The genetic network of greater sage-grouse: Range-wide identification of keystone hubs of connectivity

Genetic networks can characterize complex genetic relationships among groups of
individuals, which can be used to rank nodes most important to the overall connectivity
of the system. Ranking allows scarce resources to be guided toward nodes integral
to connectivity. The greater sage-grouse (Centrocercus urophasianus) is a species of conservation concern that breeds on spatially discrete leks that must remain connected by genetic exchange for population persistence. We genotyped 5,950 individuals from 1,200 greater sage-grouse leks distributed across the entire species’ geographic range. We found a small-world network composed of 458 nodes connected by 14,481 edges. This network was composed of hubs—that is, nodes facilitating gene flow across the network—and spokes—that is, nodes where connectivity is served by hubs. It is within these hubs that the greatest genetic diversity was housed. Using indices of network centrality, we identified hub nodes of greatest conservation importance. We also identified keystone nodes with elevated centrality
despite low local population size. Hub and keystone nodes were found across the
entire species’ contiguous range, although nodes with elevated importance to
network-wide connectivity were found more central: especially in northeastern, central,
and southwestern Wyoming and eastern Idaho. Nodes among which genes are
most readily exchanged were mostly located in Montana and northern Wyoming, as
well as Utah and eastern Nevada. The loss of hub or keystone nodes could lead to the
disintegration of the network into smaller, isolated subnetworks. Protecting both hub
nodes and keystone nodes will conserve genetic diversity and should maintain network
connections to ensure a resilient and viable population over time. Our analysis
shows that network models can be used to model gene flow, offering insights into its
pattern and process, with application to prioritizing landscapes for conservation.