Timing is everything: In which an intimate relationship turns out to be rather one-sided

Euglossine bee collecting scent

A euglossine bee collects scent from an orchid

Orchids have some of the most remarkable pollination relationships of all the flowering plants. Their flowers are adapted into wild shapes for placing packets of pollen on precisely the right part of a pollinator’s body, and many species attract pollinators with lures that are somewhat kinkier than simply offering nectar—such as mimicking a female pollinator’s scent and appearance, to dupe males of the species into, er, making intimate contact.

ResearchBlogging.orgA somewhat less exploitative orchid-pollinator interaction involves offering scent compounds to euglossine bees. Male euglossines collect scents from their environment—things that smell pleasant to humans, as well as things that really don’t—in special structures on their legs. It’s thought that they use the collected scents to attract females. Three large, diverse groups of orchids transport pollen by generating bee-attractive scent compounds, then saddling any bee who comes to collect the scent with a packet of pollen.

From the outside, this looks like a mutually beneficial relationship. The bees get their perfume, the orchids a pollen transporter. Over millions of years, such an interaction should lead bees and orchids to diversify together—when one orchid species splits into two, the bees that collect scent from them might very well speciate with the orchids. A recent paper in Science provides pretty good evidence that, over the long history of euglossines and the orchids that perfume them, the interaction hasn’t worked like that at all.

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