Jeffrey D. Karron Associate Professor B.A., Princeton Univ. 1981 Ph.D., Univ. of Colorado 1987 Postdoctoral Fellow Univ. of New Mexico 1988-90	Office: Lapham 585 Phone: 414-229-6003 FAX: 414-229-3926 Email: karron@uwm.edu Electronic Reserve Materials:
Pollination Ecology; Plant Evolutionary Ecology

Research Interests For publication list and PDF reprints, click here

Research in my lab group focuses on evolutionary processes occurring 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. In collaboration with Dr. Randy Mitchell (Univ. of Akron) we have studied how ecological factors, such as population density and the presence of competitors for pollination, and genetic factors, such as floral morpology and floral display size, influence selfing rates and patterns of paternity in monkeyflower (Mimulus ringens). At our study site in SE Wisconsin this wetland perennial is pollinated by five sympatric species of bumble bees (Bombus). Through the use of genetic markers to unambiguously determine paternity, we have developed an unparalleled data set documenting fine-scale variation in mating patterns. For example, we have discovered that adjacent flowers open on the same day differ strikingly in selfing rates and number of outcross pollen donors. Nearly all fruits are multiply sired, averaging 4.92 outcross donors per fruit. With support from the National Science Foundation we are exploring the following questions: All photos on this web page are copyrighted, and may not be copied, used in teaching or research presentations, or republished without written authorization from Jeffrey Karron. Pollinator images and multiple paternity figure by Jeffrey Karron; SEM of pollen grains by John Bell; image of field researchers by Pete Amland (UW-Milwaukee I&MT Visual Imaging). 1) What mechanisms are responsible for the high levels of multiple paternity observed in Mimulus ringens fruits? In Mimulus ringens multiple paternity results from two mechanisms. When a pollinator probes a flower, it deposits a mixture of pollen from 1-3 sires. Within 20 minutes of the first probe, a second pollinator often visits the same flower and deposits pollen from 1-3 additional pollen donors. See Karron et al. 2006 PDF. 2) Why do selfing rates of flowers from the same daily floral display vary so dramatically? Selfing rates of individual flowers are influenced by the amounts of within-flower (autogamous) and among-flower (geitonogamous) self-pollen deposited on stigmas. In a pollinator visitation sequence the first flower probed is predominantly outcrossed, with just 20% of the ovules fertilized by autogamy. Since pollen carryover is very limited, flowers visited sequentially receive increasing proportions of geitonogamous self pollen. Geitonogamous selfing rates are therefore highest on large floral displays. See Karron et al. 2004 PDF 3) How does floral display size influence patterns of pollinator visitation? Bumble bees strongly prefer large Mimulus ringens floral displays, and probe more flowers in sequence on large displays than on small displays. See Mitchell et al. 2004 PDF 4) How does floral display size influence male and female fitness? Analysis of total fertility through male and female function confirms that plants with larger displays mother and sire more seeds. However, siring success per flower declines sharply with increasing display size, while female success per flower does not vary with display. Total fitness per flower (accounting for greater expression of inbreeding depression with increased selfing rate) also declines strongly with floral display. 5) What is the extent of pollen carryover in Mimulus ringens? Dr. Karsten Holmquist demonstrated that pollen carryover is very limited in Mimulus ringens, and most genes are dispersed to the first five recipient flowers in the visitation sequence. Dr. Holmquist received his PhD in 2005 and is now a post-doctoral researcher at Univ. of Wisconsin-Madison. 6) How do competitors for pollination influence reproductive success and the mating system? Dr. John Bell demonstrated that the presence of Lobelia siphilitica, a competitor for pollination, leads to a 37% reduction in Mimulus seed set. In addition, Mimulus had a significantly lower rate of outcrossing when grown in competition with Lobelia. This is the first study to demonstrate that competition for pollination directly influences outcrossing rates. See Bell et al. 2005 PDF Dr. Bell received his PhD in 2004 and is now Vice President of Applied Ecological Services, one of the largest environmental restoration companies in North America. Rebecca Flanagan, a current doctoral student in my laboratory, is studying how multiple species interact when competing for pollinators. By establishing arrays with different combinations of Mimulus ringens, Lobelia siphilitica, and invasive Lythrum salicaria, she is exploring whether the effects of these competitors on Mimulus are additive or synergistic. She is also quantifying mechanisms of competition for pollination.

