Date of Award

Spring 5-1-2006

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Life Sciences

First Advisor

Michael J. Angilletta

Second Advisor

Diana K. Hews

Third Advisor

Steven L. Lima

Abstract

Selection for rapid growth in cold environments results in a geographic pattern known as countergradient variation. The eastern fence lizard, Sceloporus undulatus, exhibits countergradient variation in growth rate across latitudinal clines. In a common-garden experiment, S. undulatus embryos from cold environments grew more efficiently than embryos warm environments, even when the energetic contents of eggs were equalized. To examine the physiological mechanisms of higher growth efficiency, I measured the energetics of embryos during the first 49 days of incubation. Specifically, I recorded body mass, residual yolk, total respiration, and developmental stage for embyos from two populations (Virginia and South Carolina). I assessed both miniaturized and unmanipulated eggs to control for effects of energy availability on growth and development. Embryos from VA used yolk more quickly, reached a larger relative size and developed to a more advanced stage than embryos from SC, even after equalizing energy availability between populations. The increase in yolk uptake occurred without a consistently higher allocation to respiration. Therefore, the increased growth efficiency of VA embryos was likely due to the increased uptake of yolk without a corresponding increase in respiration. The high growth efficiency of VA embryos probably imposes a cost by reducing the amount of yolk that is available for growth after hatching.

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