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Link to Jeff Karron's CV
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Ecology of plant-pollinator interactions
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Welcome to the Karron Lab!
Research in my lab focuses on evolutionary processes in flowering plant populations. My students and I are particularly interested in understanding how plant mating systems evolve and how patterns of pollinator visitation influence male and female reproductive success. Our field experiments explore how ecological factors, such as the presence of co-flowering species, and heritable traits, such as floral morphology and floral display size, influence selfing rates and patterns of paternity in monkeyflower (Mimulus ringens). At our study sites in Wisconsin and Ohio Mimulus ringens is pollinated by several sympatric bumble bee species (especially Bombus fervidus, Bombus impatiens, and Bombus vagans). Through the use of genetic markers to unambiguously determine selfing rates and siring success of individual plants, we have developed an unparalleled data set documenting fine-scale variation in plant mating systems. Our work has shown that selfing rates increase markedly with increasing floral display size, due to the effects of geitonogamous self-pollination. Fruits are typically sired by 3-5 donors, and this high level of mate diversity results both from simultaneous deposition of mixed pollen loads as well as subsequent visits bringing in additional donors not represented in the initial visit.
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A description of our NSF-funded research on the evolution of plant mating systems is provided below. Please see our Research page for descriptions of several additional projects in our Lab, including our research on pollinator conservation, which is especially relevant in light of recent declines of several bumble bee species in North America and Europe. In particular, we are investigating whether a sudden decline of the bumble bee Bombus griseocollis would influence Asclepias verticillata reproductive success. We also have studied how invasive plants, such as Lythrum salicaria (purple loosestrife), influence native plant pollination success (Flanagan et al. 2010). Negative effects of invasives on native plant reproductive success are especially likely when generalist pollinators foraging amongst native and non-native co-flowering species cause pollen loss due to grooming or to pollen misplacement on floral structures of the invasive species. We hope you will also visit our Pollination Gallery, which highlights the dynamics of the pollination process in both Mimulus and Asclepias. Our gallery includes SEM images showing interactions of Mimulus pollen grains as they germinate on the Mimulus stigma.
Does the presence and abundance of a co-flowering species change the pattern of selection on the mating system?
NSF collaborative awards 1654943, 1654967, 1654951 (Evolutionary Ecology Program)
A major conceptual challenge for evolutionary theory is the frequent occurrence of intermediate rates of self-fertilization in flowering plant populations. This pattern in nature is not consistent with classical genetic models, which predict that disruptive selection will cause intermediate selfing rates to be rare and transitory. Populations with low inbreeding depression should evolve predominant selfing because more maternal alleles are transmitted through self-fertilized seeds than through outcross seeds. By contrast, populations with high inbreeding depression should evolve predominant outcrossing because the transmission advantage of selfing is offset by inbreeding depression. Since populations with intermediate selfing rates are common, researchers have sought to develop and test models that explore conditions favoring stable mixed mating. Several models have highlighted the key role of tradeoffs between siring success and selfing. However, most models ignore a fundamental aspect of plant-pollinator interactions, which is that pollinator movements between species often waste pollen by depositing it on flowers of other species. Such pollen losses reduce outcross siring, increase selfing, and lower seed production, changing tradeoffs and altering selection. Community context can therefore be an important driver of plant mating system evolution, yet it remains largely unstudied.
Does the presence and abundance of a co-flowering species change the pattern of selection on the mating system?
