Mark Rausher - US grants

Although it is widely accepted that plant characters such as secondary chemistry, trichomes, and tough leaves have evolved primarily as defenses against herbivores, particularly insects, little direct evidence exists indicating that herbivorous insects impose natural selection on such resistance traits. the goal of the research proposed here is to determine whether insects exert natural selection on genetic variation for resistance in the morning glory, Ipomoea purpurea. The basic technique will be to examine how the experimental removal of four types of insects (the corn earworm, flea beetles, tortoise beetles, and generalist folivores) affects the magnitude of selection these insects impose on resistance to herbivory. In addition, whether resistance is due at least in part to tolerance or compensation (the ability of a plant to maintain a constant seed production despite herbivory) will be determined. Finally, the physiological and morphological characters that are responsible for resistance in insects in I. purpurea will be identified. Once these characters are known, whether and how insects exert selection on such characters will be examined.

9318919 Rausher Genetic variation is the raw material for evolutionary change. Consequently, understanding the processes that produce and maintain genetic variation in natural populations is a requisite for understanding how, and at what rate, organisms evolve. In addition, understanding how genetic variation is maintained in natural populations may contribute to the development of strategies for conserving genetic diversity in natural ecosystems. Over the last thirty years, numerous investigations have indicated that natural populations of organisms harbor extensive amounts of genetic variation. Nevertheless, although theoretical investigations have indicated that there are more than a dozen processes that could maintain these levels of genetic variation in natural populations, very few definitive examples of any of these processes exist. Consequently, understanding of why organisms are so genetically variable is at best rudimentary. The purpose of this research is to address this issue using flower color variation in the annual morning glory, Ipomoea purpurea, as a model system. In particular, the goal of this project is to determine why genetic variation for flower color persists in natural populations of this species. Through a series of field and laboratory experiments, the evolutionary forces that act on a gene that influences the intensity of pigmentation (the W locus) at all stages of the life cycle will be assessed. From these assessments, a determination will be made of which, if any, of the theoretically described processes for maintaining genetic variation operate on this character.***

9322462
Rausher

Plants display and impressive array of characters thought to defend them against attack by herbivores and pathogens. Many biologists have interpreted the principal function of these plant resistance characters to be the defense of the plant against its natural enemies. However, others have suggested that these resistance characters serve other functions and that the effects of these characters on herbivores are incidental. Despite this ambiguity, the interaction between herbivores and plant resistance characters has played a critical role in the development of theories on the coevolution of plants and herbivores.
Two assumptions mark theories on the evolution of plant resistance characters such as secondary chemicals and trichomes (1) resistance has evolved primarily as a defense against natural enemies of plants and (2) resistance is costly in terms of fitness to the plant. Neither of these assumptions has been adequately tested. This research aims to test these assumptions using both laboratory strains and natural populations of the annual plant, Arabidopsis thaliana (Brassicaceae), in both the field and a growth chamber. In particular, this research will use quantitative genetical techniques to determine: (1) whether herbivorous insects and pathogens exert selection on genetic variation for resistance and (2) whether resistance characters are evolutionarily costly. The results of this research will shed light on the mechanisms of the evolution of resistance in plants to herbivores and pathogens.

9707223 Rausher The goal of this project is to attempt to understand the degree to which a model organism, the morning glory Ipomorea purpurea, is optimally adapted to various environments it encounters. Specifically, this project seeks to characterize empirically the optimal value for several traits in different environments and then determine whether natural populations have evolved to exhibit those values in the respective environments. The project also seeks to characterize any constraints that may prevent populations from evolving to those optimal values. Characteristics of the range of natural environments normally encountered by I. purpurea will initially be surveyed. Using this information, two field experiments will be conducted in which I. purpurea is grown either a gradient of soil nutrient levels or a gradient of competitive intensity. The pattern of natural selection acting on traits related to plant growth and size will be measured to determine how far the means of these traits are from their optima in each environment. A set of breeding and selection experiments will provide a characterization of any genetic constraints acting to prevent evolution toward these optima, and the importance of these constraints will be evaluated by computer simulation. Evolution by natural selection is a compromise between what is favored (how selection acts) and what is possible (determined by the genetics of organisms). While biologists have made great strides understanding evolution in model organisms (e.g. fruit flies) living in simple, controlled environments, much less is known about the evolutionary responses of plant and animal populations to complex natural environments. The broad aim of this project is to begin to provide an understanding of such a response in an organism that typically encounters a complex environment.

