Thursday, January 29, 2026

This flower evolved a new shape so that different birds could pollinate it. Then, it spread.

Most lipstick vines have flowers that are shaped like a tube of lipstick— but not this one. Scientists dug into the plants’ family tree to figure out when and where this oddball evolved.

Field Museum

Short-beaked bird with short-flowered plant — image:
White-eared Sibia (Heterophasia auricularis) visiting the shorter and wider flowers of Aeschynanthus acuminatus in Xitou, central Taiwan. Pollen deposited during the visit is visible on the Sibia's forehead. Photo by Jing-Yi Lu.
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Credit: Photo by Jing-Yi Lu.

Lipstick vines get their name from their bright red, tube-shaped flowers. But one member of this group of plants has lost its lipstick-like appearance— its flowers are shorter, wider, and yellowish green in color. It also attracts shorter-beaked birds than its crimson cousins do, and it’s found in different places. Scientists wanted to know how this plant evolved from its lipstick-like relatives. After observing birds visiting hundreds of plants and examining the plants’ DNA, the researchers found that the story of the green flower’s evolution contradicts a long-standing scientific “rule” about how plants evolve into new species.

The green flower at the center of the discovery (and the subject of a paper detailing said discovery in the journal New Phytologist) is called Aeschynanthus acuminatus. Its range extends across Southeast Asia from northern India and the Himalayas, across Indo-Chinese countries like Vietnam and Thailand, and into southern China. It’s also found off the coast of mainland China on the island of Taiwan.

“Compared to the rest of its genus, this species has weird, unique flowers,” says Jing-Yi Lu, the study’s lead author and a research associate at the Field Museum who recently graduated with his PhD at the University of Chicago. Lu wanted to know how these flowers got to be so odd.

The red flowers of the other lipstick vines help attract sunbirds, whose long, slender beaks fit perfectly into the skinny, tube-shaped blooms. By going from flower to flower and drinking nectar, the sunbirds spread the plants’ pollen. But while sunbirds are found throughout the mainland where the other lipstick vines live, there are no sunbirds on Taiwan.

When Lu was an undergraduate student in Taiwan, he began wondering about the short, green-flowered A. acuminatus growing on the island. “It made me curious about how this species could occur in Taiwan. Since we don’t have sunbirds, there must be something else to pollinate it,” says Lu.

Figuring out which species of birds pollinate a type of plant can be a tricky task. “Most of the time, you don't really see the birds, because they don't come too often, and they are shy,” says Lu. To solve this problem, he set up camera traps that recorded birds coming and going from the flowers, and determined that a variety of birds with shorter beaks than sunbirds were visiting the short, wide, green flowers of A. acuminatus.

However, A. acuminatus doesn’t only live in Taiwan— it’s also found throughout mainland Southeast Asia, where there are plenty of long-beaked sunbirds. This presented an evolutionary riddle to Lu and his fellow scientists, something like the question of what came first, the chicken or the egg. Did A. acuminatus’s ancestors find themselves transported to sunbird-less Taiwan, where they then had to evolve shorter, wider flowers to accommodate the shorter-beaked birds that lived there? Or did they split off from their tube-shaped cousins while they were still on the mainland, even though there were sunbirds around, and arrive in Taiwan later on? And, what kinds of birds pollinate the shorter, wider A. acuminatus flowers on the mainland?

“At the heart of our study is a question of where species originate,” says Rick Ree, a curator at the Field Museum’s Negaunee Integrative Research Center and the study’s senior author. “There must have been a switch when this species evolved, when it went from having narrow flowers for sunbirds to wider flowers for more generalist birds. Where and when did the switch occur?”

For more than 50 years, botanists have turned to a sort of rule called the Grant-Stebbins model that aims to answer questions like these. “The Grant-Stebbins model says that when a plant species extends its range into an area with new pollinators or without its ancestral pollinator, that switch to a new pollinator will drive speciation,” says Ree. “This model basically predicted that A. acuminatus should have evolved in Taiwan— when its ancestor colonized Taiwan, it left behind its old pollinators and evolved into a new species that could accommodate the new pollinators in its new home.”

To test whether the Grant-Stebbins model was accurate for A. acuminatus, Ree and Lu analyzed the DNA of A. acuminatus specimens growing in Taiwan and in mainland Asia, as well as the DNA of other species of lipstick vines. The researchers used software that compared the similarities and differences in these plants’ DNA and built family trees showing the likeliest explanations for how the plants were related to each other. The results were surprising.

“The branching patterns on the family trees we made revealed that the A. acuminatus plants on Taiwan descended from other A. acuminatus plants from the mainland— the species originated on the mainland,” says Ree. Even though the lipstick vines on the mainland lived alongside sunbirds that could pollinate their skinny flowers, some of them split off into a new species that accommodated birds with shorter beaks (in addition to sunbirds, which were still capable of feeding from the shorter flowers). The Grant-Stebbins model, for this particular example of plant evolution, didn’t fit.

“It was really exciting to get these results, because they don’t follow the classic ideas of how we would have imagined the species evolved,” says Lu.

While the mystery of A. acuminatus’s origin has been solved, that discovery opens up new questions. “Why did this pollinator switch happen, when the original pollinator, the sunbird, is still there?” says Ree. “Our hypothesis is that at some point in the past, sunbirds stopped being optimal or sufficient pollinators for some of the plants on the mainland. There must have been circumstances under which natural selection favored this transition toward generalist passerine birds with shorter beaks as pollinators.”

Beyond answering questions about the evolution of one particular species of flowering vine, Ree says that the project offers a look at the work that goes into scientific discoveries.

