Dispersal and population genetic structure in two flyways of sandhill cranes (Grus canadensis).

摘要

I studied dispersal patterns in Sandhill Cranes using distances travelled by banded and radio-tagged birds and estimates of gene flow using genetic markers. In Wisconsin, territorial Sandhill Cranes showed long-term pair bonds and strong site fidelity, however, 58% of 119 banded pairs ended due to mate switch (divorce or mate death). Territory retention was high following any mate switch. The bird leaving the territory moved (on average) 0.9 km to an adjacent territory. Sandhill Crane chicks dissociated from their parents before fall migration (12%), over winter (79%), or following spring migration (9%). Using mark-recapture analysis, timing of separation did not affect long-term chick survival estimates (92%). Following independence, home ranges of one-year-old birds were larger than two-year-olds and three-year-olds. Females traveled further from their natal area than males, but both sexes returned near their natal area by three-years-old. Sandhill Cranes obtained breeding territories at 4.5 years-old and males nested closer (2.3 km) to their natal area than females (10.7 km).;Significant population genetic structure occurred among breeding sites in the Eastern Population. Pairwise Fst and assignment of birds to genetic clusters suggest long-distance dispersal was prevalent following the population bottleneck in the 1930's. Re-colonization in the northeastern U.S. likely resulted from eastward expansion of the EP and southern expansion of the Mid-continent Population from Hudson's Bay. Three populations (Pacific Flyway Population, Central Valley Population, and British Columbia Coast Population) in western North America also showed significant population genetic structure. PFP Lessers and CVP Greaters each formed two genetic clusters. BCCP Canadians clustered with one CVP cluster, but on a separate topological branch. Three birds from Sauvie Island, Oregon formed a fifth genetic cluster, likely representing individuals from unrelated populations. Population genetic structure in these study populations of Sandhill Cranes is modulated by strong natal philopatry and infrequent, but effective long-distance dispersal. This research provides a framework to study natural recolonization wild crane populations. Despite passage through population bottlenecks, remnant genetic diversity in all study populations of Sandhill Cranes is substantial. These results indicate that population bottlenecks had a greater effect on dispersal processes than loss of genetic variation during recovery.