Patterns of pollen dispersal and mating in a population of the clonal plant Sagittaria latifolia

1) Increased plant size is generally expected to have negative
consequences for mating by increasing pollen transfer between flowers of
the same plant. Such geitonogamous self-pollination would then reduce
sexual fitness through both female and male function. However, recent
theoretical work has indicated that when plants grow clonally, the outward
expansion of plants caused by clonal growth might have positive effects on
siring without substantially increasing rates of self-pollination. 2) We
investigated patterns of pollen dispersal, selfing, and siring in a
monoecious population of the clonal plant Sagittaria latifolia, in which
clones varied in size and the extent of intermingling with other clones. A
spatially-explicit statistical model based on the inferred
pollen-dispersal kernel was constructed to examine the mechanisms
underlying observed mating patterns. 3) Pollen dispersal typically
occurred over distances that exceeded the spatial extent of clones. There
was a positive association between clone size (measured as the number of
ramets per genet) and the likelihood that clones were intermingled with
the shoots of other clones. Together, these patterns of pollen dispersal
and clonal intermingling resulted in a weak positive association between
clone size and selfing rates and a strong positive association between
clone size and outcross siring success. These patterns were replicated in
the spatially-explicit model, indicating that the intermingling of clones
is an important determinant of mating patterns in this population. 4)
Synthesis. Our study provides the first examination of the pollen
dispersal kernel for a clonal plant. It is the first study providing
empirical support for model predictions that potentially negative effects
of increased selfing in large clones might be offset by increased siring
success. This implies that the negative consequences of becoming large do
not necessarily apply to clonal plants.