Literaturdatenbank
Literaturdatenbank |
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Webb, G. J. W., Choquenot, D., & Whitehead, P. J. (1986). Nests, eggs and embryonic development of carettochelys insculpta (chelonia: carettochelidae) from northern australia. J. Zool. Lond. B, 1(3), 521–550.
Added by: Admin (24 Aug 2008 20:04:47 UTC) Last edited by: Beate Pfau (27 Oct 2009 11:44:26 UTC) |
| Resource type: Journal Article DOI: 10.1111/j.1096-3642.1986.tb00646.x BibTeX citation key: Webb1986 View all bibliographic details  |
Categories: General Keywords: Australien = Australia, Carettochelyidae, Carettochelys, Carettochelys insculpta, Fortpflanzung = reproduction, Habitat = habitat, Schildkröten = turtles + tortoises, Zeitigung = incubation Creators: Choquenot, Webb, Whitehead Collection: J. Zool. Lond. B |
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| Abstract |
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Carettochelys insculpta Ten Curettochelys insculptu nests from the Daly River, in the Northern Territory of Australia, are described. Eggs were in sand banks beside the river and were laid during August and September, in the dry season. Mean clutch size was 12.7±3.3 eggs (SD). Eggs are hard-shelled and spherical (mean egg diameter 38.7 k0.13 mm) and weigh 33.7±3.5 g. Embryonic development rate varies as a function of incubation temperature. Using as an endpoint the stage at which residual yolk is internalized, incubation times are approximately 53 days (at 32° C), 69 days (30° C) and 101 days (28° C). Embryonic metabolic rate increases exponentially during early development and is highest when the residual yolk is internalized. Hatching is delayed for a considerable period after yolk internalization (224±8.6 days at 30° C and 32° C). During the period between yolk internalization and hatching (the 'hatching delay') metabolic rate decreases precipitously, embryonic growth ceases and 0.04-0.05 g of yolk (at 28° C to 32° C) plus an unmeasured amount of body fat are used for maintenance each day. Hatching can be stimulated by reducing oxygen availability, either through submerging eggs in water or perfusing them with nitrogen. In the field hatching is probably stimulated by early wet season rains and/or rises in water level. Total egg weight losses during incubation varied between 1% and 11% of the original weight, but no significant relationship between weight loss and hatchling size could be demonstrated. Hatchling size is largely determined by egg size and development rate. Formulae for predicting various hatchling dimensions from each other and from egg size are presented. The redistribution of egg contents that occurs during development and the spreading field of shell opacity that accompanies development are both described. The proportion of albumen and yolk in Curettochelys insculpta eggs is similar to that in marine turtle eggs, which is consistent with a minimum amount of water-laden albumen being necessary for yolk rotation to occur after laying (to position the embryo on the upper surface of the egg). Curettochelys insculptu has environmental sex determination. Embryos incubated at 28° C and 30° C become males whereas those incubated at 32° C become females. Females have smaller body sizes and a greater mass of residual yolk than males from eggs of the same size, but these differences appear to be consequences of varying development rates rather than being linked in any causal fashion with sex. Added by: Admin Last edited by: Beate Pfau |