Yunnan scholars have revealed the origin mechanism of plant “sleep” through fossils dating back 250 million years

Kunming, Feb. 16 (Chen Jing) The reporter learned from the Institute of Paleontology of Yunnan University on the 16th that Feng Zhuo’s team used a unique insect bite structure to skillfully confirm the existence of fossil plants nocturnal (leaves unfold during the day, close or droop at night), pushing the origin time of plant nocturnal nature to 250 million years ago, and proposed that the “sleep movement” of plant leaves may have multiple independent origins in different plant branches, representing the result of a convergent evolution.

Some plants possess the magical ability that their leaves unfold during the day and close or droop at night, known as nyctinasty. In 1880, Charles Darwin, in his magnum opus The Power of Movement in Plants, figuratively called this phenomenon “the sleep movement of plants.” However, due to the lack of fossil evidence, little is known about the origin and evolution of the “sleeping” habit of leaves.

The picture shows the fossils of two large-feathered odontodonts found by Feng Zhuo’s team Courtesy of the Institute of Paleontology, Yunnan University

The picture shows the “insect eye” bitten out after the leaves of living plants are closed at night Courtesy of the Institute of Paleontology, Yunnan University

Feng Zhuo’s team found an insect bite structure symmetrically arranged on both sides of the leaf midrib on the leaves of two large-feathered sheeptooth plants (Gigantonoclea) collected 250 million years ago in Qujing, Yunnan. However, the bite structure on both sides of the midrib showed certain regular differences in morphology and size, that is, the closer to the midrib or closer to the base of the leaf, the greater the difference in morphology and size of the bite structure on both sides of the midrib. Through extensive comparative research with living plants, Feng Zhuo et al. found that the bite structure of fossil insects was consistent with the structure left by insects when the leaves of nocturnal plants were closed, so they proposed that the insect bite structure on the leaves of the large feathered sheep tooth was formed when they closed along the midrib, which confirmed that the fossil leaves had nocturnal movement.

At present, the earliest angiosperm fossils appeared in the early Cretaceous period 120 million years ago, and Feng Zhuo and other previous studies showed that the large feather odont became completely extinct after the end-Permian mass extinction event 250 million years ago. There is a nearly 130 million year time gap between the appearance of angiosperms and the extinction of the large-feathered tooth, indicating that there may not be any related relationship between the two groups of plants. In today’s plant kingdom, nocturnal phenomena occur in all but one reliable case in ferns, especially legumes and sorrels, and have not been definitively found in other plant groups. Therefore, Feng Zhuo et al. proposed that the “sleep movement” of plant leaves may have multiple independent origins in different plant branches, representing a converging evolution.

The study, titled “Specialized herbivory in fossil leaves reveals convergent origins of nyctinasty,” was published online in the internationally renowned academic journal Current Biology on February 16, 2023. Feng Zhuo, the leader of the plant paleoecology team of Yunnan University, is the first and only corresponding author of the paper. The research has been funded by the Strategic Leading Science and Technology Project of the Chinese Academy of Sciences, the Second Qinghai-Tibet Scientific Expedition, the “Yunling Scholar” Special Project of Yunnan Province, and Yunnan University.

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