Self-Hybridization in Leishmania major.

Genetic exchange between different strains in the sand fly vector has been experimentally demonstrated and is supported by population genetic studies. In nature, opportunities for interstrain mating are restricted to flies biting multiply infected hosts or through multiple bites of different hosts. In contrast, self-mating could occur in any infected sand fly. By crossing two recombinant lines derived from the same Leishmania major strain, each expressing a different drug-resistance marker, self-hybridization in L. major was confirmed in a natural sand fly vector, , and in frequencies comparable to interstrain crosses. We provide the first high resolution, whole-genome sequencing analysis of large numbers of selfing progeny, their parents, and parental subclones. Genetic exchange consistent with classical meiosis is supported by the biallelic inheritance of the rare homozygous single nucleotide polymorphisms (SNPs) that arose by mutation during the generation of the parental clones. In contrast, heterozygous SNPs largely failed to be transmitted in Mendelian ratios for reasons not understood. SNPs that were heterozygous in both parents, however, recombined to produce homozygous alleles in some hybrids. For trisomic chromosomes present in both parents, transmittal to the progeny was only altered by self-hybridization, involving a gain or loss of somy in frequencies predicted by a meiotic process. Whole-genome polyploidization was also observed in the selfing progeny. Thus, self-hybridization in , with its potential to occur in any infected sand fly, may be an important source of karyotype variation, loss of heterozygosity, and functional diversity. are parasitic protozoa that cause a wide spectrum of diseases collectively known as the leishmaniases. Sexual reproduction in has been proposed as an important source of genetic diversity and has been formally demonstrated to occur inside the sand fly vector midgut. Nevertheless, in the wild, opportunities for genetic exchange between different species or strains are restricted by the capacity of different strains to colonize the same sand fly. In this work, we report the first high resolution, whole-genome sequence analysis of intraclonal genetic exchange as a type of self-mating in Our data reveal that self-hybridization can occur with comparable frequency as interstrain mating under experimental lab conditions, leading to important genomic alterations that can potentially take place within every naturally infected sand fly.