Sexual dimorphism and reproductive traits over time in Sceloporus aeneus (Squamata: Phrynosomatidae), based on a population in the Transmexican Volcanic Belt, Mexico

Very little information is documented about variation in sexual size dimorphism between years within populations of a single species, and studies covering related topics are very scarce. We present information on sexual size dimorphism and reproductive traits obtained during the years 1980-1983, in a population of the lizard Sceloporus aeneus from the Transmexican Volcanic Belt. Adult males of this species showed a snout-vent length (SVL) range from 37-55 mm, whereas adult females ranged from 40-55 mm. Males were larger than females in all morphometric features. Differences in SVL occurred between years for either sex, whereas no differences were found between years within either sex in all other morphological characteristics. Mean of vitellogenic follicles (VF) and oviductal eggs were similar over the years. Considering VF and eggs together, the mean clutch size was 6.4 ± 0.15 eggs. Clutch size was significantly related to female SVL. Females produce at least two clutches during the reproductive period every year. Clutch size varied between years with the mean clutch size from 1982 being greater than those of 1981 and 1983. Egg masses and volumes were similar over the years investigated. The results of this study suggest that environmental factors (precipitation and temperature) can influence morphological and reproductive traits of Sceloporus aeneus from one year to the next.