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Current Research I am involved in a NSF-funded project investigating the mode of evolution within the white proteas, a monophyletic clade endemic to the Cape region of South Africa. Species in this clade include Protea aurea, P. lacticolor, P. punctata, P. mundii, P. venusta, and P. subvestita. Our research asks if these species diversified predominately through adaptive (habitat specialization) or non-adaptive (geographic isolation and drift) processes. This work is collaboration with the South African National Biodiversity Institute and Rachel Prunier, and the principal investigator is Kent Holsinger.
Our research methods combine field-based ecological measurements, common garden experiments, molecular data, and phylogenetic analyses. I am based part-time in Cape Town, collecting seeds and data in wild populations from 35 locations across the Western Cape, Eastern Cape, and KwaZulu-Natal and maintaining two common gardens. My focus has been on determining if among-population differences in vegetative traits are related to natural selection and local adaptation within the clade. By comparing selection gradients in the wild and between the common gardens, we have evidence that ecologically-based divergent selection maintains some of the differences in SLA, leaf area and growth among white protea populations.
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Independent postdoctoral research My side project explores how different flower-color morphs of the same species are able to persist side-by-side in Protea populations, which as a genus has 40% of species with co-occurring pink-flowered and white-flowered plants. By comparing traits of pink and white morphs in 10 populations of four species, we revealed the following differences. Although white-flowered plants generally produced heavier, more germinable seeds, pink-flowered plants were occasionally less susceptible to seed-eating larvae, perhaps because pink pigment is associated with toxic or distasteful secondary plant chemicals. Increased seed predation thereby offsets the benefits of producing higher quality seed for white morphs in some populations, and together these factors promote the maintenance of both morphs in a world where seed predator pressures likely vary over space and time.
Because trends were repeated across four species, we suggest that similar processes may also occur in other Proteas, placing a new emphasis on seed predators for influencing some of South Africa's amazing floral diversity.
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Ph.D. Research My dissertation research focused on the interactions between a Neotropical plant species and its floral enemies and pollinators. Chrysothemis friedrichsthaliana [Gesneriaceae] is a hummingbird-pollinated herb found in lowland rainforests throughout Central America. In one series of experiments, I linked floral rewards, pollinator behavior and plant reproductive success. My objective was to test adaptive hypotheses for male-biased nectar production, i.e., increased nectar production during the male relative to female phase of dichogamous flowers. Male-biased nectar production, as is seen in this and > 15 other species, results in variable floral rewards between flowers on a plant, as well as an increased incentive for pollinators to visit male-phase flowers. I demonstrated that in Chrysothemis, male-biased nectar production was partially explained by pollinator-mediated selection on traits that more strongly promote pollen removal as opposed to pollen delivery (i.e., sexual selection). I found limited evidence that selection to reduce geitonogamy could also contribute to the maintenance of the trait.
I also examined floral herbivory and the functional significance of the water calyx of C. friedrichsthaliana. The enlarged, cup-like calyx holds and secretes liquid, such that immature flowers develop under water. In a calyx draining experiment, I demonstrated that a highly detrimental microlepidopteran herbivore (Alucitidae), was partially deterred by the water-filled calyces, relative to calyces without water. These results suggest that the water calyx of Chrysothemis functions in part as a physical floral defense.
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