Who was the earliest "flower thief" 100 million years ago? -

Author Shen Chunlei

Most angiosperms (flowering plants) are pollinated by insects, and insect pollination is also considered to be the key factor for the outbreak of angiosperms in the middle Cretaceous (about 654.38 billion years ago). So, when did insect pollination appear on the earth?

On 20021April 12, Nature-Plants published online the research of an international cooperative team led by Cai Chenyang, a researcher from Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. The research shows that the cooperative team found a rare short-winged beetle in Burmese amber in the middle Cretaceous, which provides direct evidence for Cretaceous beetles to feed on pollen.

On February 24th, 65438, Nature-Plant published the research of Bao Tong, an assistant professor at the School of Ecology, Sun Yat-sen University. According to the description and conclusion in the last paper of Cai Chenyang's team, Bao Tong's team redesigned the experiment of entomology and palynology, and put forward a new understanding by combining theoretical analysis and experimental data.

Therefore, China Science News contacted the main authors of two articles to listen to their opinions. Can you find out who was the earliest flower thief 100 million years ago?

20 19 Bao Tong first discovered the direct evidence that angiosperms were pollinated by beetles (primitive flower fleas) in amber from Myanmar in the middle Cretaceous, and related research results were published in Nature-Plants. The results of this study confirmed scholars' long-standing conjecture that Cretaceous beetles were pollinators of early angiosperms, which filled the blank of evidence of pollination of early angiosperms. "This is also the earliest' flower thief' discovered that year." Bao Tong said.

In 20021year, Cai Chenyang's team found the pollen and pollen mass of higher angiosperms and two kinds of beetle droppings composed of a large amount of pollen on the body surface and its vicinity, thus revealing that the short-winged beetle was the earliest "flower thief".

Bao Tong's team disagrees with this view.

Cai Chenyang's team's article points out that the amber samples in his research contain short-winged coral fossils, suspected "fecal fossils" and some "angiosperm pollen" particles. After physiological analysis of living insects, Bao Tong's team thought that the size of this "dung fossil" obviously exceeded the possible size of the beetle's digestive tract, and it was difficult to confirm its relationship with this short-winged beetle.

"In many insect groups represented by beetles, when the pollen they eat is excreted through the digestive tract, the pollen structure will be squeezed, deformed or destroyed to a certain extent, and the membrane structure will remain on the surface of insect feces." Bao Tong told China Science that none of the "fecal fossils" displayed in Cai Chenyang's team's research reflected the above characteristics.

Cai Chenyang's team article mentioned that beetles are surrounded by more than 100 pollen grains, and there are four clustered pollen groups near the beetles, which belong to typical three-furrow pollen (the three-furrow pollen has three germination furrows with the same angle of 120, which is the characteristic of true dicotyledonous plants, and true dicotyledonous plants belong to one of the evolutionary branches of angiosperms), and the "dung fossils" preserved in this amber.

In this regard, Bao Tong's team proved that this kind of pollen is "three-furrow pollen" rather than three-furrow pollen, but belongs to an extinct gymnosperm, Erdtmanithecales. There are also three "grooves" in the three-groove pollen, but one of them is wider than the other two, so it is easy to mistake this pollen for angiosperm pollen without careful observation.

"We are studying Anthuridae, not ladybugs. The former is the exposed tail beetle superfamily; The latter is omnivorous, mostly predatory, and belongs to ladybug superfamily. " Cai Chenyang told the China Journal of Science, "Questioning the experimental design mentioned in the article, I think the control experiment needs to be done with the same beetle."

Regarding the identification of pollen, Cai Chenyang said: "Our pollen types are the same as those mentioned in the article Nature-Plants published by Bao Tong team in 20 19, and they have also been confirmed by pollen appraisers. Atypical three-furrow pollen exists in extinct amber flowers or modern monocotyledonous plants.

"The original flower flea studied by Bao Tong's team is actually a synonym for short-tailed flower flea." Cai Chenyang and others retorted in the article: "We don't know why Bao Tong and others should use the pollen digestion of ladybugs as a benchmark to evaluate the dung fossils of Mesozoic short-winged beetles, because these two families are not immediate relatives. The former is mainly a polyphagous aphid eater, and the latter is a specialized pollen eater. The pollen digestion mechanism of the short-winged scarab is still unclear. "

At the end of the rebuttal article, it wrote: "The newborn pink beetle (the beetle found in the questioned article) did provide the earliest direct dietary evidence that the beetle ate angiosperm pollen, which marked an important change in the diversified evolution of angiosperm in the early Cretaceous."

Academic research needs a hundred schools of thought to contend. Huang, a researcher at Nanjing Institute of Paleontology, is also one of the authors of this questioned article. He told the China Science Journal: "Paleontological research is difficult to be 100% correct because it is full of all kinds of speculations."

In recent years, the research team of Mesozoic Terrestrial Ecosystem Research Center of Nanjing Institute of Paleontology systematically collected and excavated a large number of Burmese amber insect fossils, which initially revealed that angiosperms gradually replaced gymnosperms in the pollination relationship between insects and plants since the Cretaceous Agrarian Revolution (65.438+0.25 billion to 80 million years ago).

Huang et al reported on 20 16 that a large number of purple pollen was found in the abdomen of amber in Myanmar, which revealed the pollination relationship between insects and higher angiosperms in the middle Cretaceous for the first time. 20 18 Cai Chenyang and others found a unique flat beetle and its Cycas (commonly known as Cycas, gymnosperms) pollen in Burmese amber, which proved that the pollination relationship between beetles and Cycas was established not later than the early Jurassic, but much earlier than the origin and prosperity of angiosperms and their pollinators.

Can these arguments prove who is right and who is wrong in the research of Bao Tong and Cai Chenyang?

Relevant researchers said: "The identification of sporopollen has been discussed in academic circles, and the reviewers also said that the fossil identification used by Cai Chenyang's team was ignored." The researcher said that it is estimated that new research results will come out soon.