Symposium Participants
Leo Joseph
The Academy of Natural Sciences
1900 Ben Franklin Pkwy.
Philadelphia, PA 19103
Phone 215.299.3797
Fax 215.299.1182
Evolution of Migration in a South American Temperate-Tropical Migrant, Swainson's Flycatcher
Abstract
Migratory populations in the M. swainsoni complex are not each other's closest relatives. The migratory subspecies M. s. swainsoni, which breeds in south-eastern South America , is not closely related to the rest of the complex. The remaining migratory populations of the subspecies M. s. ferocior and M. s. ferocior x M. s. swainsoni and M. s. swainsoni x M. s.pelzelni intergrade populations are extremely closely related to non-migratory populations with which they form a well-supported clade despite substantial morphological differentiation from each other. Within this clade of migrants and non-migrants, net divergence across 4,000 km of lowland South America is zero and most diversity is distributed among individuals not populations. Mismatch analyses and significant values of Tajima's D and Fu's Fs suggest the clade has undergone a very recent range expansion. Migration and the shifts of breeding distribution that accompanied its evolution evolved twice within what has recently been considered the polytypic species M. swainsoni. Furthermore, these shifts of range probably occurred at very different times as parts of different southward "pulses" of humid, Amazonian taxa.
Evolution of temperate-tropical migration in the M. swainsoni complex has been spatio-temporally layered on the South American landscape. The analysis cautions that the historical biogeography underlying a single present-day migration system need not have been driven by a single set of environmental factors operating at one time. We suggest directions for further study of ecology and demography in zones of apparent contact between various migratory and non-migratory populations.
Methods Description
Application of molecular tools to unravelling the intricacies of the evolution of migration is in its infancy. The tools of molecular population genetics and phylogeny are means with which we can tease apart the evolutionary history of a population or a group of populations or, similarly, a species and it component subspecies. An example from my work is that what we thought were closely related members of one species turn out to be not closely related at all. This means that migration must have evolved more than once in the group. Further, when we add the additional findings that one group is substantially older than the other and that the more recent group has undergone a range expansion across South America in relatively recent evolutionary time, we can go still further and integrate these findings with the palaeoenvironmental literature. This enables us to link landscape changes with what we can infer of the history of the birds themselves. We can begin to get a temporal perspective on how migration has evolved in a given group of birds. The potential to extend this approach is as broad as the number of migrants.
A key factor in realizing this potential is that of ornithologists across South and North America working together to gather and analyze samples.
The basic tools are those of DNA sequencing and analyses of DNA sequence data for both population genetics and phylogeny. One looks forward to incorporating new tools from the ever-growing inventory of molecular techniques.
Estimated Cost
It can be pretty expensive in the lab as one extracts DNA and sequences it. The laboratory work alone can cost around five thousand dollars for all the lab supplies and so on to really thoroughly analyze say 50 individuals. It can get closer to ten thousand dollars if a lot of filed work involves large travel distances for the researchers to get to the field.
Related Literature
Joseph, L., Wilke, T., Bermingham, E., Alpers, D and Ricklefs, R. 2004. Towards a phylogenetic framework for the evolution of shakes, rattles and rolls in Myiarchus tyrant-flycatchers (Aves: Passeriformes: Tyrannidae). Molecular Phylogenetics and Evolution. 31: 139-152.
Joseph, L., Wilke, T., and Alpers, D. 2003. Independent evolution of migration on the South American landscape in a long-distance temperate-tropical migratory bird, Swainson's Flycatcher (Myiarchus swainsoni). Journal of Biogeography 30: 925-937.