Mark F. Dybdahl: Research Summary

Research Interests

What factors maintain sexual reproduction when strains within a species that reproduce asexually could invade and displace sexuals? As an evolutionary ecologist, my research focuses on the ecological and evolutionary consequences of sexual and asexual modes of reproduction.

In my lab, many of us work with an ideal system for the questions outlined above, a New Zealand freshwater snail Potamopyrgus antipodarum. Natural populations of this species are comprised of males, sexual females, and clonal females. These populations are infected by a dozen species of trematode parasites, and we are able to carry out experimental studies with the dominant parasite among these (Microphallus sp.). Populations of Potamopyrgus have become established in novel habitats and biological communities as introduced species in 7 distinct regions worldwide. Hence this system offers the opportunity to study host-parasite coevolution in natural populations, evolutionary responses in introduced populations, and clonal invasion in the native and introduced ranges. In my lab, we use molecular genetic marker studies, laboratory infection experiments, and studies of natural populations to address our main questions.

The questions addressed so far include the following:

Coevolution between hosts and parasites and the maintenance of sexual reproduction

Clonal invasion: Ecology and evolution of sexual and asexual reproduction

Invasion ecology: the ecology of a clonal invasion

Population structure and life history evolution

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Coevolution between hosts and parasites: the maintenance of sex and the Red Queen hypothesis

According to the Red Queen hypothesis, host-parasite coevolution should favor the production of genetically diverse offspring through sexual recombination. Theoretical models of the Red Queen coevolutionary process predict that parasites should attack common host genotypes, assuming that the interaction between parasite and host is genetically based. My work has focused on testing assumptions and predictions of this hypothesis.

To address this question, I have been studying a freshwater snail that is endemic to lakes in New Zealand and their trematode parasites (collaboration with C. Lively and J. Jokela). The results of a long-term study of a natural population of clonal snails, along with a laboratory infection experiment, suggest that parasites track common host clones over time. This suggests that parasites can prevent clonal reproduction from replacing sexual reproduction.

If parasites attack common clones, then the parasites should also prevent any single clone from dominating populations, thereby maintaining a diversity of clones. Tracking of common clones is possible if the interaction between host and parasite is genetically determined and constant over time, leading to local adaptation. In order to prevent a successful clone from spreading, local adaptation should occur rapidly. My research is continuing to examine these questions with studies of coevolution in the field and the genetic basis of host-parasite interactions.

Fromme, A. and M.F. Dybdahl. 2006. Resistance in introduced populations of a freshwater snail to native range parasites. Journal of Evolutionary Biology. In Press

Fromme and Dybdahl 2006

Dybdahl, M.F. and A.C. Krist. 2004. Genotypic vs. condition effects on parasite-driven rare advantage. Journal of Evolutionary Biology 17:967-973

Dybdahl and Krist 2004

Lively, C.M., M.F. Dybdahl, et al. 2004. Host sex and local adaptation by parasites in a snail-trematode interaction. American Naturalist 164:S6-S18

Lively, Dybdahl, et al. 2004

Dybdahl, M.F. and A. Storfer. 2003. Parasite local adaptation: Red Queen versus Suicide King. Trends in Ecology and Evolution 18(10):523-530

Dybdahl and Storfer 2003

Lively, C.M. and M.F. Dybdahl. 2000. Parasite adaptation to locally common host genotypes. Nature 405:679-681

Lively and Dybdahl 2000

Dybdahl, M.F. and C.M. Lively. 1998. Host-parasite interactions: evidence for a rare advantage and time-lagged selection in a natural population. Evolution 52:1057-1066

A commentary on this paper in TREE

Jokela, J., C.M. Lively, M.F. Dybdahl, and J.A. Fox. 1997. Evidence for a cost of sex in the freshwater snail Potamopyrgus antipodarum. Ecology 78:452-460

Dybdahl, M.F. and C. M. Lively. 1996. The geography of coevolution: comparative population structures for a snail and its trematode parasite. Evolution 50:2264-2275.

Dybdahl, M.F. and C.M. Lively. 1995 Host-parasite interactions: infection of common clones in natural populations of a freshwater snail (Potamopyrgus antipodarum). Proceedings of the Royal Society, London, B. 260:99-103

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Clonal invasion: The ecology and evolution of asexual populations

Clonal reproduction is expected to have a two-fold advantage over sexual reproduction. The paradox of sexual reproduction assumes that clones could invade and displace a sexual population. However, an inability of a clonal population to evolve and adapt is expected limit their capacity to invade new environments. One mechanism that might allow a clonal population to overcome this limitation is generalismÑ the capacity to grow and reproduce under a broad spectrum of conditions.

