Professor Thomas J. Givnish

Adaptive radiation, phylogenetic reconstruction, and historical biogeography
Adaptive radiation - the rise of a diversity of ecological roles within a lineage - is a major focus of research. My colleagues, students, and I use variation in DNA sequences, restriction sites, and AFLPs to derive phylogenies for groups of related species, and then use these family trees to reconstruct patterns of morphological evolution and geographic speciation. We are studying the pattern and tempo of speciation and adaptive divergence in Hawaiian lobeliads, South American bromeliads and rapateads, Australian Banksia and Dryandra, and North American Calochortus and Platanthera. I am coordinating efforts by Chris Pires, Sean Graham, and several other colleagues to produce an ndhF phylogeny of the monocots and use it to trace the repeated evolution of net venation and fleshy fruits upon invasion of shaded habitats. We have found that both traits evolved independently more than 20 times, almost always in association with shade and often in association with each other. The tempo of adaptive shifts appears to have declined exponentially over the past 90 million years, as would be expected as the monocot radiation began to "fill" open and shaded habitats on different continents around the world. Paul Berry, Ken Sytsma, and I are investigating the congruence between phylogeny and geography in several plant groups with species restricted to individual tepuis of the Guayana Shield, with special focus on Bromeliaceae and Rapateaceae. We are now organizing an international effort to derive a fully resolved, well-supported, multi-gene phylogeny for Bromeliaceae. Results from the first set of analyses, based on ndhF alone, resolve several new subfamilies and indicate that the genera of this large family have differentiated from each other largely in the last 25 million years. Rebecca Montgomery, Guillermo Goldstein, and I are studying the ecology and evolution of photosynthetic light adaptations in the Hawaiian lobeliads, using field studies, physiological measurements, and common-garden experiments to re-examine several classic ecological questions in a phylogenetic context and test whether the lobeliads have, in fact, undergone an adaptive radiation. We have shown that different lineages have radiated into different portions of the light gradient on moist substrates in Hawai`i; that the lobeliads show the expected shifts in a variety of photosynthetic parameters and whole-plant light compensation points upon invasion of different light regimes; and that species show adaptive cross-over in photosynthetic response. To analyze our comparative physiological data, we are using a cpDNA sequence phylogeny for the Hawaiian taxa derived by Kendra Milliam, Terra Theim, Austin Mast, Ken Sytsma, and myself. Austin Mast and I recently showed that Banksia (including Dryandra) arose in southwestern Australia and soon split into two lineages: /Cryptostomata, with tough leaves, mostly native to extremely infertile, dry sites; and /Phanerostomata, with softer leaves, native to moister coastal areas. Adaptation and speciation on islands are recurring themes of my research, and I am eager to recruit a student interested in directly testing my recent model for the evoluton of woodiness in island plants. Photographs: TOP - Portrait of the scientist as a young man among Nymphaea; Brocchinia hechtioides (Bromeliaceae), one of two carnivorous species in the genus with the greatest diversity of nutrient-capture mechanisms in all flowering plants; Trematolobelia kauaiensis (Lobeliaceae) growing in boggy subalpine openings on Kaua`i, representing one of the most sun-adapted lineages of the Hawaiian lobeliads; Platanthera ciliaris (Orchidaceae), pollinated by day-flying hawkmoths in a group marked by exceptional pollinator diversity; and Calochortus pulchellus (Liliaceae), a serpentine endemic limited to Mt. Diablo, and member of a genus characterized by repeated, parallel adaptive radiations in floral syndrome (fairy lantern in this case) and serpentine tolerance. *Photograph of Platanthera ciliaris* © 1996 Jeffrey R. Hapeman, reprinted with permission; photograph of Calochortus pulchellus © 2000 Robert M. Case, reprinted with permission.** Courses \| Research Group \| Home \| COS Listing \| Ecology Section \| Botany Department © 2000 University of Wisconsin Department of Botany Last updated: 19 November 2000

Adaptive radiation, phylogenetic reconstruction, and historical biogeography

Adaptive radiation - the rise of a diversity of ecological roles within a lineage - is a major focus of research. My colleagues, students, and I use variation in DNA sequences, restriction sites, and AFLPs to derive phylogenies for groups of related species, and then use these family trees to reconstruct patterns of morphological evolution and geographic speciation. We are studying the pattern and tempo of speciation and adaptive divergence in Hawaiian lobeliads, South American bromeliads and rapateads, Australian Banksia and Dryandra, and North American Calochortus and Platanthera.

I am coordinating efforts by Chris Pires, Sean Graham, and several other colleagues to produce an ndhF phylogeny of the monocots and use it to trace the repeated evolution of net venation and fleshy fruits upon invasion of shaded habitats. We have found that both traits evolved independently more than 20 times, almost always in association with shade and often in association with each other. The tempo of adaptive shifts appears to have declined exponentially over the past 90 million years, as would be expected as the monocot radiation began to "fill" open and shaded habitats on different continents around the world.

Paul Berry, Ken Sytsma, and I are investigating the congruence between phylogeny and geography in several plant groups with species restricted to individual tepuis of the Guayana Shield, with special focus on Bromeliaceae and Rapateaceae. We are now organizing an international effort to derive a fully resolved, well-supported, multi-gene phylogeny for Bromeliaceae. Results from the first set of analyses, based on ndhF alone, resolve several new subfamilies and indicate that the genera of this large family have differentiated from each other largely in the last 25 million years.

Rebecca Montgomery, Guillermo Goldstein, and I are studying the ecology and evolution of photosynthetic light adaptations in the Hawaiian lobeliads, using field studies, physiological measurements, and common-garden experiments to re-examine several classic ecological questions in a phylogenetic context and test whether the lobeliads have, in fact, undergone an adaptive radiation. We have shown that different lineages have radiated into different portions of the light gradient on moist substrates in Hawai`i; that the lobeliads show the expected shifts in a variety of photosynthetic parameters and whole-plant light compensation points upon invasion of different light regimes; and that species show adaptive cross-over in photosynthetic response. To analyze our comparative physiological data, we are using a cpDNA sequence phylogeny for the Hawaiian taxa derived by Kendra Milliam, Terra Theim, Austin Mast, Ken Sytsma, and myself.

Austin Mast and I recently showed that Banksia (including Dryandra) arose in southwestern Australia and soon split into two lineages: /Cryptostomata, with tough leaves, mostly native to extremely infertile, dry sites; and /Phanerostomata, with softer leaves, native to moister coastal areas.

Adaptation and speciation on islands are recurring themes of my research, and I am eager to recruit a student interested in directly testing my recent model for the evoluton of woodiness in island plants.

Photographs: TOP - Portrait of the scientist as a young man among Nymphaea; Brocchinia hechtioides (Bromeliaceae), one of two carnivorous species in the genus with the greatest diversity of nutrient-capture mechanisms in all flowering plants; Trematolobelia kauaiensis (Lobeliaceae) growing in boggy subalpine openings on Kaua`i, representing one of the most sun-adapted lineages of the Hawaiian lobeliads; Platanthera ciliaris (Orchidaceae), pollinated by day-flying hawkmoths in a group marked by exceptional pollinator diversity; and Calochortus pulchellus (Liliaceae), a serpentine endemic limited to Mt. Diablo, and member of a genus characterized by repeated, parallel adaptive radiations in floral syndrome (fairy lantern in this case) and serpentine tolerance. Photograph of Platanthera ciliaris © 1996 Jeffrey R. Hapeman, reprinted with permission; photograph of Calochortus pulchellus © 2000 Robert M. Case, reprinted with permission.