BREEDING SYSTEM AND EARLY STAGE INBREEDING DEPRESSION IN A NOVA SCOTIAN POPULATION OF THE GLOBAL RARITY, SAB ATI A KENNEDYANA (GENTIANACEAE)

摘要

The survival of populations of rare plant species may be affected both by total levels of seed production and by inbreeding depression expressed upon self-fertilization. We examined natural seed production and rates of self-fertilization in a Nova Scotian lakeshore population of the globally rare Atlantic Coastal Plain plant, Sabatia kennedyana Fernald (Gentianaceae), and determined the effect of self and cross pollinations on fitness at early plant life stages. Seed production was not limited by natural pollination levels. Furthermore, flowers from which pollinators were excluded produced 66% as many seeds as unprotected, naturally pollinated plants, indicating that substantial seed set can occur in the absence of pollinators. The selfing rate of naturally pollinated flowers was estimated as 21% using the inbreeding depression method. Stage-specific inbreeding depression was 19% at germination, and cumulative inbreeding depression from fertilization through germination was 23%. Seed formation (seeds per fertilized ovule) was correlated with proportional germination suggesting linkage or pleiotropy of genes affecting these two life-history stages. Low, early acting inbreeding depression may result from purging of deleterious mutations in low population times during the post-glacial migration of founders into Nova Scotia from the now submerged Continental Shelf habitat. Alternatively, the inbreeding depression values documented for early developmental stages may underestimate its severity at laterstages. Crosses between plants in the study population and those at another lake, four km distant, suffered no decrease in performance ("outbreeding depression") at these early life stages.