9701330 Rausher The response of plants to herbivory has long been of interest to biologists. The majority of work in this area has focused on how plants defend themselves against herbivores - plant "resistance". However, plants may also tolerate herbivory (i.e. minimize the effect that herbivory has on productivity). Although plant tolerance to herbivore damage may dramatically alter how biologists think about plant-herbivore interactions, little is known about the ecology or genetics of tolerance. We will use field experiments and quantitative genetics to study the tolerance of the common morning glory, Ipomoea purpurea, to three types of herbivore damage. Specifically, we will i) measure genetic variation for tolerance, ii) characterize the genetic relationship between tolerance and other ecologically important traits, including resistance, and iii) measure the relationship between tolerance and plant productivity. The study of plant tolerance to herbivory may have important implications for agriculture. Herbivores are a major problem in modern agriculture leading to loss of productivity and requiring large inputs of expensive and environmentally harmful pesticides. Developing strains of crop plants that are more tolerant of herbivory may minimize the need to eliminate herbivore pests and therefore may contribute to more economically and environmentally sustainable agriculture. This study will provide important information on the genetics and ecology of tolerance which will be necessary for evaluating the role that plant tolerance may have in agricultural systems.

Rausher 9800876 Mutualisms are ecological interactions between species in which both species benefit from the interaction. This project will evaluate the assumptions and predictions of the cost-benefit framework for the extrafloral nectar-mediated mutualism between ants and Chamaecrista fasciculata, the partridge pea. A field experiment will evaluate four assumptions: 1) the mutualistic trait (extrafloral nectar) is costly to provide, 2) the extrafloral nectar provides a benefit through reduction of herbivore damage by ants attracted to the nectar, 3) the balance of costs and benefits produces stabilizing selection favoring an intermediate optimum, and 4) manipulation of costs and benefits should change the value of the selective optimum. In addition, this project will assess whether the cost-benefit framework can explain geographic variation in extrafloral nectar traits in C. fasciculata. Geographic variation in the trait will be surveyed, and the hypothesis that variation between populations is consistent with the presence of different selective optima will be tested using a reciprocal transplant experiment. Mutualisms are ubiquitous, but theoretical and mechanistic understanding of the processes that underlie them has progressed slowly. Of the models that have been used to explain the evolution of mutualisms, the cost-benefit approach is the most general and the most appropriate framework for understanding the evolution of adaptive traits involved in mutualisms. This project will evaluate the assumptions and predictions of the cost-benefit approach in regard to a mutualism between ants and a common annual plant of the eastern United States, Chamaecrista fasciculata (the partridge pea). Data from this project should provide an important empirical basis for future discussion of the pattern of selection on mutualistic traits.

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Rausher

While physical and chemical defenses provide plants with immunity from nearly all of the potential natural enemies in their environment, most plants are still attacked by a community of herbivores that are able to overcome these defenses. A major question in evolutionary ecology is what prevents plants from evolving improved resistance to herbivory. The thesis of this research is that there are potential constraints on the evolution of resistance that are revealed only by examining the entire community of herbivores that feed on a host plant. Through a series of field experiments using the insect herbivore community of horsenettle (Solanum carolinense), this research will investigate these constraints by assessing genetic variation for resistance, characterizing natural selection acting on resistance, and investigating the ecological interactions among the insects and their host plant.

This research addresses basic scientific questions regarding plant-herbivore coevolution and the nature of potential competition among plant-eating insects. In addition, horsenettle is an economically important weed, and its close kinship with a number of crop species enables it to act as a reservoir for a number of crop pests. Therefore, this research will also provide information that is of interest to weed control and pest management programs.

Rausher
0107172

Natural populations of the tall morning glory (Ipomoea purpurea) are commonly infected by a fungal pathogen, Coleosporium ipomoeae. This plant has a single gene with two alleles that condition either complete resistance or susceptibility to infection. Both alleles are represented in natural populations of the tall morning glory, a pattern found in many wild plant species. This observation contradicts the intuitive prediction that an allele providing resistance against a harmful pathogen should approach a frequency of one. Hypotheses proposed to explain the resistance/susceptibility allele paradox suggest the net benefit of a resistance allele is mediated by inherent costs when the pathogen population is dynamic. This project will use field experiments to explore the potentially conditional benefits of the resistance allele in the tall morning glory.

