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Talk abstract
IMA Special Minisymposium:
Evolutionary Consequences of Invasions by Exotic Species
April 12-13, 2002

Mathematics in Geosciences, September 2001 - June 2002

Diane Campbell (Department of Ecology, Evolutionary Biology, University of California Irvine)  drcampbe@uci.edu

Evolutionary Consequences of Hybridization with Invasive Plants: Two Key Questions

Many invasive plants hybridize with other species. Hybridization can potentially impact the reproductive rate of the invaded population, or it can lead to replacement of native genotypes by hybrid genotypes (genetic assimilation). This talk explores conditions for these processes by focusing on two key questions - the rate of hybrid formation and the fitness of hybrids - in model systems of hybridization between natives and between exotics and natives.

Friday Evening, April 12, 2002, 7:00 pm, Physics 150

Keynote Address (Public Lecture)

James Carlton
Professor of Marine Sciences, Williams College, Williamstown, Massachusetts and Director, Williams-Mystic, The Maritime Studies Program of Williams College and Mystic Seaport

The Flood of Exotic Species Invasions of America's Coastal Oceans: Why Now. Why We Should Care and What We Can Do About It.

America's coasts are itching with new invasions of exotic species: Indo-Pacific jellyfish have invaded the Gulf of Mexico, Mediterranean and Asian seaweeds are newly established in southern California, the Japanese Rapa Whelk is now well-entrenched in Chesapeake Bay, and thousands of species have invaded the fresh, brackish, and marine waters of the United States in the past 200 years, and yet invasions continue, seemingly at a growing pace. Why is the rate of invasions increasing? Why should we care? And what can we do about it?

Richard Gomulkiewicz (Department of Mathematics and School of Biological Sciences, Washington State University, Pullman, WA)  gomulki@wsu.edu  http://www.wsu.edu:8080/~gomulki/

Evolution, Population Dynamics, and the Potential for Invasions in Demographic Sinks

Many invasions succeed because of initially favorable environmental conditions. This talk will describe simple models that explore the potential for successful establishment via evolutionary change in environments that are initially hostile to the invader. The theory suggests that the influence of population dynamics on adaptive evolution tends to severely restrict the scope for successful invasions in environments that are initially demographic sinks.

James Hancock (Department of Horticulture, Michigan State University, East Lansing, MI)  hancock@pilot.msu.edu

How analogous are exotic introductions to genetically engineered plants?

Genetically engineered crops are not analogous to exotic introductions. Exotic species commonly become invasive when they are introduced into a new area where there are few to none of the natural constraints with which they evolved, and so they fill a new niche and their numbers explode. Most of the successful exotics are already good colonizers somewhere else and carry a whole syndrome of traits associated with weediness. Hybridization with local relatives may facilitate this process. Transgenic crops present a very different situation. The crop antecedents are generally poor competitors outside the agroecosystem and carry few weediness traits. After the crop is engineered, it will not be removed from the complex array of natural constraints that currently faces it, and in most cases only one of those constraints will be removed by the addition of a new trait. In fact, it is much easier to predict the environmental risk of transgenic crops than an exotic introduction, as the level of risk in transgenics can be measured by evaluating the fitness impact of a single engineered trait, rather than a whole syndrome of potentially invasive traits. The risk of most transgene deployments can be effectively predicted by considering the phenotype of the transgene and the overall invasiveness of the crop itself.

Ann M. Hirsch (Department of Molecular, Cell and Developmental Biology and Molecular Biology Institute, University of California, Los Angeles, CA 90095-1606)  ahirsch@ucla.edu  http://www.mcdb.ucla.edu/Research/Hirsch   http://www.mcdb.ucla.edu/Research/Hirsch/sweetclover.html

Rhizobium species form biofilms: A survival strategy?

Joint work with N.A. Fujishige, K.S. Jankaew, and C.J. Butcher (Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles).

