| Abstract: | Genetically divergent lineages (biotypes) often coexist within local populations of the selfing annual Amphicarpaea bracteata (Leguminosae). At one site, a rapid change in lineage frequency was observed, with one biotype decreasing from 41% to 16% of the population over a 2 year period. During 6 additional years of censuses, this lineage showed no tendency to recover to its former abundance. An experimental population was constructed with approximately equal numbers of individuals from the two dominant biotypes in this population, and plants were allowed to grow and reproduce without interference for 3 generations. The same lineage that declined in the natural habitat was also strongly selected against in this experimental population, with a selection coefficient (0.57 per generation) comparable to that inferred from the initial decline in frequency of this lineage in nature (0.47). A greenhouse experiment suggested that differential adaptation to high vs. low light environments could be one factor affecting relative success of these lineages. Differences in reproductive allocation and disease resistance to local pathogens are also key factors likely to affect relative fitness. Overall, these results show that the genetic structure of selfing plant populations can be highly dynamic, with intense selection and sudden shifts in relative abundance of different lineages. |
