Sage-grouse are a lekking galliform species in which males congregate on communal display grounds (leks) and females select a mate, breed, and then incubate eggs and raise young on their own (Wiley 1973; Gibson 1996). Sage-grouse are endangered at the provincial (Alberta Sage-Grouse Recovery Action Group 2005) and federal (Lungle and Pruss 2008) levels in Canada where they are located at the northern periphery of the species’ range. Sage-grouse in Canada have declined by 66-92% over the last 35 years (Aldridge and Brigham 2003) with a population crash in 1994. The current estimated population size is approximately 300 – 400 birds based on 2006 – 2009 lek counts, which has dropped substantially from the 1999 estimation of 813-1204 birds (Aldridge and Brigham 2003). Historically, the species inhabited three Canadian provinces (Alberta, Saskatchewan, and British Columbia) and 16 U.S. states, but presently occurs only in southeastern Alberta, southwestern Saskatchewan, and 11 U.S. states (Schroeder et al 2004). Rangewide, the amount of sagebrush habitat has decreased by greater than 50% (Schroeder et al. 2004) and in Canada, potential habitat has declined from 100 000 km2 to 6000 km2 (Aldridge & Brigham 2003). Only 6% of potential habitat remains in Canada, where there are currently two disjunct regions supporting sage-grouse separated by more than 100 km. Suggested causes for the decline include oil and gas development (Braun et al. 2002), intensive livestock grazing (Aldridge et al. 2004), wildlife viewing, changes in the predator community, climate change, and widespread destruction of habitat in neighboring Montana (Alberta Sage-Grouse Recovery Action Group 2005). Throughout most of the species’ range, sage-grouse are associated with big sagebrush (Artemisia tridenta), but in Canada, the species is dependent on silver sagebrush (A. cana), as its main food and source of cover (Alberta Sage-Grouse Recovery Action Group 2005). The distribution of silver sagebrush is naturally patchy, so birds have adapted to move large distances to find suitable habitat.
To investigate the existence of genetic impacts
connected with a demographic decline, individuals from the entire time span of
the decline should be assessed. Therefore, we expanded our contemporary
research to include Canadian sage-grouse samples from 1895 to present to
investigate four main questions. (1) Has genetic diversity declined over time?
(2) Has the sage-grouse population in Canada become more genetically structured
with decreases in available habitat? (3) Is there evidence for a genetic
bottleneck accompanying the demographic bottleneck in the 1990s? (4) What is
the current and past effective population size? While the demographic decline
in Canada has been severe, contemporary genetic diversity is comparable to
regions not experiencing drastic declines. This suggests that
diversity has been maintained through immigration from the southern part of the
population. Sage-grouse in Canada presently show little genetic structure even
in the presence of habitat loss and degradation, therefore historic birds that
inhabited less fragmented habitat should exhibit little structure as well. We
expected to find a genetic signature from the population crash in 1994 due to
its severity and the fact there has been no recovery in the past 15 years. Finally, we expected a reduction in Ne, as it is
tied to population size and should mirror the documented population decline
(Connelly et al. 2004; Lungle and Pruss 2008).