Rodney Mauricio

University of Georgia, Athens, GA, United States

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Publications (27)183.81 Total impact

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    V A Koelling, J L Hamrick, R Mauricio
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    ABSTRACT: Self-fertilization is a common mating system in plants and is known to reduce genetic diversity, increase genetic structure and potentially put populations at greater risk of extinction. In this study, we measured the genetic diversity and structure of two cedar glade endemic species, Leavenworthia alabamica and L. crassa. These species have self-incompatible (SI) and self-compatible (SC) populations and are therefore ideal for understanding how the mating system affects genetic diversity and structure. We found that L. alabamica and L. crassa had high species-level genetic diversity (H(e)=0.229 and 0.183, respectively) and high genetic structure among their populations (F(ST)=0.45 and 0.36, respectively), but that mean genetic diversity was significantly lower in SC compared with SI populations (SC vs SI, H(e) for L. alabamica was 0.065 vs 0.206 and for L. crassa was 0.084 vs 0.189). We also found significant genetic structure using maximum-likelihood clustering methods. These data indicate that the loss of SI leads to the loss of genetic diversity within populations. In addition, we examined genetic distance relationships between SI and SC populations to analyze possible population history and origins of self-compatibility. We find there may have been multiple origins of self-compatibility in L. alabamica and L. crassa. However, further work is required to test this hypothesis. Finally, given their high genetic structure and that individual populations harbor unique alleles, conservation strategies seeking to maximize species-level genetic diversity for these or similar species should protect multiple populations.
    Heredity 02/2011; 106(2):310-8. · 4.11 Impact Factor
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    Vanessa A Koelling, Rodney Mauricio
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    ABSTRACT: Reproductive barriers play a major role in the origin and maintenance of biodiversity by restricting gene flow between species. Although both pre- and postzygotic barriers often isolate species, prezygotic barriers are thought to contribute more to reproductive isolation. We investigated possible reproductive barriers between Leavenworthia alabamica and L. crassa, parapatric species with high morphological and ecological similarity and the ability to hybridize. Using greenhouse and field experiments, we tested for habitat isolation and genetic incompatibilities. From controlled crosses, we identified unilateral incompatibility (a partial prezygotic barrier associated with the self-incompatibility system), but no evidence of other genetic incompatibilities. We found a small reduction in pollen viability of F(1) hybrids and early germination of F(1), F(2), and BC hybrids relative to L. alabamica and L. crassa in a common garden experiment, but the effect on fitness was not tested. Field studies of hybrid pollen viability and germination are needed to determine if they contribute to reproductive isolation. In a reciprocal transplant, we found no evidence of habitat isolation or reduced hybrid survival (from seedling to adult stage) or reproduction. These data suggest unilateral incompatibility partially reproductively isolates L. alabamica and L. crassa, but no other reproductive barriers could be detected.
    American Journal of Botany 03/2010; 97(3):412-22. · 2.59 Impact Factor
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    ABSTRACT: Evolutionary ecologists have long been intrigued by the fact that many plant species can inhabit a broad range of environmental conditions and that plants often exhibit dramatic differences in phenotype across environmental gradients. We investigated responses to salinity treatments in the salt marsh plant Borrichia frutescens to determine if the species is responding to variation in edaphic salt content through phenotypic plasticity or specialized trait response. We grew seedlings from fruits collected in high- and low-salt microhabitats, assigned seedlings to high- and low-salt treatments in a greenhouse, and measured traits related to salt tolerance. All traits were highly plastic in response to salinity. Plants from the two microhabitats did not differ in trait means or respond differently to the treatments. These results suggest that environmental differences between the two microhabitats are not creating genotypes adapted to high and low salt levels. In addition, despite evidence for variation in allozyme markers in this population, there was no significant genotypic variation (family effect) in any of the trait means measured across microhabitats. There was variation in plasticity for only leaf Na and leaf B concentration. The high degree of plasticity for all traits and the lack of differences among microhabitats across the salinity gradient suggest plasticity in many traits may be fixed for this species.
