Living at the dry limits: ecological genetics of Tillandsia landbeckii lomas in the Chilean Atacama Desert

The northern Chilean Atacama Desert is among those regions on Earth where life exists at its dry limits. There is almost zero rainfall in its core zone, and the only source of water is a spatio-temporally complex fog system along the Pacific coast, which is reaching far into the hyperarid mainland. Hardly any vascular plants grow in these areas, and, thus, it is intriguing to be faced with a vegetation-type build-up by one single and highly specialized bromeliad species, Tillandsia landbeckii Phil., forming regular linear structures in a sloped landscape. We studied the genetic make-up of a population system extending an area of approximately 1500 km² and demonstrated a fine-scale correlation of genetic diversity with spatial population structure and following an elevational gradient of approximately 150 m. Increase in genetic diversity is correlated with increased fitness as measured by flowering frequency, and evidence is provided that outbreeding is linked with a large-distance flying pollinator feeding occasionally as generalist on its flowers, but not using the plant as source for larvae feeding. Our data demonstrate that establishment of linear vegetation structure is in principle a process driven by clonal growth and propagation of ramets over short distances. However, optimal conditions (slope, elevation, fog occurrence) for linear growth pattern formation also increase sexual plant reproductive fitness, thus providing the reservoir for newly combined genetic variation and counteracting genetic uniformity. Our study highlights the Tillandsia vegetation, also called Tillandsia lomas, as unique and genetically diverse system, which is highly threatened by global climate change and disturbance of the coastal fog system.