Abstract
Functional connectivity (i.e., the movement of individuals across a landscape) is essential for the maintenance of genetic variation and persistence of rare species. However, illuminating the processes influencing functional connectivity and ultimately translating this knowledge into management practice remains a fundamental challenge. Here, we combine various population structure analyses with pairwise, population-specific demographic modeling to investigate historical functional connectivity in Graham’s beardtongue (Penstemon grahamii), a rare plant narrowly distributed across a dryland region of the western US. While principal component and population structure analyses indicated an isolation-by-distance pattern of differentiation across the species’ range, spatial inferences of effective migration exposed an abrupt shift in population ancestry near the range center. To understand these seemingly conflicting patterns, we tested various models of historical gene flow and found evidence for recent admixture (~ 3400 generations ago) between populations near the range center. This historical perspective reconciles population structure patterns and suggests management efforts should focus on maintaining connectivity between these previously isolated lineages to promote the ongoing transfer of genetic variation. Beyond providing species-specific knowledge to inform management options, our study highlights how understanding demographic history may be critical to guide conservation efforts when interpreting population genetic patterns and inferring functional connectivity.
Highlights
Intensifying interactions between habitat destruction and climate change are a major threat to the persistence of many native species across the globe (Travis 2004; MantykaPringle et al 2012)
The maintenance of functional connectivity between populations of rare species experiencing habitat fragmentation is essential for the conservation of biodiversity (Allendorf et al 2012)
As we demonstrate through our investigation of spatial genetic patterns in P. grahamii, correct interpretation of contemporary genetic patterns may necessitate the inclusion of a historical perspective to best inform management
Summary
Intensifying interactions between habitat destruction and climate change are a major threat to the persistence of many native species across the globe (Travis 2004; MantykaPringle et al 2012) As these processes fragment a species’ range, isolated populations may experience stronger genetic drift and inbreeding, leading to the loss of genetic diversity and increasing the chance of local extinction over time (Wright 1931; Allendorf et al 2012). 2 U.S Geological Survey, Southwest Biological Science Center, Moab, UT, USA functional connectivity (i.e., the movement of individuals and genes across the landscape; Crooks & Sanjayan, 2006) between populations of rare species in the face of increasing habitat fragmentation is essential for the conservation of biodiversity (Allendorf et al 2012). Regions of a species’ range marked by relatively sharp transitions in genetic differentiation may occur when current gene flow is restricted by environmental gradients (Manthey and Moyle 2015; Weber et al 2017), physical barriers
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