REPRODUCTIVE-BIOLOGY OF THE LIZARD UROSAURUS-BICARINATUS-BICARINATUS (REPTILIA, PHRYNOSOMATIDAE) FROM RIO-BALSAS BASIN, MEXICO

We studied the reproductive biology of two populations of the arboreal lizard Urosaurus b. bicarinatus from 1980-1984 in western Mexico. One population is located in the elevated portion of the Rio Balsas Basin , in the state of Morelos, and the other at a lowland site of the basi n in the stale of Michoacan. Data were obtained from specimens collect ed in the field and from museum collections. Females and males of both populations exhibit a pattern of late spring and summer reproduction. Males show maximal testicular volume and activity during the late spr ing and summer months in Michoacan and during the spring and summer mo nths in Morelos. Vitellogenesis begins in April in both populations, w ith most females ovulating in the summer. Incubation occurs during the summer with hatching in late summer and early fall. Individuals reach sexual maturity within a year. Mean clutch size for oviductal eggs wa s 7.7 +/- 2.4 and 6.7 +/- 1.8 in populations from Morelos and Michoaca n respectively. No correlation between snout-vent length of females an d clutch size was found.