Reproductive interactions between hybridizing species of Piriqueta

Post-pollination mechanisms can play an important role in limiting or promoting natural hybridization in plants. I used controlled hand pollinations with mixtures of genetically marked pollen to study these mechanisms in two species of Piriqueta that hybridize in central Florida: Piriqueta caroliniana and P. viridis. More F₁ hybrids were produced by P. viridis plants than by P. caroliniana. Relative pollen-tube growth rates were significantly different between the two species, with P. caroliniana tubes outperforming P. viridis tubes in both intra-specific and inter-specific styles. Although pollen competition may not limit the formation of hybrids in P. viridis, pre-fertilization gamete attrition apparently acts against the formation of hybrids. Pollen competition acts as an inter-specific insolating mechanism in P. caroliniana, but there may also be selective abortion of intra-specific ovules after fertilization in this species. Experimental crosses show that there is asymmetric hybridization in Priqueta, with P. caroliniana being more successful in siring hybrid seeds and a more selective mother than P. viridis. Backcross seeds were formed at higher frequencies in P. viridis than in P. caroliniana indicating introgression is likely to occur in the direction of P. viridis populations after initial F₁ establishment. Further work is needed to compare the results predicted from mating interactions to field experiments.