LIZARD REPRODUCTION: ANNUAL VARIATION AND ENVIRONMENTAL CORRELATES IN THE IGUANID LIZARD UROSAURUS GRACIOSUS

Abstract

Samples of male and female Urosaurus graciosus were collected in 1974 and 1975 in south-central Arizona to elucidate seasonal and yearly aspects of reproductive and fat-body cycles. In both years, males had enlarged testes and produced sperm May-July, followed by rapid testicular and epididymal regression during August. Onset of reproduction by females was delayed in 1974, with greatest reproductive activity in July and August. All females in 1975 were reproductive in May and again in July. Many females in May 1975 contained both oviducal eggs and enlarged, yolking follicles, confirming seasonal iteroparity. In 1975, there was a correlation between snout-vent length and clutch size, but no similar correlation existed in 1974. Fat-body cycles of males and females were similar, both sexes containing small fat reserves during the reproductive season and large reserves thereafter. Females contained large fat bodies in April (prebreeding) and in late fall (postbreeding), suggesting little use of fat reserves during winter. Differences in timing and frequency of reproduction in U. graciosus between 1974 and 1975 presumably resulted from differences in resource availability, as suggested by weather data. Individuals are apparently able to respond reproductively to proximal environmental cues (probably resource levels), which presumably represents an adaptation to unpredictable conditions. We suggest that geographic comparisons of reproductive variables should stress variances rather than means, as variances should be inversely related to environmental pre- dictability.