American Society of Naturalists

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“Did mammals bring the first mistletoes into the tree-tops?”

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David M. Watson (Dec 2020)

Mistletoes are the quintessential bird-dispersed plants, but ancient mammals may have first brought them to the treetops

Read the Article (Just Accepted)

<i>Amyema preissii</i> (Loranthaceae) with pink fruits 10&nbsp;mm in diameter.<br />(Credit: David M. Watson, ©&nbsp;University of Chicago Press)
Amyema preissii (Loranthaceae) with pink fruits 10 mm in diameter.
(Credit: David M. Watson, © University of Chicago Press)

Abstract

As the only woody parasitic plants that infect host canopies, the growth habit of mistletoes represents a key innovation. How this aerially-parasitic habit originated is unknown—mistletoe macrofossils are relatively recent, from long after they adapted to canopy life and evolved showy bird-pollinated flowers, sticky bird-dispersed seeds and woody haustoria diverting water and nutrients from host branches. Since the transition to aerial parasitism predates the origin of their contemporary avian seed dispersers by 20–30 million years, this begs the question—who were the original mistletoe dispersers? By integrating fully resolved phylogenies of mistletoes and aligning the timing of historic events, I identify two ancient mammals as likely candidates for ‘planting’ the Viscaceae and Loranthaceae in the canopy. Just as modern mouse lemurs and galagos disperse Viscaceous mistletoe externally (grooming the sticky seeds from their fur), Cretaceous primates (such as Purgatorius) may have transported seeds of root-parasitic understory shrubs up into the canopy of Laurasian forests. In the Eocene, ancestors of the today’s mistletoe-dispersing marsupials Dromiciops likely fed on the nutritious fruit of root-parasitic Loranthaceous shrubs, depositing them atop western Gondwanan forest crowns. Having colonized the canopy, subsequent mistletoe evolution and diversification coincided with the rise of nectar and fruit-dependent birds.