Evolutionary and biogeographical implications of the karyological variations in the oviparous and viviparous forms of the lizard Lacerta (Zootoca) vivipara

The lizard Lacerta (Zootoca) vivipara, a has two modes of reproduction and is variable karyologically. Wr describe its karyological variation from lit erature data and from new data on two viviparous populations from France, o n two oviparous populations from the Pyrenees in south-western France and o n three oviparous populations recently discovered in Slovenia. Malts have 3 6 chromosomes, whereas females have only 35 chromosomes in ail viviparous p opulations and in the Pyrenean oviparous populations. This karyotype has be en interpreted to result from a fusion of an ancestral sexual W chromosome with an autosome from the Z1 or from the Z2 pair. The karyotype formula is 32 autosomes +Z1Z2W for the female and 32 autosomes +Z1Z1Z2Z2 for the male. The karyotype of the Slovenian oviparous populations, 34 autosomes +ZZ in the male and 34 autosomes +ZW in the female. represents an evolutionary sta ge that preceded the chromosomal fusion. There is minor karyological variat ion, mainly concerning the W and Z2 chromosomes. within the Pyrenean ovipar ous populations. This parallels the geographic variation of the W-linked al leles of the MPI enzyme and suggests that allopatric: differentiation of th ese oviparous populations might have occurred in the vicinity of the Pyrene es during the Pleistocene. The viviparous populations from western Europe carry a metacentric W chromo some, whereas oviparous populations from south-western Europe and eastern v iviparous populations both show an acrocentric, or a subtelocentric, W chro mosome. This suggests that the acrocentric-subtelocentric W is a primitive character and that viviparity probably arose in an eastern lineage of the s pecies.