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[Information for SCRP Applicants]

 

 

Chris Smith

Assistant Professor

Willamette University

 

 

 

Ph: 503 370 6181

Email: csmith <at> willamette <dot> edu

 

 

 

 

 

 

 

 

 

[Bio] [Research] [Publications] [CV] [Pictures] [Email] [Links]

 

 

Research Interests:

 

My work examines the role of ecological processes in shaping evolutionary patterns over both microevolutionary and macroevolutionary time. I am particularly interested in exploring ecological and evolutionary questions in the context of interactions between plants and insects, and in understanding how spatial structure shapes coevolutionary processes. Much of my work relies on coalescent and phylogenetic analyses of DNA sequence data and coalescent simulations datasets, but I also incorporate many traditional methods in field ecology.

 

Current projects:

 

į      A geographic mosaic of coevolution in the Joshua tree pollination mutualism:

The major project that I developed during my postdoctoral work in OlleÕs lab examined interactions between Joshua trees (Yucca brevifolia) and their pollinators. This system is among the most remarkable pollination mutualisms in the world.  Yucca moths, which are the exclusive pollinators of yuccas, lay their eggs in yucca flowers using a specialized, blade-like ovipositor, before deliberately depositing a ball of pollen directly onto the stigmatic surface using unique, tentacle-like mouthparts that extend from the maxillary palps.

 

Joshua trees are distributed across the Sonoran and Mojave deserts in a series of isolated, populations. Trees in different parts of this range are pollinated by two different species of moths that differ in body size as well as in the size of their ovipositors. Recent work that I published in The American Naturalist and that was profiled by Smithsonian Magazine shows that Joshua trees pollinated by different species of moths differ in the gross morphology, as well as in specific floral features associated with the pollination mutualism. A second study in this system, which was recently selected as the cover article in journal Evolution, used relaxed-clock methods to estimate divergence times between the two pollinators and their associated hosts. The results revealed surprising incongruence between the divergence times in the plants and those in their pollinators.

 

 

 

į      The role of pollinator host specificity in mediating species boundaries in Yuccas:

 

One unexpected finding from the chloroplast DNA data used to estimate divergence times between Joshua tree morphotypes  (above), was that there is considerable asymmetry in the degree of genetic isolation between western and eastern populations of Joshua tree. The genetic data indicated significant gene flow from eastern populations into western populations, but no gene flow moving in the opposite direction. This finding may indicate that the two moth species may differ in their degree of host specificity and in their pollination success when visiting the non-native host. My lab is using passive sampling regimes and manipulative experiments, in combination with microsatellite genotyping to examine pollinator movement and oviposition success in a hybrid zone where the two moth species co-occur. The results of these studies suggest that the western variety of Joshua trees receive pollen from both eastern and western moths, but that eastern trees are pollinated almost exclusively by the eastern species of moth. Additionally, moths ovipositing on their non-native host produce many fewer larvae than when laying eggs on their native host. This work is currently in press at Molecular Ecology, and will be profiled in a forthcoming News and View article.

 

 Working in collaboration with Olle PellmyrÕs lab, I have developed microsatellite markers for Joshua trees and for their pollinators. These markers should enable us to examine fine-scale gene flow within the hybrid zone, and to determine whether patterns of gene flow match the mothÕs host specificity and the large-scale patterns of gene flow across the treesÕ entire range seen in the chloroplast data.

 

 

į      The role of Coevolution in the diversification of plants and insects:

 

One of my ongoing interests is in coevolutionary interactions between yuccas and their exclusive pollinators, moths in the genera Tegeticula and Parategeticula. A long-standing question about plant insect interactions general, and about this system in particular, is whether specialization promotes increased rates of speciation. Using molecular phylogenetic data and relaxed molecular clocks, IÕve been looking at whether specialized yucca-moth pollination has produced accelerated rates of diversification in Yuccas. Work IÕve recently published in The Proceedings of the Royal Society of London showed that the mega-diverse group Agave sensu lato is the sister group to Yucca, and despite specialized pollination and a surprisingly recent radiation, Yuccas have not diversified more quickly than their sister group. 

 

 

 

į      Impacts of Pleistocene Climate Change:

One of my long-standing research interests is the impact of Pleistocene climate changes on the biogeography and demographic history of terrestrial ecosystems, particularly in western North America.  As recently as 13,000 years ago, much of North America was covered in glaciers several kilometers in depth; the retreat of the glaciers and climate change since the end of the ice age had profound impacts on the distribution of nearly every terrestrial ecosystem, with many desert and tropical organisms experiencing profound population expansions. The advent of DNA sequencing technology and Bayesian methods for estimating population genetic parameters have opened a new frontier for exploring how past climate changes affected speciesÕ distributions. I discussed some of these changes in a recent invited review in the journal, Current Biology. During my dissertation work in Brian FarrellÕs lab at the Museum of Comparative Zoology, I looked at the impact of these climate changes on three groups of flightless beetles in the genus Moneilema, two desert species and one montane species. This work, published in the journal Molecular Ecology showed that the desert species have experienced significant range expansions and population growth, but the montane species has experienced range fragmentation and isolation. I am currently undertaking a similar project looking at population size changes in Joshua trees and four species of associated Yucca moths. The latter project links population genetic work with palaeoclimate data and ecological niche modeling; both approaches show surprising evidence for population expansion, rather than population decline.

 

 

 

 

į      Impacts of modern climate change on desert ecosystems:

A new project that IÕve started in the last two years combines the population genetic and ecological niche modelling approaches IÕve used previously to look at past climate changes, and applies these to ongoing global warming, with a particular focus on Mojave Desert ecosystems and Joshua trees. Current climate models predict that many populations of Joshua trees, including those in Joshua Tree National Park and the Mojave National Preserve are likely to go extinct in the next 100 years due to ongoing global warming. The time scale on which these changes are likely to occur is unclear, but demographic data IÕve collected suggest that these changes are already evident throughout much of the southwest. In many areas, formerly large populations are reduced to a few senescing individuals, with few or no seedlings to replace them. This project combines demographic and population genetic data with climate modeling to predict which populations are likely to be hardest hit by these effects.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Population declines in central-Mojave desert populations of Joshua tree.

 

 

 

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Research Publications:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Commentaries and Invited Reviews: