Speciation in the face of long-range dispersal: population
genomic structure within a species complex of biting midges
Phillip Shults1*, Matthew Hopken2,
Pierre-Andre Eyer1, Alexander
Blumenfeld1, Mariana Mateos3, Lee W.
Cohnstaedt4*, Edward L. Vargo1
1 - Department of Entomology, Texas A&M University, College Station,
TX, 77843, USA
2 - USDA APHIS Wildlife Services National Wildlife Research Center, Fort
Collins, CO, 80521, USA, and Department of Microbiology, Immunology, and
Pathology, Colorado State University, Fort Collins, CO, 80523, USA
3 - Department of Ecology and Conservation Biology, Texas A&M
University, College Station, TX, 77843, USA
4 - USDA-ARS Arthropod Borne Animal Disease Research Unit, 1515 College
Ave, Manhattan, KS 66502, USA.
*Corresponding authors: Phillip Shults
(ptshults@tamu.edu) and Lee
Cohnstaedt
(lee.cohnstaedt@usda.gov).
Abstract: The level of gene flow between diverging lineages
ultimately determines the outcome of a speciation event. If secondary
contact occurs before this process is complete, reproductive isolation
barriers must exist or evolve to prevent hybridization. The selective
pressures facilitating and maintaining genetic divergence do not always
involve an observable phenotypic response, thus cryptic species form.
The inability to distinguish between sibling species can be a
particularly serious problem in groups responsible for pathogen
transmission. Culicoides biting midges occur almost world-wide
and vector many disease-causing pathogens that affect wildlife and
livestock. In North America, the C. variipennis species complex
contains three currently recognized species, only one of which is a
vector, and limited molecular and morphological differences have
hindered vector surveillance. Here, genomic methods were used to
investigate speciation and genetic structure within this complex. Single
nucleotide polymorphism (SNP) data were generated using ddRAD sequencing
for 206 individuals originating from 17 locations throughout the United
States and Canada. Clustering analyses consistently suggest the
occurrence of five putative species with significant differentiation
occurring in both sympatric and allopatric populations. Evidence of
hybridization was detected in three different species pairings,
indicating a lack of pre-zygotic reproductive isolation within the
complex. Mitochondrial genes were used to trace the hybrid parentage of
these individuals, which illuminated discordance with the SNP data. In
this study, we highlight the potential role of geographic, ecological,
and behavioral isolation in speciation and in maintaining species
boundaries, despite hybridization and long range dispersal.