Chromosome evolution in pseudoxyrhophiine snakes from M adagascar: a wide range of karyotypic variability

In this first cytogenetic survey on the lamprophiid snake subfamily P seudoxyrhophiinae, we studied the karyology of ten snake species belonging to seven genera from M adagascar ( C ompsophis , L eioheterodon , L iophidium , L ycodryas , M adagascarophis , P hisalixella and T hamnosophis ) using standard and banding methods. Our results show a wide range of different karyotypes ranging from 2 n  = 34 to 2 n  = 46 elements ( FN from 40 to 48), with nucleolus organizer regions ( NORs ) on one (plesiomorphic) or two (derived/apomorphic) microchromosome pairs, and W chromosome at early or advanced states of diversification from the Z chromosome. The observed W chromosome variations further support the most accepted hypothesis that W differentiation from the Z chromosome occurred by progressive steps. We also propose an evolutionary scenario for the observed high karyotype diversity in this group of snakes, suggesting that it is derived from a putative primitive pseudoxyrhophiine karyotype with 2 n  = 46, similar to that of L eioheterodon geayi , via a series of centric fusions and inversions among macrochromosomes and translocations of micro‐ either to micro‐ or to macrochromosomes. This primitive P seudoxyrhophiinae karyotype might have derived from a putative Lamprophiidae ancestor with 2 n  = 48, by means of a translocation of a micro‐ to a macrochromosome. In turn, the karyotype of this lamprophiid common ancestor may have derived from the assumed primitive snake karyotype (2 n  = 36 chromosomes, with 16 biarmed macro‐ and 20 microchromosomes) by a series of centric fissions and one inversion. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society , 2014, 112 , 450–460.