Biology subjects

Baucom, R. S.

Publications and source records attributed to Baucom, R. S..

12 recordsLinked to original sources

bioRxiv2025

Color, size, shape: The drivers of floral variation in Hesperis matronalis (Dames Rocket)

Evolutionary biologists have long been intrigued by the factors that sustain genetic and phenotypic variation within and among natural populations. Polymorphisms underlying components of floral display - such as floral color, size, and shape - are uniquely of interest since variation in these traits impact pollinator attraction, rates of visitation, and pollinator efficiency, which ultimately influence patterns of plant reproduction and therefore fitness. We leverage existing floral variation present within and among populations of Hesperis matronalis (Dames Rocket) to disentangle the relative influence of natural selection and genetic drift in shaping floral trait variation. We employ a multi-tiered approach: we determine if variation in floral traits (color, size, and petal shape) is influenced by geography or environmental variables such as temperature and precipitation, we evaluate whether selection underlies trait variation by comparing phenotypic divergence (PST) with neutral genetic structure (FST), and we perform a Lande-Arnold selection analysis to explore the relationship between fitness and floral trait variation within natural populations. We find that selection underlies the divergence of floral color, floral size, and petal width among H. matronalis populations, with PST > FST for each trait. We find no indication, however, that variation in size in this species is influenced by the environment, but some evidence that variation in floral color and petal shape may be influenced by temperature. Finally, selection analyses of contemporary populations indicate divergent selection affecting combinations of color, petal shape, and plant size. These results suggest that the variation in floral shape in this species may be maintained due to environmental pressures, whereas floral color is influenced by pollinator visibility and the presence of different pollinator groups.

evolutionary biology↗

bioRxiv2025

A resurrection experiment reveals reduced adaptive potential in a common agricultural weed

Teaser TextAdaptive evolution is essential for populations facing rapid anthropogenic change, yet realized evolutionary responses often fall short of expectations. Using a resurrection experiment with Ipomoea purpurea, we reveal that the genetic covariance structure underlying pollination and mating-system traits has become more constraining over time. Traits involved in pollinator attraction evolved within a decade, but flowering phenology--critical for coping with climate-driven shifts--was hindered by increasingly restrictive genetic covariances. Our findings suggest that temporal changes in genetic constraints can substantially dampen adaptive potential, even when selection pressures are strong. Adaptive evolution is critical to population responses under accelerating anthropogenic global change. Although theory and some empirical work suggest that contemporary rates of environmental change can be met by equally rapid evolutionary shifts, mismatches between expected and realized evolution remain common in natural systems. Using a resurrection approach, we demonstrate that the structure of genetic covariances among pollination and mating-system traits in the common morning glory (Ipomoea purpurea) is increasingly constraining evolutionary trajectories. Pollinator-attracting traits evolved or became more favored on a rapid time scale of less than ten years, but genetic covariances between traits limited the adaptive rate and evolutionary trajectory of flowering phenology, a trait with widely recognized importance in adapting to climatic shifts. Our results show that changing patterns of genetic constraint can substantially reduce adaptive potential even when selection favors rapid trait evolution.

evolutionary biology↗

bioRxiv2024

Off-target drift of the herbicide dicamba disrupts plant-pollinator interactions via novel pathways

Assessing the impact of herbicide drift on plant-pollinator interactions is crucial for providing insight into the causes of ongoing pollinator declines. The recent exponential increase in the use of the synthetic auxin herbicide dicamba, which is known to drift long distances following application, renders this concern especially acute. However, experimental data on the consequences of dicamba drift on plant-pollinator interactions are lacking from weed communities in natural settings. We assessed the indirect effects of dicamba drift on pollinator visits for 11 weeds of agricultural crops using a common garden field experiment, focusing on the potential for changes in pollinator abundance and alterations to both plant traits and patterns of pollinator visitation. We found variation among plant species in the extent of damage from dicamba drift exposure, and variation in how growth, flowering time, and flower displays were impacted, with some species showing negative impacts and others showing little effect. Pollinator frequencies were reduced in dicamba-exposed plots, and pollinator approaches and foraging visits were reduced for some weed species yet not others. Structural equation modeling revealed that the relationship between flower display and pollinator visits was disrupted in the presence of dicamba compared to control plots. Our study provides the most comprehensive picture to date of the impacts of dicamba drift on plant-pollinator interactions, with findings that highlight an underappreciated role of services supplied by weedy communities at the agroecological interface.