Earlier research from the native range showed that clones are specialists, but the pattern of invasion worldwide invaders by a few clones (US, Europe, Great Britain, Japan, Australia) suggests that some clones are generalists. My work has focused on resolving this paradox. We are using clonal lineages of Potamopyrgus from the native range and around the world to study the evolutionary and ecological capacity of clonal populations to invade.

Dybdahl, M.F. and S.L. Kane. 2005. Adaptation versus phenotypic plasticity in the success of a clonal invader. Ecology. 86:1592-1601

Dybdahl and Kane 2005

Jokela, J., M.F. Dybdahl, and C.M. Lively. 1999. Habitat-specific variation in life-history traits, clonal population structure, and parasitism in a freshwater snail (Potamopyrgus antipodarum). Journal of Evolutionary Biology 12:350-360

Jokela, J., C.M. Lively, M.F. Dybdahl, and J.A. Fox. 1997. Evidence for a cost of sex in the freshwater snail Potamopyrgus antipodarum. Ecology 78:452-460

Jokela, J., C.M. Lively, J.A. Fox, and M.F. Dybdahl. 1997. Flat reaction norms and 'frozen' phenotypic variation in clonal snails (Potamopyrgus antipodarum). Evolution 51:1120-1129.

Fox, J.A., M.F. Dybdahl, J. Jokela, and C.M. Lively. 1996. Genetic structure of coexisting sexual and clonal subpopulations in a freshwater snail (Potamopyrgus antipodarum). Evolution 50:1541-1548

Dybdahl, M.F. and C.M. Lively. 1995. Diverse, endemic, and polyphyletic clones in mixed populations of a freshwater snail Potamopyrgus antipodarum. J. Evol. Biol. 8:385-398

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Invasion ecology: the ecology of a clonal invader

Successful invasion is judged by whether populations become locally abundant and ecologically dominant. Collaboration with community and ecosystem ecologists (Dr. R.O. Hall at University of Wyoming and Dr. Billie Kerans at Montana State University) have shown that single clonal populations of Potamopyrgus in the western US are extremely abundant, and ecologically dominant over competitors. Finally, we examined ecological consequences at the community and ecosystem level in two studies. First, we showed that Potamopyrgus dominated carbon and nitrogen cycling in one stream . Second, we measured the degree to which Potamopyrgus dominated secondary production, relative to native animals. We found that Potamopyrgus was the most productive taxon, sequestering a large fraction of the available carbon. The skewed dominance in production by a single species was similar to that observed in highly polluted ecosystems.

Hall, R.O., M.F. Dybdahl, and M.C. VanderLoop. 2006 Invasive species and energy flow: Extremely high secondary production of introduced snails in rivers. Ecological Applications 16:1121-1131

Hall, Dybdahl and Vanderloop 2006

Kerans B. L., M.F. Dybdahl, M. M. Gangloff, and J. E. Jannot. 2005. Macroinvertebrate assemblages and the New Zealand mud snail, a recent invader to streams of the Greater Yellowstone Ecosystem. Journal of the North American Benthological Society. 24:123-138

Hall, R.O, J. L. Tank, and M.F. Dybdahl. 2003. Exotic snails dominate nitrogen and carbon cycling in a highly productive stream. Frontiers in Ecology and the Environment. 1(8):407-411

Hall, Tank and Dybdahl 2003

Population structure and life-history evolution

Evolution in subdivided populations is unpredictable; some vagile species are adapted to local conditions, while some philopatric species are not. I studied a Pacific coast species of tidepool copepod Tigriopus because it has limited migratory ability and strong differentiation in genetic markers along rocky shorelines. I was particularly interested in the evolution of life-history adaptation among populations on different rock outcrops from protected and exposed shorelines. These populations differed in allozyme frequencies, and in important life-history traits, but laboratory studies suggested that these differences were the result of a plastic response to environmental heterogeneity. However, the heritability of life-history traits was very low, and may have slowed a response to selection, hence minimizing local adaptation.

What process generates differentiation in genetic markers, when there is no adaptive variation? Tidepool habitats are ephemeral, and theoretical models, which have been adopted by conservation genetics, have suggested that population recolonization patterns should increase genetic differentiation. I studied metapopulation ecology and its relationship to genetic differentiation in Tigriopus, and found that extinction/recolonization leads to homogenization of differentiation, which points out that the genetic consequences of habitat fragmentation depend on both recolonization and on the pattern of extinction in the metapopulation.

Dybdahl, M.F. 1994. Extinction, recolonization, and the genetic structure of tidepool copepods. Evolutionary Ecology 8:113-124

Dybdahl, M.F. 1995. Selection on life-history traits across a wave exposure gradient in the tidepool copepod Tigriopus californicus. J. Exp. Mar. Biol. Ecol. 192(2):195-210