Influence of voltine ecotype and geographic distance on genetic and haplotype variation in the Asian corn borer

Diapause is an adaptive dormancy strategy by which arthropods endure extended periods of adverse climatic conditions. Seasonal variation in larval diapause initiation and duration in the Asian corn borer, Ostrinia furnacalis, influences adult mating generation number (voltinism) across local environmental conditions. Degree of mating period overlap between sympatric voltinism ecotypes influences hybridization level, but impact on O. furnacalis population genetic structure and evolution of divergent adaptive phenotypes remains uncertain. Genetic differentiation was estimated between voltinism ecotypes collected from 8 locations in Jilin Province, China [3 single generation (univoltine), 3 two generation (bivoltine), and 2 sympatric locations] in 2014. Bayesian and phylogenetic clustering partitioned mitochondrial cytochrome c oxidase subunit I (COI) haplotypes mostly into groups corresponding to historically uni- or bivoltine population origins, whereas samples from sympatric locations were interspersed between voltinism-specific clusters. Additionally, analyses of single nucleotide polymorphism (SNP) genotype data implicate voltinism, as opposed to geographic distance, as a factor contributing to differentiation among sample site. Temporal analysis of SNP genotypes from a sympatric location showed significant variation between adult moths collected within non-overlapping periods corresponding to bivoltine and univoltine flights. Regardless, only 11 of 257 SNP loci were predicted to be under selection and contribute > 72% of the total genomic divergence, suggesting population genetic homogenization except at loci in proximity to factors responsible for locally adaptive or voltinism-specific traits. These findings suggest that divergent voltinism ecotype-specific traits and mitochondrial haplotypes may be maintained in allopatric as well as sympatric areas despite relatively high rates of nuclear gene flow.