ecology↗

bioRxiv2023

The double life of trichomes: understanding their dual role in herbivory and herbicide resistance

External features of organisms often serve as the first line of defense in their immediate environments. Trichomes are hair-like appendages on plant surfaces that can defend against damaging agents such as pathogens, herbivores, and UV radiation. It is currently unknown if the variation observed in trichome traits represents dual or conflicting roles against different types of stressors. Here, we assess whether trichomes serve as an herbicide resistance trait and how it coincides with the conventionally studied defensive strategy of herbivory resistance. In a series of experiments, we exposed the annual invasive velvetleaf (Abutilon theophrasti) to glyphosate (active ingredient in the herbicide Roundup) to investigate whether trichome traits (shape and density) are linked to herbicide resistance and to test whether herbicide alters selection on plant trichomes. We found that an increased proportion of branched trichomes positively impacted herbicide resistance as well as chewing herbivory resistance. We also found evidence that glyphosate imposes positive selection on branched trichomes in velvetleaf. Overall, our results indicate that branched trichomes can contribute to both herbicide and herbivory resistance, serving as a dual structural form of resistance reducing plant injury. If our results are to be applied more broadly, it would suggest that herbicide exposure can alter the composition of plant trichomes, potentially impacting trichome-mediated defenses against various external stressors.

evolutionary biology↗

bioRxiv2022

Not just flowering time: A resurrection approach shows floral attraction traits are changing over time

Contemporary anthropogenic changes in climate and landscape form a complex set of selective pressures acting on natural systems, yet, in many systems, we lack information about both whether and how organisms may adapt to these changes. In plants, research has focused on climate-induced changes in phenology and the resultant potential for disruption of plant-pollinator interactions, however there remains a paucity of knowledge regarding how other pollinator-mediated traits may be involved in adaptive response. Here, we use resurrection experiments to investigate the phenotypic basis of adaptation in a mixed-mating system plant, the common morning glory (Ipomoea purpurea). Specifically, we measure temporal and spatial changes in traits grouped into three categories relevant to plant-pollinator interactions - floral morphology, floral rewards, and floral phenology. We show a significant temporal increase in corolla size and shift to earlier flowering times, as well as a potential for increased investment in floral rewards, all of which are driven primarily by populations at more northern latitudes. Additionally, we find evidence for directional selection on floral morphology and phenology, and evidence of balancing selection acting on anther-stigma distance. Overall, these results show an adaptive response in line with greater investment in pollinator attraction rather than self-pollination and fine-scale spatial differences in adaptive potential.

evolutionary biology↗

bioRxiv2021

Dicamba drift alters plant-herbivore interactions at the agro-ecological interface

Natural populations evolve in response to biotic and abiotic changes in their environment, which shape species interactions and ecosystem dynamics. Agricultural systems can introduce novel conditions via herbicide exposure to non-crop habitats in surrounding fields. While herbicide drift is known to produce a variety of toxic effects in plants, little is known about its impact on non-target wildlife species interactions. In a two-year study, we investigated the impact of herbicide drift on plant-herbivore interactions with common weed velvetleaf (Abutlion theophrasti) as the focal species. The findings reveal a significant increase in the phloem feeding silverleaf whitefly (Bermisia tabaci) abundance on plants exposed to herbicide at drift rates of 0.5% and 1% of the field dose. We also identified a significant phenotypic tradeoff between whitefly resistance and herbicide resistance in addition to whitefly resistance and relative growth rate in the presence of dicamba drift after increasing the populations grown in year two. In a follow-up greenhouse study, we found evidence that dicamba drift at 0.5% of the field dose significantly increased average chlorophyll content (mg/cm2) along with a positive correlation between whitefly abundance and chlorophyll content. Overall, these findings suggest herbicide exposure to non-target communities can significantly alter herbivore populations, potentially impacting biodiversity and community dynamics of weed populations found at the agro-ecological interface.

