Post‐pollination barriers in an assemblage of Bromeliaceae in south‐eastern Brazil

The co‐occurrence of different species and genera of Bromeliaceae in a plant community in south‐eastern Brazil gave us the opportunity to test for pre‐ and post‐zygotic barriers to interspecific gene flow. We evaluated the inhibition of pre‐zygotic pollen tube growth in 13 species of Bromeliaceae in an assemblage with a large overlap of flowering periods and similar guild of flower visitors. After controlled heterospecific pollinations, we searched for arrested pollen tube growth or congruous ovule penetration using fluorescence microscopy techniques. We observed congruous crosses in 27 (26.5%) and incongruity phenomena in 75 (73.5%) out of 102 heterospecific crosses performed. We recorded ovule penetration in six out of 28 interspecific crosses (21%) and 21 out of 74 intergeneric crosses (28%). In incongruous crosses, we recorded pollen tube inhibition in the pistil, which is evidence for pre‐zygotic post‐pollination barriers. Species including Aechmea araneosa and Quesnelia quesneliana showed a high frequency of congruous ovule penetration after heterospecific crosses, occasionally reciprocally with the pollen donor. Although we conclude that hybridization is feasible in the assemblage, our results also suggest that post‐pollination reproductive barriers involving pollen inhibition are the primary mechanisms preventing heterospecific gene flow as pre‐pollination barriers (phenological and ethological) appear to be weak.