title: Genetic differentiation between resistance phenotypes in the phytophagous flea beetle, Phyllotreta nemorum.
abstract: The flea beetle Phyllotreta nemorum L. (Coleoptera: Chrysomelidae) is genetically polymorphic for resistance against the defences of one of its host plants, Barbarea vulgaris R.Br. (Brassicales: Brassicaceae). Whereas resistant flea beetles are able to use B. vulgaris as well as other cruciferous plants as food, non-resistant beetles cannot survive on B. vulgaris. This limitation to host plant use of non-resistant beetles could potentially lead to asymmetric gene flow and some degree of genetic isolation between the different resistance-genotypes. Therefore, we studied the extent of genetic differentiation at neutral allozyme loci between samples of flea beetles that were collected at different locations and first tested for resistance phenotype. Since earlier work has shown a weak, but significant, effect of geographical distance between the samples on their genetic differentiation, in the present study variation at the neutral allozyme loci in P. nemorum was partitioned between geographical distance and resistance-phenotype. Both sources independently contributed statistically significantly to population differentiation. Thus, there appears to be a limitation to genetic exchange between the resistant and non-resistant flea beetles when corrections are made for their geographic differentiation. This is consistent with the presence of some degree of host race formation in this flea beetle.
authors.affiliation: Laboratory of Entomology, Wageningen University, PO Box 8031, 6700 EH Wageningen, The Netherlands. Peter.dejong@wur.nl
authors.forename: Peter W
authors.initials: PW
authors.lastname: de Jong
authors.forename: Casper J
authors.initials: CJ
authors.lastname: Breuker
authors.forename: Helene de
authors.initials: Hd
authors.lastname: Vos
authors.forename: Kim M C A
authors.initials: KM
authors.lastname: Vermeer
authors.forename: Keiko
authors.initials: K
authors.lastname: Oku
authors.forename: Patrick
authors.initials: P
authors.lastname: Verbaarschot
authors.forename: Jens Kvist
authors.initials: JK
authors.lastname: Nielsen
authors.forename: Paul M
authors.initials: PM
authors.lastname: Brakefield
mesh_terms: D000818:Animals; D031216:Barbarea / Q000737:chemistry; D001517:Coleoptera / Q000235:genetics* / Q000502:physiology; D005247:Feeding Behavior; D051456:Gene Flow; D005843:Geography; D015810:Linkage Disequilibrium; D010641:Phenotype; D010802:Phylogeny; D058974:Phylogeography; D011110:Polymorphism, Genetic