Pollination efficiency of hummingbirds and flowerpiercers at the flowers of Lobelia laxiflora (Campanulaceae): morphological fit matters

TL;DR

This study shows that the hummingbird Colibri cyanotus is an efficient pollinator of Lobelia laxiflora due to a perfect match between its bill length and the flower's corolla tube, while another bird, Diglossa plumbea, fails to pollinate.

Contribution

The study provides empirical evidence of morphological trait matching and bird behavior influencing pollination efficiency in a rare plant-hummingbird one-to-one interaction.

Findings

Colibri cyanotus efficiently pollinates Lobelia laxiflora due to morphological fit and behavior.

Diglossa plumbea does not act as a pollinator despite visiting flowers.

Lobelia laxiflora is completely self-incompatible.

Abstract

Research on pollination systems has largely focused on structures of mutualistic networks, whereas pollinator efficiency defining the quality of visits received much less attention. Different flower-visiting animals can vary in their pollination efficiency, e.g. due to their morphology, size or visitation frequency. Here, we analyse several reproductive traits, including flower morphology and reproductive system of Lobelia laxiflora and compare pollination efficiency of flower visitors based on seed set. We found experimentally that Lobelia laxiflora is completely self-incompatible and that the flowers are frequently visited by Colibri cyanotus, which did not show preferences for one flower sex. Diglossa plumbea was a more rare visitor and concentrated on female flowers Diglossa forced their bills deeply into the dorsally open corolla tube but did not pierce flowers. Corolla tube length perfectly fitted bill length of Colibri cyanotus and lots of pollen was deposited on its heads. In contrast, Diglossa plumbea visited flowers by sitting in different positions to them. Therefore, the reproductive flower organs got in contact with different parts of its body. Consequently, Colibri cyanotus was a very efficient pollinator probably due to the high level of trait matching, whereas Diglossa plumbea was not pollinating at all. In conclusion, our study documents a rare case of a temporally limited one-to-one dependency of a plant and a hummingbird species on the population level. Additionally, it highlights the significant role of morphological trait matching and bird´s behaviour in flower handling for efficient pollination and demonstrates that non-adapted flower visitors may fail as pollinators.

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