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The tremendous variation in structure, number and arrangement of flowers pollinated by animals suggests adaptation to strong and diverse selection. Indeed, Darwin used flowers to refine his ideas about natural selection and evolution. My research program investigates floral diversity using perspectives from pollination biology and life-history evolution.
In recent years I have become interested in the community context of reproductive success and the balance between mutualistic and antagonistic relationships between interacting species. Much of this work involves threatened species and habitats.
Currently we are conducting research on:
See the three sections below for details.
The flowers of many plant species are visited by a wide variety of animals. These visitors may differ greatly in how much pollen they transfer, and some may consume pollen without contacting female sex organs. Historically, research in pollination biology has emphasized selection by one or a few effective pollinators, i.e. visitors that contribute to seed set. Recent interest has focused on the full range of visitors in natural populations.
Our model system for these studies is Polemonium brandegeei, a perennial herb native to the Rocky Mountains of Colorado and Wyoming. Visitors to Polemonium brandegeei flowers are diverse and include hummingbirds, hawkmoths, small bees and pollen-consuming syrphid flies.
Former Ph.D. student, Mason Kulbaba, used experimental populations to quantify natural selection on floral design by hummingbirds and hawkmoths in Polemonium brandegeei. Mason’s work suggested that some floral traits might “specialize” toward the optimum for one of the pollinators (e.g., width of the floral tube) whereas others may evolve toward a generalist “compromise” phenotype (e.g., female and male sex organs close together).
Former, B.Sc. Honour’s student, Jian-fei Shao, showed that prior deposition of sterile self-pollen may reduce outcrossed seed production. Thus his work confirmed a potential cost of having sex organs close together.
Current M.Sc. student, Dawn Wood, is working in natural populations to evaluate how pollen movement and seed production caused by large, nectar-foraging visitors (hawkmoths & hummingbirds) compares to the influence of smaller, pollen (and nectar) foraging bees and flies.
“Generalized food mimics” produce no nectar or pollen reward for visitors but have colours and scents similar to those in rewarding flowers. Because pollinators learn to avoid food mimics, visit rates and pollinator fidelity are often low, resulting in pollen limitation of fruit set and increased movement between species. The co-flowering community is particularly important for food mimics because rewarding flowers sustain pollinator populations, but may act as competitors on a local scale. Fruit set in food mimics may be enhanced by colour similarities to rewarding species, or earlier flowering than in rewarding species. The relative importance of these strategies is unknown.
In collaboration with Dr. Bruce Ford, we are studying how flower shape combines with the diversity of plants and pollinators to determine reproductive success in lady’s slipper orchids (Cypripedium). These rewardless orchids trap insect visitors in their slipper-shaped petal, and escape routes lead the insects past the sex organs. Our work to date has been on the threatened tall-grass prairie specialist, C. candidum, and widespread C. parviflorum.
Thesis research on this system has been conducted by former students Melissa Pearn (now Grantham, M.Sc.), Jessica Guezen, Kaman Choi, and Steven Anderson (Honours B.Sc.).
Current M.Sc. student, Steven Anderson, is surveying populations of C. candidum across a latitudinal gradient from Iowa to Manitoba. He will compare fruit set across populations in relation to the diversity and abundance of potential insect pollinators and co-flowering rewarding species. This work will begin to explore the potential for competition versus facilitation in this system.
Hybridization occurs between threatened tall grass specialist, C. candidum and widespread C. parviflorum where they co-occur and may be due to low pollinator fidelity in these food mimics. Genetic fingerprints in 16 populations confirmed first and later generation hybrids. Interestingly, these data indicated greater gene flow from the endangered to the widespread species. This work was with former summer student, Lauren Sawich, and research associate, Habib Ghazvini.
Pollination networks describe community wide interactions between plants and animal pollinators. Early work on networks (including theoretical treatments of community stability) involved qualitative descriptions of interaction patterns with the simplifying assumption that each visit from an animal to a plant has the same pollination benefit. Recent studies have begun to examine the validity of this assumption and implications of variation in visitor quality.
Former MSc student, Sarah Semmler described the short-term effects of fire pollination network structure by examining changes in plant and insect communities. Sarah also investigated how pollination services are affected by the identity and activity of pollinators. Sarah’s work was in Manitoba’s tall grass prairie, a critically endangered ecosystem.
This work was done in conjunction with CANPOLIN (Canadian Pollination Initiative), a strategic NSERC network.
Sara Halwas, Ph.D. Candidate (Individual Interdisciplinary Program: Biological Sciences & Anthropology). Thesis Title: Domesticating Chenopodium: applying genetic techniques & archaeological data to recreate prehistoric plant use.
Steven Anderson, M.Sc. Candidate (co-supervised with Dr. Bruce Ford). Thesis Title: Latitudinal variation in prairie communities and the reproductive success of rewardless orchids.
Dawn Wood, M.Sc. Candidate. Thesis Title: Selection by pollen consumers on floral traits in Polemonium brandegeei.
Sarah Semmler, M.Sc. 2016. Thesis title: Effects of fire on community diversity and plant-pollinator interactions in the tall grass prairie. Current position: Director, Living Prairie Museum, City of Winnipeg
Steven Anderson, B.Sc. Honours 2015 (co-supervised with Dr. Bruce Ford). Thesis title: Effective pollinators of two rewardless orchids, Cypripedium candidum and Cypripedium parviflorum, and the influence of floral characteristics on reproductive success. Current position: M.Sc. Candidate, University of Manitoba
Jian-fei Shao, B.Sc. Honours 2014. Thesis title: Sexual interference in Polemonium brandegeei. Current position: MSc. Candidate, University of Manitoba
Kaman Choi, B.Sc. Honours 2014. Thesis title: The effect of colour and two UV manipulation treatments on the floral longevity and reproductive success of Cypripedium parviflorum and Dasiflora fruticosa. Current position: B.Sc. Candidate, Faculty of Education, University of Manitoba
Jessica Guezen, B.Sc. Honours 2013. Thesis title: Short-term limitations to the reproductive output of two rewardless orchids. Current position: MSc. Candidate, University of Ottawa.
Melissa Pearn, M.Sc. 2013 (co-supervised with Dr. Bruce Ford). Thesis Title: Pollination and comparative reproductive success of Cypripedium candidum, Cypripedium parviflorum, and their hybrids in southern Manitoba. Current position: Assistant Conservation Biologist, Nature Conservancy of Canada, Manitoba Region.
Mason Kulbaba, Ph.D. 2012. Thesis Title: Floral evolution in Polemonium brandegeei (Polemoniaceae). Current position: postdoctoral fellow, University of Minnesota.