Darren Irwin

Our research is directed toward understanding how new species arise, how geographical variation within species is produced, and how behaviors evolve. We study carefully chosen model systems using an integrative approach, employing techniques such as DNA sequencing, computer-assisted analysis of vocalizations, observation and experimentation in the field, and computer simulation. Research systems have included passerine birds in Asia, Europe, and North America. (If you are a prospective graduate student, please click here for more info)

Asia
Greenish warblers in Asia show how geographic variation within a species can be used to reconstruct how new species arise.Click here to learn more about this ring species. Collaborators include Staffan Bensch, Jessica Irwin, and Trevor Price.
Postdoctoral researcher Alex Rubtsov studied molecular differentiation between Yellowhammers and Pine Buntings, which hybridize in central Siberia. The two species differ strongly in nuclear DNA and appearance, yet mitochondrial DNA is indistinguishable between them. Apparently this is a result of rapid introgression of mitochondria from one species into the other, perhaps due to a selective sweep. PDF (preprint) Link
Yellow-browed warblers and Hume's leaf warblers in Asia are examples of cryptic species, two forms that look very similar but in fact are very different genetically and behaviorally. There are many others such cryptic species of Old World warblers. PDF (large file: 12.4 MB)
North America
Many species of terrestrial vertebrates in western Canada were confined to several southern refugia during the ice age glaciations, when much of western Canada was covered by glaciers. When the glaciers receded, groups that had differentiated in different southern refugia expanded into western Canada. Now, there are many contact zones between these groups. We are studying these zones to learn about the causes of reproductive isolation, the importance of hybridization in evolution, and the role of different migratory behaviors in promoting differentiation. Case studies include the following:
In northeastern British Columbia, near the town of Tumbler Ridge, we have found a contact zone between distinct western and eastern forms of winter wrens. These forms differ dramatically in songs and genetics, and the two forms are reproductively isolated. Dave Toews (who did his M.Sc. on this system) and I have proposed that the western form be elevated to species status as the "Pacific wren." In 2010 the American Ornithologists' Union officially recognized two distinct species in North America: the Pacific wren (Troglodytes pacificus) and the winter wren (Troglodytes hiemalis), both now distinct from the Eurasian wren (Troglodytes troglodytes). Click here to learn more, and to listen to their songs.
A hybrid zone between Audubon's and myrtle warblers was discovered in the 1960's, causing the two to be lumped into a single species as yellow-rumped warblers. Ph.D. student Alan Brelsford (defended July 2010) studied molecular, phenotypic, and behavioral variation across the hybrid zone. He found that the hybrid zone is stable, and that there is some form of selection against hybrids maintaining the zone. For the publication, click here. Alan also led a study of genetic variation throughout the entire yellow-rumped warbler complex, showing that the Audubon's warbler most likely originated through hybrid speciation. Click here for the paper, and here for the associated News and Views.
We have recently discovered a hybrid zone between MacGillivray's and mourning warblers, in the Peace Region of northeastern British Columbia. At right is a hybrid (a "MacMourning warbler") identified using molecular markers. PDF Link
In the same region, we have also discovered a hybrid zone between Townsend's and black-throated green warblers. At right is a hybrid. Ph.D. student Dave Toews is now conducting an in-depth study of this hybrid zone.
Ph.D. student Julie Lee-Yaw is studying geographic variation and range limits of various subspecies of long-toed salamanders. These salamanders are the most widely distributed and ecologically diverse amphibians of western Canada.
Wilson's warblers of North America are serving as a model system for a study of migratory connectivity. In collaboration with Tom Smith at the UCLA Center for Tropical Research and Frank Moore at the University of Southern Mississippi, we are conducting a survey of genetic variation in Wilson's warblers across both their breeding areas in Canada and the U.S. and wintering areas in Mexico and central America, as well as stopover sites in Ariziona. We can use the genetic variation to link specific breeding and wintering populations, providing important information to researchers interested in the evolution, ecology, and conservation of migratory birds.
Ph.D. student Andrew Rush used molecular variation to show extensive hybridization between Pacific-slope and cordilleran flycatchers in south-central British Columbia. Link
Europe
Willow warblers in Sweden have an interesting migratory pattern. The form breeding in northern Sweden migrates southeastward toward its breeding grounds in eastern Africa, while the form breeding in southern Sweden migrates southwestward toward southwestern Europe before migrating to western Africa. The two groups are avoiding the more difficult migration route in the middle, across the widest parts of the Mediterranean Sea and Sahara Desert. This 'migratory divide' raises the possibility that hybrids between these forms in central Sweden would have an inferior migratory behavior and therefore be selected against. This could promote the evolution of reproductive isolation and speciation. My research on willow warblers was in collaboration with Staffan Bensch and Susanne Åkesson at Lund University. PDF