This work attempts to explain how natural selection may act to maintain genetic variation using the resistance/susceptibility allele paradox as a case study. In addition to contributing to the resolution of a fundamental issue in evolutionary biology, this work may also have applications to crop breeders who have historically incorporated resistance alleles from the wild progenitors of crop plants. As many countries become increasingly skeptical of transgenic crops, there is a renewed need to understand how natural selection acts on resistance alleles in natural populations, both to better utilize current resistant crops and to better conserve the natural resource that resistance alleles represent.

Most investigations of molecular evolution examine single genes, without respect to their interactions with other genes. However, most genes do not act in isolation, but interact with many other genes, which are likely to influence each other's evolution. One goal of this project is to determine whether and how such interactions actually cause predictable variation among genes in their rates of evolution. Specifically, genes of the anthocyanin pigment pathway in morning glories (genus Ipomoea) will be examined to determine whether observed evolutionary rate variation is due to differences in selective constraint (i.e. whether genes downstream in the pathway are less subject to purifying natural selection because they influence fewer characters). A second goal of this project is to begin examining the relative importance of regulatory and structural genes in adaptive divergence between species by determining the molecular basis of phenotypic divergence. The long-term goal of this project is to examine a large number of species whose color pattern has diverged from the presumed ancestral type of cyanidin-based blue/purple pigmentation throughout the corolla limb and throat. For each species the relative contribution of structural and regulatory genes to divergence will be determined. However, the current objective is more limited: to characterize the genetic changes that have resulted in the production of white flowers by two species, I. alba and I. igualensis. Initially, investigation will concentrate on these two species to demonstrate the feasibility of the proposed approach.

Rausher
0107172

Natural populations of the tall morning glory (Ipomoea purpurea) are commonly infected by a fungal pathogen, Coleosporium ipomoeae. This plant has a single gene with two alleles that condition either complete resistance or susceptibility to infection. Both alleles are represented in natural populations of the tall morning glory, a pattern found in many wild plant species. This observation contradicts the intuitive prediction that an allele providing resistance against a harmful pathogen should approach a frequency of one. Hypotheses proposed to explain the resistance/susceptibility allele paradox suggest the net benefit of a resistance allele is mediated by inherent costs when the pathogen population is dynamic. This project will use field experiments to explore the potentially conditional benefits of the resistance allele in the tall morning glory.

This work attempts to explain how natural selection may act to maintain genetic variation using the resistance/susceptibility allele paradox as a case study. In addition to contributing to the resolution of a fundamental issue in evolutionary biology, this work may also have applications to crop breeders who have historically incorporated resistance alleles from the wild progenitors of crop plants. As many countries become increasingly skeptical of transgenic crops, there is a renewed need to understand how natural selection acts on resistance alleles in natural populations, both to better utilize current resistant crops and to better conserve the natural resource that resistance alleles represent.

Flower color is an important ecological trait because it is used by plants to attract pollinators. Differences in flower color between species of Ipomoea (morning glories) will often lead to the presence of different sets of pollinators and a lack of pollen exchange. In order to understand the genetic basis for differences in flower color, one can study the major biosynthetic genes that produce flower pigments. Differences in these genes should be manifest as differences in DNA sequence, expression level, or expression time. A combination of crossing studies, DNA sequencing, and gene expression assays will be used to identify the gene or genes responsible for flower differences between two closely related species of Ipomoea: the white-flowered I. lacunosa and the purple-flowered I. triloba.
The number and type of mutations fixed during adaptive evolution is a long-standing question in biology. Recent work has suggested that, contrary to longstanding views, only a few mutations of large effect may be involved in adaptation. Furthermore, with increasing evidence of the conservation of most proteins over long time periods, it has been suggested that important mutations may occur primarily in regulatory sequences. In order to address these issues, the genetic basis of flower color differences between I. lacunosa and I. triloba will be examined.

Self-fertilizing species have evolved repeatedly from outcrossing ancestors in a number of plant species. Despite the long history of work on plant mating system evolution, however, there are major gaps in the understanding of the ecological context in which this evolutionary transition occurs. Several hypotheses link the evolution of self-fertilization to environmental conditions. One such hypothesis suggests that self-fertilization can be advantageous when two species co-occur and compete for shared pollinators, as a means of reducing reliance on such pollinators or as an isolating mechanism to prevent gene flow between them. The purpose of the proposed work is to examine this hypothesis in the two morning glory species Ipomoea hederacea and I. purpurea.

