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First published online September 14, 2007
Journal of Experimental Biology 210, 3415-3421 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.005652
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Rapid assimilation of yolk enhances growth and development of lizard embryos from a cold environment

Melissa A. Storm and Michael J. Angilletta, Jr*

Department of Ecology and Organismal Biology, Indiana State University, Terre Haute, IN 47809, USA

* Author for correspondence (e-mail: mangilletta{at}indstate.edu)

Accepted 12 June 2007

Selection for rapid growth and development in cold environments results in a geographic pattern known as countergradient variation. The eastern fence lizard, Sceloporus undulatus, exhibits countergradient variation in embryonic growth and development along latitudinal clines. To identify the proximate causes of countergradient variation, we compared the energy budgets of embryos from a cold environment (Virginia) and a warm environment (South Carolina) during development at a realistic thermal cycle. The difference in mean egg size between populations was controlled by removing yolk from large eggs and performing a sham manipulation on other eggs. Respiration was measured every 4 days throughout 48 days of incubation. After this period, eggs were dissected and the energy contents of embryos and yolk were determined by calorimetry. As expected from previous experiments, embryos from Virginia reached a more advanced stage of development and deposited more energy within tissues than embryos from South Carolina. The greater absorption of yolk by embryos from Virginia was associated with a higher rate of respiration. Assimilation of yolk by rapidly growing embryos could reduce growth or survival after hatching. Such costs might explain the maintenance of countergradient variation in S. undulatus.

Key words: countergradient variation, growth rate, Sceloporus, tradeoff, yolkectomy






© The Company of Biologists Ltd 2007