Health,  Life

The Secret of Angiosperms’ Explosive Evolution

   In spring, as soon as the signal for the recovery of all things is sent out, new buds appear on the branches, and buds that are about to bloom hang all over the branches. When the time comes, all kinds of flowers usher in a big explosion. Colorful flowers make nature fade away from the monotonous colors and make the world full of vitality. However, more than a hundred years ago, when the British biologist Charles Darwin saw such a scene, he was very angry-where did these flowers come from?
   Of course, Darwin was not allergic to pollen, nor did he hate flowers, but his theory of evolution seemed to be challenged by flowers. Based on the fossil record known at the time, angiosperms appear to have undergone a sudden origin and explosive diversification starting about 100 million years ago (the mid-Cretaceous period). By the Late Cretaceous, they had spread across the continents, and came in a wide variety of shapes and sizes, presenting a rich diversity. Darwin’s theory of evolution holds that the evolution of species proceeds slowly, driven by natural selection. So, do the flowers of angiosperms really appear and diversify in a short period of time? How do they do it?
   Darwin was bogged down with these questions about flowers, and never found an answer. These same questions have troubled other biologists for more than a hundred years. Now, various new research results seem to have found the answers to these questions, which is expected to “rescue” Darwin from the confusion of flowers.
DNA multiplication in flowering plants

   Judging from the plant fossils held by Darwin, there is no evidence to show which kind of plants the angiosperms evolved from, and there is no evidence to show their evolution process. They seem to be on the fast track of evolution and complete it at an extremely fast speed. evolved. Over the past 100 years, as more angiosperm fossils have been discovered, it can be proved that angiosperms did not appear suddenly, but they did evolve faster.
   In New Caledonia, a small Pacific island, grows a plant called camphor. Scientists believe that camphor is a survivor of one of the earliest branches in the evolution of angiosperms, which goes back to the last common ancestor of all flowering plants. From the study of camphor, we may be able to learn about the last common ancestor of all flowering plants.
   In 2013, scientists’ research on the oil-free camphor genome showed that the first angiosperms appeared about 200 million years ago, which is about 100 million years earlier than the earliest appearance of angiosperms thought in the Darwin era. And scientists believe that the first angiosperms may have evolved from a certain type of fern.
   So why did ferns evolve into angiosperms? The study revealed that what contributed to this evolution was a special kind of genetic mutation – a “DNA doubling event”. The so-called DNA doubling event is to obtain a “double dose” of genetic material through mutation. In vertebrates, a similar event occurs, but the mutation is usually fatal. Plants, on the other hand, often survive such conditions and sometimes benefit from duplicated genomes. Typically, over a period of several generations, most of the duplicated genes from DNA-multiplication events disappear. Sometimes, however, repeated gene segments are used to breed more efficient and specialized new functions for the entire genome. For example, some gene segments produced by the DNA multiplication event in plants about 200 million years ago took on the responsibility. Functions that control the development of floral organs.
   This DNA multiplication event occurred more than once during the evolution of angiosperms, which added a large amount of DNA to the genomes of different angiosperms, and they also evolved various new functions, which made angiosperms more diverse change. Arguably, flowering plants as we know them today might not exist without the genes that DNA doubling events help create.
   In addition to the DNA doubling events that explain how angiosperms suddenly diversify, do angiosperms have some special way of speeding up their own evolution?
A magic trick to speed up evolution – shrinking the genome

   The secret of the accelerated evolution of angiosperms lies in them. Scientists from Yale University and San Francisco State University collected nearly 400 species of angiosperms, ferns, and gymnosperms, and compared their genome size, cell size, and stomatal density (the number of stomata, or microscopic pores on the leaves). et al. conducted research. They found that the genomes of angiosperms began to shrink about 140 million years ago. During this period, dinosaurs were still roaming the earth, and angiosperms were rapidly “expanding” on the earth. So, is there a connection between genome shrinkage and angiosperm blooms?
   Scientists believe that the size of the genome is closely related to the size of the cell, because the size of the nucleus where the genome resides determines the minimum size of the cell. And for flowering plants, smaller genomes, and therefore smaller cells, are beneficial. Because this allows their tissues to accommodate more cells than other plant tissues of the same volume, which greatly improves metabolic efficiency. Smaller cells also allow for more veins and stomata on angiosperm leaves, which increase the plant’s transpiration, photosynthesis, and growth rates. All this undoubtedly accelerated the evolution rate of angiosperms.
   So why did the cells of angiosperms shrink 140 million years ago? How do they do this? In a study of ancient climates, scientists have discovered that during a period 140 million years ago, carbon dioxide levels in Earth’s atmosphere dropped, which was bad for plants that depend on carbon dioxide to survive. Scientists speculate that in order to adapt to changes in the environment, angiosperms shrink their own cells, which is consistent with Darwin’s theory of evolution.
Anthers with hidden mysteries

