title: Sympatric diversification vs. immigration: deciphering host-plant specialization in a polyphagous insect, the stolbur phytoplasma vector Hyalesthes obsoletus (Cixiidae).
abstract: The epidemiology of vector transmitted plant diseases is highly influenced by dispersal and the host-plant range of the vector. Widening the vector's host range may increase transmission potential, whereas specialization may induce specific disease cycles. The process leading to a vector's host shift and its epidemiological outcome is therefore embedded in the frameworks of sympatric evolution vs. immigration of preadapted populations. In this study, we analyse whether a host shift of the stolbur phytoplasma vector, Hyalesthes obsoletus from field bindweed to stinging nettle in its northern distribution range evolved sympatrically or by immigration. The exploitation of stinging nettle has led to outbreaks of the grapevine disease bois noir caused by a stinging nettle-specific phytoplasma strain. Microsatellite data from populations from northern and ancestral ranges provide strong evidence for sympatric host-race evolution in the northern range: Host-plant associated populations were significantly differentiated among syntopic sites (0.054 < F(HT) < 0.098) and constant over 5 years. While gene flow was asymmetric from the old into the predicted new host race, which had significantly reduced genetic diversity, the genetic identity between syntopic host-race populations in the northern range was higher than between these populations and syntopic populations in ancestral ranges, where there was no evidence for genetic host races. Although immigration was detected in the northern field bindweed population, it cannot explain host-race diversification but suggests the introduction of a stinging nettle-specific phytoplasma strain by plant-unspecific vectors. The evolution of host races in the northern range has led to specific vector-based bois noir disease cycles.
authors: Department of Ecology, Institute of Zoology, Johannes Gutenberg-University of Mainz, Mainz, Germany.
authors: Miriam
authors: M
authors: Imo
authors: Michael
authors: M
authors: Maixner
authors: Jes
authors: J
authors: Johannesen
mesh_terms: D000818:Animals; D005075:Biological Evolution; D014644:Genetic Variation; D006430:Hemiptera / Q000235:genetics* / Q000382:microbiology; D054884:Host-Pathogen Interactions; D018895:Microsatellite Repeats / Q000235:genetics; D010802:Phylogeny; D045582:Phytoplasma / Q000235:genetics / Q000472:pathogenicity; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D061350:Sympatry / Q000235:genetics*; D026982:Urtica dioica