NSF collaborative awards 1654943, 1654967, 1654951 (Evolutionary Ecology Program)
A major conceptual challenge for evolutionary theory is the frequent occurrence of intermediate rates of self-fertilization in flowering plant populations. This pattern in nature is not consistent with classical genetic models, which predict that disruptive selection will cause intermediate selfing rates to be rare and transitory. Populations with low inbreeding depression should evolve predominant selfing because more maternal alleles are transmitted through self-fertilized seeds than through outcross seeds. By contrast, populations with high inbreeding depression should evolve predominant outcrossing because the transmission advantage of selfing is offset by inbreeding depression. Since populations with intermediate selfing rates are common, researchers have sought to develop and test models that explore conditions favoring stable mixed mating. Several models have highlighted the key role of tradeoffs between siring success and selfing. However, most models ignore a fundamental aspect of plant-pollinator interactions, which is that pollinator movements between species often waste pollen by depositing it on flowers of other species. Such pollen losses reduce outcross siring, increase selfing, and lower seed production, changing tradeoffs and altering selection. Community context can therefore be an important driver of plant mating system evolution, yet it remains largely unstudied.
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In collaboration with Randy Mitchell (Univ of Akron), and Dorset Trapnell (Univ of Georgia), this study of Mimulus ringens (monkeyflower) combines empirical and theoretical investigations to test the hypothesis that interactions with co-flowering Lobelia siphilitica alter the evolutionary tradeoff between outcross siring and selfing. We are manipulating ecological context to determine whether a change in co-flowering species abundance shifts the pattern of natural selection on selfing rate in Mimulus ringens. To explore evolutionary response to ecological context and potential synergistic effects of changes in Mimulus floral display size, we are also quantifying selfing rates, pollen limitation, and inbreeding depression in natural populations of Mimulus that differ in ecological context and floral display.
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Prospective Students and Postdoctoral Researchers: Please contact me if you would like more information about our lab group or the Ecology, Evolution, and Behavior Group in the UWM Department of Biological Sciences. Also, here is information about the UWM campus, the UWM Field Station and the UWM Greenhouse.
Information about Jeffrey Karron's Professional service activities: I have edited four special issues of Annals of Botany, which has a longstanding tradition of excellence in the fields of Plant Reproductive Biology and the Ecology and Evolution of Plant Mating Systems: Plant-Pollinator Interactions (2009), Plant Mating Systems (2012), Pollinator-Driven Speciation (2014) and Ecology and Evolution of Plant Reproduction (2019). Here is a link to one of my talks at the Botanical Society of America:
Information about Jeffrey Karron's Professional service activities: I have edited four special issues of Annals of Botany, which has a longstanding tradition of excellence in the fields of Plant Reproductive Biology and the Ecology and Evolution of Plant Mating Systems: Plant-Pollinator Interactions (2009), Plant Mating Systems (2012), Pollinator-Driven Speciation (2014) and Ecology and Evolution of Plant Reproduction (2019). Here is a link to one of my talks at the Botanical Society of America:
Research publications: PDF reprints of my papers may be found both on Google Scholar and on Researchgate.
Selected Publications -- please see Publications page for complete list
Mitchell RJ, Starvaggi D, Fitzgerald V, and Karron JD. 2024. The timing of visits by large and small bees differentially affects pollination success in Mimulus ringens. American Journal of Botany, DOI: 10.1002/ajb2.16375 PDF
Shelton WR, Mitchell RJ, Christopher DA, Jack LP and Karron JD. 2023. Among‐individual variation in flowering phenology affects flowering synchrony and mating opportunity. AMERICAN JOURNAL OF BOTANY, doi.org/10.1002/ajb2.16269 Article Link
Christopher DA, Karron JD, Semski WR, Smallwood PA, Trapnell DW, Mitchell RJ. 2021. Selfing rates vary with floral display, pollinator visitation and plant density in natural populations of Mimulus ringens. JOURNAL OF EVOLUTIONARY BIOLOGY https://doi.org/10.1111/jeb.13781 PDF
Karron JD, Christopher DA and Semski WR. 2021. Pollen transport: Illuminating a key mechanism of disassortative pollination. CURRENT BIOLOGY 31: 893-895. PDF
Christopher DA, Mitchell RJ, Karron JD. 2020. Pollination intensity and paternity in flowering
plants, ANNALS OF BOTANY 125: 1–9. PDF
Christopher DA, Mitchell RJ, Trapnell DW, Smallwood PA, Semski WR, Karron JD. 2019. Hermaphroditism promotes mate diversity in flowering plants. AMERICAN JOURNAL OF BOTANY 106: 1131–1136. PDF
Minnaar C, Anderson B, de Jager ML, Karron JD. 2019. Plant-pollinator interactions along the pathway to paternity. ANNALS OF BOTANY 123: 225-245. PDF
Whitehead MR, Lanfear R, Mitchell RJ, Karron JD. 2018 Plant mating systems often vary widely among populations. FRONTIERS IN ECOLOGY AND EVOLUTION 6:38 PDF
Krauss SL, Phillips RD, Karron JD, Johnson SD, Roberts DG, Hopper SD. 2017. Novel consequences of bird pollination for plant mating. TRENDS IN PLANT SCIENCE 22: 395-410.
