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Annexe III
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can be detrimental and cause rupture of shell membrane and the death of the embryo. The
structure of eggshell might thus become another crucial component in hatching success, with
flexible-shelled eggs susceptible to be more resistant to water potential variations than rigidshelled
eggs.
However, several studies report a possible mortality of the embryos due to water potential in
species with flexible-shelled eggs (Packard, 1991a; Tucker et al., 1997; Packard, 1999a; Ji et
al., 2001; Rimkus et al., 2002). If most of authors describe an increase mortality of embryos
with the dryness of the incubation substrate, others reported that flooding might be a
significant factor to nest failure (Moll et al., 1971; Janzen, 1994), with an increasing mortality
associated with increasing immersion intervals (Plummer, 1976; Kam, 1994). In the first case,
extreme dry conditions can lead to important water loss and desiccation of shell and cause
death of the embryo that needs a minimal quantity of water to achieve the development
(Muth, 1980; Packard, Packard & Birchard, 2000). In the other case, embryo death may result
from the important influx of water into the egg with consequent egg swelling and rupture of
the shell and membranes. Moreover, extremely moist conditions may also increase possible
fungal infections or microorganisms’ invasion (Tracy, 1980) and may reduce gas exchange
(Packard & Packard, 1984).
These controversy results with ours might be due to a combined effect of water potential and
temperature. Indeed, it was shown that pattern of water uptake by eggs in substrate with the
same water potential depend greatly on temperature (Ji et al., 2001) and all the more on
fluctuating temperatures. In our case, we performed our experiment under constant
temperature of 28.9°C, which corresponds to mean incubation temperature frequently
encountered in natural nests of Trachemys scripta elegans (Tucker et al., 1998). At higher
temperatures, water uptake and loss might be stronger and hatching success might be lower.
Thus, it is crucial to consider the combined effect of temperature and moisture on hatching
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