    Estuaries and Coasts 01/2009; DOI 10.1007/s12237-009-9186-4. · 2.56 Impact Factor
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    Regina S Baucom, Rodney Mauricio
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    ABSTRACT: Evolutionary biologists explain the maintenance of intermediate levels of defense in plant populations as being due to trade-offs, or negative genetic covariances among ecologically important traits. Attempts at detecting trade-offs as constraints on the evolution of defense have not always been successful, leading some to conclude that such trade-offs rarely explain current levels of defense in the population. Using the agricultural pest Ipomoea purpurea, we measured correlations between traits involved in defense to glyphosate, the active ingredient in Roundup, a widely used herbicide. We found significant allocation costs of tolerance, as well as trade-offs between resistance and two measures of tolerance to glyphosate. Selection on resistance and tolerance exhibited differing patterns: tolerance to leaf damage was under negative directional selection, whereas resistance was under positive directional selection. The joint pattern of selection on resistance and tolerance to leaf damage indicated the presence of alternate peaks in the fitness landscape such that a combination of either high tolerance and low resistance, or high resistance and low tolerance was favored. The widespread use of this herbicide suggests that it is likely an important selective agent on weed populations. Understanding the evolutionary dynamics of herbicide defense traits is thus of increasing importance in the context of human-mediated evolution.
    Evolution 10/2008; 62(11):2842-54. · 4.86 Impact Factor
  • Rodney Mauricio, Shu-Mei Chang, Regina S. Baucom
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    ABSTRACT: Plant death is the most common effect resulting from the application of glyphosate, the active ingredient in the herbicide Roundup®. Individual seedlings of the morning glory, Ipomoea purpurea L.Roth, however, have been shown to exhibit tolerance to glyphosate, surviving after what should have been a lethal dose. Those that grow and reach reproductive maturity often exhibit deformed anthers within what appear to be normally developed flowers. Ipomoea purpurea has a mixed mating system and normally has hermaphroditic flowers that are capable of both selfing and outcrossing. The deformed anthers do not produce pollen, essentially converting a hermaphroditic flower to a female. Here we describe this morphological change and investigate the reproductive consequences of anther deformation. First, there is phenotypic variation for the propensity of an individual to exhibit male sterility through deformed anthers in response to treatment, but a series of field and greenhouse studies suggest that this variation is not genetic. The male sterility is also transient; within an individual, the frequency of flowers with deformed anthers declines over time. Although flowers with deformed anthers do not produce pollen, we observed mixed effects on female function of such flowers. In the greenhouse, flowers with deformed anthers that were hand-pollinated produced as many seeds as flowers with normal anthers, suggesting no effect on female fertility. In the field, however, plants with a higher proportion of anther deformation set significantly fewer seeds than those untreated, suggesting either reduced female fertility, or a reproductive penalty in flowers with deformed anthers due to the inability to self pollinate. Thus, the presence of this trait could alter the selfing to outcrossing ratio in populations that are sprayed with the herbicide. Individuals that exhibited a higher proportion of anther deformation also produce fewer total flowers than untreated plants, suggesting that anther deformation is part of a suite of responses to damage by glyphosate.L'application de glyphosate, agent actif de l'herbicide Roundup®, conduit généralement à la mort de la plante. On a cependant démontré que des plantules individuelles de la gloire du matin, Ipomoea purpurea L. Roth, montrent une tolérance au glyphosate en survivant à une dose qui aurait dû s'avérer létale. Les plantes qui se développent et atteignent la maturité montrent souvent des anthères déformées dans ce qui apparaît comme une fleur au développement normal. L'I.purpurea possède un double système de croisement impliquant normalement des fleurs hermaphrodites capables d'autofécondation et de fécondation croisée. Les anthères déformées ne produisent pas de pollen, convertissant ainsi la fleur hermaphrodite en fleur femelle. Les auteurs décrivent cette modification morphologique et examinent les conséquences reproductives de la déformation des anthères. D'abord, on observe une variation phénotypique pour la propension d'un individu à afficher une stérilité mâle par des anthères déformées suite au traitement, mais une série d'études en serres et aux champs suggère que cette variation ne soit pas génétique. La stérilité mâle est également transitoire; chez un individu, la fréquence des fleurs avec anthères déformées diminue avec le temps. Bien que les fleurs avec anthères déformées ne produisent pas de pollen, les auteurs observent des effets mixtes sur la fonction femelle de telles fleurs. En serres, les fleurs avec anthères déformées soumises à une pollinisation manuelle produisent autant de graines que des fleurs avec des anthères normales, suggérant l'absence d'effet sur la fertilité femelle. Aux champs,cependant, les plantes avec une forte proportion de déformation des anthères produisent significativement moins de graines que les plantes témoins, ce qui suggère soit une réduction de la fertilité femelle ou soit une pénalité reproductive chez les fleurs avec anthères déformées, liée à l'incapacité d'autofécondation. Ainsi, la présence de ce caractère pourrait altérer le ratio d'auto fécondation vs la fécondation croisée dans les populations traitées avec l'herbicide.