Hallett AC, Mitchell RJ, Chamberlain ER, Karron JD. 2017. Pollination success following loss of a frequent pollinator: the role of compensatory visitation by other effective pollinators.
AOB PLANTS 10.1093/aobpla/plx020 PDF
Sorin YB, Mitchell RJ, Trapnell DW, Karron JD. 2016. Effect of pollination and postpollination processes on selfing rate in Mimulus ringens. AMERICAN JOURNAL OF BOTANY 103: 1524-1528. PDF
Mitchell RJ, Wilson WG, Holmquist KG, Karron JD. 2013. Influence of pollen transport dynamics on sire profiles and multiple paternity in flowering plants. PLOS One 8(10) 1-7. PDF
Karron JD, Mitchell RJ. 2012. Effects of floral display size on male and female reproductive success in Mimulus ringens. ANNALS OF BOTANY 109: 563-570 PDF
Holmquist KG, Mitchell RJ, Karron JD. 2012. Influence of pollinator grooming on pollen-mediated gene dispersal in Mimulus ringens (Phrymaceae). PLANT SPECIES BIOLOGY 27: 77-85. PDF
Karron JD, Ivey CT, Mitchell RJ, Whitehead MR, Peakall R, Case AL. 2012. New perspectives on the evolution of plant mating systems. ANNALS OF BOTANY 109: 493-503. PDF
Nunziata SO, Karron JD, Mitchell RJ, Lance SL, Jones KL, Trapnell DW. 2012. Characterization of 42 polymorphic microsatellite loci in Mimulus ringens (Phrymaceae) using Illumina sequencing. AMERICAN JOURNAL OF BOTANY 99 (12) e 477-e480. PDF
Medrano M, Requerey R, Karron JD, Herrera CM. 2012. Herkogamy and mate diversity in the wild daffodil Narcissus longispathus: beyond the self-outcrossing paradigm in the evolution of mixed mating. PLANT BIOLOGY 14: 801-810. PDF
Flanagan RJ, Mitchell RJ, Karron JD. 2011. Effects of multiple competitors for pollination on bumblebee foraging patterns and Mimulus ringens reproductive success. OIKOS 120: 200-207. PDF
Flanagan RJ, Mitchell RJ, Karron JD. 2010. Increased relative abundance of an invasive competitor for pollination, Lythrum salicaria, reduces seed number in Mimulus ringens. OECOLOGIA 164: 445-454. PDF
Karron JD, Holmquist KG, Flanagan RJ, Mitchell RJ. 2009. Pollinator visitation patterns strongly influence among-flower variation in selfing rate. ANNALS OF BOTANY 103: 1379-1383. PDF
Flanagan RJ, Mitchell RJ, Knutowski D, Karron JD. 2009. Interspecific pollinator movements reduce pollen deposition and seed production in Mimulus ringens (Phrymaceae). AMERICAN JOURNAL OF BOTANY 96: 809–815. PDF
Mitchell RJ, Flanagan RJ, Brown BJ, Waser NM, Karron JD. 2009. New frontiers in competition for pollination. ANNALS OF BOTANY 103: 1403–1413. PDF
Karron JD, Mitchell RJ, Bell JM. 2006. Multiple pollinator visits to Mimulus ringens (Phrymaceae) flowers increase mate number and seed set within fruits. AMERICAN JOURNAL OF BOTANY 93: 1306-1312. PDF
