Population genetic structure of a specialist leafhopper on Zea: likely anthropogenic and ecological determinants of gene flow

Abstract

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 Manantlán) 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. 4 km), whereas Itinerant corn leafhoppers separated by hundreds of kilometers (>800 km), 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 9 000 years.

Lack of Genetic Differentiation between Contrasted Overwintering Strategies of a Major Pest Predator Episyrphus balteatus (Diptera: Syrphidae): Implications for Biocontrol

“…Ecological speciation was previously shown in relation to differences in spring emergence time in Rhagoletis pomonella (Walsh) (the apple maggot fly) [34], habitat in Dalbulus maidis (Delong & Wolcott) (a specialist corn leafhopper) [35], or selection against immigrants in walking–stick insects [36]. However, the present results clearly demonstrate that there is no reproductive isolation between populations using different overwintering strategies in E. balteatus.…”

Complex Patterns of Local Adaptation in Teosinte

“…All of our measured environmental variables are abiotic, but biotic factors (e.g., herbivory, competition) undoubtedly play an important selective role and may not be perfectly reflected in our environmental PCs. For example, the presence of the Zea specialist leafhopper Dalbulus maidis is thought to depend on the local abundance of maize and proximity to bodies of water (Medina et al 2012), and Moeller and Tiffin (2008) hypothesize localized selection pressure in herbivory as an explanation for evidence of local adaptation in their sequence analysis of immunity genes in parviglumis. Biotic interactions are likely critical in local adaptation in a number of species.…”

Physical leaf defenses – altered by Zea life‐history evolution, domestication, and breeding – mediate oviposition preference of a specialist leafhopper

“…3 mm long 9 1 mm wide may still have sufficient space to maneuver unimpeded over the leaf surface, between trichomes, to feed and lay eggs. A prior study showed that D. maidis in Mexico consists of at least two genetically distinct subpopulations, one on maize in agricultural habitats and another on perennial teosinte in temperate forest, and isolated from maize fields (Medina et al, 2012;JS Bernal, unpubl. Moreover, the Hybrid maize should produce more biomass than the Landrace maize (e.g., Rosenthal & Dirzo, 1997), which implies that higher trichome density is compatible with higher productivity, contrary to the prediction of the 'resource allocation hypothesis'.…”