Haplotype divergence supports ancient asexuality in the oribatid miteOppiella nova

Abstract

Sex strongly impacts genome evolution via recombination and segregation. In the absence of these processes, haplotypes within lineages of diploid organisms are predicted to accumulate mutations independently of each other and diverge over time. This so-called ‘Meselson effect’ is regarded as a strong indicator of the long-term evolution under obligate asexuality. Here, we present genomic and transcriptomic data of three populations of the asexual oribatid mite species Oppiella nova and its sexual relative Oppiella subpectinata. We document strikingly different patterns of haplotype divergence between the two species, strongly supporting Meselson effect like evolution and ancient asexuality in O. nova: (I) Variation within individuals exceeds variation between populations in O. nova but vice versa in O. subpectinata. (II) Two O. nova sub-lineages feature a high proportion of heterozygous genotypes and lineage-specific haplotypes, indicating that haplotypes diverged independently within the two lineages after their split. (III) The deepest split in gene trees generally separates haplotypes in O. nova, but populations in O. subpectinata. (IV) Tree topologies of the two haplotypes match each other. Our findings provide positive evidence for the absence of sex over evolutionary time in O. nova and suggest that asexual oribatid mites can escape the dead-end fate usually associated with asexual lineages.

Cosegregation of recombinant chromatids maintains genome-wide heterozygosity in an asexual nematode

“…Species that maintain some level of heterozygosity do not expose deleterious mutations and as such may circumvent some of the drawbacks of asexuality. In agreement with this expectation, a number of asexual lineages display appreciable amounts of heterozygosity (7)(8)(9)(10). Yet, except in species for which a total loss of recombination has been demonstrated [for instance, (11,12)], the mechanisms of heterozygosity maintenance are still debated (7).…”