    Botany 05/2008; 86(6):587-594. · 1.23 Impact Factor
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    ABSTRACT: Plant death is the most common effect resulting from the application of glyphosate, the active ingredient in the herbicide Roundup 1 . Individual seedlings of the morning glory, Ipomoea purpurea L. Roth, however, have been shown to exhibit tolerance to glyphosate, surviving after what should have been a lethal dose. Those that grow and reach reproduc-tive maturity often exhibit deformed anthers within what appear to be normally developed flowers. Ipomoea purpurea has a mixed mating system and normally has hermaphroditic flowers that are capable of both selfing and outcrossing. The de-formed anthers do not produce pollen, essentially converting a hermaphroditic flower to a female. Here we describe this morphological change and investigate the reproductive consequences of anther deformation. First, there is phenotypic var-iation for the propensity of an individual to exhibit male sterility through deformed anthers in response to treatment, but a series of field and greenhouse studies suggest that this variation is not genetic. The male sterility is also transient; within an individual, the frequency of flowers with deformed anthers declines over time. Although flowers with deformed anthers do not produce pollen, we observed mixed effects on female function of such flowers. In the greenhouse, flowers with de-formed anthers that were hand-pollinated produced as many seeds as flowers with normal anthers, suggesting no effect on female fertility. In the field, however, plants with a higher proportion of anther deformation set significantly fewer seeds than those untreated, suggesting either reduced female fertility, or a reproductive penalty in flowers with deformed anthers due to the inability to self pollinate. Thus, the presence of this trait could alter the selfing to outcrossing ratio in popula-tions that are sprayed with the herbicide. Individuals that exhibited a higher proportion of anther deformation also produce fewer total flowers than untreated plants, suggesting that anther deformation is part of a suite of responses to damage by glyphosate. Résumé : L'application de glyphosate, agent actif de l'herbicide Roundup 1 , conduit généralement à la mort de la plante. On a cependant démontré que des plantules individuelles de la gloire du matin, Ipomoea purpurea L. Roth, montrent une tolérance au glyphosate en survivant à une dose qui aurait dû s'avérer létale. Les plantes qui se développent et atteignent la maturité montrent souvent des anthères déformées dans ce qui apparat comme une fleur au développement normal. L'I. purpurea possède un double système de croisement impliquant normalement des fleurs hermaphrodites capables d'au-tofécondation et de fécondation croisée. Les anthères déformées ne produisent pas de pollen, convertissant ainsi la fleur hermaphrodite en fleur femelle. Les auteurs décrivent cette modification morphologique et examinent les conséquences re-productives de la déformation des anthères. D'abord, on observe une variation phénotypique pour la propension d'un indi-vidu à afficher une stérilité mâle par des anthères déformées suite au traitement, mais une série d'études en serres et aux champs suggère que cette variation ne soit pas génétique. La stérilité mâle est également transitoire; chez un individu, la fréquence des fleurs avec anthères déformées diminue avec le temps. Bien que les fleurs avec anthères déformées ne pro-duisent pas de pollen, les auteurs observent des effets mixtes sur la fonction femelle de telles fleurs. En serres, les fleurs avec anthères déformées soumises à une pollinisation manuelle produisent autant de graines que des fleurs avec des anthè-res normales, suggérant l'absence d'effet sur la fertilité femelle. Aux champs,cependant, les plantes avec une forte propor-tion de déformation des anthères produisent significativement moins de graines que les plantes témoins, ce qui suggère soit une réduction de la fertilité femelle ou soit une pénalité reproductive chez les fleurs avec anthères déformées, liée à l'incapacité d'autofécondation. Ainsi, la présence de ce caractère pourrait altérer le ratio d'auto fécondation vs la féconda-tion croisée dans les populations traitées avec l'herbicide. Les individus qui montrent une plus forte proportion de défor-mation des anthères produisent également un nombre total de fleurs plus faible que les plants témoins, ce qui suggère que la déformation des anthères constitue une partie des dommages causés par le glyphosate.
