Pollen flow within and among isolated populations of two rare, self-compatible plant species from inselbergs of Northeast Brazil

Abstract

Endangered species in isolated habitats (e.g., inselbergs) may escape mate limitation during patch colonization through autonomous self-pollination. After colonization, the higher the number of plants breeding randomly within populations through cross-pollination, the lower is genetic erosion caused by genetic drift and inbreeding. Additionally, pollen flow among patches can increase population genetic variation [natural genetic recovery (NGR)]. Autonomous self- and cross-pollination were investigated within small isolated populations of the rare hummingbird-pollinated Ameroglossum pernambucense and A. manoel-felixii from inselbergs of Northeastern Brazil. We also used A. manoel-felixii and the widespread Encholirium spectabile (mainly bat-pollinated) to compare potential for NGR. In both Ameroglossum species, we performed controlled pollination experiments to test for autonomous self-pollination. Additionally, we compared fruit and seed production (reproductive output) between flowers exposed to and isolated from pollinators to test the potential for cross-pollination. We assessed the extent of cross-pollination within populations, using Wright?s genetic neighborhood model. In A. manoel-felixii and E. spectabile, we tested the potential for NGR among three nearby inselbergs. Pollen movement was tracked using fluorescent dyes. Populations of both Ameroglossum species self-pollinate, but pollinators increased fecundity, revealing potential for cross-pollination. Nonetheless, the area comprising random cross-pollination corresponded to ~ 3% of the area occupied by the Ameroglossum populations, suggesting poor capacity to counteract genetic erosion. In contrast, although both species showed potential for NGR, bat pollination in E. spectabile may facilitate NGR in more remote populations. This study suggests the predominant role of cross-pollination among small, isolated populations as the main force against genetic erosion.