Life in the desert: habitat spatial complexity, gene flow, and
functional connectivity in Ivesia webberi
Abstract
Habitat protection, by itself, is not sufficient to conserve
range-restricted species with disjunct populations. Indeed, it becomes
critical to characterize gene flow among the populations and factors
that influence functional connectivity in order to design effective
conservation programs for such species. In this study, we genotyped 314
individuals of Ivesia webberi, a United States federally threatened
Great Basin Desert perennial forb using six microsatellite loci, to
estimate genetic diversity and population genetic structure, as well as
rates and direction of gene flow among 16 extant I. webberi populations.
We assessed the effects of Euclidean distance, landscape features, and
ecological dissimilarity on the genetic structure of the sampled
populations, while also testing for a relationship between I. webberi
genetic diversity and diversity in the vegetative communities. The
results show low levels of genetic diversity overall (He = 0.200–0.441;
Ho = 0.192–0.605) and high genetic differentiation among populations.
Genetic diversity was structured along a geographic gradient, congruent
with patterns of isolation by distance. Populations near the species’
range core have relatively high genetic diversity, supporting a
central-marginal pattern, while peripheral populations have lower
genetic diversity, significantly higher genetic distances, higher
relatedness, and evidence of genetic bottlenecks. Genotype cluster
admixture results support a predominant west to east gene flow pattern
for populations near the species’ range center, as well as smaller
genotype clusters with a narrow north to south distribution and little
admixture, suggesting that dispersal direction and distance vary on the
landscape. Pairwise genetic distance strongly correlates with actual
evapotranspiration and precipitation, indicating a role for isolation by
environment, which the observed phenological mismatches among the
populations also support. The significant correlation between pairwise
genetic distance and dissimilarity in the soil seed bank suggest that
annual regeneration of the floristic communities contributes to the
maintenance of genetic diversity in I. webberi.