Shift in flowering time allows diploid and autotetraploid Anacamptis pyramidalis (Orchidaceae) to coexist by reducing competition for pollinators

How autopolyploids establish when competing with diploid progenitors is still poorly understood. Here, we investigate the effects of morphological and phenological divergence on the reproductive success of co-occurring diploid and autotetraploid individuals of Anacamptis pyramidalis to disentangle the mechanisms allowing their c-oexistence. We estimated reproductive success in terms of absolute and relative fruit production and recorded morphological and phenological traits of the two cytotypes. We also estimated correlations between traits within cytotypes and the related phenotypic selection patterns. The two cytotypes experience similar levels of reproductive success, but they differ significantly in their morphological and phenological traits. Correlations among floral traits were weaker in autotetraploids than in diploids, but among-individuals variation was higher in diploids. For most flower traits, the strength of phenotypic selection was different in the two cytotypes. We found selection on flower number in both cytotypes, whereas selection for earlier flowering time was only found in late-flowering diploids. Our results suggest that a shift in flowering time may have allowed diploid and autotetraploid A. pyramidalis individuals to reduce competition for naïve pollinators. Consequently, the two cytotypes can coexist by attaining similar levels of reproductive success and, at same time, reducing the likelihood of inter-cytotype mating.