Selected Publications

KARRON, J. D., R. J. Mitchell, and J. M. Bell. 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, J. M., J. D. KARRON, and R. J. Mitchell. 2005. Interspecific competition for pollination lowers seed production and outcrossing in Mimulus ringens. Ecology 86: 776-785. PDF Mitchell, R. J., J. D. KARRON, K. G. Holmquist, and J. M. Bell. 2005. Patterns of multiple paternity in fruits of Mimulus ringens (Phrymaceae). American Journal of Botany 92: 885-890. PDF KARRON, J. D., R. J. Mitchell, K. G. Holmquist, J. M. Bell, and B. Funk. 2004. The influence of floral display size on selfing rates in Mimulus ringens. Heredity 92: 242-248. PDF Mitchell, R.J., J. D. KARRON, K. G. Holmquist, and J. M. Bell. 2004. The influence of Mimulus ringens floral display size on pollinator visitation patterns. Functional Ecology 18: 116-124. ARTICLE PDF       JOURNAL COVER PHOTO Linhart, Y. B., L. M. Ellwood, J. D. KARRON, and J. L. Gehring. 2002. Genetic differentiation in the dwarf mistletoes Arceuthobium vaginatum and Arceuthobium americanum on their principal and secondary hosts. International Journal of Plant Sciences 164: 61-69. Reinartz, G. E., J. D. KARRON, R. B. Phillips, and J. L. Weber. 2000. Patterns of microsatellite polymorphism in the range-restricted bonobo (Pan paniscus): considerations for interspecific comparison to chimpanzees (P. troglodytes). Molecular Ecology 9: 315-328 . KARRON, J. D. 1998. Genetic consequences of different patterns of distribution and abundance. Chapter 10 in The Biology of Rarity. W. E. Kunin and K. J. Gaston, eds. Chapman & Hall, London, pp. 174-189. KARRON, J. D., R. T. Jackson, N. N. Thumser, and S. L. Schlicht. 1997. Outcrossing rates of individual Mimulus ringens genets are correlated with anther-stigma separation. Heredity 79: 365-370. PDF Thumser, N. N., J. D. KARRON and M. S. Ficken. 1996. Interspecific variation in the calls of Spheniscus penguins. The Wilson Bulletin 108: 72-79. KARRON, J. D., R. Tucker, N. N. Thumser and J. A. Reinartz. 1995. Comparison of pollinator flight movements and gene dispersal patterns in Mimulus ringens. Heredity 75: 612-617. KARRON, J. D., N. N. Thumser, R. Tucker and A. J. Hessenauer. 1995. The influence of population density on outcrossing rates in Mimulus ringens. Heredity 75: 175-180. KARRON, J. D. and D. L. Marshall. 1993. Effects of environmental variation on fitness of singly and multiply sired progenies of Raphanus sativus (Brassicaceae). American Journal of Botany 80: 1407-1412. KARRON, J. D. 1991. Patterns of genetic variation and breeding systems in rare plant species. Chapter 6 in Genetics and Conservation of Rare Plants. D. A. Falk and K. E. Holsinger, eds. Oxford University Press, Oxford. KARRON, J. D. and D. L. Marshall. 1990. Fitness consequences of multiple paternity in wild radish, Raphanus sativus. Evolution 44: 260-268. KARRON, J. D. 1989. Breeding systems and levels of inbreeding depression in geographically restricted and widespread species of Astragalus (Fabaceae). American Journal of Botany 76: 331-340. KARRON, J. D., Y. B. Linhart, C. A. Chaulk and C. A. Robertson. 1988. Genetic structure of populations of geographically restricted and widespread species of Astragalus (Fabaceae). American Journal of Botany 75: 1114-1119.