Genetic diversity and demographic patterns of a key South American species: Implications for dryland conservation

Abstract

Numerous processes shape genetic diversity in widespread species, with significant implications for conservation planning. In particular, understanding plant demographic patterns is essential for elucidating past evolutionary processes and informing future conservation strategies. We investigated the genetic diversity and demographic patterns of Larrea divaricata, a Zygophyllaceae shrub that dominates the largest dryland of southern South America. We obtained 223 (plastid) and 200 (nuclear) DNA sequences across the species’ range and conducted independent analyses. The plastid DNA revealed 34 locally restricted haplotypes, each differing from the most common haplotype by a single base pair, while the nuclear DNA identified 10 haplotypes. We examined population patterns across four phytogeographic regions: Prepuna, Central and Austral Monte, and Dry Chaco. Our results indicate that populations in the Prepuna region remained stable for extended periods, allowing them to accumulate genetic diversity and exclusive haplotypes, with potential demographic expansions into the other regions. The high plastid diversity and its spatial structure may be explained by limited pollen dispersal and by paternal inheritance of cpDNA, which is uncommon among angiosperms. Meanwhile, the low nuclear genetic diversity and structure suggest shared ancestral haplotypes and a relatively recent origin of genetic diversity. These findings underscore the urgent need for conservation areas, which are scarce in the southern South American drylands. We recommend implementing strategies that prioritize conserving local genetic variants. Additionally, our results offer insights into how plant species cope with harsh environments through demographic adjustments, thereby enhancing our understanding of the ecological dynamics of expanding arid regions under future climate change scenarios.