Natures wonders: plants using heat to attract pollinators (Introduction)

by David Turell , Sunday, April 27, 2025, 18:24 (4 days ago) @ David Turell

Ugly, stinking flowers or looking like corpses, as examples:

https://knowablemagazine.org/content/article/living-world/2025/how-thermogenic-plants-w...

"These are the flowers of the Eastern skunk cabbage (Symplocarpus foetidus), and flies and other pollinators are drawn by their putrid odor as well as by the flowers’ warmth. Skunk cabbage is one of a smattering of plants that can generate remarkable amounts of heat, an ability called thermogenesis: Its floral tissues can reach a toasty 84 degrees Fahrenheit (28.9 degrees Celsius), even on days that are near freezing.

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"Yet thermogenesis has been documented in 14 different plant families, some of them with more than a hundred heat-generating species. The sacred lotus (Nelumbo nucifera) can crank up its flowers to 95°F (35°C) and maintain that heat over days; the famed giant corpse flower (Amorphophallus titanum) reaches similar steamy temperatures, generating its heat in pulses.

“'Thermogenesis should be energetically costly for an organism, right? You’re just burning energy; you’re burning carbohydrates that you made,” says chemical ecologist Shayla Salzman of the University of Georgia in Athens. “So, if it is energetically costly, then it is something that you should have lost over evolutionary time — unless it had some equally valuable benefit.”

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"...for plants studied thus far, the benefit seems to be that warm flowers help them to have sex.

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"Among the most famous of thermogenic plants are those in the arum family (Araceae), which counts among its members skunk cabbage and the giant titan arum or corpse plant. Both these plants have large, darkly colored floral parts that, along with their heat generation, are a ruse: They are disguising themselves as decomposing carcasses and thus cozy, food-rich places to lay eggs. The hoodwinked flies or beetles crawl about and get dusted with pollen that they deliver to other flowers as their hunt continues for a proper brood site.

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"It’s well-established that carbon dioxide attracts insects (that’s what attracts mosquitos to people, for example). The gas bubbles out of decaying matter, including decomposing bodies, and in Claudel’s studies, it was present in the cloud of chemicals released by all the investigated thermogenic Amorphophallus species.

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"Plants that employ brood-site mimicry as the corpse plant does are cheaters — they lure pollinators with the scent and look of decay, but offer no food reward. Yet some plants offer real brood sites rich with nutritious pollen as part of a mutualistic relationship. These mutualisms are common among the cycads, an evolutionarily ancient plant group of nearly 400 species, almost all of them thermogenic.

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"...and tested their responses to various concentrations of 1,3-octadiene, the primary chemical attractant emitted by the cones.

"Sure enough, in male cones, the concentration of 1,3-octadiene reached its peak each evening, prompting a mass exodus of weevils, Salzman and her colleagues reported in 2020 in Science Advances. In female cones, the emission of 1,3-octadiene peaked at milder, attractive levels that beckoned pollen-bearing weevils fleeing the male cones.

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"The heater itself — the enzyme that most plants seem to use to crank up the temperatures of their tissues — is evolutionarily ancient. All plants seem to have it, even non-thermogenic species, says biochemist Anthony Moore...In fact, the heater enzyme also is found in many bacteria and fungi, he notes, and even some primitive animals such as sponges (Moore did much of the research on the structure of the enzyme and coauthored a paper on its role in the Annual Review of Plant Biology). That spread suggests the enzyme arose quite early on life’s family tree.

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"Harnessing the heater to attract pollinators may have first happened more than 300 million years ago, scientists recently proposed in Nature Plants. This was before the grand explosion of diversity in pollinating insects — before butterflies, before bees — and before the dramatic rise of flowering plants.

"So perhaps, at the dawn of pollination, heat was the original enticement. It may have lured early insects like beetles and thrips with a toasty respite from the outside world and quickly become intertwined with fragrance. The astonishing diversity of showy, elaborate flowers that attract pollinators of many plants today? Those visual bells and whistles would have come later, buoyed by the warmth and perfumes of plants past.

Comment: an amazing complexity of ways that plants arrange to have a sexual reproduction. Looks designed to me.