Zoology Homepage | Zoology Faculty
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CAROL EUNMI LEE430 Lincoln Drive |
Zoology Homepage | Zoology Faculty
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CAROL EUNMI LEE430 Lincoln Drive |
Evolvability of Invasive PopulationsInvasive species provide rare opportunities for observing ongoing rapid evolution. They also offer compelling systems for exploring fundamental constraints on niche evolution. Of the large number of species that are introduced into new habitats, few are successful as invaders (Williamson and Fitter 1996). What allows some species to invade, when most cannot? There is increasing recognition that response to selection can be important (Lee 2002). As successful invaders are aberrations from the norm, their habitat shifts could yield insights into fundamental constraints on evolvability and adaptation.
A comparative and integrative approach offers the power to infer characteristics of invasive populations. Thus, I am comparing patterns of phenotypic evolution (1) between ancestral source and invading populations, (2) among multiple independent invasions, and (3) between invasive and noninvasive populations within species. Direct comparisons of source and invading populations reveal evolutionary adaptations that are associated with habitat transitions (Lee et al. 2003; Eads et al. In Prep.; Skelly et al. Submitted). Analysis of multiple independent invasions offers insights into repeatability of evolutionary pathways (Lee 1999; Eads et al. In Prep.). Finally, comparing invasive and noninvasive populations uncovers properties that are exclusive of successful invaders (Skelly et al. Submitted). In addition, links between colonization and speciation (Mayr 1942) have led me to examine (4) patterns of reproductive isolation and incipient speciation following geographic separation (Lee 2000; Lee and Frost 2002). My lab focuses on some of the most pervasive invaders in aquatic ecosystems, such as the copepod Eurytemora affinis and zebra and quagga mussels(Dreissena polymorpha and D. bugensis).
Physiological Adaptation during Independent Invasions
C. H. Waddington recognized that invasive species present valuable opportunities for studying adaptation in response to environmental stress (Baker and Stebbins 1965). As most animal phyla have evolved in the sea, fresh water imposes physiological challenges for most taxa (Hutchinson 1957; Lee and Bell 1999). Curiously, many species have recently invaded fresh water from saline or brackish habitats as a result of human activity (Lee and Bell 1999). For example, the vast majority of recent invaders into the Great Lakes have originated from the Black and Caspian Sea region (Ricciardi and MacIsaac 2000). Such phenomena are forcing us to explore evolutionary constraints on species distributions, and factors that allow the distributions to shift.
The copepod Eurytemora affinis provides an exceptional model for exploring mechanisms of niche evolution. Within the past century, this species has invaded freshwater habitats from saline sources throughout the Northern Hemisphere. My phylogenetic analysis has revealed that freshwater invasions have occurred multiple times independently from genetically distinct sources (Lee 1999) (Fig. 1). Most notably, some clades have given rise to invasive populations, while others have not (Lee 1999) (Fig. 1). Given that invasive and noninvasive clades often coexist in their native range (Skelly et al. Submitted), it is likely that both were introduced into fresh water, but only the invasive clades survived.
Research in my laboratory has yielded several key results. For example, common-garden experiments revealed evolutionary shifts in osmotic tolerance and life history traits during freshwater invasions (Lee et al. 2003; Lee et al. 2007). Freshwater populations showed increases in freshwater tolerance and reduced saltwater tolerance relative to their saline progenitors (Lee et al. 2003; Lee et al. 2007). These shifts appear to have arisen through selection on alternative genotypes within saline source populations (Lee et al. 2003) rather than through acclimation (Lee and Petersen 2003).
Selection regime of the source habitat might have profound effects on the propensity to invade (Winkler et al. 2007). The fact that noninvasive clades tend to occur in more constant habitats might account for their limited range expansions. Populations from invasive and noninvasive clades showed striking differences in their response to fresh water. Of the two sympatric clades in the St. Lawrence estuary (red and teal), only one clade (red) has invaded freshwater habitats (Lee 1999; Winkler et al. 2007) (Fig. 1). Laboratory experiments revealed differences in osmotic tolerance between saline source populations from these clades, with greater low-salinity tolerance and starvation resistance in the invasive clade (Skelly et al. Submitted). Interestingly, the two clades experience osmotic stress at different life-history stages, suggesting differences in osmoregulatory function (Skelly et al. Submitted).
