Variation and evolution of Class I Mhc in sexual and parthenogenetic geckos

Abstract

We present the first Mhc class I sequences in geckos. We compared Mhc variation in gekkonid species that reproduce sexually (Hemidactylus frenatus, Lepidodactylus aureolineatus, L. moestus, L. sp. Arno, L. sp. Takapoto) to others reproducing parthenogenetically (H. garnotii, L. lugubris). These comparisons include the known maternal (L. moestus) and paternal (L. sp. Arno) ancestors of the asexual L. lugubris. Sequences similar to other vertebrate species were obtained from both nuclear and cDNA templates indicating that these sequences are derived from expressed class I Mhc loci. Southern blot analysis using gecko class I probes, revealed that parthenogenetic clonal lineages of independent evolutionary origin have no within-clone band variation at class I loci and that no detectable recombination between restriction sites had taken place. Variability in the sexual species was similar to mammalian taxa, i.e. class I genes are highly variable in outbreeding sexual populations. Sequence analysis of the alpha-2 domain of class I genes identified point mutations in a clonal lineage of L. lugubris which led to amino acid substitutions. Potential transspecific allelic lineages were also observed. The persistence of asexual lineages with little or no class I diversification over thousands of generations seems to argue against strong selection for Mhc multi-allelism caused by pathogen-Mhc allele specificity. On the other hand, the high level of heterozygosity in the parthenogenetic species (a consequence of their hybrid origin) may provide clonal lineages with adequate antigen presenting diversity to survive and compete with sexual relatives.

MHC genes and parasitism in Carassius gibelio, a diploid-triploid fish species with dual reproduction strategies

“…lower MHC genotype diversity and the reduced diversity of MHC class I and class IIB alleles was found in asexual Amazon molly compared to sexual Sailfin molly [10,22]. Lower diversity in MHC class I genes was also found in a parthenogenetic gecko species compared to closely related sexual gecko species [40]. The difference in genotype and allelic diversities between asexually and sexually reproducing gibel carp could be the result of sexual selection and/or selection from pathogens and parasites, or may be due to genetic drift or the bottleneck effect after introduction, as was suggested for asexual Amazon mollies by Schaschl et al .…”

The evolutionary ecology of the major histocompatibility complex

“…As a result, MHC gene phylogenies can pre-date the species phylogenies from which they were derived. Such trans-species allelism has been identified in a wide range of taxa including salmonids (Miller and Withler, 1997;Garrigan and Hedrick, 2001), ungulates (Van Den Bussche et al, 2002), pinnipeds (Hoelzel et al, 1999), rodents (Musolf et al, 2004), geckos (Radtkey et al, 1996) and warblers (Richardson and Westerdahl, 2003). However, transspecies polymorphism is apparently not ubiquitous for MHC genes.…”

Parasites in sexual and asexual mollies ( Poecilia , Poeciliidae, Teleostei): a case for the Red Queen?

“…However, empirical data are not unequivocal, since lower mite infestations were found in asexual geckos (Brown et al 1995;Hanley et al 1995) and it was hypothesized that asexual vertebrates may have a higher resistance to parasites owing to their hybrid origin (Brown et al 1995;Hanley et al 1995;Radtkey et al 1996).…”