Canada geese and the epidemiology of avian influenza viruses.

Canada geese (Branta canadensis) are numerous, highly visible, and widely distributed in both migratory and resident populations in North America; as a member of the order Anseriformes, they are often suggested as a potential reservoir and source for avian influenza (AI) viruses. To further examine the role of Canada Geese in the ecology of AI, we re-evaluated existing literature related to AI virus in this species and tested breeding populations of Canada Geese from three states (Georgia, West Virginia, and Minnesota, USA) by virus isolation and serology. The ability of AI virus to persist in goose feces under experimental conditions also was evaluated as an additional measure of the potential for this species to serve as an AI virus reservoir. Virus was not isolated from 1,668 cloacal swabs and type-specific antibody prevalence was low (4/335, 1.2%). Finally, under experimental conditions, AI virus persistence in goose feces and in water contaminated with goose feces was limited as compared to published estimates from duck feces and water. Our results are consistent with historic reports of a low prevalence of AI virus infection in this species, and we suggest that Canada Geese play a minor, if any, role as a reservoir for low pathogenic AI viruses that naturally circulate in wild bird populations.

Microbialite resurgence after the Late Ordovician extinction.

Microbialites, including biogenic stromatolites, thrombolites and dendrolites, were formed by various microbial mats that trapped and bound sediments or formed the locus of mineral precipitation. Microbialites were common and diverse during the Proterozoic, but declined in abundance and morphological diversity when multicellular life diversified during the Cambrian Radiation. A second decline occurred during the Ordovician Radiation of marine animals, and from then until the present microbialites have been confined largely to high-stress environments where multicellular organisms are rare. The microbialite declines in the Phanerozoic are attributed to disruption of the mats by animals. A resurgence of stromatolite abundance and size during reduced animal diversity after the Permian extinction has been documented anecdotally. Here we show, with statistical support, that a microbialite resurgence also occurred after the Late Ordovician extinction event in western North America. The resurgences were associated with loss of mat-inhibiting animals, providing insights into shallow-water community structures after extinction events.