The significance of self- and cross-fertilization has interested evolutionary biologists from Darwin's time to the present. The proposed research will be a step towards a greater understanding of the transition between these two reproductive modes. The competitive interaction between I. hederacea and I. purpurea will be used as a model to examine the role self-fertilization may play as a reproductive isolating mechanism, and to address more mechanistic questions about the specific conditions under which competition for pollination is likely to favor self-fertilization.

This research by Dr. Mark Rausher and David Des Marais seeks to understand what happens over evolutionary time when an organism has two copies of the same genetic material. The general logic is that if, historically, an organism only needs one copy of a gene to survive, then a second copy of the same gene will be unnecessary. Three general fates have been proposed for what might happen to these duplicated pairs: one copy might keep functioning as it did as a single copy while the second copy experiences mutations that either cause it to lose function or to gain novel function, or the two copies might end up sharing the ancestral functions and thereby both become necessary for the organism's survival. These latter two fates provide a rich source for the origin of new features that lead to an increase in biological diversity.

The proposed research is valuable to the scientific community because it will help explain some of the findings of recent genome sequencing projects; namely, why do duplicate genes persist and what are they doing? The project will also help to expand interest in exploring natural observations using a scientific approach through training high school and college students who routinely spend summers in our laboratory.

It has been long recognized that the success of a mating type depends on its frequency in the population. Although a few empirical examples of frequency-dependent selection exist, its general importance in the evolutionary dynamics of plant mating has yet to be documented. The proposed study will use Solanum carolinense, a species that carries both male and hermaphroditic flowers within individuals, as a model system to answer: i) What is the pattern of selection acting through both female and male components of fitness on the relative production of male flowers? ii) Is selection acting on this trait frequency-dependent, as predicted by theory? iii) If so, does this frequencydependent selection explain the maintenance of intermediate proportions of male flowers in natural populations? These questions will be addressed through a combination of field and greenhouse experiments, and genetic fingerprinting of individual plants.

The intellectual merit of this proposal is to test a fundamental prediction in sexual theory, i.e. that selection on male-biased allocation is frequency-dependent, thus contributing information needed for a more thorough understanding of plant mating systems. The broader impact of this project will enhance the academic community by encouraging the participation of diverse groups, particularly undergraduate and Latino students with an interest in science.

This project is an extension of previous findings that strongly suggest that adaptive evolution of flower color in a species of morning glory, Ipomoea quamoclit, is accompanied by degeneration of part of the anthocyanin pigment pathway. The primary objectives of this project are (1) to determine definitively whether such pathway degeneration has occurred in I. quamoclit, and (2) to determine how general an evolutionary phenomenon such degeneration is. Pathway degeneration will be assessed by using in vitro enzyme assays and in vivo complementation assays to determine whether individual genes in the pathway retain their ancestral function. Phylogenetic analyses and ancestral state reconstruction will be used to determine whether some loss-of-function substitutions occurred after the adaptive transition shift in pigmentation, as would be expected if those substitutions reflect pathway degeneration. In addition to examining I. quamoclit and closely related red-flowered species in more detail, we will also assess whether anthocyanin pigment pathway degeneration has occurred in white-flowered morning glories in the Calonyction group, and in the model species Arabidopsis thaliana, in which only blue and not red anthocyanins are produced.

A general principle in evolutionary biology is that evolutionary loss of characters is often permanent. While many investigations have documented this pattern, little is known about why character loss is irreversible. The general scientific importance of this research is that it seeks to evaluate, and provide mechanistic justification for or against, the hypothesis that irreversibility results from the evolutionary breakdown of complex characters that are not currently used.

Coevolution between organisms and their enemies is a widespread phenomenon that may contribute to the generation of biological diversity. The genetic mechanism believed to underlie relationships between plants and their enemies, termed the gene-for-gene concept, is thought to involve pairwise interactions of plant genes and herbivore genes. The genetics of a natural plant-fungus (host-parasite) system will be examined to determine whether the evolution of resistance in this system is accurately described by the gene-for-gene model of plant-pathogen coevolution. Prior research on the pathology of this system will serve as a starting point for characterizing the genetic basis of resistance. Additional insight will be gained because the system includes multiple host species, providing a more realistic multispecies context for host-pathogen coevolution.
Though the genetics of coevolution has been studied in many agricultural plant systems, few such interactions have been studied in natural systems. Understanding the mechanisms and impacts of natural plant-pathogen coevolution should help in the development of strategies for long term maintenance of resistance, which will become ever more important as cultivation becomes increasingly globalized, and as human activity results in increased introduction of natural pathogens to endangered or cultivated plant populations.

