Characterization of a non-sexual population of Strongyloides stercoralis with hybrid 18S rDNA haplotypes in Guangxi, Southern China

摘要

Author summary The vast majority of multicellular organisms reproduce sexually. Sexual reproduction is believed to be advantageous because meiotic recombination separates beneficial and deleterious mutations and generates new, possibly better allele combinations. However, sexual reproduction comes at a cost. Beneficial allele combinations are broken up and, in gonochoristic species, there is the "two-fold cost of sex" due to the investment in "unproductive" males. Strongyloides stercoralis, the causing agent of the grossly neglected but sometimes fatal human strongyloidiasis, appears to get the best of both worlds. Depending on the environmental conditions, S. stercoralis switches between asexual parasitic and sexual free-living generations. In the Guangxi province (China) we identified a population of S. stercoralis that appears to have recently transitioned to predominantly if not exclusively reproducing asexually. We failed to detect sexual stages and, in the genomes, we found indication of asexuality such as a high heterozygosity, compared with other populations of S. stercoralis. Additionally, global within-species phylogenetic analysis showed that in our study area, all S. stercoralis form one group of fairly close relatives, suggesting a rather recent common origin. In contrast, the hookworms (Necator americanus), which are phylogenetically distant from but share the infection route with S. stercoralis, in a within-species phylogenetic comparison fall into various groups, suggesting much greater diversity.