ИСТИНА

Transition to asexual reproduction is often regarded as an evolutionary dead-end. However the mere existence of ancient asexuals challenges this point of view [1]. Bdelloid rotifers are a large group of putative ancient asexuals that have presumably abandoned sexual reproduction tens of millions of years ago. Neither males nor meiosis have ever been observed in this clade [2]. In line with that genome structure of bdelloid rotifers seems to be incompatible with conventional meiosis [3] However several studies based on the sequences of individual genes report that genetic exchange appears to occur in bdelloid rotifers. To address the possibility of recombination in the bdelloid rotifer Adineta vaga on a wholegenome scale we sequenced genomes of 10 A. vaga clonal lineages. Genomes of bdelloid rotifers pose substantial challenges for standard genome assembly approaches due to high degree of heterozygosity and atypical genomic structure devoid of homologous chromosome pairs. We obtained the draft genome assembly for one of 10 clonal A. vaga lineages using a combination of short insert paired-end libraries sequenced on the MiSeq platform and large insert mate-pair libraries sequenced on the HiSeq platform. The resulting assembly is used as a reference for downstream analysis of other sequenced samples. We employ reference-based mapping approaches to look for recombination signatures in the whole genome polymorphism data for 10 A. vaga individuals. A decay of LD with physical distance is observed in A. vaga population suggesting that A. vaga might engage in some form of sexual reproduction. We noted a significant excess of homozygotes in the sequenced samples. Sliding-window analysis of the genome revealed extended tracts of homozygosity some of which are shared between samples. These observations are consistent with widespread gene conversion in the genomes of bdelloid rotifers.