   In addition to the timing, rapid evolution and diversity, Darwin was puzzled by how quickly angiosperms could spread across the planet. A study of anthers seems to offer some clues to that question.
   Researchers at the University of California in the United States have studied the flower of alba, and they have discovered a mystery in the flower. Anthers are the reproductive organs of a flower and are part of the stamens, which contain pollen. Only by passing the pollen from the anthers of a flower to the stigma of the pistil can the flower bear fruit. Typically, each flower has two sets of anthers that differ in color, size, and location. It has long been thought that there is a division of labor between these two groups of anthers, with one group of anthers being used to attract and feed pollinators, while the other, less conspicuous group of anthers is responsible for quietly spreading pollen to pollinators Yes, so pollinators can help pollinate without knowing it. But the new study suggests that the two groups of anthers may not have a division of labor, and their role is to attract pollinators as well. So, why do you need two sets of anthers?
   Studies have shown that this is where flowers are “smart”. The two groups of anthers release pollen at different times, and each group of anthers can only release a small amount of pollen at a time, which means that pollinators can only get a small amount of pollen from one flower at a time, so pollinators have to patronize other flowers. flowers to collect enough pollen. In the process, pollinators unknowingly pass the pollen from one flower to another.
   It is flowering plants that have evolved this method of optimizing the behavior of pollinators to maximize the transfer of pollen between flowers, making it possible to reproduce a large number of offspring. This may have fueled the proliferation of angiosperm populations and hastened their spread around the world.
sunken secret

   Today, part of Darwin’s puzzles about flowers has been solved, but most of these answers are traced back to ancient angiosperms through existing plants. What was the original angiosperm like? What plants did they evolve from? How have they changed in the long history? Scientists have found no related fossils and cannot see their changes. Darwin was unable to solve this problem and had to propose that the earliest flowering plants may have slowly evolved in a remote and isolated place, and then spread across the land. And that place was unreachable in Darwin’s time, and perhaps it is unreachable in modern times, because it may have sunk into the vast ocean.
   In 2017, some geologists claimed that Zealandia was discovered on the seabed off the coast of eastern Australia, which seemed to confirm Darwin’s conjecture. Zealandia, which once formed part of the landmass along with Australia and Antarctica, broke off from the Great Plate between 105 million and 80 million years ago. Subsequently, due to the influence of various geological tectonic movements, it sank to the bottom of the sea. The highest points of Zealandia are now above the sea, and they are New Caledonia and New Zealand. In these places, the researchers found the largest number of the oldest surviving groups of angiosperms. Not only that, Australia, which was once a neighbor of Zealandia, also has the oldest surviving angiosperm group. Therefore, scientists speculate that ancient angiosperms once grew in Zealandia.
   And Zealandia, which is separated from the big plate, is an independent continent. From a certain perspective, it is an island similar to New Zealand and New Caledonia. Due to environmental constraints, some endemic species can often be produced on the island, such as the oil-free camphor in New Caledonia. The researchers believe that angiosperms may have originated in Zealandia, became endemic to Zealandia, evolved diversity, and then spread to other parts of the world. This may be why scientists have not found the earliest fossils of angiosperms.
   With the efforts of several generations of scientists, the mystery of flowering plants that plagued Darwin has gradually been solved. However, in order to fully answer the questions about flowering plants, it may be necessary to find the source of flowering plants. Only in this way can Darwin be truly “rescued” from the confusion about flowers.

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