title: Morphological differentiation despite gene flow in an endangered grasshopper.
abstract: BACKGROUND
  Gene flow is traditionally considered a limitation to speciation because selection is required to counter the homogenising effect of allele exchange. Here we report on two sympatric short-horned grasshoppers species in the South Island of New Zealand; one (Sigaus australis) widespread and the other (Sigaus childi) a narrow endemic.
  
  
  RESULTS
  Of the 79 putatively neutral markers (mtDNA, microsatellite loci, ITS sequences and RAD-seq SNPs) all but one marker we examined showed extensive allele sharing, and similar or identical allele frequencies in the two species where they co-occur. We found no genetic evidence of deviation from random mating in the region of sympatry. However, analysis of morphological and geometric traits revealed no evidence of morphological introgression.
  
  
  CONCLUSIONS
  Based on phenotype the two species are clearly distinct, but their genotypes thus far reveal no divergence. The best explanation for this is that some loci associated with the distinguishing morphological characters are under strong selection, but exchange of neutral loci is occurring freely between the two species. Although it is easier to define species as requiring a barrier between them, a dynamic model that accommodates gene flow is a biologically more reasonable explanation for these grasshoppers.
authors.affiliation: Ecology Group, IAE, Massey University, Private Bag 11222, Palmerston North, 4442, New Zealand. Eddy.Dowle@cawthron.org.nz.|Coastal and Freshwater Group, Cawthron Institute, Nelson, New Zealand. Eddy.Dowle@cawthron.org.nz.
authors.forename: Eddy J
authors.initials: EJ
authors.lastname: Dowle
authors.affiliation: Ecology Group, IAE, Massey University, Private Bag 11222, Palmerston North, 4442, New Zealand. M.Morgan-Richards@massey.ac.nz.
authors.forename: Mary
authors.initials: M
authors.lastname: Morgan-Richards
authors.affiliation: Ecology Group, IAE, Massey University, Private Bag 11222, Palmerston North, 4442, New Zealand. S.Trewick@massey.ac.nz.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Trewick
mesh_terms: D000818:Animals; D004272:DNA, Mitochondrial / Q000235:genetics; D056727:Endangered Species; D051456:Gene Flow; D005787:Gene Frequency; D006110:Grasshoppers / Q000033:anatomy & histology / Q000145:classification* / Q000235:genetics*; D018895:Microsatellite Repeats; D009520:New Zealand; D061350:Sympatry
chemical_list: D004272:DNA, Mitochondrial