    Botany 01/2008; 86:587-594. · 1.23 Impact Factor
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    Regina S. Baucom, Rodney Mauricio
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    ABSTRACT: Understanding how genetic variation is organized over geography has long been of interest to evolutionary biologists given that traits can vary within and among populations, across regions, and at continental or global scales. The pattern of regional variation can have an important impact on trait evolution at the local or population level. Using a common garden, we asked whether a geographically variable mosaic of tolerance to the widely applied herbicide RoundUp® existed in two closely related co-occurring species of morning glory, Ipomoea purpurea and I. hederacea. We assayed RoundUp tolerance in over 1,700 plants representing 290 families from 29 populations in the southeastern United States. Our findings suggest that the two species of morning glory partition their respective levels of genetic variation for tolerance to glyphosate differently. Variation for tolerance in I. purpurea appears to exist among maternal lines and regions, whereas in I. hederacea, variation in tolerance existed only among populations. In addition, we find a significant hotspot of tolerance or positive spatial aggregation of this trait on a local scale in I. purpurea populations from the Coastal Plain. This suggests that either similar regimes of selection or gene flow between populations can produce a geographic mosaic of tolerance. These results highlight the fact that the genetic variation underlying an adaptive trait can exist at many different scales, whether it be within- or among-populations, among geographical ‘hotspots,’ or among distinct ecological regions. Given these results, the partitioning of genetic variation should be considered before making predictions about an adaptive trait’s evolutionary trajectory.
    Evolutionary Ecology 01/2008; 22(1):85-101. · 2.41 Impact Factor
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    ABSTRACT: The extent to which epistasis contributes to adaptation, population differentiation, and speciation is a long-standing and important problem in evolutionary genetics. Using recombinant inbred (RI) lines of Arabidopsis thaliana grown under natural field conditions, we have examined the genetic architecture of fitness-correlated traits with respect to epistasis; we identified both single-locus additive and two-locus epistatic QTL for natural variation in fruit number, germination, and seed length and width. For fruit number, we found seven significant epistatic interactions, but only two additive QTL. For seed germination, length, and width, there were from two to four additive QTL and from five to eight epistatic interactions. The epistatic interactions were both positive and negative. In each case, the magnitude of the epistatic effects was roughly double that of the effects of the additive QTL, varying from -41% to +29% for fruit number and from -5% to +4% for seed germination, length, and width. A number of the QTL that we describe participate in more than one epistatic interaction, and some loci identified as additive also may participate in an epistatic interaction; the genetic architecture for fitness traits may be a network of additive and epistatic effects. We compared the map positions of the additive and epistatic QTL for germination, seed width, and seed length from plants grown in both the field and the greenhouse. While the total number of significant additive and epistatic QTL was similar under the two growth conditions, the map locations were largely different. We found a small number of significant epistatic QTL x environment effects when we tested directly for them. Our results support the idea that epistatic interactions are an important part of natural genetic variation and reinforce the need for caution in comparing results from greenhouse-grown and field-grown plants.
