass was greatest in the months immediately after the rainy season. Amount of fat stored differed among three sites, and females stored more fat than males. Clutch size is typically one very large egg, but some females may produce two eggs. Although clutch mass/body mass ratio is typical for the genus, egg mass/body mass is greatest for any Cnemidophorus or Ameiva known and among the highest for any lizard (x = 0.126). Dorsal color is sexually dimorphic; females are brown, and juvenile males are also brown, changing to bright blue as they grow. However, many males never reach the brightest color morph and may retain the juvenile color form for years. Several features of the biology of C. murinus are unusual for the genus and for lizards in general (size at reproductive maturity, small clutch size, large relative egg mass, color variation in males).