The Role Of Co-Flowering Dynamics In Mediating Heterospecific Pollen Effects On Plant Reproductive Success

Flowering plants require pollen transfer between flowers of the same species for successful pollination. Pollination can fail when pollen is transferred between different species because heterospecific pollen (HP) deposition can reduce seed production. However, strong variation in the magnitude of HP effects has been observed among plant species and the underlying causes are largely unknown. We propose that HP effects are stronger between donor and recipient pairs with a low degree of co-flowering (low HP exposure), compared with pairs that often flower together and hence have high HP exposure. To test this, we conducted a greenhouse experiment where we hand pollinated a focal plant species with different pollen-mixes of co-flowering and non-co-flowering species. We found that greater co-flowering overlap increases tolerance to HP and can even enhance fitness, whereas limited overlap leads to stronger negative fitness effects. These findings may help explain broader patterns of variation in HP effects.