title: Dynamics of the continent-wide spread of a Drosophila defensive symbiont.
abstract: Facultative symbionts can represent important sources of adaptation for their insect hosts and thus have the potential for rapid spread. Drosophila neotestacea harbours a heritable symbiont, Spiroplasma, that confers protection against parasitic nematodes. We previously found a cline in Spiroplasma prevalence across central Canada, ending abruptly at the Rocky Mountains. Resampling these populations 9 years later revealed that Spiroplasma had increased substantially across the region, resembling a Fisherian wave of advance. Associations between Spiroplasma infection and host mitochondrial DNA indicate that the increase was due to local increase of Spiroplasma-infected flies. Finally, we detected Spiroplasma west of the Rocky Mountains for the first time and showed that defence against nematodes occurs in flies with a western genetic background. Because nematode infection is common throughout D. neotestacea's range, we expect Spiroplasma to spread to the Pacific coast.
authors.affiliation: Department of Biology, University of Victoria, PO Box 3020, Station CSC, Victoria, British Columbia, V8W 3N5, Canada. stevep@uvic.ca
authors.forename: Sarah N
authors.initials: SN
authors.lastname: Cockburn
authors.forename: Tamara S
authors.initials: TS
authors.lastname: Haselkorn
authors.forename: Phineas T
authors.initials: PT
authors.lastname: Hamilton
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Landzberg
authors.forename: John
authors.initials: J
authors.lastname: Jaenike
authors.forename: Steve J
authors.initials: SJ
authors.lastname: Perlman
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D002170:Canada; D004272:DNA, Mitochondrial; D004330:Drosophila / Q000235:genetics / Q000382:microbiology* / Q000469:parasitology*; D003576:Electron Transport Complex IV / Q000235:genetics; D005260:Female; D005298:Fertility; D014644:Genetic Variation; D012641:Selection, Genetic; D013149:Spiroplasma / Q000472:pathogenicity / Q000502:physiology*; D013559:Symbiosis; D017187:Tylenchida / Q000472:pathogenicity; D020577:Wolbachia
chemical_list: D004272:DNA, Mitochondrial; D003576:Electron Transport Complex IV