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My lab is in the process of linking genomic analyses with physiological function. We are currently exploring physiological and genetic targets of selection during parallel freshwater invasions. Examining the repeatability of mechanisms underlying freshwater adaptation could reveal whether these evolutionary pathways are labile or constrained (Gould 1989; Bell and Foster 1994; Travisano et al. 1995; Cooper et al. 2003).
My long-term research interests focus on evolutionary dynamics at the interface between habitat boundaries, and factors that allow shifts in habitat type. Results from my work not only have broad implications for biological invasions, but also for global change, habitat restoration and acclimatization, and macroevolutionary processes, such as the colonization of land. The approaches I have outlined above, integrating phylogenetics, physiology, biochemistry, and gene expression can be used to address diverse questions regarding physiological and biochemical responses to environmental clines (such as gradients in temperature, oxygen, irradiation, and nutrients). I welcome graduate students with a strong background or interest in evolutionary biology or physiological ecology, preferably with experience in laboratory molecular genetics or strong quantitative skills.
References
Baker, H. G., and G. L. Stebbins. 1965. The Genetics of Colonizing Species. Academic Press, New York.Bell, M. A., and S. A. Foster. 1994. The Evolutionary Biology of the Threespine Stickleback. Oxford University Press, Oxford.
Cooper, T. F., D. E. Rozen, and R. E. Lenski. 2003. Parallel changes in gene expression after 20,000 generations of evolution in Escherichia coli. Proc. Nat. Acad. Sci. USA 100:1072-1077.
Eads, B. D., G. W. Gelembiuk, M. Posavi, and C. E. Lee. In Prep. Evolutionary shifts in gene expression across independent invasions by the copepod Eurytemora affinis.
Gould, S. J. 1989. Wonderful Life: The Burgess Shale and the Nature of History. W. W. Norton & Company, New York.
Hutchinson, G. E. 1957. A Treatise on Limnology. John Wiley & Sons, Inc., New York.
Lee, C. E. 1999. Rapid and repeated invasions of fresh water by the saltwater copepod Eurytemora affinis. Evolution 53:1423-1434.
Lee, C. E. 2000. Global phylogeography of a cryptic copepod species complex and reproductive isolation between genetically proximate "populations". Evolution 54:2014-2027.
Lee, C. E. 2002. Evolutionary genetics of invasive species. Trends in Ecology and Evolution 17:386-391.
Lee, C. E., and M. A. Bell. 1999. Causes and consequences of recent freshwater invasions by saltwater animals. Trends in Ecology and Evolution 14:284-288.
Lee, C. E., and B. W. Frost. 2002. Morphological Stasis in the Eurytemora affinis species complex (Copepoda: Temoridae). Hydrobiologia 480:111-128.
Lee, C. E., and C. H. Petersen. 2003. Effects of developmental acclimation on adult salinity tolerance in the freshwater-invading copepod Eurytemora affinis. Physiological and Biochemical Zoology 76:296-301.
Lee, C. E., J. L. Remfert, and Y.-M. Chang. 2007. Response to selection and evolvability of invasive populations. Genetica 129:179-192.
Lee, C. E., J. L. Remfert, and G. W. Gelembiuk. 2003. Evolution of physiological tolerance and performance during freshwater invasions. Int. Comp. Biol. 43:439-449.
Mayr, E. 1942. Systematics and the Origin of Species, Columbia University Press, New York.
Ricciardi, A., and H. J. MacIsaac. 2000. Recent mass invasion of the North American Great Lakes by Ponto-Caspian species. Trends in Ecology and Evolution 15:62-65.
Skelly, D., F. C. Chau, G. Winkler, Y.-M. Chang, and C. E. Lee. Submitted. Functional contrasts between sympatric invasive and noninvasive populations of the copepod Eurytemora affinis.
Travisano, M., J. A. Mongold, A. F. Bennett, and R. E. Lenski. 1995. Experimental tests of the roles of adaptation, chance, and history in evolution. Science 267:87-90.
Williamson, M., and A. Fitter. 1996. The varying success of invaders. Ecology 77:1661-1666.
Winkler, G., J. Dodson, and C. E. Lee. 2007. Heterogeneity within the native range: Population genetic analyses of sympatric invasive and noninvasive populations of the freshwater invading copepod Eurytemora affinis. Molecular Ecology, In Press.
Evolutionary Biology at UW-Madison
