Population genomics of Tillandsia landbeckii reveals unbalanced genetic diversity and founder effects in the Atacama Deserts in the Atacama Desert

Abstract

In hyper-arid habitats vegetation tends to be highly patchy with individual plant populations set widely apart from each other. In the Atacama Desert of northern Chile, rainfall is essentially absent, but fog occurring both at the coast and sometimes reaching inland areas supports patches of vegetation in an otherwise barren environment. Tillandsia landbeckii (Bromeliaceae), a epiarenic plant without functional roots, completely depends on fog as source for water, therefore it is found only in fog corridors. Here, we investigate the genetic connectivity within and between populations of T. landbeckii, using genome-wide single-nucleotide-polymorphisms (SNP) obtained through genotyping-by-sequencing (GBS). The 21 sampled populations from the Chilean Atacama Desert are distributed in three geographically ordered south to north clusters, with the southern cluster containing only one population that is genetically very distant from the others. From our study we obtained three genetic groups that corresponded to these three geographical clusters, with the exception of the two populations 16 and 18, where genetic affiliation lies at least in part with the central cluster. Further, our results show uneven distribution of genetic diversity among the populations with highest diversity in the central cluster. We found large amounts of shared heterozygous SNPs as well as negative values for the inbreeding coefficient F-IS in the populations of the north and south. They indicate that these populations are strongly affected by clonal reproduction, while the populations in the center are mostly reproducing sexually. We interpret these data as the result of genetic bottlenecks due to founder events involving few dispersing genotypes combined with strong geographical isolation for the northern and southern populations, following stepping stone dispersal of Tillandsia during more climatically favorable episodes.