Bell JM, Karron JD, Mitchell RJ. 2005. Interspecific competition for pollination lowers seed production and outcrossing in Mimulus ringens. ECOLOGY 86: 776-785. PDF
Mitchell RJ, Karron JD, Holmquist KG, Bell JM. 2005. Patterns of multiple paternity in fruits of Mimulus ringens (Phrymaceae). AMERICAN JOURNAL OF BOTANY 92: 885-890. PDF
Karron JD, Mitchell RJ, Holmquist KG, Bell JM, Funk B. 2004. The influence of floral display size on selfing rates in Mimulus ringens. HEREDITY 92: 242-248. PDF
Mitchell RJ, Karron JD, Holmquist KG, Bell JM. 2004. The influence of Mimulus ringens floral display size on pollinator visitation patterns. FUNCTIONAL ECOLOGY 18: 116-124. PDF
All images on this web site are protected by copyright. Please contact Jeff Karron if you would like to use them for non-commercial purposes.
Mitchell RJ, Starvaggi D, Fitzgerald V, and Karron JD. 2024. The timing of visits by large and small bees differentially affects pollination success in Mimulus ringens. American Journal of Botany, DOI: 10.1002/ajb2.16375 PDF
Shelton WR, Mitchell RJ, Christopher DA, Jack LP and Karron JD. 2023. Among‐individual variation in flowering phenology affects flowering synchrony and mating opportunity. AMERICAN JOURNAL OF BOTANY, doi.org/10.1002/ajb2.16269 Article Link
Christopher DA, Karron JD, Semski WR, Smallwood PA, Trapnell DW, Mitchell RJ. 2021. Selfing rates vary with floral display, pollinator visitation and plant density in natural populations of Mimulus ringens. JOURNAL OF EVOLUTIONARY BIOLOGY https://doi.org/10.1111/jeb.13781 PDF
Karron JD, Christopher DA and Semski WR. 2021. Pollen transport: Illuminating a key mechanism of disassortative pollination. CURRENT BIOLOGY 31: 893-895. PDF
Christopher DA, Mitchell RJ, Karron JD. 2020. Pollination intensity and paternity in flowering
plants, ANNALS OF BOTANY 125: 1–9. PDF
Christopher DA, Mitchell RJ, Trapnell DW, Smallwood PA, Semski WR, Karron JD. 2019. Hermaphroditism promotes mate diversity in flowering plants. AMERICAN JOURNAL OF BOTANY 106: 1131–1136. PDF
Minnaar C, Anderson B, de Jager ML, Karron JD. 2019. Plant-pollinator interactions along the pathway to paternity. ANNALS OF BOTANY 123: 225-245. PDF
Whitehead MR, Lanfear R, Mitchell RJ, Karron JD. 2018 Plant mating systems often vary widely among populations. FRONTIERS IN ECOLOGY AND EVOLUTION 6:38 PDF
Krauss SL, Phillips RD, Karron JD, Johnson SD, Roberts DG, Hopper SD. 2017. Novel consequences of bird pollination for plant mating. TRENDS IN PLANT SCIENCE 22: 395-410.
Hallett AC, Mitchell RJ, Chamberlain ER, Karron JD. 2017. Pollination success following loss of a frequent pollinator: the role of compensatory visitation by other effective pollinators.