We found that transfer of Sinorhizobium meliloti nod genes to Bradyrhizobium japonicum and to Rhizobium leguminosarum bv. viciae allowed these strains, which normally nodulate soybean and pea, respectively, to form nodules on the roots of transgenic alfalfa plants that carried either the soybean (SBL) or the pea (PSL) lectin genes. Moreover, significantly more bacteria attached to the transgenic roots than to the non-transgenic roots (van Rhijn et al., 2001). From preliminary studies using the electron microscope, we observed that the transconjugant bacterial strains were decorated with numerous pili/fimbriae, which as a rule are very difficult to see with TEM in rhizobial species. Because fimbriae are important for biofilm formation in numerous other bacteria, these observations led us to examine whether or not rhizobial species were capable of forming biofilms on abiotic surfaces, in addition to biotic surfaces, with the goal of identifying genes that are important for biofilm formation. Rhizobial species do not form spores and hence, it is unclear how they survive in the absence of their hosts or in soils that are N-sufficient where their hosts do not develop nitrogen-fixing nodules. Because biofilms are a strategy that many bacteria use to survive in aquatic and terrestrial environments, we analyzed biofilm formation by rhizobial species. We focused our studies on S. meliloti because the genome has been completely sequenced, although we have data demonstrating that R. leguminosarum bv. viciae also forms biofilms in vitro. Preliminary experiments indicate that there are major differences between the one-dimensional protein profiles of biofilmed versus planktonic rhizobia.

van Rhijn, P., Fujishige, N.A., Lim, P.-O., and Hirsch, A.M. 2001. Sugar-binding activity of pea (Pisum sativum) lectin is essential for heterologous infection of transgenic alfalfa (Medicago sativa L.) plants by Rhizobium leguminosarum biovar viciae. Plant Physiol. 125:133-144.

John L. Maron (Division of Biological Science, University of Montana, Missoula, MT 59812)  john.maron@mso.umt.edu

Altered size, fecundity and herbivore defense in introduced versus native St. John's Wort (Hypericum perforatum): Evolution or plasticity?

Joint work with Montserrat Vila (Centre de Recerca EcolÚgica i Aplicacions Forestals, Universitat AutÚnoma de Barcelona, 08193 Bellaterra, Spain) and J.T. Arnason (Department of Biology, University of Ottawa, Box 450, Station A, Ottawa, Ontario, Canada).

My research explores two issues concerning the evolutionary consequences of plant invasions: first, do introduced plants evolve greater size or fecundity compared with native conspecifics? Second, do introduced plants gain or lose herbivore resistance depending on whether or not they have been exposed to biological control? To address these questions, we have initiated common gardens in Washington and Spain containing St. John's Wort (Hypericum perforatum) from three regions: the native range in Europe, the introduced range in central North America where populations have been long liberated from natural enemies, and the introduced range in western North America where populations have been exposed to over 55 years of successful biological control. For the last two years we have examined how size, fecundity and herbivore defense varies depending on region of plant origin. Across both gardens, introduced and native plants were not consistently different in size. In the Washington garden, introduced plants from western North America produced significantly more seed capsules than native plants from Europe. Central North American and European plants did not differ significantly in fecundity. In the Spain garden, in 2000 results were similar to those found in Washington. In 2001, pathogens killed many plants before they set seed in Spain. Not only were a greater fraction of individuals from western North America killed than plants from the other two regions, but those western North American plants that died produced significantly more seed capsules in 2000 than surviving western North American plants. Because these high fecundity western North American plants were eliminated, there were no differences in fecundity between introduced and native plants in year two. In both gardens, introduced plants from both regions of North America contained substantially lower levels of the defensive secondary compound hypericin than did native plants. On-going work is evaluating how this variation in plant defensive chemistry influences plant resistance to a variety of pathogens and a widespread biocontrol agent, Chyrsolina quadrigemina.

Michael Gordon Milgroom (Department of Plant Pathology, Cornell University)  mgm5@cornell.edu

The chestnut blight fungus and its viruses: an example of Murphy's Law for introduced species?

Chestnut blight is one of the most ecologically devastating plant diseases known to result from the introduction of an exotic pathogen. Countless millions of chestnut trees died as a result of the introduction of the chestnut blight fungus into North America and Europe from east Asia. Before this introduction, the American chestnut was the dominant tree in the Appalachian region; sprouts from old root systems are now killed by blight before they can fruit or reach canopy height. Along with the fungus, however, fungal viruses were also introduced into Europe from Asia. Unlike most fungal viruses, these viruses cause marked reductions in host fitness and have invaded some European fungus populations, exerting some degree of biological control on chestnut blight. Attempts to introduce these viruses into North America for biological control have failed despite some aggressive strategies. This system will be discussed in relation to the evolution of virulence, founder effects in introduced populations, and the interaction of ecological or demographic factors.


Mathematics in Geosciences, September 2001 - June 2002