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Annexe III _____________________________________________ INTRODUCTION In oviparous sauropsids, hatching success and hatchling phenotype depend greatly upon the environmental conditions, especially when females lays eggs in a subterranean nest cavity and abandon them, such as turtles and most crocodilians and squamate species do (Gutzke & Packard, 1987; Brooks et al., 1991; Shine & Harlow, 1997). In the absence of parental care, embryos and hatchlings are strongly affected by the physical conditions of the nest and particularly by the temperature and moisture within the nest (Ewert, 1985). Incubation thermal environment strongly influences embryonic growth rate (Pieau & Dorizzi, 1981; Webb et al., 1987; Deeming & Ferguson, 1989; Georges et al., 2005), incubation length (Yntema, 1978), survival of embryos (Brooks et al., 1991) and even sex phenotype in species with temperature-dependent sex determination (Bull, 1980; Janzen & Paukstis, 1991; Ewert, Jackson & Nelson, 1994). Variations in nest temperature also influence neonate morphology (Congdon, Fischer & Gatten, 1995; Brana & Ji, 2000; Ji & Du, 2001), physiology (Angilletta, Winters & Dunham, 2000; Demuth, 2001; Vanhooydonck et al., 2001; Blumberg, Lewis & Sokoloff, 2002; Lee et al., 2003), behavior (Shine et al., 1997; Burger, 1998; Nebeker & Bury, 2000) and survival (Brooks et al., 1991; Pepin, 1991) in diverse species. Despite the large amount of studies on the influence of temperature, this latter effect was often analyzed regardless of substrate moisture effects (Willingham, 2005). However, in natural nests, substrate moisture fluctuates greatly during the incubation period, in association with the pattern of atmospheric temperatures and precipitations (Packard et al., 1985; Bodie, Smith & Burke, 1996). These variations of water potential are particularly important for species that bury shallow nests as aquatic turtles, where eggs may encounter several drought and flooding events during incubation period (Moll & Legler, 1971; Plummer, 1976; Janzen, 1994; Kam, 1994). 2
Annexe III _____________________________________________ Water potential partly controls water exchanges between the eggs and the nesting environment within the nest and may be crucial in embryonic development (Feder, Statel & Gibbs, 1982; Packard, 1991a). During incubation, eggs gain or loss water in association with available moisture in substrate; substrate moisture affects thereby the hydric environment inside the egg (Cagle et al., 1993). Embryos need sufficient water to develop during incubation period (Packard, 1999a), the amount of water absorbed by eggs during incubation playing a key role in reserve production among others. It may thus decisively influence hatching success and life-history traits of hatchling (Gutzke et al., 1987; Janzen, Ast & Paukstis, 1995; Finkler, 1999). Others criterion might be crucial in water exchange between eggs and incubation substrate during incubation such as egg size, correlated to the surface area of the egg that may be in contact with substrate, physical structure of soil and the structure of the eggshell that controlled the porosity and its associated diffusion coefficient (Tracy & Snell, 1985; Gutzke et al., 1987; Marco, Diaz-Paniagua & Hidalgo-Vila, 2004). In turtles, different types of eggshell structure co-exist (Iverson & Ewert, 1991): (i) flexibleshelled eggs (e.g. in painted turtles) with a lightly calcified outer layer, that allows eggs to swell or shrink relatively easily (Tracy, 1980; Feder et al., 1982; Ackerman et al., 1985), and (ii) rigid-shelled eggs (e.g. in softshell turtles) with a heavily calcified outer layer, that relatively may hamper egg swelling and shrinking as much as flexible-shelled eggs (Iverson et al., 1991; Packard, 1991a, 1999a). Several authors studied the influence of substrate water potential on eggs, embryos and hatchlings, and obtained controversial results. To date, no significant influence of hydric environment on sex phenotype was clearly demonstrated (Gutzke & Paukstis, 1983; Paukstis, Gutzke & Packard, 1984 vs. Ji, 1999 #14; Packard, Packard & Benigan, 1991b). Some authors found significant effects of water availability in incubation substrate on embryo's growth rate 3
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N° d’ordre : UNIVERSITE PARIS-SU
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Remerciements Je remercie tout d’
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Introduction ______________________
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Introduction ______________________
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Introduction ______________________
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I - La tortue à tempes rouges, un
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II - Les tortues à tempes rouges,
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III - Etudes expérimentales des pr
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Conclusion & Perspectives _________
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Page 151 and 152: TABLE DES ANNEXES A. Supplementary
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TURTLE, AN EXOTIC AND INTRODUCED SP
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