# Contrasting effects of pollinators on the pollination success of floral morphs of a distylous bowl-shaped flower

## TL;DR

This study explores how different pollinators affect the pollination success of two floral morphs in a distylous plant species.

## Contribution

The study introduces a novel method to assess pollination quality using the relationship between pollen tubes and pollen grains.

## Key findings

- Short-styled flowers showed lower pollen quality when visited less by Usia genus insects.
- Usia pollinators were found to promote disassortative pollination in L. narbonense.
- Pollination success varied depending on the pollinator environment and flower visitor composition.

## Abstract

In distylous species, the reciprocal arrangement of sexual organs between long-styled and short-styled individuals promotes disassortative pollen flow through a fine-tuned interaction with pollinators. Despite its evolutionary importance, deviation from this expectation due to suboptimal pollinator performance has been little studied in species with open corollas. This study addresses which insects visiting the flowers of Linum narbonense (Linaceae) promote or break down the expected patterns of pollination.

Sixteen samplings performed in 12 populations allowed me to analyse the relationship between flower visitors and pollination performance of each floral morph. A total of 3494 stigmas were analysed to measure two components of pollination success: a quantity component that included the proportion of pollinated stigmas and pollen load on stigmas; and a quality component that included for the first time the relationship between pollen tubes and pollen grains on stigmas. Hand-pollination experiments made it possible to characterize the breeding system and to construct a null model of the pollen tube response to legitimate pollen.

Contrary to long-styled flowers, flowers with short stigmas showed wide variation in the quality of pollen receipt across sampling units, usually being lower than expected by the null model. This variation depended on the proportion of flower visits by insects from the Usia genus (Bombyliidae): low visitation rates by these insects were associated with lower pollen quality deposited on short stigmas.

This study demonstrates the value of addressing the quantity and quality of pollen receipt to correlate pollination success with contemporary pollinator environment. The novel use of the relationship of pollen tube to pollen grain demonstrated the importance of Usia pollinators in promoting disassortative pollination in the distylous L. narbonense. These findings emphasize the importance of identifying which flower visitors promote the functioning of distyly or, conversely, disrupt it, biasing the functional gender of floral morphs.