REPRODUCTIVE-BIOLOGY OF THE WATER SNAKE NERODIA RHOMBIFER FROM VERACRUZ, MEXICO, WITH COMPARISONS OF TROPICAL AND TEMPERATE SNAKES

We collected Nerodia rhombifer on the Papaloapan River and nearby lago ons, near Tlacotalpan, Veracruz, Mexico. Females reach maturity at a s nout-vent length (SVL) of 670 mm. Reproduction is aseasonal with some females undergoing vitellogenesis throughout the year, but the majorit y of females ovulate in May and June. Litter sizes ((x) over bar = 17. 1), based on vitellogenic follicles and embryos, are significantly cor related with SVL. Based on sperm in the vas deferens, males reach matu rity at a SVL of approximately 475 mm. The spermatogenic cycle is pren uptial. In the majority of snakes, spermatogenesis begins in September and progresses to the spermatid stage by October. Peak spermatogenesi s occurs from November to early January. Hypertrophy of the sexual seg ment of the kidney begins in January, and the sexual segment remains h ypertrophied into early June. The staining intensity of the granules i n the sexual segment of the kidney is most intense from late January t hrough June. Clutch size in the population from Veracruz was significa ntly smaller than in temperate populations. To examine if this trend e xisted in other species, we compared clutch sizes for 17 oviparous col ubrid snakes from tropical regions with 15 species of roughly equivale nt temperate species. Our analysis indicated that tropical species did not differ from temperate species in mean clutch size, the mean frequ ency of reproduction, or the overall net annual fecundity (clutch size x frequency).