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Assessment of Virus Movement across Continents and among Populations: Using Dunlin as a Test Case
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There is serious concern over the probability that migratory waterbirds might spread highly pathogenic avian influenza H5N1 (HPAI) from Asia to North America. For this to occur, infected, virus-shedding wild birds must cross the inter-continental boundary, and when these birds intermix with other wild bird populations, there must be successful intra- or inter-specific transmission of the virus. That migratory birds can carry the HPAI virus between continents now seems likely that they have or can transmit the virus to other wild or domestic stocks of birds remains a topic of considerable interest. The propensity for such inter-continental and inter/intra-specific transmission will require additional study on live, migratory birds that visit HPAI infected areas. Given the rarity of HPAI, examination of other virus subtypes in wild birds can be a useful means for predicting the probability and pathway of HPAI dispersal from Asia to North America. Over the past year, a non-HPAI subtype has been identified in 10 species of shorebirds (i.e., Charadriiformes). Preliminary tests indicate that 1-2 % of the shorebirds sampled have a non-HPAI subtype, but avian influenza prevalence is known to change depending on the time of year sampled. These non-HPAI viruses are useful surrogates for evaluating how readily viruses move across populations.
Prior to an avian influenza outbreak in North America, it is critical that we understand population structure and movement patterns of those species identified as being most at risk of inter-continental transmission of AI to identify the origin of infected populations, and where they are headed next on migration so that appropriate health precautions can be taken. Thus, there is an urgent need to develop population-specific genetic markers for high risk species that will determine where a specific individual may have originated and where it (or other infected individuals) may head next. Alternative methods could include extensive banding or radio telemetry throughout the range of each species. However costs, in terms of time and money, for these efforts would be prohibitive and carry no guarantee of being successful. We have worked on these types of connectivity issues for years and have published the only paper on population-specific movements of shorebirds using molecular markers. In addition, we have been collecting samples for many years and have accumulated an extensive back log of samples from many different breeding, migration, and wintering sites in the western hemisphere. Hence, we have the expertise to bring this project to a quick and successful conclusion.
Dunlin are an ideal candidate species for modeling the potential spread of HPAI across continents because two subspecies that occur in Alaska intermix in post-breeding flocks each fall before migrating to separate nonbreeding sites, one along the Pacific coast of North America and the other in South and East Asia. The arcticola Dunlin spend the nonbreeding season in South and East Asia where HPAI is prevalent and then travel to northern Alaska to breed. During the nonbreeding season, arcticola Dunlin intermix with sakhalina Dunlin that migrate to Russia’s Far Eastern Federal District to breed. Pacifica dunlin, in contrast, winter along the Pacific Coast of North America where HPAI has not been detected and then travel to western Alaska to breed. The two Alaskan subspecies remain apart during the breeding season until they intermix in large roosting flocks during fall staging on the Yukon Delta. These distinct migratory pathways and subsequent intra-specific roost formations provide an unprecedented opportunity to evaluate cross-continental and intra-specific transfer of viruses. These facts will enable us to use population specific molecular markers to link breeding, migration, and wintering sites of Dunlin subspecies and document in detail the movements of Dunlin subspecies and populations, and thus the potential for this population to interact with other waterbirds in Asia that may have the virus.
We will use more than 15 years of tissue samples we have collected from breeding, migration, and wintering Dunlin (Calidris alpina) in Alaska, Russia’s Far Eastern Federal District, China, and along the Pacific coast of North America to develop and use population-specific molecular markers for linking breeding, migration, and wintering sites of this species. This information is critical to identify the population structure of this "at risk" species prior to an outbreak of avian influenza (AI) in Alaska and the birds’ subsequent migration, as it will allow managers to identify the origin of infected populations and where they are headed next on migration so that appropriate health precautions can be taken.
We are addressing one of six priority tasks and priority species set out by the U.S. Fish and Wildlife Service Flyway Councils’ National Interagency Strategy Plan -- Interagency HPAI Early Detection Working Group, the Pacific Flyway AI Plan and the USGS Western Region AI Plan (2006). In addition, this work will address needs set out in the U.S. (Canada, and Mexican) National and Regional Shorebird Plans. In particular, the Dunlin has been identified as a species of special concern.
Broadly stated (from the AI plans), we will conduct complementary population delineation studies on migratory birds. More specifically, we will:
- Develop variable microsatellite primers for Dunlin. We will use existing primers if available.
- Screen samples from specific breeding areas across each subspecies range to determine population or region-specific markers.
- Test population-specific markers on samples from migration and/or wintering sites where individuals from known breeding sites have been sampled.
- Use population-specific markers to screen samples from multiple migratory stop-over sites to produce a picture of overall timing of movement of specific populations through migratory stop-over sites throughout North America.
Haig, Susan M. - Supervisory Research Wildlife Biologist
Phone: 541-750-7482
Email: susan_haig@usgs.gov
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