Effects of frugivorous birds on seed dispersal and population genetic diversity of Phytolacca americana

Phytolacca americana (pokeweed), a toxic North American invasive plant, has established novel seed-dispersal mutualisms with native frugivorous birds in China, facilitating its rapid spread. We investigated this plant-bird interaction by integrating field surveys, germination experiments, gut microbiota analyses, and population genetics. Infrared monitoring identified Streptopelia orientalis and Cyanopica cyanus as primary fruit consumers. Compared with the control seeds, gut passage by Streptopelia orientalis significantly accelerated the seed germination dynamics and increased the final germination proportions. Gut microbiota analysis revealed that P. americana consumption induced marked enrichment of Lactobacillus plantarum and Massilia spp.—bacteria known to degrade saponins and sequester heavy metals, the plant’s principal toxins. Microsatellite genotyping of 300 individuals across two generations showed moderate genetic diversity, low generational differentiation, and fine-scale structure (optimal K = 5). Effective population size was extremely low, suggesting limited evolutionary resilience despite demographic success. Our findings demonstrate that consumption of P. americana fruits alters the gut microbiota of native frugivorous birds. This interaction elevates seed germination dynamics and final germination proportions, which may facilitate the spread of invasive P. americana , and influences its population genetic architecture. This plant-bird-microbiota nexus appears to facilitate the invasion success of chemically defended alien plants.