Connectivity of a patchy Mojave Desert shrub: Examining landscape genetics at multiple spatial and temporal scales

Background/Question/Methods

The influence of landscape on movement is an essential part of understanding the mechanisms and limitations of dispersal. In a changing habitat this informs predictions of future response to a variable environment. New tools using graphical and multivariate statistics have increased our ability to identify more nuanced sub-structuring patterns that are often concealed by basic F statistics. Acacia greggii A Gray is a patchy desert shrub whose movement is likely influenced by several landscape features. In the Mojave National Preserve, we have previously shown that local population density and pollinator communities affect reproduction in this species, suggesting pollen movement is defined at a local scale. Seed dispersal is likely limited by water availability and habitat restrictions. Sporadic rainfall events may account for a large portion of dispersal, moving seeds along washes where new establishment can occur and restricting movement in lower more arid elevations. We examine the effect of these landscape features on the connectivity of A. greggiiat two spatial and temporal scales by extensively sampling leaf and seed tissue regionally and locally. We used 10 variable microsatellite loci to genotype 500 adults.

Results/Conclusions

Our analysis shows a species with distinct landscape effects on gene flow. The region has well connected populations, with a history of frequent gene flow events, but more limited movement locally. Graphical analysis suggests limitation to dispersal along certain landscape elements; mountain chains are facilitative to long distance movement and low lying valleys act as barriers. Our fine scale analysis shows more defined genetic structuring. We showed significant structure between parallel washes suggesting washes serve as corridors for movement in this species. Genetic variation, however, was best explained by elevation. We have documented a strong effect of elevation on phenology of A. greggii and it is possible that differences in flowering times between high and low populations may impose limitation to pollen flow in this species.