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 literature data and from new data on two viviparous populations from France, on two oviparous populations from the Pyrenees in south-western France and on three oviparous populations recently discovered in Slovenia. Malts have 36 chromosomes, whereas females have only 35 chromosomes in ail viviparous populations and in the Pyrenean oviparous populations. This karyotype has been 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 stage that preceded the chromosomal fusion. There is minor karyological variation, mainly concerning the W and Z2 chromosomes. within the Pyrenean oviparous populations. This parallels the geographic variation of the W-linked alleles of the MPI enzyme and suggests that allopatric: differentiation of these oviparous populations might have occurred in the vicinity of the Pyrenees during the Pleistocene. The viviparous populations from western Europe carry a metacentric W chromosome, whereas oviparous populations from south-western Europe and eastern viviparous populations both show an acrocentric, or a subtelocentric, W chromosome. This suggests that the acrocentric-subtelocentric W is a primitive character and that viviparity probably arose in an eastern lineage of the species.