Variation in plant defense traits and population genetics within a Sonoran Desert cotton endemic, Gossypium davidsonii and boll weevil, Anthonomus grandis

→Gossypium davidsonii, a long lived cotton endemic species to the Sonoran Desert, Baja California, Mexico, has been documented to express large (nearly 10-fold) variation in plant defenses (gossypol, a defense compound, gossypol-containing cavity density, and trichome density) across a narrow species range (100s of kilometers). Potential sources of variation explored were from phenotypic plasticity from variable environments, the stochastic events of migration and genetic drift, or a result from natural selection. →From greenhouse studies testing extreme herbivory, nutrient and water conditions on defense trait expression, we found that most variation in defense traits were attributable to genetic differentiation among sampled populations. We also detected divergent selection on all defense traits, by comparing phenotypic differentiation (PST) to genetic differentiation (FST) among populations, thought the cause of selection is still poorly understood. →Variation in defense traits may influence the interaction with associated insect herbivores. We extended the analysis of defense trait phenotypes, genetic relatedness, and spatial structuring of populations of G. davidsonii on fitness responses and seed and leaf damage. Using Multiple Regressions on Distance Matrices (MRDM), we found no common explanatory variables on fitness response variables across four sampled populations, which could be explained by the large environmental variability across site locations. →We also determined whether ancestral and contemporary gene flow within the boll weevil, A. grandis, and associated populations of G. davidsonii were symmetrical. We found a two-fold difference between plant and herbivore in the degree of population differentiation and that methods detecting gene flow revealed significant incongruence in the geographical network of ancestral gene flow. This incongruence suggests that gene flow in the two species has been influenced by different geographical barriers to dispersal. →Lastly, we assessed the population genetic structure of the boll weevil in North America on cultivated and wild cotton hosts. Genetic data favor a two-variant classification that takes into account the Sierra Madre Occidental mountain range which likely represents a large barrier to gene flow. We believe that classification of boll weevil would benefit from a phylogeographic perspective, consisting of two geographically distinct forms, each of which utilizes multiple host species

Shifts in outcrossing rates and changes to floral traits are associated with the evolution of herbicide resistance in the common morning glory

Humanâ mediated selection can strongly influence the evolutionary response of natural organisms within ecological timescales. But what traits allow for, or even facilitate, adaptation to the strong selection humans impose on natural systems? Using a combination of laboratory and greenhouse studies of 32 natural populations of the common agricultural weed, Ipomoea purpurea, we show that herbicideâ resistant populations selfâ fertilise more than susceptible populations. We likewise show that antherâ stigma distance, a floral trait associated with selfâ fertilisation in this species, exhibits a nonlinear relationship with resistance such that the most and least resistant populations exhibit lower antherâ stigma separation compared to populations with moderate levels of resistance. Overall, our results extend the general finding that plant mating can be impacted by humanâ mediated agents of selection to that of the extreme selection of the agricultural system. This work highlights the influence of humanâ mediated selection on rapid responses of natural populations that can lead to unexpected longâ term evolutionary consequences.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135395/1/ele12703_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135395/2/ele12703.pd

Fitness costs of herbicide resistance across natural populations of the common morning glory, Ipomoea purpurea

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134117/1/evo13016_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134117/2/evo13016.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134117/3/evo13016-sup-0001-FigS1.pd

Population Structure and Genetic Diversity of the Boll Weevil (Coleoptera: Curculionidae) on Gossypium in North America

Although the boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), is a devastating pest in the United States and Mexico, its population structure and genetic diversity in Mexico on wild and cultivated cotton hosts (genus Gossypium) is poorly understood. Past studies using morphology, host use, and distribution records suggest that A.grandis grandis comprises three forms with host-associated characteristics: the southeastern form (from domesticated Gossypium hirsutum L., southeastern United States and northeastern Mexico), the thurberia form (from Gossypium thurberi Todaro, Arizona and northwestern Mexico), and the Mexican form (from multiple Gossypium species and other malvaceous plant genera in the remainder of Mexico and Central America). However, the phylogenetic relationships, host preferences, and distributions of these forms are not completely understood. An alternative hypothesis of an eastern and western form of the boll weevil is suggested by the suspected phylogeographic range expansion from an ancestral distribution in the tropics northward along both Mexican coasts, culminating in the maximally contrasting phenotypes observed in the northeastern and northwestern arms of the current distribution. In this study, we sequenced one mitochondrial and four nuclear genes to gain insight into the evolutionary relationships among the putative forms and their distributions on wild and domesticated cotton hosts. Using models of evolution, we compared the three-form to the two-form classification and to two alternative classifications that incorporate geography and host use traits. The genetic data at most loci provide stronger support for the two-form than the three-form hypothesis, with an eastern and western group separated by the Sierra Madre Occidental mountain range. They do not support separate taxonomic status for boll weevils developing onG. thurberi

Variation in plant defense traits and population genetics within a Sonoran Desert cotton endemic, Gossypium davidsonii and boll weevil, Anthonomus grandis

