by Horne, Brian D

Abstract (Summary)
I studied how the expression, timing, and duration of embryonic diapause (ED), morphogenesis, and embryonic aestivation (EA) relate to variation in environmental conditions experienced by turtle embryos. ED and EA are putative mechanisms that increase embryonic survivorship. ED arrests development before main morphogenesis and is induced before the onset of adverse environmental conditions. EA prolongs incubation by depressing the metabolism of the embryo after completion of morphogenesis. I tested two hypotheses with regard to the environmental conditions that stimulate ED and EA based on climatic patterns. My first hypothesis suggested a single suitable developmental period (SDT; periods when soil moisture and temperature of nesting substrate are within the physiological tolerances of developing embryos) during the dry seasons, and my second hypothesis predicted two SDTs at the transition from the rainy and dry seasons. Incubation experiments using white-lipped mud turtle, Kinosternon leucostomum, embryos confirmed that temperature is an important factor in determining the duration of both ED and morphogenesis, and that morphogenesis occurs during the dry season SDT. Female size generally correlates positively with egg and offspring size. However, when embryos experience prolonged incubation periods, females may alter their reproductive investment strategies to offset potential additional embryonic energy expenditures. When accounting for female size, larger clutches had eggs with greater mass than smaller clutches; and egg size increased with female size. Thus in K. leucostomum the typical relationship between egg size and clutch size as it pertains to division of maternal resources per propagule is weakened by the embryo’s ability to arrest development during extended incubation periods. Nearly 50% of all turtle taxa are undocumented as to the expression of ED. I used categorical data modeling to create probabilities for predicting ED expression. Results indicate that greater than one-half of the undocumented species have a high probability of expressing ED. Conservation projects that alter incubation conditions of eggs may alter life history patterns and create unforeseen implications for population viability. Thus, it is critical for biologists performing ex-situ chelonian conservation projects with species which posses prolonged incubation periods to understand the role of ED and EA has in chelonian developmental ecology.
Bibliographical Information:


School:Ohio University

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:ecology embryonic diapause turtles kinosternon conservation


Date of Publication:01/01/2007

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