Many genetic changes affect several different traits, and the same locus can have both benefits and costs, realized through its effects on different traits. This study combines molecular genetic and field experimental techniques to investigate the genetic and ecological basis of a flower color polymorphism in the Texas wildflower Phlox drummondii. Most P. drummondii have blue flowers caused by the production of anthocyanins, which are produced by a biochemical pathway that is common in plants. Anthocyanins, which are also produced throughout plants' vegetative tissue, are believed to have other effects, including defense against herbivores and protection from UV damage. White-flowered P. drummondii lack anthocyanin. This study will determine the genetic basis of the white flower color and investigate the environmental effects of anthocyanin levels that are related to traits other than flower color.

This study has implications for understanding novel adaptation and the maintenance of biodiversity. The project will provide diverse research-based training for the graduate student CoPI and for undergraduate and high school students that the CoPI will mentor and train

This project will examine the evolutionary processes responsible for flower-color divergence between populations of Phlox drummondii in areas with and without the closely related P. cuspidata. This divergence represents one of the best purported cases in plants of reproductive character displacement, in which two similar species with overlapping ranges evolve to minimize the amount of hybridization due to selection against gamete wastage. Combining both measures of individual fitness and analysis of patterns of molecular variation in the genes responsible for the flower-color change, the planned experiments will test whether this divergence satisfies a set of criteria for character displacement that have been developed over the past two decades, and thus determine whether this divergence truly constitutes character displacement. They will also test alternative explanations for the observed divergence, including local adaptation to an environmental factor unrelated to interaction with P. cuspidata.

An integral component of the research program outlined here is the teaching and training of students at a variety of educational levels. Funds are explicitly requested to support the training of one postdoctoral fellow and one graduate student. As in the past, undergraduates will be actively engaged in this research, both as Independent Study students during the academic year, and as summer research assistants. At the high school and undergraduate levels, women and minorities under-represented in science will be targeted for training in research.

When a particular evolutionary change, such as a color, has evolved independently in related organisms, the change could be due to a mutation in the same stage of a developmental pathway in all the groups, or it could be due to different mutations. The PIs will examine this problem by using the wildflower genus Penstemon, which is made up of nearly 300 species, most of which have blue or purple flowers. However, bright red flowers are found in about 15-20 subgroups, and these changes evolved independently at least 10 times. The red flowers are probably an adaptation to attract hummingbirds as pollinators. The biochemical pathway that produces the types of flower pigments found in Penstemon is well-understood. The PIs intend to test whether these repeated or parallel episodes of adaptive evolution are due to similar genetic changes across subgroups of plants or different genetic changes in different subgroups. This study is one of a very few that addresses the genetic basis of parallel evolution, and whether certain types of genetic changes are more often observed to underlie adaptive evolution than others. Furthermore, it will address the broader question of whether the genetic basis of adaptive evolution is predictable or unpredictable.

The PIs are integrating mentorship of local high school and Duke University undergraduate students into this project. This study system provides a clear and easily described example of parallel adaptive evolution; the PIs will work towards developing it as a potential textbook example for understanding the genetic basis of parallel evolution.

This project will test five evolutionary explanations for why plants self-pollinate, which will deepen our understanding of an important characteristic of plant evolution and will improve our breeding of self-pollinating crops such as tomatoes, corn and soybeans. Plants reproduce in a variety of ways, and 10-15% of plant species are primarily self-pollinating. The evolutionary transition from outcrossing to selfing is often accompanied by reductions in many floral traits. The researchers will determine the genetic bases for these changes in the morning glory. The study species are closely related to the sweet potato, a key global food resource that has proven challenging for modern selective breeding. Genetic resources developed in this study may help in the creation of more vigorous and disease-resistant sweet potatoes.

The transition to selfing is often accompanied by reductions in flower size, nectar production, pollen-ovule ratio, pigmentation, and the distance between the anther and stigma, collectively called the selfing syndrome. Five models of selfing syndrome evolution (resource allocation, marginal environment and florivory, efficiency of autogamous selfing, and general size reduction in response to inbreeding depression) will be tested by a combination of field and greenhouse experiments. Researchers will develop hybrid backcrossed lines between the morning glory species Ipomoea lacunosa, a selfing species, and its sister species, I. cordatotriloba, which both outcrosses and self-pollinates. The project will determine (1) whether traits in I. lacunosa characteristic of the selfing syndrome evolved in response to direct selection or were correlated responses to selection on other traits and, (2) what selective pressures encourage the adoption of the selfing syndrome. The investigators will measure selection on three selfing syndrome traits (pollen number, nectar volume, and corolla size) in a field experiment comprising 2400 individuals from a set of nearly isogenic lines and wild-type controls. Fitness will be assessed through three proxy measures: survival after transplant, seed set, and outcross paternity.

