Ressource pédagogique : Dr Liliana D’Alba - Eggshell mineralization in relation to nesting ecology in reptiles

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Egg morphology is essential for animal survival, mediating the interactions between embryos and their environment, and a result have evolved into an enormous diversity of forms and functions in modern vertebrates. Reptiles show considerable variation in the degree eggshell calcification, which through evolution shows a tendency to increase. Several hypotheses have been proposed to explain the advantages of intensified mineralization, for example that calcified eggshells increase protection of embryos from mechanical and biological stressors, modulate gas exchange and water physiology or that calcification might be a detoxification mechanism. However, these hypotheses still await experimental validation. Moreover, a vast proportion of reptiles successfully reproduce based on eggshells with incipient or no calcification. Thus, the questions of why the process of increasing calcification of eggshells occurred or about the advantages of shell calcification still remain. In this study I characterized eggshell structure and chemical composition of eggshells of 96 species, and performed comparative phylogenetic analyses to investigate the relationship between life-history, nesting ecology and functional properties on the evolution of calcification of reptile eggshells. The findings show that reptile eggs display larger diversity in egg phenotypes than previously thought and that this diversity is coupled with a large range of functional properties. Calcium content is correlated with adult body size but it seems a poor predictor of its functional performance. At a large scale, the nesting environment seems to play a minor role in determining the level of mineralization of eggshells but specific nesting microclimates might lead to particular calcification patterns. Inferences generated in this project will contribute to increase our understanding about the importance of reptile eggs on vertebrate evolution and diversification.  

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• Biochimie (572)

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