ecology↗

bioRxiv2021

Inter-chromosomal linkage disequilibrium and linked fitness cost loci influence the evolution of nontarget site herbicide resistance in an agricultural weed

The adaptation of weedy plants to herbicide is both a significant problem in agriculture and a model for the study of rapid adaptation under regimes of strong selection. Despite recent advances in our understanding of simple genetic changes that lead to resistance, a significant gap remains in our knowledge of resistance controlled by many loci and the evolutionary factors that influence the maintenance of resistance over time. Here, we perform a multi-level analysis involving whole genome sequencing and assembly, resequencing and gene expression analysis to both uncover putative loci involved in nontarget herbicide resistance and to examine evolutionary forces underlying the maintenance of resistance in natural populations. We found loci involved in herbicide detoxification, stress sensing, and alterations in the shikimate acid pathway to be under selection, and confirmed that detoxification is responsible for glyphosate resistance using a functional assay. Furthermore, we found interchromosomal linkage disequilibrium (ILD), most likely associated with epistatic selection, to influence NTSR loci found on separate chromosomes thus potentially mediating resistance through generations. Additionally, by combining the selection screen, differential expression and LD analysis, we identified fitness cost loci that are strongly linked to resistance alleles, indicating the role of genetic hitchhiking in maintaining the cost. Overall, our work strongly suggests that NTSR glyphosate resistance in I. purpurea is conferred by multiple genes which are maintained through generations via ILD, and that the fitness cost associated with resistance in this species is a by-product of genetic-hitchhiking.

plant biology↗

bioRxiv2019

The soil microbial community alters patterns of selection on flowering time and fitness related traits in Ipomoea purpurea

Premise of the studyPlant flowering time plays an important role in plant fitness and thus evolutionary processes. Soil microbial communities are diverse and have a large impact, both positive and negative, on the host plant. However, owing to few available studies, how the soil microbial community may influence the evolutionary response of plant populations is not well understood. Here we sought to uncover if below-ground microbial communities act as an agent of selection on flowering and growth traits in the common morning glory, Ipomoea purpurea.\n\nMethodsWe performed a controlled greenhouse experiment in which genetic lines of I. purpurea were planted into either sterilized soils, or soils that were sterilized and re-inoculated with the microbial community from original field soil. This allowed us to directly test the influence of alterations to the microbial community on plant growth, flowering, and fitness, as well as assess patterns of selection in both soil microbial environments.\n\nResultsWe found that a more complex soil microbial community resulted in larger plants that produced more flowers. Selection strongly favored earlier flowering when plants were grown in the complex microbial environment than compared to sterilized soil. Additionally, we uncovered a pattern of negative correlational selection on growth rate and flowering time, indicating that selection favored different combinations of growth and flowering traits in the simplified versus complex soil community.\n\nConclusionsTogether these results suggest the soil microbial community is a selective agent on flowering time and ultimately that soil microbial community influences important plant evolutionary processes.

evolutionary biology↗

bioRxiv2019

Parallel and nonparallel genomic responses contribute to herbicide resistance in Ipomoea purpurea, a common agricultural weed

The repeated evolution of herbicide resistance has been cited as an example of genetic parallelism, wherein separate species or genetic lineages utilize the same genetic solution in response to selection. However, most studies that investigate the genetic basis of herbicide resistance examine the potential for changes in the protein targeted by the herbicide rather than considering genome-wide changes. We used a population genomics screen and targeted exome re-sequencing to uncover the potential genetic basis of glyphosate resistance in the common morning glory, Ipomoea purpurea, and to determine if genetic parallelism underlies the repeated evolution of resistance across replicate resistant populations. We found no evidence for changes in 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), glyphosates target protein, that were associated with resistance, and instead identified five genomic regions that show evidence of selection. Within these regions, genes involved in herbicide detoxification--cytochrome P450s, ABC transporters, and glycosyltransferases--are enriched and exhibit signs of selective sweeps. One region under selection shows parallel changes across all assayed resistant populations whereas other regions exhibit signs of divergence. Thus, while it appears likely that the physiological mechanism of resistance in this species is likely the same among resistant populations, we find patterns of both similar and divergent selection across separate resistant populations at particular loci.

