Negative reproductive interactions are likely to be strongest between close relatives
and may be important in limiting local coexistence. In plants, interspecific pollen
flow is common between co-occurring close relatives and may serve as the key mechanism
of reproductive interference. Agamic complexes, systems in which some populations
reproduce through asexual seeds (apomixis), while others reproduce sexually, provide
an opportunity to examine effects of reproductive interference in limiting coexistence.
Apomictic populations experience little or no reproductive interference, because apomictic
ovules cannot receive pollen from nearby sexuals. Oppositely, apomicts produce some
viable pollen and can exert reproductive interference on sexuals by siring hybrids.
In the Crepis agamic complex, sexuals co-occur less often with other members of the
complex, but apomicts appear to freely co-occur with one another. We identified a
mixed population and conducted a crossing experiment between sexual diploid C.atribarba
and apomictic polyploid C.barbigera using pollen from sexual diploids and apomictic
polyploids. Seed set was high for all treatments, and as predicted, diploid-diploid
crosses produced all diploid offspring. Diploid-polyploid crosses, however, produced
mainly polyploidy offspring, suggesting that non-diploid hybrids can be formed when
the two taxa meet. Furthermore, a small proportion of seeds produced in open-pollinated
flowers was also polyploid, indicating that polyploid hybrids are produced under natural
conditions. Our results provide evidence for asymmetric reproductive interference,
with pollen from polyploid apomicts contributing to reduce the recruitment of sexual
diploids in subsequent generations. Existing models suggest that these mixed sexual-asexual
populations are likely to be transient, eventually leading to eradication of sexual
individuals from the population.