    Genetics 01/2006; 171(4):2013-27. · 4.39 Impact Factor
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    Rodney Mauricio
    New Phytologist 11/2005; 168(1):1-4. · 6.74 Impact Factor
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    Russell L Malmberg, Rodney Mauricio
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    ABSTRACT: The extent to which epistasis contributes to adaptation and speciation has been a controversial topic in evolutionary genetics. One experimental approach to study epistasis is based on quantitative trait locus (QTL) mapping using molecular markers. Comparisons can be made among all possible pair-wise combinations of the markers, irrespective of whether an additive QTL is associated with a marker; several software packages have been developed that facilitate this. We review several examples of using this approach to identify epistatic QTLs for traits of evolutionary or ecological interest. While there is variability in the results, the number of epistatic QTL interactions is often greater than or equal to the number of additive QTLs. The magnitude of epistatic effects can be larger than the additive effects. Thus, epistatic interactions seem to be an important part of natural genetic variation. Future studies of epistatic QTLs could lead to descriptions of the genetic networks underlying variation for fitness-related traits.
    Genetics Research 11/2005; 86(2):89-95. · 2.00 Impact Factor
  • Rodney Mauricio
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    ABSTRACT: The suggestion that speciation involves non-adaptive processes needs further research, not more argument.Mr Darwin's position might, we think, have been stronger than it is if he had not embarrassed himself with the aphorism, “Natura non facit salturn”, which turns up so often in his pages. We believe…that Nature does make jumps now and then and a recognition of the fact is of no small importance in disposing of many minor objections to the doctrine of transmutation (i.e. speciation).
    Genetica 03/2005; 123(1-2):1-2. · 1.68 Impact Factor
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    Rodney Mauricio
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    ABSTRACT: Ecologists study the rules that govern processes influencing the distribution and abundance of organisms, particularly with respect to the interactions of organisms with their biotic and abiotic environments. Over the past decades, using a combination of sophisticated mathematical models and rigorous experiments, ecologists have made considerable progress in understanding the complex web of interactions that constitute an ecosystem. The field of genomics runs on a path parallel to ecology. Like ecology, genomicists seek to understand how each gene in the genome interacts with every other gene and how each gene interacts with multiple, environmental factors. Gene networks connect genes as complex as the 'webs' that connect the species in an ecosystem. In fact, genes exist in an ecosystem we call the genome. The genome as ecosystem is more than a metaphor--it serves as the conceptual foundation for an interdisciplinary approach to the study of complex systems characteristic of both genomics and ecology. Through the infusion of genomics into ecology and ecology into genomics both fields will gain fresh insight into the outstanding major questions of their disciplines.
    Genetica 03/2005; 123(1-2):205-9. · 1.68 Impact Factor
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    Stacy Jørgensen, Rodney Mauricio
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    ABSTRACT: Hybridization is increasingly recognized as a significant creative force in evolution. Interbreeding among species can lead to the creation of novel genotypes and morphologies that lead to adaptation. On the Hawaiian island of O'ahu, populations of two species of plants in the endemic genus Lipochaeta grow at similar elevations in the northern Wai'anae Mountains. These two species represent extremes of the phenotypic distribution of leaf shape: the leaves of Lipochaeta tenuifolia individuals are compound and highly dissected while leaves of L. tenuis are simple. Based primarily on leaf shape morphology, a putative hybrid population of Lipochaeta located at Pu'u Kawiwi was identified. Individuals in this population exhibit a range of leaf shapes intermediate in varying degrees between the leaf shapes of the putative parental species. We analyzed individuals from pure populations of L. tenuifolia, L. tenuis and the putative hybrids using 133 AFLP markers. Genetic analysis of these neutral markers provided support for the hybrid origin of this population. The correlation between genetic background and leaf morphology in the hybrids suggested that the genome of the parental species with simple leaves might have significantly contributed to the evolution of a novel, compound leaf morphology.
