Revista Chilena de Historia Natural 82 (4): 553-563, 2009
RESEARCH ARTICLE
Sexual dimorphism and reproductive cycle in the arboreal spiny lizard Sceloporus
formosus Wiegmann (Squamata: Phrynosomatidae) from central Oaxaca, Mexico
It is well known that geographic variation occurs in life history characteristics among
populations of lizards. Variations in life histories found in some studies are possibly adaptations to environmental pressures. In
southwestern México, the reproductive characteristics of the endemic species Sceloporus formosus have been poorly
studied throughout its geographic range. We used specimens from scientific collections to describe male and female reproductive
cycles and sexual dimorphism of S. formosus. Other viviparous Sceloporus from high elevations show
sexual dimorphism, with males being larger in many morphological characteristics than females. We therefore expected that S.
formosus would show sexual dimorphism. However, we found no sexual dimorphism. Males reached sexual maturity at a
smaller (47 mm) snout-vent length (SVL) than females (50 mm). There were no significant differences between sexes and months in
liver mass. However, fat body mass in females was greater than in males. For males, there was significant relationship between log10-
testis volume and log<sub>10</sub>-SVL. Testis volume was positively correlated with temperature and was smallest
during October, November, and December. For females, there was no significant effect of month on gonad volume. Vitellogenesis
occurred from April to November. Vitellogenic follicles and embryonic development were significantly correlated with precipitation
(Pearson correlation, r = 0.80, n = 10, P = 0.0081) and photoperiod (Pearson correlation, r = 0.72, n = 10, P < 0.0001). Litter size
based on embryos was correlated with SVL (Pearson correlation, r = 0.82, n = 10, P = 0.0034). Relative litter mass was not correlated
with female SVL (Pearson correlation, r = 0.43, n = 10, P = 0.2110). The fall reproductive pattern found in this species is typical of
viviparous species from high elevation, where temperature is low, and precipitation and relative humidity are high. If so, it would
suggest that convergence in reproductive cycle could be associated with a shift to montane habitats in these species.
Key words:
litter size, reproductive
cycles, reproductive strategy, tropical lizards