AOB PLANTS 10.1093/aobpla/plx020 PDF
Sorin YB, Mitchell RJ, Trapnell DW, Karron JD. 2016. Effect of pollination and postpollination processes on selfing rate in Mimulus ringens. AMERICAN JOURNAL OF BOTANY 103: 1524-1528. PDF
Mitchell RJ, Wilson WG, Holmquist KG, Karron JD. 2013. Influence of pollen transport dynamics on sire profiles and multiple paternity in flowering plants. PLOS One 8(10) 1-7. PDF
Karron JD, Mitchell RJ. 2012. Effects of floral display size on male and female reproductive success in Mimulus ringens. ANNALS OF BOTANY 109: 563-570 PDF
Holmquist KG, Mitchell RJ, Karron JD. 2012. Influence of pollinator grooming on pollen-mediated gene dispersal in Mimulus ringens (Phrymaceae). PLANT SPECIES BIOLOGY 27: 77-85. PDF
Karron JD, Ivey CT, Mitchell RJ, Whitehead MR, Peakall R, Case AL. 2012. New perspectives on the evolution of plant mating systems. ANNALS OF BOTANY 109: 493-503. PDF
Nunziata SO, Karron JD, Mitchell RJ, Lance SL, Jones KL, Trapnell DW. 2012. Characterization of 42 polymorphic microsatellite loci in Mimulus ringens (Phrymaceae) using Illumina sequencing. AMERICAN JOURNAL OF BOTANY 99 (12) e 477-e480. PDF
Medrano M, Requerey R, Karron JD, Herrera CM. 2012. Herkogamy and mate diversity in the wild daffodil Narcissus longispathus: beyond the self-outcrossing paradigm in the evolution of mixed mating. PLANT BIOLOGY 14: 801-810. PDF
Flanagan RJ, Mitchell RJ, Karron JD. 2011. Effects of multiple competitors for pollination on bumblebee foraging patterns and Mimulus ringens reproductive success. OIKOS 120: 200-207. PDF
Flanagan RJ, Mitchell RJ, Karron JD. 2010. Increased relative abundance of an invasive competitor for pollination, Lythrum salicaria, reduces seed number in Mimulus ringens. OECOLOGIA 164: 445-454. PDF
Karron JD, Holmquist KG, Flanagan RJ, Mitchell RJ. 2009. Pollinator visitation patterns strongly influence among-flower variation in selfing rate. ANNALS OF BOTANY 103: 1379-1383. PDF
Flanagan RJ, Mitchell RJ, Knutowski D, Karron JD. 2009. Interspecific pollinator movements reduce pollen deposition and seed production in Mimulus ringens (Phrymaceae). AMERICAN JOURNAL OF BOTANY 96: 809–815. PDF
Mitchell RJ, Flanagan RJ, Brown BJ, Waser NM, Karron JD. 2009. New frontiers in competition for pollination. ANNALS OF BOTANY 103: 1403–1413. PDF
Karron JD, Mitchell RJ, Bell JM. 2006. Multiple pollinator visits to Mimulus ringens (Phrymaceae) flowers increase mate number and seed set within fruits. AMERICAN JOURNAL OF BOTANY 93: 1306-1312. PDF
Bell JM, Karron JD, Mitchell RJ. 2005. Interspecific competition for pollination lowers seed production and outcrossing in Mimulus ringens. ECOLOGY 86: 776-785. PDF
Mitchell RJ, Karron JD, Holmquist KG, Bell JM. 2005. Patterns of multiple paternity in fruits of Mimulus ringens (Phrymaceae). AMERICAN JOURNAL OF BOTANY 92: 885-890. PDF
Karron JD, Mitchell RJ, Holmquist KG, Bell JM, Funk B. 2004. The influence of floral display size on selfing rates in Mimulus ringens. HEREDITY 92: 242-248. PDF
Mitchell RJ, Karron JD, Holmquist KG, Bell JM. 2004. The influence of Mimulus ringens floral display size on pollinator visitation patterns. FUNCTIONAL ECOLOGY 18: 116-124. PDF
All images on this web site are protected by copyright. Please contact Jeff Karron if you would like to use them for non-commercial purposes.
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Dr. Jeffrey Karron Professor of Biology Department of Biological Sciences P.O. Box 413 University of Wisconsin-Milwaukee Milwaukee, WI 53201 USA [email protected] |