Host Races

Did maize domestication and early spread mediate the population genetics of corn leafhopper?

“…Geographic variation in the occurrence of host‐associated differentiation has been observed in other hemipterans (Goodman et al ., ; Forbes et al ., ). Moreover, the durations of processes putatively beginning with either instance of maize farming retreat, whether hundreds or dozens of years, are consistent with the lengths of processes leading to genetic structuring in other insect herbivores (Winter, ; Claridge, ; Cocroft et al ., ; Bennett & O'Grady, ; Medina, , ; Goodman et al ., ; Forbes et al ., ). Thus, the results of our AFLP analysis appear to be consistent with the chronology of maize spread to and retreat from perennial teosinte habitat, as known from historical and archaeological studies (Kelly, ; Benz et al ., ; Laitner‐Benz & Benz, ; Figueroa‐Rangel et al ., , ).…”

“…Evidence from AFLP marker analysis It is plausible that the genesis of corn leafhopper genetic structuring revealed by our AFLP data began with the declining intensity of maize agriculture in perennial teosinte habitat beginning 800 YBP (Kelly, 1945;Benz et al, 1990;Laitner-Benz & Benz, 1994;Figueroa-Rangel et al, 2010, 2012, and intensified beginning ß30 years ago when maize agriculture was proscribed at our Las Joyas site following the creation of the Sierra de Manantlán Biosphere Reserve, particularly the Reserve's "core" area containing the Las Joyas site. Establishment of the core area and proscription of maize agriculture plausibly created a buffer zone partially isolating perennial teosinte habitat, so promoting reproductive isolation between the perennial teosinte population and the maize population and resulting in the genetic differentiation observed in Las Joyas (Medina, 2012(Medina, , 2017Forbes et al, 2017). Thus, while our AFLP results do not provide a timeline for the evolution of genetic structuring in corn leafhopper, either instance of maize farming retreat from the vicinity of perennial teosinte habitat (i.e., ß800 or ß30 years ago) may have promoted a localized process of habitat-or host-associated differentiation at this particular location, consistent with our hypothesis derived from our haplotype analysis (above).…”

“…Evidence from mtDNA haplotype analysis The hypothesis of Nault (1990) and Medina et al (2012) presumes standing genetic variation in corn leafhopper prior to maize domestication so that one or more corn leafhopper genotypes were particularly capable of colonizing and exploiting maize upon its domestication. Also, the hypothesis presumes that the genotypic diversity of maize colonists narrowed relative to ancestral diversity on Balsas teosinte, a narrowing consistent with domestication processes generally, and seemingly with the evolution of pests (Larson, 2011;Medina, 2012Medina, , 2017. Similarly, human-driven plant range expansions, such as that of crops following their domestication, have been associated with narrowing genetic diversity in insect herbivore populations colonizing novel hosts, so that diversity is greater on the evolutionarily archaic segments of a species' host range compared to that on modern, recently colonized hosts (Oliver, 2006;Alvarez et al, 2007).…”

“…For example, common‐garden studies showed that the abundances of important pests of sunflower and maize were higher in crops compared to crop wild ancestors, partly due to enhanced performance and lower parasitism of those pests on the former compared to the latter hosts (Bernal et al ., ; Chen, ). Overall, the evidence accumulated to date shows that crop domestication and the spread of agriculture mediated the evolution and ecology of herbivores that are presently considered pests (Medina et al ., ; Chen et al ., ; Chen, ; Medina, ; Forbes et al ., ).…”

“…The study of crop domestication and agricultural evolution is relevant to understanding contemporary agri-the chronology and genetics of domestication and spread of important crops, for example, maize (Zea mays mays L.) (Staller et al, 2006;Kato et al, 2009;Staller, 2010;Hufford et al, 2012;Blake, 2015), comparatively little is known about how today's pest assemblages may have been shaped partly by agricultural, ecological and evolutionary processes over the last ß10K years. For example, weakening of herbivore defenses by domestication may have facilitated host shifts to poorly defended and abundant crop plants, while promoting reproductive isolation of herbivore populations left behind on ancestral host plants (Medina, 2012(Medina, , 2017Medina et al, 2012;Chen, 2016;Forbes et al, 2017). Similarly, crop domestication may have altered trophic interactions among crop plants, herbivores, and herbivore antagonists, such as parasitoids, so that herbivores are more abundant on crop plants compared to crop wild ancestors (Macfadyen & Bohan, 2010).…”