Two's company, three's a crowd: new insights on spruce budworm species boundaries using genotyping-by-sequencing in an integrative species assessment (Lepidoptera: Tortricidae)

Species delimitation requires an assessment of varied traits that can contribute to reproductive isolation, as well as of the permanence of evolutionary differentiation among closely related lineages.Integrative taxonomy, including the combination of genome-wide molecular data with ecological data, offers an effective approach to this issue.We use genotyping-by-sequencing together with a review of ecological divergence to assess the traditionally recognized species status of three closely related members of the spruce budworm species complex, Choristoneura fumiferana (Clemens), C.occidentalis Freeman (= C.freemani Razowski) and C.biennis Freeman, each of which is a major defoliator of conifer forests.We sampled a broad region of overlap between these three taxa in Alberta and British Columbia (Canada) where potential for gene flow provides a strong test of the durability of divergence among lineages.A total of 2218 single nucleotide polymorphisms (SNPs) were assayed, and patterns of differentiation were evaluated under the biological, ecological, genotypic cluster and phylogenetic species concepts.Choristoneura fumiferana was genetically distinct with substantial barriers to genetic exchange with C.occidentalis and C.biennis.Conversely, divergence between C.occidentalis and C.biennis was limited to a small subset of outlier loci and was within the range observed within any one of the taxa.Considering both population genetic and ecological patterns of divergence, C.fumiferana should continue to be recognized as a distinct species, and C.biennis (syn.n.) should be treated as a subspecies (C.occidentalis biennis Freeman, 1967) of C.occidentalis, thereby automatically establishing the nominate name C.occidentalis occidentalis Freeman, 1967 for univoltine populations of this species.