For my dissertation research, I studied both living North American pikas and their tapeworm and roundworm parasites, and developed independent DNA sequence data sets for the hosts and their parasites. My work had several goals:

1) trace population size fluctuations through time and relate changes to the history of climatic oscillation during the Quaternary

2) examine the history of isolation and gene flow between major pika genetic lineages to understand the drivers of diversification

3) test for congruence between host and parasite phylogeographic structure to determine the extent to which host and parasite population histories are linked

4) reconstruct the biogeographic history of the two living pika species in North America based on concordant phylogenetic relationships shared among their parasites

I uncovered a history of climate-driven population fluctuations that caused intermittent isolation and contact among the populations of five major mountain systems in western North America.  Though deeply divergent mitochondrial lineages indicated long-term isolation among regional populations, the distribution of genetic variation in nuclear genetic markers was consistent with a history of periodic gene flow.  Phylogeographic analysis of parasites corroborated the nuclear perspective, suggesting widespread host-mediated dispersal.  Dispersal likely occurred as a consequence of pika range expansion during glacial periods, which is consistent with the fossil record. Certainly dispersal among mountain ranges is unlikely to be common under current conditions!

An especially interesting result stemmed from a close look at relationships between parasite populations associated with both pika species in North America. In this case, parasites clarified the biogeographic history of the pikas and turned the traditional view of that history upside down. The pika genus (Ochotona) originated in central Asia, and based on the distribution of the 2 North American species (plus the fact that they are each other's closest relatives) scientists have long presumed that during some past glacial period their common ancestor crossed the Bering Land Bridge, expanded southward along North America's western mountain ranges, and then speciated during a subsequent glacial period when their distribution was sundered by continental ice sheets. Under such a history, northern populations (Collared pikas) might be expected to be paraphyletic with respect to southern populations (American pikas). However, this scenario fails to explain a deeper and more complex fossil record for pikas at low latitudes relative to those at high latitudes. An alternative explanation is that pikas crossed into North America and early on became established across what is now the Lower 48 states of the U.S. The original population in Beringia was lost somewhere along the way, but the region was recolonized by pikas from the south. This south-to-north dispersal scenario could result in southern populations to be paraphyletic with respect to those in the north. Alternatively, if the population splitting event was old enough, northern and southern populations would be expected to be reciprocally monophyletic, which would yield no information regarding the pattern of colonization. This is the case for Collared and American pikas at the genetic markers that have been examined to date, so it appears that the genetic signature of their dispersal history has been lost over time. However, their host-specific parasites offer an independent perspective on their biogeographic history, and for a variety of reasons may be expected to retain genetic signatures much longer than their hosts. Indeed, my analysis of the parasites of North American pikas revealed multiple instances in which northern populations rendered southern populations paraphyletic, strongly implicating a south-to-north colonization history. There is even evidence of westward expansion into Siberia, a reversal of the dominant flow of diversity across the Bering Land Bridge during the Quaternary. Thus parasites provided a window onto a history that has apparently been lost in the host itself, and in so doing demonstrated a biogeographic pattern that has rarely been seen in other animals.

Pika tissues and voucher specimens are archived at the Cornell University Museum of Vertebrates and the Museum of Southwestern Biology. Parasite specimens are archived in the US National Parasite Collection. This work is supported by grants from the National Science Foundation (DEB 0506042), American Society of Mammalogists, Cornell's Andrew Mellon Research Fund, Theodore Roosevelt Memorial Fund, Sigma Xi, and Cornell's Department of Ecology and Evolutionary Biology.

Publications that resulted from this work:

• Galbreath K, Hafner D, Agnew K, and Zamudio K. 2010. Isolation and introgression in the Intermountain West: contrasting gene genealogies reveal the complex biogeographic history of the American pika (Ochotona princeps). Journal of Biogeography. 37:344-362.

• Galbreath K, Hafner D, and Zamudio K. 2009. When cold is better: climate-driven elevation shifts yield complex patterns of diversification and demography in an alpine specialist (American pika, Ochotona princeps). Evolution 63:2848-2863.

• Hoberg E, Pilitt P, and Galbreath K. 2009. Why museums matter: a tale of pinworms (Oxyuroidea: Heteroxynematidae) among pikas (Ochotona princeps and O. collaris) in the American West. Journal of Parasitology 95:490-501.