Research Focus

My laboratory works in the general area of evolutionary biology, with a focus on aquatic organisms. Most of our research involves a blend of laboratory and field work that aims to address issues of conceptual importance. From a methodological perspective, we exploit a broad range of techniques for the molecular characterization of populations including allozymes, microsatellites and DNA sequencing. We also maintain strong field programs, that operate at a continental scale when appropriate. The following six areas of investigation form the target of our current work:

  1. Biological Identifications Through DNA Barcodes

Technological advances are providing exciting new opportunities to gain the genomic information needed to probe the relationships of life and the processes important in its diversification. At a practical level, this work offers hope to those frustrated by the slow progress towards the inventory of life on our planet and the difficulties in gaining taxonomic identifications. DNA barcodes will soon offer a supplement to morphological approaches. This work not only promises to revolutionize the business of taxonomy but will also expedite the inventory of life's diversity. Our work, which aims to establish the feasibility of this approach, is focusing on the use of a segment of the cytochrome c oxidase I gene as the basis for an identification system for animal life.

Selected References

Hebert, P.D.N., A. Cywinska, S.L. Ball, and J. R. deWaard. 2003. Biological identifications through DNA barcodes. Proc Roy Soc. Lond. Ser B: in press

Witt, J.D.S., and P. D.N. Hebert. 2000. Cryptic species diversity and evolution in the amphipod genus Hyalella within central glaciated North America: a molecular phylogenetic approach. Can J. Fish Aquat. Sci. 57: 687-698.

2. The Evolution of Breeding Systems

My laboratory has carried out studies relating to breeding system evolution for more than 25 years with a special emphasis on parthenogenesis, although we have also worked on selfing. Our studies have focused on three groups of invertebrates (aphids, cladocerans, ostracodes) and have aimed to extend understanding of both the forces promoting transitions from sexuality to parthenogenesis and clarifying the ultimate fate of asexuals. We have shown that most asexuals are very genetically diverse and have broad geographic distributions, but seem doomed to soon become extinct. The paradoxical success of asexuals in space but not time remains unresolved.

Selected References:

Cywinska, A. and P.D.N. Hebert. 2002. Origins of clonal diversity in the hypervariable asexual ostracod Cypridopsis vidua. J. Evol. Biol. 15: 134-145.

Weider, L.J., A. Hobaek, F. Dufresne, J.K. Colbourne, T.J. Crease and P.D.N. Hebert. 1999. Holarctic phylogeography of an asexual species complex I. Mitochondrial DNA variation in arctic Daphnia. Evolution 53: 777-792.

Chaplin, J.A., J.E. Havel and P.D.N. Hebert. 1994. Sex and ostracods. Trends in Ecology and Evolution 9: 435-439.

3. The Modulation of Genome Sizes

The genome sizes of organisms show extraordinary diversity, both among species and within the bodies of single individuals. Our work is exploring the extent of variation in basal (gametic) genome size among closely allied species, and examining the impact of this variation on life history traits. We have also devoted substantial effort to the study of the origins of polyploids and the patterning of genetic diversity in them. Aside from examining variation in basal genome sizes, we have also worked on the evolutionary significance of the modulation in genome sizes through endopolyploidy and chromatin diminution which occurs in the bodies of most higher organisms.

Selected References:

Hardie, D.C., T.R. Gregory and P.D.N. Hebert. 2002. From pixels to picograms: a beginner's guide to genome quantification by Feulgen image analysis densitometry. J. Histochem. and Cytochem. 50: 735-749.

Gregory, T.R. and P.D.N. Hebert. 1999. The modulation of DNA content: proximate causes and ultimate consequences. Genome Research 9: 317-324.

Dufresne, F. and P.D.N. Hebert. 1997. Pleistocene glaciations and polyphyletic origins of polyploidy in an arctic cladoceran. Proc. Roy Soc. B 264: 201-206.

4. The Pattern and Pace of Evolution

The diversification of life is the heart of the evolutionary process. My laboratory is examining a number of systems to gain more understanding of the rates and nature of character state evolution. Our most intensive studies involve a planetary-scale survey of phylogenetic relationships among members of the genus Daphnia, the most widely studied freshwater zooplankter. Our work has shown that rates of evolutionary diversification in this group have been extraordinarily slow and characterized by frequent instances of trait convergence. We are also examining the role of extraordinary environmental conditions on rates of molecular evolution.

Selected References:

Hebert, P.D.N., E.A. Remigio, J.K. Colbourne, D.J. Taylor and C.C. Wilson. 2002. Accelerated molecular evolution in halophilic crustaceans. Evolution 56: 909-926.

Hebert, P.D.N. 1998. Variable environments and evolutionary diversification in inland waters. P. 267-290. In: Advances in Molecular Ecology. Ed. G.R. Carvalho. IOS Press, Amsterdam.

Colbourne, J.K., P.D.N. Hebert and D.J. Taylor. 1997. Evolutionary origins of phenotypic diversity in Daphnia. In T. Givnish and K. Systema. Eds. Molecular Evolution and Adaptive Radiation. Cambridge University Press.

5. Crustacean Biodiversity

My laboratory is carrying out a range of projects which aim to revitalize the taxonomy of freshwater crustaceans. Much of this work has focused on the cladoceran crustaceans with a particular emphasis on the genus Daphnia, but we have also worked on anostracans, amphipods and copepods. Our work, which exploits genetic analysis to aid in the recognition of species boundaries, is revolutionizing our knowledge of taxon diversity in these groups. We are, as well, active in the creation of CD-ROM’s which are employed to disseminate taxonomic information on these groups.

Selected References:

Cristescu, M.E.A. and P.D.N. Hebert. 2002. Phylogeny and adaptive radiation in the Onychopoda (Crustacea: Cladocera): evidence from multiple gene sequences. J. Evol. Biol. 15: 838-849.

Witt, J.D.S. and P.D.N. Hebert. 2000. Cryptic species diversity and evolution in the amphipod genus Hyalella within central glaciated North America: a molecular phylogenetic approach. Can. J. Fish Aquat. Sci. 57: 687-698.

Hebert, P.D.N. 1995. The Daphnia of North America: An Illustrated Fauna. CD-ROM, University of Guelph.

6. Phylogeography of Canada’s Aquatic Life

There are two major themes to our Phylogeographic investigations. Our first area of work involves efforts to reconstruct the postglacial recolonization of Canada from glacial refugia. Most of our initial studies involved fish, but we have now broadened the analyses to include aquatic invertebrates. Our second area of research focuses on species invasions, with a particular emphasis on the Great Lakes. Our work exploits genetic markers to gain a better understanding of the incidence of cryptic invaders.

Selected References:

Hebert, P.D.N., J.D.S. Witt and S.J. Adamowicz. 2003. Phylogeographic patterning in Daphnia ambigua: regional divergence and intercontinental cohesion. Limnol. Oceanograph. 48: 261-268.

Hebert, P.D.N. and M.E.A. Cristescu. 2002. Genetic perspectives on invasions: the case of the Cladocera. Can. J. Fish. Aquat. Sci. 59: 1229-1234.

Cox, A.J. and P.D.N. Hebert. 2001. Colonization, extinction and phylogeographic patterning in a freshwater crustacean. Mol. Ecol. 10: 371-386.