Coevolution, the reciprocal evolution of species, is hypothesized to be one of the major processes producing biological diversity. Interacting species in different geographic areas can coevolve with each other resulting in each species becoming locally adapted to variation in the other species. This will produce a geographic mosaic of genetically differentiated populations of each species. Local adaptation of organisms has frequently been documented, but the contribution of coevolution to local adaptation has been difficult to quantify. The PIs will measure the role of coevolution in producing local adaptation among a plant, a specialized herbivorous insect, and a wasp that parasitizes that insect. Studying this tightly interacting group of species will be the first step towards understanding coevolution at the level of the ecological community. Each of these species shows evidence of local adaptation, but the role of coevolution in producing this adaptation has not been determined. To measure coevolution the PIs will reciprocally transplant populations of each species among three sites with different environments to create all possible combinations of the local populations of the three species. By measuring the survival and reproduction of each species they will quantify the relative contribution of coevolution and other environmental factors to local adaptation.
The results will have implications for agriculture, forestry, and conservation efforts because movement of populations to new locations is common in all these disciplines. The research will provide training for a large number of undergraduates in ecological research techniques.
Intellectual Merit We experimentally tested predictions of the geographic mosaic of coevolution theory by measuring geographic variation in the interaction among a host plant, Solidago altissima, a gall-inducing fly Eurosta solidaginis, and a parasitoid wasp Eurytoma gigantea in the forest biome, the prairie biome and on the forest-prairie border. We used a unique reciprocal transplant design to measure the fitness of all possible interactions of the populations of these three species in all three locations. This is the first research to experimentally manipulate a three-trophic-level community in a manner capable of measuring local adaptation in all three species. Coevolution is the reciprocal evolution of species, and it is an important process in the evolution and organization of earth’s biodiversity. The geographic mosaic of coevolutionary theory predicts that interactions of populations of interacting species will differ among localities because evolutionary pressures vary geographically. This is important because it will result in populations within species becoming geographically differentiated which can be the first step in the evolution of new species. This has important implications for evolutionary theory as it may represent a major unmeasured source of genetic variation within species driving the evolution of new species. We found strong evidence that that there is a geographic mosaic of coevolution in the interaction of the Solidago, Eurosta and Eurytoma as demonstrated by the local adaptation of populations of each species in the interaction to population of other species in the interaction. Our data is consistent with the hypothesis that there is an antagonistic coevolutionary arms race in Solidago resistance and Eurosta ability to attack the plant, and in Eurosta ‘s ability to induce large galls and Solidago resistance to the induction of large galls. There is also evidence of antagonistic coevolution of Eurosta gall size and Eurytoma ovipositor length. An indirect geographic mosaic of coevolution is found between Solidago and Eurytoma: the parasitoid exerts selection on the fly for larger gall size and the fly exerts selection on the plant for allocation of tissue to gall growth. The response of the plant in allocation of tissue to gall tissue influences the evolution of the parasitoid. In concert with our main experiments we conducted a number of other studies with birds, and other insects that impact Eurosta and Eurytoma. We found that the beetle, Mordellistena preference among local Eurosta populations was matched by adaptive local changes in gall shape which could also be interpreted as a coevolved relationship. Birds exert selection for local adaptation in gall size, but we did not measure whether there was local adaptation among bird populations. Broader Impacts Understanding the role of coevolutionary forces in local adaptation is critical for predicting and mitigating the impact of human disturbance of ecosystems. It is important in applied fields such as forestry, agriculture and conservation biology as many species are being introduced in new geographic areas to which they are not adapted, and this may have important impacts interactions with local species. Altering species interactions may have widespread ecological consequences with social and economic impacts. Our work shows it is possible to measure the individual evolutionary impacts within a community. One of the major grant objectives was to train undergraduate and graduate research students. We involved undergraduates and graduate students in all aspects of this research including: experimental design, data collection, data analysis and writing. We assigned students specific responsibilities for experiments to gain experience in managing research. Students were encouraged to develop their own related research projects; as a result ten undergraduate student UROP (U of M Undergraduate Research Opportunity Program) grants were awarded $17,000 to support independent research. Four graduate students were supported in their M.S. degrees. All of the students presented their work at local, national or international meetings, and many have prepared or are preparing publications in peer-reviewed journals. Public outreach to disseminate the results of this research was another goal of the project. At our border site, the Cedar Creek Ecosystem Science Reserve, we worked with the education department to develop labs involving field and laboratory work for use by K-12 schoolteachers. We participated in daylong sessions with teachers on how to bring evolutionary principles into science teaching using the Solidago-Eurosta-Eurytoma interaction. We presented our work to undergraduate interns and graduate students at CCESR every summer. Our prairie garden site was used in teaching activities at the MSUM (Moorhead State University Moorhead) Regional Science Center in K-12 education. We promoted undergraduate research at MSUM through presentations to the Biology Department. We have used our forest research site at the University of Minnesota Duluth Jean Duluth Field Research and Teaching Center for classes and public presentations. Our research and teaching labs have been presented in publications, on the web site, and outreach presentations to local groups.
