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Annexe III
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dramatically lost mass in the last third (see Figure 1). These results are in agreement with
previous works, which also indicate that the influence of moisture on water exchange occurs
during the final two-third of incubation (Gutzke et al., 1986; Kennett, Christian & Bedford,
1998; Booth, 2002).
All strong differences observed in egg growth rate during the last third of incubation may
partly be explained by a modification of the eggshell structure during incubation. Particularly
in flexible-shelled eggs species, water potential of substrate modify the gain of water and so
the volume and shape of the eggs (Packard, 1980; Feder et al., 1982; Iverson et al., 1991).
Moreover, in these species, Packard (1980) have found that the outer mineral layer gradually
exfoliates late in incubation. All these physical conditions may provoke a structural
modification of the eggshell pores and of their water conductance (Feder et al., 1982).
We also found a “memory effect” of the previous moisture substrate encountered by eggs five
days before on the egg growth rate. Contrary to Gutzke (1986), we found this effect in the two
last periods of incubation and not only in the middle third (Table 2.1, model 2). This latter
phenomenon represents the dependence of the rate of water uptake by eggs on the hydric
conditions encountered before (Clark, 1953; Gutzke et al., 1986). This may certainly increase
the modification of hydric environment inside eggs in response to fluctuating water potential
and thus the modification of the diffusion coefficient between eggs and their environment. To
resume, eggs appear particularly affected by moisture environment in the last third of
incubation.
In the other hand, we detected a significant effect of clutch identity on egg growth rate, which
suppose a possible heritable component in the response of eggs to hydric environment. This
result is confirmed by the significant influence of initial egg mass on water uptake capacities
of the eggs (Table 2.1). Finally, we did not detect a significant influence of substrate moisture
on sex determination of hatchlings.
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