Right and left chiral flowers in Hypericum perforatum (Hypericaceae) do not contribute to directed pollen movement

Background/Question/Methods

Corolla chirality (i.e petals overlap to the right or to the left), is a highly understudied mirror image case in flowers even though it is present in 19 families. Enantiostylous species have mirror image flowers with styles deviated either to the right or two the left. This case of reciprocal herkogamy increases the outcrossing rate when compared to non enantiostylous species. In monomorphic enantiostyly, both morphs are found within an individual at equal frequencies. This 1:1 ratio is reported to be important to assure high outcrossing rates. Corolla chirality differs from enantiostyly for not having a reciprocal stamen to pistil arrangement between flowers, but is similar for having mirror image flowers at a 1:1 ratio. Thus we raise the question whether corolla chirality leads to asymmetric pollen-movement between right and left flowers similar to enantiostylous flowers. This could be achieved through differential pollinator behavior between right and left flowers or by pollen-stigma incompatibility between the two chirality morphs. In this study we attempt to quantify how chirality influences mating patterns. We quantified basic reproductive traits and pollinator interactions both for right and left flowers in two populations of Hypericum perforatum.

Results/Conclusions

We found no significant differences in the reproductive traits and pollinator interactions between right and left flowers for H. perforatum. Right and left flowers did not differ in pollen and ovule number, pollinators seemed indifferent to corolla chirality and we found no difference in pollen deposition or pollen-stigma incompatibility between right and left flowers. In addition, we found a 1:1 ratio of right and left flowers at the population level as well as a random distribution of chirality types within an inflorescence.

Our results indicated no role for corolla chirality on pollen movement and hence no observable effect on mating patterns. This study provides initial evidence suggesting that corolla chirality, unlike other mirror image floral designs, plays no role in mating patterns.