    Genetica 03/2005; 123(1-2):171-9. · 1.68 Impact Factor
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    Rodney Mauricio
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    ABSTRACT: Although much is known about the molecular genetic basis of trichome development in Arabidopsis thaliana, less is known about the underlying genetic basis of continuous variation in a trait known to be of adaptive importance: trichome density. The density of leaf trichomes is known to be a major determinant of herbivore damage in natural populations of A. thaliana and herbivores are a significant selective force on genetic variation for trichome density. A number of developmental changes occur during ontogeny in A. thaliana, including changes in trichome density. I used multiple interval mapping (MIM) analysis to identify QTL responsible for trichome density on both juvenile leaves and adult leaves in replicate, independent trials and asked whether those QTL changed with ontogeny. In both juvenile and adult leaves, I detected a single major QTL on chromosome 2 that explained much of the genetic variance. Although additional QTL were detected, there were no consistent differences in the genetic architecture of trichome density measured on juvenile and adult leaves. The finding of a single QTL of major effect for a trait of known adaptive importance suggests that genes of major effect may play an important role in adaptation.
    Genetica 03/2005; 123(1-2):75-85. · 1.68 Impact Factor
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    S Jørgensen, R Mauricio
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    ABSTRACT: We investigated neutral genetic variation within and among 53 wild-collected populations of the weedy annual plant, Arabidopsis thaliana, in North America, using amplified fragment length polymorphism (AFLP) markers. A. thaliana is thought to have been introduced to North America from Eurasia by humans; such an introduction might be expected to leave a clear geographical signal in the genetic data. To detect such patterns, we sampled populations at several hierarchical geographical levels. We collected individuals from populations in two areas of the Southeast and one in the Midwest, as well as individuals from populations in the Pacific Northwest and Northeast. To estimate within-population variation, we sampled eight individuals from each of six populations in the Southeast and Midwest. Among all 95 individuals analysed, we detected 131 polymorphic AFLP fragments. We found no evidence for continental or regional diversification. Individuals sampled from Midwestern and Southeastern populations intermingled in a neighbour-joining tree, and Mantel tests conducted within the Midwestern and Southeastern regions as well as the full data set failed to detect any significant relationship between geographical and genetic distance. These results mirror those found for most global surveys of neutral genetic variability in A. thaliana. Surprisingly, we detected substantial amounts of neutral genetic variability within populations. The levels of genetic variation within populations, coupled with the nongeographical nature of divergence among populations, are consistent with contemporary gene flow and point to a complex and dynamic population history of A. thaliana in North America.
    Molecular Ecology 12/2004; 13(11):3403-13. · 6.28 Impact Factor
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    Regina S Baucom, Rodney Mauricio
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    ABSTRACT: Glyphosate, the active ingredient in the herbicide RoundUp, has increased dramatically in use over the past decade and constitutes a potent anthropogenic source of selection. In the southeastern United States, weedy morning glories have begun to develop tolerance to glyphosate, representing a unique opportunity to examine the evolutionary genetics of a novel trait. We found genetic variation for tolerance, indicating the potential for the population to respond to selection by glyphosate. However, the following significant evolutionary constraint exists: in the absence of glyphosate, tolerant genotypes produced fewer seeds than susceptible genotypes. The combination of strong positive directional selection in the presence of glyphosate and strong negative directional selection in its absence may indicate that the selective landscape of land use could drive the evolutionary trajectory of glyphosate tolerance. Understanding these evolutionary forces is imperative for devising comprehensive management strategies to help slow the rate of the evolution of tolerance.
    Proceedings of the National Academy of Sciences 10/2004; 101(36):13386-90. · 9.81 Impact Factor
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    ABSTRACT: In salt marsh habitats, noted for their extreme environments, a widely held assumption is that a few large clones dominate plant populations. Using a large number of polymorphic genetic markers, we were able to test this assumption for two salt marsh plants known to span extreme salinity gradients. For both species, clonal diversity was surprisingly high across populations: Simpson’s diversity indices were 0.96 and 0.99. Although clonal diversity was high, there was no pattern of association between specific clones or alleles with salt microhabitat. Our findings suggest that sexual reproduction and recruitment from seeds may have been generally underappreciated as an important ecological force in the salt marsh. Furthermore, clonal diversity has implications for conservation and restoration of these critical coastal habitats, particularly with regard to buffering environmental change or disease. Recent studies also suggest that high levels of intraspecific diversity can affect a variety of community and ecosystem processes.