→Gossypium davidsonii, a long lived cotton endemic species to the Sonoran Desert, Baja California, Mexico, has been documented to express large (nearly 10-fold) variation in plant defenses (gossypol, a defense compound, gossypol-containing cavity density, and trichome density) across a narrow species range (100s of kilometers). Potential sources of variation explored were from phenotypic plasticity from variable environments, the stochastic events of migration and genetic drift, or a result from natural selection. →From greenhouse studies testing extreme herbivory, nutrient and water conditions on defense trait expression, we found that most variation in defense traits were attributable to genetic differentiation among sampled populations. We also detected divergent selection on all defense traits, by comparing phenotypic differentiation (PST) to genetic differentiation (FST) among populations, thought the cause of selection is still poorly understood. →Variation in defense traits may influence the interaction with associated insect herbivores. We extended the analysis of defense trait phenotypes, genetic relatedness, and spatial structuring of populations of G. davidsonii on fitness responses and seed and leaf damage. Using Multiple Regressions on Distance Matrices (MRDM), we found no common explanatory variables on fitness response variables across four sampled populations, which could be explained by the large environmental variability across site locations. →We also determined whether ancestral and contemporary gene flow within the boll weevil, A. grandis, and associated populations of G. davidsonii were symmetrical. We found a two-fold difference between plant and herbivore in the degree of population differentiation and that methods detecting gene flow revealed significant incongruence in the geographical network of ancestral gene flow. This incongruence suggests that gene flow in the two species has been influenced by different geographical barriers to dispersal. →Lastly, we assessed the population genetic structure of the boll weevil in North America on cultivated and wild cotton hosts. Genetic data favor a two-variant classification that takes into account the Sierra Madre Occidental mountain range which likely represents a large barrier to gene flow. We believe that classification of boll weevil would benefit from a phylogeographic perspective, consisting of two geographically distinct forms, each of which utilizes multiple host species.</p

Data from: The geographic mosaic of herbicide resistance evolution in the common morning glory, Ipomoea purpurea: evidence for resistance hotspots and low genetic differentiation across the landscape

Strong human-mediated selection via herbicide application in agroecosystems has repeatedly led to the evolution of resistance in weedy plants. Although resistance can occur among separate populations of a species across the landscape, the spatial scale of resistance in many weeds is often left unexamined. We assessed the potential that resistance to the herbicide glyphosate in the agricultural weed Ipomoea purpurea has evolved independently multiple times across its North American range. We examined both adaptive and neutral genetic variations in 44 populations of I. purpurea by pairing a replicated dose–response greenhouse experiment with SSR genotyping of experimental individuals. We uncovered a mosaic pattern of resistance across the landscape, with some populations exhibiting high-survival postherbicide and other populations showing high death. SSR genotyping revealed little evidence of isolation by distance and very little neutral genetic structure associated with geography. An approximate Bayesian computation (ABC) analysis uncovered evidence for migration and admixture among populations before the widespread use of glyphosate rather than the very recent contemporary gene flow. The pattern of adaptive and neutral genetic variations indicates that resistance in this mixed-mating weed species appears to have evolved in independent hotspots rather than through transmission of resistance alleles across the landscape

Mating System Genotypes 2012

Genotypes used to estimate mating system from the 2012 sampling of populations

Spatial and Temporal Floral Phenotypes

This data file contains floral phenotypic data for populations sampled in 2012 and 2003. The spatial analysis uses only data from 2012. The 'temporal' label (1) indicates if populations were paired between 2003 and 2012

Data from: A resurrection experiment finds evidence of both reduced genetic diversity and potential adaptive evolution in the agricultural weed Ipomoea purpurea

Despite the negative economic and ecological impact of weeds, relatively little is known about the evolutionary mechanisms that influence their persistence in agricultural fields. Here, we use a resurrection approach to examine the potential for genotypic and phenotypic evolution in Ipomoea purpurea, an agricultural weed that is resistant to glyphosate, the most widely used herbicide in current-day agriculture. We found striking reductions in allelic diversity between cohorts sampled nine years apart (2003 vs. 2012), suggesting that populations of this species sampled from agricultural fields have experienced genetic bottleneck events that have led to lower neutral genetic diversity. Heterozygosity excess tests indicate that these bottlenecks may have occurred prior to 2003. A greenhouse assay of individuals sampled from the field as seed found that populations of this species, on average, exhibited modest increases in herbicide resistance over time. However, populations differed significantly between sampling years for resistance: some populations maintained high resistance between the sampling years whereas others exhibited increased or decreased resistance. Our results show that populations of this noxious weed, capable of adapting to strong selection imparted by herbicide application, may lose genetic variation as a result of this or other environmental factors. We probably uncovered only modest increases in resistance on average between sampling cohorts due to a strong and previously identified fitness cost of resistance in this species, along with the potential that nonresistant migrants germinate from the seed bank

Data from: Shifts in outcrossing rates and changes to floral traits are associated with the evolution of herbicide resistance in the common morning glory

Human-mediated selection can strongly influence the evolutionary response of natural organisms within ecological timescales. But what traits allow for, or even facilitate, adaptation to the strong selection humans impose on natural systems? Using a combination of laboratory and greenhouse studies of 32 natural populations of the common agricultural weed, Ipomoea purpurea, we show that herbicide-resistant populations self-fertilise more than susceptible populations. We likewise show that anther–stigma distance, a floral trait associated with self-fertilisation in this species, exhibits a nonlinear relationship with resistance such that the most and least resistant populations exhibit lower anther–stigma separation compared to populations with moderate levels of resistance. Overall, our results extend the general finding that plant mating can be impacted by human-mediated agents of selection to that of the extreme selection of the agricultural system. This work highlights the influence of human-mediated selection on rapid responses of natural populations that can lead to unexpected long-term evolutionary consequences