“This study shows the importance of natural history, of actually going out into nature and observing ecological interactions,” says Ree. “It takes a lot of human effort that cannot be replicated by AI, it can’t be sped up by computers— there’s no substitute for getting out there like Jing-Yi did and spending months traveling to different field sites to see where these plants grow and what kinds of birds pollinate them. There’s no substitute for that.”

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Journal

New Phytologist

DOI

10.1111/nph.70871

Article Title

Testing macroevolutionary predictions of the Grant-Stebbins model in the origin of Aeschynanthus acuminatus

Article Publication Date

27-Jan-2026

Female Black-throated Sunbird (Aethopyga saturata) visiting the typical sunbird-pollinated Aeschynanthus bracteatus in Pingbian, southeastern Yunnan, China. Photo captured by a motion-triggered camera, courtesy of Jing-Yi Lu

White-eared Sibia (Heterophasia auricularis) visiting the shorter and wider flowers of Aeschynanthus acuminatus in Xitou, central Taiwan. Pollen deposited during the visit is visible on the Sibia's forehead. Photo by Jing-Yi Lu.

Female Black-throated Sunbird (Aethopyga saturata) visiting the typical sunbird-pollinated Aeschynanthus bracteatus in Pingbian, southeastern Yunnan, China. Photo captured by a motion-triggered camera, courtesy of Jing-Yi Lu.

The short, yellowish-green flowers of A. acuminatus, compared with the long, red flowers of its cousin, A. bracteatus, a more typical lipstick vine. Courtesy of Jing-Yi Lu.

The short, wide, yellow-green flowers of A. acuminatus, an atypical lipstick vine.

Courtesy of Jing-Yi Lu.

Looking for plants of Aeschynanthus acuminatus in the subtropical montane cloud forest in Malipo, southeastern Yunnan, China. Photo by Dr. Chih-Chieh Yu.

Credit

Photo by Dr. Chih-Chieh Yu.

96% accurate footprint tracker for tiny mammals could help reveal ecosystem health

New footprint identification technology can identify ecosystem-critical species which were once only distinguishable by DNA

Frontiers

image:
A Bushveld sengi (Elephantulus intufi), photographed by Dr Maria Oosthuizen.
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Credit: Dr Maria Oosthuizen

It might be less visible than dwindling lion populations or vanishing pandas, but the quiet crisis of small mammal extinction is arguably worse for biodiversity. These species are crucial indicators of environmental health, but they can be very hard to monitor, and many species with very different ecological niches look almost identical. But now scientists have developed a new way of identifying and monitoring these tiny mammals using their footprints, tested on two near-identical species of sengi and found to be up to 96% accurate.

“We had two key motivations for undertaking this study,” said Dr Zoë Jewell of Duke University Nicholas School of the Environment, co-author of the article in Frontiers in Ecology and Evolution. “Firstly, to find a better, more ethical, and more scientifically robust way to monitor even the tiniest species, and secondly, to provide a reliable and broad metric for ecosystem integrity that can be applied routinely and regularly — a new pulse on the planet.”

Small mammals, large impact

Small mammals play such a critical role in ecosystems and are very sensitive to any environmental changes, which means that changes in their populations can be important early warnings of ecological disturbances. But many species are near-identical ‘cryptic’ species, which makes it difficult to monitor them accurately. This is the case for the species the team used to test their footprint identification technology, Eastern Rock sengis and Bushveld sengis.

“It's often only possible to distinguish between cryptic species using DNA, which can be slow, invasive, and costly,” explained Jewell. “It's really important to know which is which, because although these species might look the same, they face different environmental threats and play different roles in the environment. For example, in our study, one of the sengis lives exclusively in rocky habitats and the other on sand, and each can act independently as an indicator in those environments.”

However, there is one important distinction between the sengis: their feet are slightly different, leaving crucial differences in their tracks. So the scientists set out to capture these differences and train a model that could distinguish between Bushveld sengis and Eastern Rock sengis’ footprints, like tracking animals with a computer.

Searching for sengis

The scientists collected sengis from two South African sites, Telperion Nature Reserve and Tswalu Kalahari Reserve. The 18 Bushveld sengis sampled were found only in Tswalu Kalahari Reserve, but a total of 19 Eastern Rock sengis were found at both sites, some occupying habitats very close to Bushveld sengis. This was an unexpected finding, because Tswalu Kalahari Reserve is outside the expected range of Eastern Rock sengis, and highlights just how important it is to improve monitoring of these species.

The sengis were captured using specially-designed traps loaded with comfortable bedding and a meal of oats, peanut butter, and Marmite — which they find particularly delicious — and then released into a box for collecting footprints. This contained special paper with charcoal dust placed at each end, so that the sengis would walk through the dust and leave behind footprints. After this, they were released unharmed where they had been found.

Digital images of the footprints were then processed using a morphometry program, to identify shape and size features which could distinguish between the two species of sengi. The scientists used front footprints, which were reliably the clearest and the most distinctive, and detected more than 100 possible features. They then ran a statistical analysis to show which combination of these could identify sengis most accurately.

Footprints don’t lie

The nine diagnostic features selected were then challenged with single images and sets of sengi tracks reserved for testing, to see how well the footprint identification technology would perform. It identified the species with 94%-96% accuracy across all the tests.

This footprint identification technology can now be used on pictures of sengi tracks, as a non-invasive, cheap, and simple way to help detect the different species’ presence and monitor changes in their populations and ranges. The scientists also plan to expand this to other species, using new datasets to train similar models. In the future they would like to compare the technology to other non-invasive methods of monitoring species, to see how they can complement each other.

“Small mammals exist in almost every ecosystem on the planet, and our tech is flexible enough to adapt to every one,” said Jewell.

An Eastern Rock sengi (Elephantulus myurus) photographed by Dr Maria Oosthuizen.

Credit

Dr Maria Oosthuizen