title: Population and demographic structure of Ixodes scapularis Say in the eastern United States.
abstract: BACKGROUND
  The most significant vector of tick-borne pathogens in the United States is Ixodes scapularis Say (the blacklegged tick). Previous studies have identified significant genetic, behavioral and morphological differences between northern vs. southern populations of this tick. Because tick-borne pathogens are dependent on their vectors for transmission, a baseline understanding of the vector population structure is crucial to determining the risks and epidemiology of pathogen transmission.
  
  
  METHODS
  We investigated population genetic variation of I. scapularis populations in the eastern United States using a multilocus approach. We sequenced and analyzed the mitochondrial COI and 16S genes and three nuclear genes (serpin2, ixoderin B and lysozyme) from wild specimens.
  
  
  RESULTS
  We identified a deep divergence (3-7%) in I. scapularis COI gene sequences from some southern specimens, suggesting we had sampled a different Ixodes species. Analysis of mitochondrial 16S rRNA sequences did not support this hypothesis and indicated that all specimens were I. scapularis. Phylogenetic analysis and analysis of molecular variance (AMOVA) supported significant differences between northern vs. southern populations. Demographic analysis suggested that northern populations had experienced a bottleneck/expansion event sometime in the past, possibly associated with Pleistocene glaciation events.
  
  
  CONCLUSIONS
  Similar to other studies, our data support the division of northern vs. southern I. scapularis genetic lineages, likely due to differences in the demographic histories between these geographic regions. The deep divergence identified in some COI gene sequences highlights a potential hazard of relying solely on COI for species identification ("barcoding") and population genetics in this important vector arthropod.
authors.affiliation: Department of Entomology, the Center for Infectious Disease Dynamics, and the Huck Institutes of The Life Sciences, The Pennsylvania State University, University Park, Pennsylvania, United States of America.
authors.forename: Joyce M
authors.initials: JM
authors.lastname: Sakamoto
authors.affiliation: Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University, Mississippi State, Mississippi, United States of America.
authors.forename: Jerome
authors.initials: J
authors.lastname: Goddard
authors.affiliation: Department of Entomology, the Center for Infectious Disease Dynamics, and the Huck Institutes of The Life Sciences, The Pennsylvania State University, University Park, Pennsylvania, United States of America.
authors.forename: Jason L
authors.initials: JL
authors.lastname: Rasgon
mesh_terms: D000818:Animals; D044822:Biodiversity; D004272:DNA, Mitochondrial; D019143:Evolution, Molecular; D005260:Female; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D006239:Haplotypes; D018884:Ixodes / Q000145:classification / Q000235:genetics*; D010802:Phylogeny; D011157:Population Dynamics; D012336:RNA, Ribosomal, 16S; D014481:United States
chemical_list: D004272:DNA, Mitochondrial; D012336:RNA, Ribosomal, 16S