Caractéristiques de la coquille des oeufs chez la souche hybride (ovipare × vivipare) du lézard Lacerta vivipara

The lizard Lacerta vivipara has both oviparous and viviparous populations. Experimental crossbreedings (oviparous strain × viviparous strain) in the laboratory have previously allowed us to obtain a hybrid strain. Hybrids have also laid eggs in the laboratory. The aim of the present study was to determine the eggshell characteristics of the hybrid and to compare them with the characteristics previously studied in the oviparous and viviparous strains. The mean thickness of the eggshell is 21 μm for the hybrid, 40 μm for oviparous eggshell, and 9 μm for the viviparous eggshell membrane. Mean dry mass of the eggshell is 3 mg for hybrids, 5 mg for the oviparous strain, and 0.6 mg for the viviparous strain. Ash mass of the eggshell is 0.79 mg for hybrids, 1.05 mg for the oviparous strain, and 0.22 mg for the viviparous strain. Fibrils were observed in both oviparous and hybrids' eggshells and in the viviparous eggshell membrane. The outer surface of the hybrids' eggs presents both places with a calcareous layer (61%) and places where fibrils are not covered with a calcareous layer (39%). These incompletely calcified eggshells are intermediate between the oviparous eggshells (complete calcareous layer) and the regressed eggshell membrane (fibrils with minor traces of calcite) observed during the gestation of the viviparous lizards. This situation is of considerable interest for further experimental studies dealing with physiological and genetic aspects of the evolution of viviparity.