REPRODUCTION IN SCELOPORUS-VIRGATUS FROM THE CHIRICAHUA MOUNTAINS OF SOUTHEASTERN ARIZONA WITH EMPHASIS ON ANNUAL VARIATION

We studied female reproductive and fat body cycles as well as annual v ariation in clutch size of Sceloporus virgatus in the Chiricahua Mount ains from 1969 through 1993. Females mature at 50 mm snout-vent length (SVL). All females are reproductive after the second winter, but only a variable (small) proportion of first year females breed. Eggs are o viposited at the beginning of the rainy season (early July), and a max imum of one clutch is produced each year. Overall mean clutch size was just over 10 eggs per clutch. Clutch size was positively correlated w ith both SVL and body mass. Relative clutch mass increased with female body size, whereas relative egg mass decreased with female body size. Fat body mass is depleted over the winter and is not accumulated agai n until after the reproductive season. Mean clutch size differed by ov er three eggs among years. A stepwise regression revealed that unadjus ted clutch size was influenced by winter precipitation, previous summe r and fall precipitation, and mean previous summer and fall temperatur e. Size-adjusted mean clutch size was correlated with mean spring temp erature and mean previous summer and fall temperature. The proportion of first-year females that reproduce was influenced by spring precipit ation, mean previous summer and fall temperature, and mean winter temp erature. We hypothesize that the variation among years is a proximate response to variation in rainfall and temperature, which influence a f emale's energy balance (interaction of activity, food, growth, and fat storage).