The Reproductive and Fat Body Cycles of the Lizard, Sceloporus formosus

Abstract

Sceloporus f. formosus exhibits a fall reproductive cycle. Females breed asynchro- nously within a distinct breeding season in which ovulation and fertilization occur during the fall months and parturition the following spring. In males, testicular volume begins to increase in February, peaks in April, and declines in June. Lipids stored in fat bodies appear to be used by both sexes for gonadal development. This energy reserve is used by females for vitellogenesis and possibly for nutrition during the winter months. Males utilize the majority of their fat body stores during the reproductive period, with little remaining for winter nutrition. Fat body and reproduc- tive cycles of females are positively correlated with precipitation, whereas the male testicular cycle is positively correlated with mean ambient temperature. Reproductive cycles are one indica- tion of the reproductive strategy of a species. Until recently, it was thought that most, if not all, temperate lizards displayed reproductive activity during the spring and summer months (Fitch, 1970). That is, gonadogenesis, court- ship, mating, ovulation, and fertiliza- tion occurred during the spring, with either oviposition or parturition occur- ring during the summer or early fall. However, Goldberg (1971) observed that Sceloporus jarrovi, a viviparous lizard, displayed a fall reproductive cycle with gonadal development, courtship and mating exhibited during the fall and early winter months. The females re- tained the fertilized eggs in utero throughout the winter until spring when parturition occurred. The rate of embryonic development in this species slowed during the winter but increased rapidly after exposure to warm spring temperatures (Goldberg, 1971; Ballin- ger, 1973; Ruby, 1977; Guillette et al., 1981). Several additional reports con- cerning fall breeding in viviparous and oviparous temperate lizards are avail- able (for review, see Guillette and Cas-