Dry-washes determine gene flow and genetic diversity in a common desert shrub

Abstract

In deserts, many plant species exhibit a patchy spatial distribution within a harsh habitat matrix, where the likelihood of propagule dispersal among patches is uncertain, but may be promoted by landscape corridors or dispersal vectors. We examine the connectivity of a representative desert plant species (Acacia (Senegalia) greggii), and the ability of three major factors (animal dispersal agents, water flow along dry-washes, and climate) to facilitate dispersal within four watersheds in the Mojave National Preserve. We genotyped 323 individuals sampled across 22 one-hectare sites using ten nuclear microsatellite markers. A hierarchical AMOVA revealed no significant differentiation among watersheds (F RT = 0.00, P > 0.10), and very little genetic structure among all sites (F ST = 0.03, P 0.05), a distance measure based on rodent dispersal (P > 0.05), and a distance measure avoiding inhospitable climate (P > 0.05). An AIC comparison of generalized linear models found that within site genetic diversity (H E and allelic richness) and average relatedness were best explained by slope (which increases seed dispersal potential via water flow) and area of the upstream watershed (which determines the number of potential seed donors), rather than plant density or habitat suitability. Together, these findings indicate that dry-washes are key landscape features that enhance dispersal and regional connectivity in this patchy desert plant.