Seed and pollen deposition on Salvia przewalskii

Generalized pollinators visit multiple co-flowering plant species and may
transfer heterospecific pollen grains. Recent studies have indicated that
the effect of heterospecific pollen (HP) on reproduction success is
variable and depends on the identity of donor and recipient species.
However, few studies have documented variation in HP receipt and evaluated
the reproductive effects of HP receipt across geographic locations under
natural conditions. We investigated the spatial variation of pollen
deposition across eight sites and how the pollen receipt related to seed
set of Salvia przewalskii, a subalpine perennial herb in Hengduan Mountain
in southwest China. We found that stigmatic pollen loads substantially
varied among sites for several metrics, including quantities of
conspecific and heterospecific pollen, the proportion of HP, and species
composition of HP donors. Five different plant families were the most
common HP source at one or two sites, and the proportion of HP ranged from
3.4–51.3% across sites. The association of conspecific pollen with seed
set was positive and variable among sites, whereas the association of HP
receipt and seed set was negative and not significantly different among
sites. Our results demonstrate variation in the quantity and fitness
effect of pollen receipt across sites, which is a precondition for
evolution of local adaptation. Further study of variation in patterns and
effects of HP receipt for the same recipient species across natural
communities would allow for better understanding of the ecological and
evolutionary consequences of HP receipt.