Ecosystem health and productivity depend on co-evolved species interactions. In terrestrial ecosystems a key interaction is between flowers and pollinators, and changes in the relative abundances of different pollinators (e.g., bees, birds) are thought to impose selective pressures that can shift floral pollination strategies and shape flowering plant communities. However, multiple forces may act to constrain the ability of a flowering plant lineage to evolve a new pollination strategy under changing environmental conditions. This research will model the rate of pollination strategy transitions in the largest flowering plant genus endemic to North America (Penstemon), and will determine both ecological and genetic processes that constrain and shape the rate of pollination strategy diversification. Understanding the forces that maintain diversity in pollination strategies informs food security and agricultural management issues.

The research integrates phylogenetic, ecological, and genetic approaches to understand the processes that determine pollination diversity. The research will test whether Penstemon has reached an evolutionary equilibrium in the relative frequencies of bee and hummingbird pollination syndromes. Additionally, the planned experiments will determine ecological and genetic processes responsible for asymmetries in pollination syndrome transitions, and in syndrome-specific speciation, and extinction rates. Field experiments will test whether interactions among floral traits constrain shifts from hummingbird to bee pollination. Genetic experiments will test whether loss-of-function mutations critical for shifts to hummingbird pollination also constrain reverse shifts from hummingbird to bee pollination. The integration of these experimental approaches will elucidate processes that determine pollination syndrome diversity in plant community assemblages.

This project examines the extent to which evolutionary change is predictable. In particular, it will test the hypothesis that different species that evolve similar characteristics do so by changes in the same genes. This hypothesis will be examined using species in the plant genus Penstemon that have independently evolved a similar suite of floral characters (e.g. long, narrow flowers, increased nectar production, lengthening of the reproductive organs) in response to pollination by hummingbirds. If this hypothesis is true, then in different hummingbird-pollinated species, genes affecting a given character should be located at similar positions in the genome. The project will test this expectation using genetic and genomic approaches applied to four hummingbird-pollinated species and closely related species pollinated by bees. In addition, this research will determine the developmental basis (e.g. changes in cell size or cell proliferation) for the character changes. In examining the main hypothesis, the project will sequence the genomes of three Penstemon species and provide genetic maps. These resources will be made available to the scientific community. The project will provide training for one postdoc and several graduate students in molecular and genomic techniques, as well as in bioinformatics and statistical analysis. Finally, it will introduce undergraduate students to the sciences of evolutionary biology and genomics through internships and independent study with the PI and co-PI of the project, with a focus on minority student participation.

This project examines parallelism across different hierarchical levels (developmental vs. genetic), across different trait types within the pollination syndrome (quantitative vs. qualitative traits), and across different origins of flowers adapted to hummingbird pollination. In doing so, it will provide the first extensive data specifically designed to determine the extent to which parallel phenotypic evolution of a complex multi-trait syndrome, comprised of multiple quantitative characters, evolved by parallel genetic and developmental mechanisms. Penstemon species pairs representing four independent transitions from bee to hummingbird pollination floral syndromes will provide the foundation of this research. For each of the four species pairs, the developmental differences that lead to divergent bee and hummingbird-adapted floral morphologies will be assessed to determine whether differences reflect parallel developmental processes. For the same four species pairs, genetic mapping combined with genome sequencing will be used to assess whether quantitative floral trait loci identified in independent transitions to hummingbird pollination correspond to homologous genomic regions containing the same set of homologous candidate genes, suggestive that parallelism extends to the genetic level. As few studies have examined genetic parallelism in quantitative traits, the project includes the development of a novel 'genetic parallelism score' to quantify the degree of genetic parallelism for both quantitative and qualitative traits. Lastly, by quantifying developmental parameters in genetic lines derived from the mapping study, the project will link genetic and developmental processes by determining how fixed genetic differences between bee- and hummingbird-adapted species alter the specific developmental processes that contribute to divergent floral traits.