Nyctinastic Plants: Insect Bite Marks Shows the Evolution of Plants’ ‘Sleeping Movements'

Extinct plants evolved foliar nyctinastic movements at such an early stage of plant evolution, which surprised Zhuo Feng of Yunnan University in Kunming, China.

Their Discovery discovery was made using an unconventional method, according to Stephen McLoughlin of the Swedish Museum of Natural History in Stockholm.

Insect bite marks show the first fossil evidence for plants leaves movement

(Photo : ANGELA WEISS/AFP via Getty Images)

McLoughlin looked for insect damage patterns that are unique to plants with nyctinastic behavior because it is impossible to tell whether a folded leaf found in the fossil record was closed because it experienced sleeping behavior or because it shriveled and bent after death, as per ScienceDaily.

McLoughlin discovered a group of fossil plants that show that the behavioral strategy has a very ancient origin.

Plants have the ability to move in unexpected ways. Some even exhibit "sleep movements," folding or raising their leaves each night before reopening them the next day.

Researchers published the first convincing evidence for these nightly movements, known as foliar nyctinasty, in fossil plants that lived more than 250 million years ago in the journal Current Biology on February 15.

Feng has long been interested in fossil plant-insect interactions and coevolution, discovering evidence of various types of insect damage in the fossil record.

He discovered an intriguing pattern of insect damage in living plants in 2013: symmetrical holes punctured through the leaves, which he later realized looked that way because insects fed on the folded leaves.

He wondered if he could find this type of damage in fossil plants as evidence for sleeping movements because it is common in nyctinastic plants.

"I was surprised by the distinct pattern of the insect damage and speculated that it might represent foliar nyctinasty in the fossil plant," said Feng.

The second fossil specimen, a different species of the same plant group, revealed the same insect-feeding damage as the leaf preserved two years earlier.

They then began to consider the specimens' scientific significance.

He then examined hundreds of samples and photos in the Xishuangbanna Tropical Botanical Garden, where he discovered even more convincing evidence for nyctinasty.

According to the researchers, the findings contribute to a better understanding of the ecology and evolution of this enigmatic group of plants.

The research now shows that they can.

The researchers turned to gigantopterids, an extinct group of seed-producing plants found in Permian Cathaysian floras 300-250 million years ago.

They reasoned that these plants were the best place to look because they are known to be frequently attacked by plant-eating (herbivorous) insects.

Insect damage is also easy to detect due to its broad leaves and robust midvein.

In 2016, they discovered the first fossil gigantopterid leaf with the symmetrical pattern they were looking for.

Some gigantopterids have hooks on their leaves and specialized water-conducting cells, indicating that at least some were climbers in early rainforest-like ecosystems, according to McLoughlin.

Sleeping behavior has now been shown to have evolved independently in various plant groups and at different times throughout Earth's history, implying that it must have some ecological benefits to the parent plant, McLoughlin continued.

The findings demonstrated that not only structures but also behavioral characteristics of fossilized plants and animals can be deduced.

According to the researchers, the biological features of ancient organisms could be deciphered from fossil specimens in the future through more detailed observations of animal interactions with both fossil and modern plants.

McLoughlin believed that evidence of fossil insect damage on leaves can reveal much more about plant 'behavior' and ecology than just herbivory.

The fossil record of plant-animal interactions contains a wealth of ecological information that has largely gone untapped.

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Nyctinasty

The nastic movement of leaves or petals of higher plants in response to darkness is referred to as nyctinasty (or the alternation of day and night), as per Biology Online.

A flower closing at dusk, for example, is a biological rhythmic event.

Another example is the sleep movement of the legume leaves at night.

Nyctinasty is not the same as tropic movement (tropism).

Tropism is the directional movement or growth response of a cell or organism to a stimulus that can be positive or negative depending on the source and type of stimulus.

In other words, tropism is associated with the plant's growth response to a stimulus.

Phototropism, for example, is a type of tropism in which plants grow toward the source of light (positive tropism).

Some plants in nyctinasty can assume a position at night that differs from their position during the day.

It is a biological rhythm because this behavior occurs on a daily basis.

These plants' sleeping positions are thought to be linked to pulvinar movement, the circadian clock, and light signal transduction via phytochrome.

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