Deadly plant kills its pollinators but nurses their young

The Arisaema plant is a death trap for the fungus gnats that pollinate it

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Jack-in-the-pulpit flowers – famed for trapping and killing their pollinators – might also serve as a nursery for the insects’ eggs, revealing a more nuanced and mutually beneficial relationship that challenges existing assumptions.

These pitcher-shaped plants, of the genus Arisaema, lure in their primary pollinators, fungus gnats, by mimicking the looks and scent of musty mushrooms. But once the insect dips into the flower’s spathe in pursuit of this pungent treat, it cannot crawl out because the flower’s elongated hood interior is too waxy. The gnat jostles and struggles inside the mottled, reddish-green cup, spreading pollen around and thoroughly pollinating the plant, but it eventually tires itself to death.

At least this is what botanists have long thought.

But when Kenji Suetsugu and his team at Kobe University in Japan incubated 62 flowers of the Asian jack-in-the-pulpit species Arisaema thunbergii, they noticed something odd. The helplessly trapped gnats laid their eggs in the flowers’ crowns. When the flowers began dying, these larvae fed on their shrivelling and decaying flesh and then popped out as adults a few weeks later.

The fact that the traps could serve a dual function – as a site of pollination and as a nursery for the next generation of pollinators – is “indeed surprising”, says Suetsugu.

Plus, some adult gnats do manage to escape the flower traps before it is too late, meaning the dupe isn’t “strictly lethal”, says Suetsugu. This suggests the plants are striking a balance between ensuring they get pollinated and not entirely depleting the population of pollinating gnats.

These findings suggest the relationship between jack-in-the-pulpits and their pollinators is much more complex than previously thought, and “cannot be neatly categorized as purely mutualistic or antagonistic”, says Suetsugu.

The relationship might represent a phase in the plant’s evolutionary process, going from purely deceiving its pollinators to developing a mutually beneficial relationship with them. Crucially, it might suggest other plant-pollinator relationships around the world also have more to them than meets the eye.

Indeed, these findings challenge some preconceived ecological ideas, says Jeff Ollerton at the University of Northampton in the UK. In this specific case, only some of the insects seem to reap the benefits, so it is a mixed bag. He says that more species of Arisaema (the genus includes more than 190 species) need to be studied in this kind of detail to learn more.

“The deeper we look into plant-pollinator interactions, the more surprises we see in the ability of plants to manipulate the behaviour of pollinators, or how pollinators can evolve strategies to gain resources,” says Ollerton.


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