HYBRIDIZATION EXPERIMENT BETWEEN OVIPAROUS AND VIVIPAROUS STRAINS OF LACERTA-VIVIPARA - A NEW INSIGHT INTO THE EVOLUTION OF VIVIPARITY IN REPTILES

The lizard Lacerta vivipara exhibits both oviparous (egg-laying) and v iviparous (live-bearing) modes of reproduction. Hybridization cannot o ccur in nature because oviparous populations are isolated in the extre me southwestern part of the distributional range. Hybridization experi ments (oviparous x viviparous, F-1, F-2, and back-crosses) enabled an analysis of the degree of reproductive isolation between viviparous an d oviparous populations and also provided insight into the evolution o f viviparity. We observed sterile eggs and embryonic mortality in both normal and hybrid crosses. Comparative analysis of breeding success f ailed to demonstrate clear-cut reproductive isolation between oviparou s and viviparous strains. This incomplete reproductive isolation agree s with previous genetic studies, which indicated that both reproductiv e strains are closely related. Hybrid females (F-1) laid eggs with an incompletely calcified eggshell. The stages of embryonic development a t egg-laying in hybrid females were intermediate (stages 35-36), betwe en those in oviparous populations (stages 31-34) and in viviparous fem ales (final stage = 40). Incubation duration was shorter for eggs of t he hybrids than for normal oviparous eggs. Our hybrid strain is thus a n interesting, although artificial, illustration of the classical mode l for evolution of viviparity in reptiles: it occupies an intermediate stage on the oviparous-viviparous continuum, and it supports predicti ons of eggshell regression, more advanced embryonic development at egg -laying, and shortening of incubation. The intermediate reproductive p henotype of first generation hybrids indicates that transmission of re productive mode is not dominant-recessive. However, more research (on F-2 hybrids) is needed before one can assert whether reproductive mode behaves like a Mendelian or a polygenic character.