Return to Beringia: parasites reveal cryptic biogeographic history of North American pikas

Authors: GALBREATH, KURT - Washington University; Hoberg, Eric

Submitted to: Proceedings of the Royal Society of London B
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2011
Publication Date: 6/15/2011
Citation: Galbreath, K.E., Hoberg, E.P. 2011. Return to Beringia: parasites reveal cryptic biogeographic history of North American pikas. Proceedings of the Royal Society of London B. 279:371-378.

Interpretive Summary: Biological invasion is a primary process that determines the distribution of complex assemblages of parasites and hosts; such processes have served as determinants of biological structure in contemporary and historical communities. Knowledge of biological structure and the forces involved in the occurrence and distribution of parasites represent important cornerstones for understanding patterns of biodiversity in space and time. Exploring a model system of hosts and parasites now reveals important insights about how the North American parasite fauna was assembled over time, and recognizes a critical role for the Bering Land Bridge. As a dispersal corridor between the northern continents, the Bering Land Bridge played a key role in shaping Holarctic biotas. The Beringian paradigm identifies the land bridge as a zone of predominantly eastward expansion (invasion) from Eurasia and a staging area for subsequent colonization of lower latitudes in North America, but its underlying assumptions have not been completely tested. We applied an analytical method called “host-parasite comparative phylogeography” (HPCP) to test this biogeographic model, based on parasites in small lagomorphs known as pikas. We studied phylogeographic patterns (population genetic structure) in five lineages of host-specific parasites shared by the Collared pika (Ochotona collaris) and American pika (O. princeps) of North America to determine whether the southern host species (O. princeps) was descended from a northern ancestor, consistent with the Beringian paradigm, or vice versa. Three parasite phylogenies revealed patterns consistent with the hypothesis of a southern origin, and four additional parasite lineages restricted to O. princeps corroborate this biogeographic inference. This finding reverses the traditional Beringian narrative. As one of the most taxonomically extensive HPCP analyses, this study demonstrates the power of HPCP for resolving complex biogeographic histories that are not revealed by characteristics of the host alone. These studies have direct implications for defining the interface for parasite faunas in general, and those that circulate in free-ranging and domestic ungulates, and other food animals of importance. As a method to resolve complex relationships in host-parasite system, we further demonstrated the utility of HPCP to address fundamental questions about the distribution of parasites and the forces that have served as determinants in both evolutionary and ecological time.

Technical Abstract: As a dispersal corridor between the northern continents, the Bering Land Bridge played a key role in shaping Holarctic biotas. The Beringian paradigm identifies the land bridge as a zone of predominantly eastward expansion from Eurasia and a staging area for subsequent colonization of lower latitudes in North America, but its underlying assumptions have not been thoroughly tested phylogenetically. Here we apply a host-parasite comparative phylogeographic (HPCP) approach to test this biogeographic model. We studied phylogeographic patterns in five lineages of host-specific parasites shared by the Collared pika (Ochotona collaris) and American pika (O. princeps) of North America to determine whether the southern host species (O. princeps) was descended from a northern ancestor, consistent with the Beringian paradigm, or vice versa. Three parasite phylogenies revealed patterns consistent with the hypothesis of a southern origin, and four additional parasite lineages restricted to O. princeps corroborate this biogeographic inference. This finding reverses the traditional Beringian narrative. As one of the most taxonomically extensive HPCP analyses, this study demonstrates the power of HPCP for resolving complex biogeographic histories that are not revealed by characteristics of the host alone.