Doctoral Dissertations

Date of Award

12-1990

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Zoology

Major Professor

Arthur C. Echternacht

Committee Members

Dewey Bunting, Justin Congdon, Neil Greenberg, Gerry Vaughan

Abstract

The green anole (Anolis carolinensis) is a small iguanid lizard that is broadly distributed in the southeastern United States. Clutch size is phylogenetically constrained in Anolis; all species produce a single-egg clutch but individuals lay many eggs over the course of the reproductive season. Sizes of green anole adults, eggs, and hatchlings all increased significantly with increasing latitude. Lizards in the northern part of the range also produced eggs and offspring that, relative to female body size, were proportionately larger than those of southern green anoles. There was a significant positive relationship between egg and female sizes in northern populations, but egg size was largely independent of female body size in southern populations. The relationships between egg and female sizes that were characteristic for northern and southern populations were not affected by different proximate environmental conditions. The size of the pelvic girdle opening appeared to constrain the egg size of northern females to a greater degree than it did in southern females. The number and quality (i.e., quantity of nonpolar lipids) of eggs laid by green anoles is largely dependent on conditions of the abiotic environment. Abundant rainfall, high humidities, moist substrates, and high ambient temperatures combine to facilitate frequent deposition of eggs containing relatively small quantities of nonpolar lipids. However, the quality of eggs was not associated with the size of females or the number of eggs they laid. Green anole eggs associated with wet incubation environments have shorter incubation periods and produce larger hatchlings than eggs associated with drier environments. Given identical incubation environments, hatchling size is positively related to egg size. Sexual size dimorphism (SSD) of hatchlings did not exist within populations, but juvenile males grew faster than females, apparently accounting for the majority of the SSD of adults. Among populations, large hatchlings grew faster than smaller hatchlings. Geographic differences in juvenile growth rates closely paralleled the differences observed in adult body sizes. I propose that increased selection pressure for large juvenile body size with increasing latitude and decreasing winter temperatures may account for the latitudinal gradation in the sizes of A. carolinensis adults, eggs, and hatchlings.

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