Insect bites have been identified on plants dating back more than 250 million years.
They provide the earliest evidence of leaves folding each night before opening again next day.
It shows the phenomenon – known scientifically as “foliar nyctinasty” – began before the age of the dinosaurs.
Study lead author Professor Zhuo Feng, of Yunnan University in China, said: “Our findings reveal it evolved in extinct plants at such an early stage of evolution – which is surprising to me.”
They may have been left by grasshoppers – among the most ancient chewing critters.
Today they are serious pests of cereals, vegetables and pasture – feeding at night as well as in the day.
Co-author Dr. Stephen McLoughlin, of the Swedish Museum of Natural History in Stockholm, said: “Our discovery is based on an unorthodox approach.
“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.
“So we looked for insect damage patterns that are unique to plants with nyctinastic behaviour. We found one group of fossil plants that reveals a very ancient origin for this behavioral strategy.”
During the day, leaves lower or spread out to absorb moisture or catch rain. At night, they rise inwards to store it – preventing evaporation.
This is when insects are most likely to tuck in – puncturing symmetrical holes while they are folded, explained Prof Feng.
The international team analyzed gigantopterids, an extinct group of seed-producers characteristic of the Permian Cathaysian floras from about 300 to 250 million years ago.
The plants’ broad leaves experienced frequent attacks from insects which are easy to spot.
Prof Feng said: “I was surprised by the distinctive pattern of the insect damage and thought it might represent foliar nyctinasty in the fossil plant.
“But to be sure, I searched for more fossil evidence to reinforce my assumption.
“The second fossil specimen – a different species of the same plant group revealed the same insect-feeding damage.
“I then began to think about the scientific significance of the specimens.”
He went on to examine hundreds of spectacular specimens from Xishuangbanna Tropical Botanical Garden – which provided even more convincing evidence.
The findings, published in the journal Current Biology, shed fresh light on the ecology and history of plants.
Dr. McLoughlin said: “In recent years, some gigantopterids have been found to possess hooks on their leaves and have specialized water-conducting cells.
“They indicate some were climbers within early rainforest-like ecosystems. We now know some folded their leaves on a daily basis.
“It is clear sleeping behavior has evolved independently in various plant groups and at different times, so it must have some ecological benefits to the parent plant.”
Biological features of ancient organisms may be deciphered in future from fossils through further detailed observations of animal interactions
Dr. McLoughlin said: “Evidence of fossil insect damage on leaves can provide a great deal more information about plant ‘behavior’ and ecology than just herbivory.
“The fossil record of plant-animal interactions is a rich and largely untouched bank of ecological data.”
Plants began colonizing land 500 million years ago during the Cambrian Period, around the same time as the emergence of the first land animals – including insects.
Prof. Feng added: “We now know the evolutionary history of the ‘sleeping movements’ of leaves can be traced back to the late Paleozoic gigantopterid plants more than 250 million years ago.”
He now plans to investigate many others that may have exhibited similar behavior.
Produced in association with SWNS Talker