    Ecology Letters 01/2004; 7:1155–1162. · 17.95 Impact Factor
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    ABSTRACT: Pathogen resistance is an ecologically important phenotype increasingly well understood at the molecular genetic level. In this article, we examine levels of avrRpt2-dependent resistance and Rps2 locus DNA sequence variability in a worldwide sample of 27 accessions of Arabidopsis thaliana. The rooted parsimony tree of Rps2 sequences drawn from a diverse set of ecotypes includes a deep bifurcation separating major resistance and susceptibility clades of alleles. We find evidence for selection maintaining these alleles and identify the N-terminal part of the leucine-rich repeat region as a probable target of selection. Additional protein variants are found within the two major clades and correlate well with measurable differences among ecotypes in resistance to the avirulence gene avrRpt2 of the pathogen Pseudomonas syringae. Long-lived polymorphisms have been observed for other resistance genes of A. thaliana; the Rps2 data suggest that the long-term maintenance of phenotypic variation in resistance genes may be a general phenomenon and are consistent with diversifying selection acting in concert with selection to maintain variation.
    Genetics 03/2003; 163(2):735-46. · 4.39 Impact Factor
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    ABSTRACT: Measuring natural selection has been a fundamental goal of evolutionary biology for more than a century, and techniques developed in the last 20 yr have provided relatively simple means for biologists to do so. Many of these techniques, however, share a common limitation: when applied to phenotypic data, environmentally induced covariances between traits and fitness can lead to biased estimates of selection and misleading predictions about evolutionary change. Utilizing estimates of breeding values instead of phenotypic data with these methods can eliminate environmentally induced bias, although this approach is more difficult to implement. Despite this potential limitation to phenotypic methods and the availability of a potential solution, little empirical evidence exists on the extent of environmentally induced bias in phenotypic estimates of selection. In this article, we present a method for detecting bias in phenotypic estimates of selection and demonstrate its use with three independent data sets. Nearly 25% of the phenotypic selection gradients estimated from our data are biased by environmental covariances. We find that bias caused by environmental covariances appears mainly to affect quantitative estimates of the strength of selection based on phenotypic data and that the magnitude of these biases is large. As our estimates of selection are based on data from spatially replicated field experiments, we suggest that our findings on the prevalence of bias caused by environmental covariances are likely to be conservative.
    The American Naturalist 11/2002; 160(4):511-23. · 4.55 Impact Factor
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    Rodney Mauricio
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    ABSTRACT: Almost forty years ago, Ehrlich and Raven (1964) hypothesized that the great diversity of plants and the herbivores that feed on them arose from a process of coevolution. Plants do possess an amazing diversity of traits that are easily imagined as having arisen from an antagonistic interaction between plants and herbivores. Two basic assumptions lie at the root of most theories of coevolution between plants and their herbivores. First, herbivores are agents of natural selection on plant resistance traits. Second, plants incur a significant fitness cost for possessing these resistance traits. An ecological genetic approach can provide rigorous evidence for these coevolutionary assumptions. In this paper, I present new experimental work on the subject of costs of resistance and review and discuss my own previous work bearing directly on these questions. Using both field experiments on natural populations of the mouse-ear cress ( Arabidopsis thaliana ) and laboratory experiments using genetically modified plants, I demonstrate that herbivores are exerting selection on both a chemical and physical resistance trait and that there are significant fitness costs to possessing these two traits. These results provide direct confirmation that our current models of the evolution of plant defenses are appropriate.
    American Zoologist 08/2001;

Publication Stats

1k Citations
183.81 Total Impact Points

Institutions

  • 2000–2011
    • University of Georgia
      • • Department of Genetics
      • • Department of Plant Biology
      Athens, GA, United States
  • 2004
    • University of Illinois, Urbana-Champaign
      Urbana, Illinois, United States
  • 1997–2003
    • University of Chicago
      • Department of Ecology & Evolution
      Chicago, IL, United States
  • 1998–2002
    • Duke University
      • Department of Biology
      Durham, NC, United States