Safe sex: ant defense does not interfere with pollination in passion flowers

ABSTRACT

Ant defense against floral enemies incurs a two-fold ant-pollinator conflict, both via pollinator deterrence and nectar or pollen collection by non-pollinating protective ants. Some ant-plants have physical barriers whereas others produce ant-repellent chemicals to avoid ant visitation to flowers and subsequent pollination interference. Passiflora coccinea is a hummingbird-pollinated myrmecophilous plant in which floral enemy repellence occurs without limiting ant access to open flowers. To test the hypothesis that ant activity is restricted within flowers to prevent contact with anthers, we compared ant defense response between reproductive (anthers and stigmas) and non-reproductive (bracts, corona and perianth) floral structures by combining an observational survey with an experimental approach. A few insect species were found to visit flowers without providing pollination service, mostly pollen-collecting bees and nectar-thieving butterflies landing on petals. Ants always attacked floral visitors that landed on non-reproductive structures, but they never attacked insects visiting reproductive structures as ants never accessed anthers. Our results suggest that the differential ant defense response is an adaptative process to prevent ant-pollinator conflict. The eventual mechanism that regulates this process could be closely linked to the corona of filaments that protects nectar chambers, simultaneously restricting ant access to nectar and pollen.

Keywords:
ant-pollinator conflict; ant protection; corona; extrafloral nectaries; extranuptial nectaries; floral enemies; flower reproductive structures; nectar thieves; Passiflora coccinea; pollination