“Bimodal pollination systems in Andean Melastomataceae involving birds, bats, and rodents”

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Agnes S. Dellinger, Lisa M. Scheer, Silvia Artuso, Diana Fernández-Fernández, Francisco Sornoza, Darin S. Penneys, Raimund Tenhaken, Stefan Dötterl, and Jürg Schönenberger (July 2019)

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Biomodal pollination systems in the Andes: nectar adaptations to birds, South African scent compounds in rodent flowers

Pollination services by mixed assemblages of vertebrate pollinators in Ecuadorian cloud forests – specialization or generalization?

Black-thighed Puffleg (Eriocnemis derbyi) sitting on infructescence of Meriania tetragona after visiting its flowers in the Tapichalaca Reserve (Jocotoco Foundation).
(© Francisco Sornoza)

A flower pollinated only by a single animal species is the most extreme case of specialization in plant-pollinator interactions and this flower will show specific adaptations to its pollinator to maximize reproductive output. On the other extreme, generalized pollination systems involve many different animal species (often of different groups, e.g. beetles, flies, butterflies) and generalist flowers are adapted to make use of all of these different pollinators simultaneously. Flowers visited by two pollinator groups (e.g. hummingbirds and bats), such as documented in a new paper in The American Naturalist by Dellinger et al., lie between these extremes and may help understand when and how specialized or generalized pollination systems evolve.

In her PhD project, Dellinger investigated floral adaptations to variable combinations of two different pollinator groups in four closely related South American plant species. She conducted pollinator observations and experiments in three different cloud forest sites in Ecuador. Dellinger et al. found that all investigated species were effectively pollinated by one diurnally active pollinator group and a nocturnally active one (hummingbirds/bats, hummingbirds/rodents, flowerpiercers/rodents). All species have widely open flowers, which allow access to the nectar reward to both pollinator groups at all times. Nectar sugar composition shows typical adaptations to diurnal bird pollinators while scent profiles indicate adaptation to nocturnal bat/rodent pollinators. Dellinger et al. conclude that these pollination systems are specialized rather than generalized and exhibit ‘bimodal’ adaptations to exploit two different pollinator groups. Apparently, being specialized on these pollinator combinations is advantageous and outweighs costs (trade-offs) reported for other pollination systems involving more than one pollinator group.


Abstract

Floral adaptation to a single most effective functional pollinator group leads to specialized pollination syndromes. However, adaptations allowing for pollination by two functional groups (bimodal pollination systems) remain a conundrum rarely investigated. We tested if floral scent and nectar traits of species visited by two functional pollinator groups indicate specialization on either one of the two or (intermediate) bimodal systems. We studied pollination biology in four species of Meriania (Melastomataceae) in the Ecuadorian Andes. Pollinator observations and exclusion experiments showed that each species was effectively pollinated by two functional groups (hummingbirds/bats; hummingbirds/rodents; flowerpiercers/rodents), nectar composition followed known bird preferences and scent profiles gave mixed support for specialization on bats and rodents. Our results suggest that nectar rewarding Meriania species have evolved stable bimodal pollination strategies with parallel adaptations to two functional pollinator groups. The discovery of rodent pollination is particularly important given its rarity outside of South Africa.

Síndromes florales bimodales en Melastomataceae Andinas incluyendo aves, murcielagos y ratones

La adaptación a solo un grupo funcional de polinizadores lleva a síndromes florales especializados, pero todavía no se entiende bien cómo las flores pueden adaptarse a la polinización por dos grupos de polinizadores (síndromes bimodales). Analizamos el olor floral y características del néctar de cuatro especies de Meriania (Melastomataceae) visitadas por dos grupos distintos de polinizadores, para evaluar si hay síndromes de polinización a un solo grupo funcional de polinizadores o muestra síndromes bimodales. Nuestros experimentos mostraron que en cada especie de Meriania dos grupos de polinizadores (colibríes/murciélagos; colibríes/ratones; pinchaflores/ratones) son eficientes en el transporte de polen. La composición del néctar indicó especialización a los polinizadores diurnos (colibríes, pinchaflores), mientras que el olor de las flores mostró más especialización por los polinizadores nocturnos (murciélagos y ratones). Nuestros resultados sugieren que especies nectaríferas de Meriania evolucionaron síndromes bimodales estables con adaptaciones paralelas a dos grupos funcionales de polinizadores. El descubrimiento de polinización por ratones es especialmente importante por la rareza con que ocurre fuera de Sudáfrica.