Population genetic structure of a specialist leafhopper on Zea: likely anthropogenic and ecological determinants of gene flow
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Corn leafhopper, Dalbulus maidis DeLong & Wolcott (Hemiptera: Cicadellidae), is a specialist herbivore on the genus Zea (Poaceae). The genera Dalbulus and Zea evolved in central Mexico. We sought to determine whether population genetic structuring is prevalent in corn leafhoppers inhabiting three of its host plants: (1) the highland species perennial teosinte (Zea diploperennis Iltis, Doebley & Guzman), (2) the mid- to lowland-species Balsas teosinte (Zea mays ssp. parviglumis Iltis & Doebley), and (3) the ubiquitous domesticated maize (Zea mays ssp. mays L.). We used amplified fragment length polymorphisms to detect population structuring and genetic differentiation among corn leafhoppers on the three host plants in western-central and -northern Mexico. Our results showed that corn leafhopper in Mexico is composed of at least two genetically discrete populations: an 'Itinerant' population associated with the annual hosts maize and Balsas teosinte, which appears to be widely distributed in Mexico, and a 'Las Joyas' population restricted to perennial teosinte and confined to a small mountain range (Sierra de Manantln) in western-central Mexico. Our results further suggested that population structuring is not due to isolation by distance or landscape features: Las Joyas and Itinerant corn leafhopper populations are genetically distinct despite their geographic proximity (ca. 4km), whereas Itinerant corn leafhoppers separated by hundreds of kilometers (>800km), mountain ranges, and a maritime corridor (Sea of Cortez) are not genetically distinct. Based on our results and on published ethnohistorical and archaeological data, we propose pre-Columbian and modern scenarios, including likely ecological and anthropogenic influences, in which the observed genetic population structuring of corn leafhopper could have originated and could be maintained. Also, we hypothesize that after evolving on the lowland Balsas teosinte, corn leafhopper expanded its host range to include maize and then the highland perennial teosinte, following the domestication and spread of maize within the last 9000years. 2012 The Authors. Entomologia Experimentalis et Applicata 2012 The Netherlands Entomological Society.