evolutionary biology↗

bioRxiv2019

Experimental evidence that belowground competition can influence the evolution of root traits in two closely related morning glory species

Although root traits play a critical role in mediating plant-plant interactions and resource acquisition from the soil environment, research examining if and how belowground competition can influence the evolution of root traits remains largely unexplored. Here we examine the potential that root traits may evolve as a target of selection from interspecific competition using Ipomoea purpurea and I. hederacea, two closely related morning glory species that commonly co-occur in the United States. We show that belowground competitive interactions between the two species can alter the pattern of selection on root traits in each species. Specifically, competition with I. purpurea changes the pattern of selection on root angle in I. hederacea, and competitive interactions with I. hederacea changes the pattern of selection on root size in I. purpurea. However, we did not uncover evidence that intraspecific competition altered the pattern of selection on any root traits within I. hederacea. Overall, our results suggest that belowground competition between closely related species can influence the phenotypic evolution of root traits in natural populations. Our findings provide a microevolutionary perspective of how competitive belowground interactions may impact plant fitness, potentially leading to patterns of plant community structure.

evolutionary biology↗

bioRxiv2019

Assessing the remarkable morphological diversity and transcriptomic basis of leaf shape in Ipomoea batatas (sweetpotato)

O_LILeaf shape, a spectacularly diverse plant trait, varies across taxonomic levels, geography, and in response to environmental differences. However, comprehensive intraspecific analyses of leaf shape variation across variable environments is surprisingly absent. Here, we perform a multi-level analysis of leaf shape using diverse accessions of sweetpotato (Ipomoea batatas), and uncover the role of genetics, environment, and GxE on this important trait.\nC_LIO_LIWe examine leaf shape using a variety of morphometric analyses, and complement this with a transcriptomic survey to identify gene expression changes associated with shape variation. Additionally, we examine the role of genetics and environment on leaf shape by performing field studies in two geographically separate common gardens.\nC_LIO_LIWe show that extensive leaf shape variation exists within I. batatas, and identify promising candidate genes underlying this variation. Interestingly, when considering traditional measures, we find that genetic factors are largely responsible for most of leaf shape variation, but that the environment is highly influential when using more quantitative measures via leaf outlines.\nC_LIO_LIThis extensive and multi-level examination of leaf shape shows an important role of genetics underlying a potentially important agronomic trait, and highlights that the environment can be a strong influence when using more quantitative measures of leaf shape.\nC_LI

plant biology↗

bioRxiv2017

Environmental Influences On The Mating System Of The Common Morning Glory

The balance between selfing and outcrossing is a life history trait of major concern with deep evolutionary consequences in mixed mating species. Yet, our current understanding of the proximate and ultimate determinants of species mating system is still unsatisfactory and largely theoretical. Indeed, evolutionary biologists are still puzzled by the often dramatic variation of mating strategies within single species. Of particular concern is the extent to which environmental conditions shape patterns of variation and covariation of mating system components within species. Here, we address this concern in the common morning glory (Ipomoea purpurea) by taking advantage of an extensive dataset of floral traits, genetic estimates of selfing and inbreeding, and relevant environmental factors compiled for 22 populations of this species distributed along a disparate set of environments along Southeast and Midwest USA. Combining a powerful array of parametric and model-free statistical approaches, we robustly identify a set of natural and anthropogenic environmental factors underlying population-level variation in selfing, inbreeding, and flower morphology. Remarkably, individual mating system components are found to be associated with different environmental factors and only loosely associated with each other, and thus potentially under multiple different selective pressures. These results not only corroborate theoretical expectations of the significant role the environment plays in the local determination of mating systems, but also provide compelling evidence of complex underlying interactions between multiple evolutionary processes.

plant biology↗