Extreme inbreeding in Leishmania braziliensis

Abstract

Leishmania species of the subgenus Viannia and especially Leishmania braziliensis are responsible for a large proportion of New World leishmaniasis cases. The reproductive mode of Leishmania species has often been assumed to be predominantly clonal, but remains unsettled. We have investigated the genetic polymorphism at 12 microsatellite loci on 124 human strains of Leishmania braziliensis from 2 countries, Peru and Bolivia. There is substantial genetic diversity, with an average of 12.4 ؎ 4.4 alleles per locus. There is linkage disequilibrium at a genome-wide scale, as well as a substantial heterozygote deficit (more than 50% the expected value from Hardy؊Weinberg equilibrium), which indicates high levels of inbreeding. These observations are inconsistent with a strictly clonal model of reproduction, which implies excess heterozygosity. Moreover, there is large genetic heterogeneity between populations within countries (Wahlund effect), which evinces a strong population structure at a microgeographic scale. Our findings are compatible with the existence of population foci at a microgeographic scale, where clonality alternates with sexuality of an endogamic nature, with possible occasional recombination events between individuals of different genotypes. These findings provide key clues on the ecology and transmission patterns of Leishmania parasites.clonality ͉ microsatellites ͉ population genetics ͉ endogamyl ͉ heterozygote defiency

Molecular approaches for a better understanding of the epidemiology and population genetics ofLeishmania

“…The substantial heterozygote deficiency and extreme inbreeding found in this study is not consistent with a strictly clonal reproduction (Rougeron et al 2009). Moreover, a strong population structure was found at a micro-geographical scale as the populations within the different countries were genetically heterogenous.…”

“…The impact of population substructure can be studied with the Bayesian analysis of genetic population structure (BAPS) software (Corander et al 2007). Using this method Rougeron et al (2009) have demonstrated that the high F is values found in their MLMT analysis of Bolivian and Peruvian L. braziliensis are only partly explained by population subdivision.…”

Adaptive mechanisms in pathogens: universal aneuploidy in Leishmania

“…Genomic plasticity, including mosaic ploidy and the maintenance of aneuploidy, is a source of diversity in the absence of sexual recombination [26,42]. Although Leishmania was thought mainly to reproduce clonally [43,44], this assumption is now challenged by population-level analysis [45] and by the demonstration of genetic recombination in the fly vector [46]. Nevertheless, aneuploidy can be considered as a non-Mendelian means to create genomic variation when recombination is absent or minimal.…”

“…Low heterozygosity can be the result of several factors involving evolution and reproduction -such as inbreeding in L. braziliensis [45] -and it can result from fluctuating chromosome copy numbers too. When a disomic chromosome with heterozygous alleles switches to trisomy, a major haplotype (two copies) and a minor haplotype (one copy) will be produced.…”

The molecular epidemiology and phylogeography of Trypanosoma cruzi and parallel research on Leishmania: looking back and to the future

“…If Leishmania are mainly clonal they should show high heterozygosity due to accumulation of random mutations, but heterozygosity could be lowered by a high rate of gene conversion. On the other hand, high rates of inbreeding could explain the high homozygosity seen in most Leishmania populations, as found for L. braziliensis (Rougeron et al 2009).…”