Dispersal and genetic exchange of lichen populations between Patagonia and the Antarctic Peninsula (with a focus on human impact)
Final Report Abstract
Climate change and increasing human activities threaten Antarctic biota with the introduction of alien species and the homogenization of isolated gene pools. We have studied lichens, the most important primary producers of Antarctic terrestrial ecosystems, and evaluated levels of genetic diversity and gene flow among and within South American and Antarctic populations. By comparing areas with high and low human impact, we tried to assess whether human activities have already changed the patterns of isolation and connectivity among populations. To reach this goal, we developed novel microsatellite markers from draft genomes of four taxa (two species of Usnea and Placopsis) and showed that they clarified previously uncertain delimitations of closely related lichen species. Between 266 and 441 individuals of Usnea antarctica and U. aurantiacoatra plus the fruticose Cetraria aculeata were subsequently used in a population genetic study based on 16-22 sampled stands from South America (incl. the Falkland Islands) and different parts of the Maritime Antarctic. The selection of target species was narrowed down to these taxa, because the other species were either not found in South America or the Antarctic or DNA quality was too low to generate draft genomes. Although South American material identified as U. antarctica did not genetically belong to this species, we included it in the study, because it allowed us to study the impact of propagation mode on genetic diversity and population differentiation of two closely related sister taxa. Levels of genetic diversity are lower in the two mostly asexual species U. antarctica and C. aculeata but patterns of population differentiation are more affected by (post)glacial population history than by reproductive mode. Diversity hotspots suggest the existence of glacial refugia on Navarino Island and Livingston or King George Island, where also U. antarctica displays highest diversity. Although we found no evidence for ongoing gene flow from southern South America into the Maritime Antarctic and vice versa, the strong genetic structure of C. aculeata calls for protective measures to avoid gene flow between isolated populations. On the other hand, Antarctic populations of U. aurantiacoatra and U. antarctica are extremely diverse and weakly isolated within the study area and do not seem to require conservation measures. The microsatellite markers developed here should be used to study genetic diversity and structure over larger areas along the Antarctic Peninsula could prove useful for monitoring short-term effects of human activities (building, maintenance of infrastructure, trampling by scientists and tourists etc.) on lichen populations. Universidad Complutense de Madrid has produced a video documentation on the lichenological expedition to Livingston Island, in which aspects of our project (although no results at that time) are outlined (https://www.youtube.com/watch?v=M2qm3AAXEGE&list=PLQ8yHMSBC8UDC8QfgUSDPx6 vnVQuxuvGn&index=15&t=0s&app=desktop).
