Restricted dispersal in the late successional species Nothofagus pumilio: consequences under global change

Abstract

Plants rely on gamete dispersal to ensure inheritance of their genes. Gene flow, mediated by pollen and seed dispersal, also fosters species’ cohesion across space and influences local adaptation. Understanding effective dispersal distance is key for management and safeguarding genetic resources, especially in the context of global change. Nothofagus pumilio is an ecologically important and emblematic tree species of the Patagonian Andes. We aim to uncover its current and historic effective dispersal distances and characterize its fine-scale genetic structure. In a naturally monospecific stand of N. pumilio located near the middle of its latitude distribution, we sampled 600 individuals (adults and seedlings). Using a modern sequencing approach (SSRseq), we developed 15 reliable microsatellite markers for genotyping. Genetic parameters and fine scale genetic structure were characterized in both generations. Dispersal distances were estimated with direct methods, using classical and Bayesian neighborhood models, and indirect methods. Height and diameter at breast height (DBH) were also measured for adults. Short average seed and pollen dispersal distances were estimated (δs = 13.33 m and δp = 24.08 m respectively), but the fat-tailed distribution of dispersal kernels also suggests some long-distance dispersal events. Indirect estimate of gene dispersal distance (σ2g = 21.62) closely aligns with the direct method. Parental assignments were possible for most seedlings (84%), which were produced by just 43% of sampled adults. Reproductive success was significantly associated with mothers’ DBH. Short seed dispersal distances mean N. pumilio distribution expansion capacity may be limited. Natural and assisted migration actions should be prioritized to mitigate future change effects.