VARIATION AND EVOLUTION OF CLASS-I MHC IN SEXUAL AND PARTHENOGENETIC GECKOS

We present the first Mhc class I sequences in geckos. We compared Mhc variation in gekkonid species that reproduce sexually (Hemidactylus fr enatus, Leipdodactylus aureolineatus, L. moestus, L. sp. Arno, L. sp. Takapoto) to others reproducing parthenogenetically (H. garnotii, L. l ugubris). These comparisons include the known maternal (L. moestus) an d paternal (L. sp. Arno) ancestors of the asexual L. lugubris. Sequenc es similar to other vertebrate species were obtained from both nuclear and cDNA templates indicating that these sequences are derived from e xpressed class I Mhc loci. Southern blot analysis using gecko class I probes, revealed that parthenogenetic clonal lineages of independent e volutionary origin have no within-clone band variation at class I loci and that no detectable recombination between restriction sites had ta ken place. Variability in the sexual species was similar to mammalian taxa, i.e. class I genes are highly variable in outbreeding sexual pop ulations. Sequence analysis of the alpha-2 domain of class I genes ide ntified point mutations in a clonal lineage of L. lugubris which led t o amino acid substitutions. Potential transspecific allelic lineages w ere also observed. The persistence of asexual lineages with little or no class I diversification over thousands of generations seems to argu e against-strong selection for Mhc multi-allelism caused by pathogen-M hc allele specificity. On the other hand, the high level of heterozygo sity in the parthenogenetic species (a consequence of their hybrid ori gin) may provide clonal lineages with adequate antigen presenting dive rsity to survive and compete with sexual relatives.