Browsing by Subject "Zea"
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Item Host Plant Influences on Performance and Haplotype Diversity of Dalbulus maidis, a Specialist Herbivore of Zea(2012-12-06) Davila-Flores, AmandaIn one study, a suite of plants from the maize genus Zea L. (Poaceae) and the specialist herbivore Dalbulus maidis (DeLong and Wolcott, 1923) (Hemiptera: Cicadellidae) were used to test the hypotheses that anti-herbivore defenses are affected by plant life-history evolution and human intervention through domestication and breeding for high yield. The suite of Zea host plants included one Mexican commercial hybrid maize Zea mays ssp. mays L., a landrace variety of maize, two populations of Balsas teosinte (Zea mays ssp. parviglumis Iltis & Doebley), and perennial teosinte (Z. diploperennis Iltis, Doebley & Guzman). This suite of host plants includes three Transitions evident within the genus Zea: life history form perennial to annual life cycle evident between perennial teosinte and Balsas teosinte, domestication transition from wild annual to domesticated annual evident between Balsas teosinte and landrace maize, and; breeding transition from landrace cultivar to a hybrid cultivar. The transitions were correlated with differences in plant defenses, as indicated by corn leafhopper performance. Results showed a performance gradient, suggesting a pattern in which plant defense is stronger in perennial than annual plants, Balsas teosinte than landrace maize, and in landraces than in hybrid maize. Furthermore, results suggested that domesticated maize would be the least defended, most suitable host for corn leafhopper. In a second study, haplotype diversity was assessed to address structuring and interconnectedness among samples of corn leafhopper collected in the southwestern region of Mexico to address microevolution. The geographic focus of the study was maintained within an area encompassing the presumed centers of radiation of Dalbulus and its host genus Zea, and of maize domestication. Samples were complemented with samples of corn leafhopper sequences available at GenBank. Results revealed seven haplotypes from three host plants within Zea: perennial teosinte, Balsas teosinte, and maize. Furthermore, genetic differentiation was present and haplotype diversity appears to correlate with differences in genetic structure between perennial teosinte and maize. One haplotype was found to be present throughout all sites, which appears to parallel the spread of maize cultivation. As maize cultivation spread beyond its area of domestication, corn leafhoppers colonized perennial teosinte, further suggesting that subsequent decreases in maize cultivation in perennial teosinte habitat created a refuge where perennial teosinte- adapted haplotypes could persist. Altogether, my research suggests that the combination of historical expansion of maize cultivation expansion and the weaker anti-herbivore defenses associated within maize domestication appears to have favored genotypes particularly adapted for exploiting maize.Item Mutual Impacts on a Specialist Herbivore and its Host Plants: Variation in Insect Morphology and Plant Tolerance(2014-12-04) Chinchilla-Ramirez, MilenaIn one study, a suite of host plants from the genus Zea L. (Poaceae) and the specialist herbivore Dalbulus maidis (DeLong and Wolcott) (Hemiptera: Cicadellidae) were used to address whether plant tolerance to direct damage by the herbivore and seedling morphometry were mediated by plant domestication and genetic improvement. Additionally, the role of shoot: root ratios in plant tolerance was included in this study. Plant tolerance was measured as regrowth rate, and a trade-off between plant tolerance and resistance was predicted based on (i) the increasing investment in growth and productivity with evolutionary history in Zea and, (ii) its negative correlation with plant resistance. The effects of the domestication transition were assessed by contrasting Balsas teosinte (Z. mays L. ssp. parviglumis Iltis & Doebley) and maize (Z. mays L. ssp. mays), while breeding transition by contrasting maize landraces and maize inbred lines. The results showed that domestication and breeding mediated changes in seedling morphometry, but did not mediate changes in plant tolerance, with Balsas teosinte, maize landraces, and maize inbred lines similarly tolerant to feeding damage by D. maidis. In contrast, domestication mediated changes in shoot: root ratios, with larger roots in the maizes, suggesting increased storage capability in domesticated taxa. In another study, morphometrics analyses were performed on D. maidis specimens collected from Perennial teosinte [Zea diploperennis Iltis (Doebley & Guzman)] and maize in western Mexico, to determine whether a correlation existed between previously documented genetic differentiation and morphological (morphometrical) differentiation. Traditional morphometrics was used to analyze body differences, and geometric morphometrics was applied for wing analysis. The results suggested that genetic and morphological differentiation are correlated in D. maidis, with individuals associated to Perennial teosinte exhibiting larger body size compared to individuals associated to maize. A strong host plant effect and a moderate habitat effect were detected, and body size was found to be as the variable explaining most of the variance between individuals. Wing differentiation between individuals associated with Perennial teosinte and maize was detected, but it was strongly correlated with allometry. It was hypothesized that different selection forces are acting on morphological and genetic differentiation because while morphological differentiation is maintained in locations where Perennial teosinte and maize coexist, genetic differentiation is lost in those locations. Overall, the study?s results suggested that evolutionary transitions in Zea have exerted changes in both the plant morphometry and insect morphology, with changes in the plant related to increased storage and productivity in roots, and changes in the insect related to overall body size.