Wolbachia infection status and genetic structure in natural populations of Polytremis nascens (Lepidoptera: Hesperiidae).

The maternally inherited obligate bacteria Wolbachia is known for infecting the reproductive tissues of a wide range of arthropods. In this study, we surveyed Wolbachia infections in Polytremis nascens (Lepidoptera: Hesperiidae) from 14 locations in China by amplifying the 16S rRNA gene with a nested PCR method and revealed the effect of Wolbachia on host mitochondrial DNA. The results show that 31% (21/67) are Wolbachia positive among all specimens and mainly prevails in southern populations in China. No significant difference in the prevalence is found between the sexes. Notably, the nucleotide diversity of Wolbachia infected butterflies is smaller compared to that of uninfected butterflies. The mitochondrial DNA of infected group appear to be not evolving neutrally (Tajima's D value=-2.3303 and Fu's F values=-3.7068). The analysis of molecular variance shows significant differentiation of mitochondrial haplotypes between infected and uninfected specimens (FST=0.6064). The mismatch analysis speculated the different expansion pattern in Wolbachia infected specimens and all P. nascens specimens. These results suggest that the populations of P. nascens may have recently been subjected to a Wolbachia-induced sweep. Additionally, phylogenetic analysis differentiated the mitochondrial haplotypes of P. nascens into three major clades. The clades are in perfect agreement with the pattern of Wolbachia infection. One of the clades grouped with the butterflies infected with Wolbachia. The remaining two clades grouped with uninfected butterflies from the central-west of China populations and Eastern and Southern China populations respectively, which are isolated mainly by the Yangtze River. The analysis of haplotype networks, geographic distribution and population size change shows that Haplotype 1 in central-west of China is the ancestral haplotype and the populations of P. nascens are expanded.