Population genetic structure and migration revealed signal of spatial and ecological divergence among populations of sugarcane borer, Diatraea saccharalis (Lepidoptera: Crambidae)

Changes of host-plant composition in the agricultural landscape can generate divergent natural selection that drives ecological adaptation and specialization. Insect host-plant association can be considered a step towards host-race formation and specialization. The objective of this study was to investigate how geographic distance and host-plant association affect the genetic differentiation of sugarcane borer, Diatraea saccharalis. Ten microsatellite markers were employed to genotype 375 individuals collected on two host-plants across the geographical distribution of this species in Brazil. A model-based Bayesian classification method (STRUCTURE method) was employed to estimate the number of interbreeding groups. Bayesian analysis identified two (k=2) and three groups (k=3) as the most likely number populations that represent the data. In k=2, individuals were split in groups representing geographical proximity. However, for k=3, individuals previously clustered in one of k=2 groups (k1|K=2) were split in two subgroups, mostly respective of host-plant affiliation. Our results suggest that geographical distance plays a major role in the genetic structure of sugarcane borer; and a low signal of host-plant affiliation was also observed and should be investigated with high-resolution molecular markers such as single-nucleotide polymorphism (SNPs). A ddRADseq library of 48 individuals from six populations (3 maize; 3 sugarcane) was generated and ~17Gb of 100bp Illumina short reads are being analyzed. This large genome survey will allow us to refine the resolution on population genetic structure, identify genomic region associated to host adaptation and to have better estimates of migration rate and gene flow between populations.