Producer: Popular Science China
Production: A group of green trees
Producer: Computer Network Information Center, Chinese Academy of Sciences
Flowers provide nectar to insects such as butterflies, which help pollinate flowers. So the question is: on Earth, are there flowers or butterflies first?
Once upon a time, most scientists thought that flowers appeared before the earliest pollinators, and insects such as butterflies and moths grew with flowers. However, the latest research suggests that primitive butterflies existed long before the first flowering plants on Earth appeared.
Glass butterfly sucking nectar / Image source: Wikipedia
Butterflies or flowers first? How do scientists know?
To know whether there were butterflies or flowers first, we need to know who first appeared on the earth with the first butterfly and the first flower, and the most common way is to look for fossils.
However, the structure of the flower is relatively fragile, difficult to preserve, and only in the most fortunate cases will fossils be formed. The oldest flower fossil found so far is a fossil of an aquatic plant found in Spain, dating back 130 million years.
Image credit: Gomez et al. / PNAS
The development of molecular biology has brought convenience to scientists to understand the evolution of flowers. Combining molecular systematics and large fossil evidence, the scientists collected 63 orders, 372 families, 793 plant species, and 13,444 characteristic data, reconstructed the ancestral flowers of angiosperm phylogeny based on the model, and found that they date back to 140 million years ago.
Ancestor flowers reconstructed from the model/Image source: Sauquet, H. 2017
Butterflies and moths are taxonomically lepidoptera insects, most notably covered with scales on and on their wings, and have a siphon-type mouthpiece, a long beak, which facilitates the intake of nectar.
Like flowers, insects such as butterflies and moths are difficult to leave fossils, and complete fossils available for study are very rare, but scientists have found new breakthroughs.
In 2012, a team of paleontologists working on spores and pollen found some unexplained tiny structures in organic sediments while searching for ancient leaf litter and sediments. The researchers eventually discovered that these tiny structures were the remains of the wings of primitive Lepidoptera insects.
Researchers found evidence of primitive butterfly and moth wings in the sediment/Image source: Bass van de Schootbrugge Utrecht University photo
According to pollen science analysis, the sedimentary layers that appeared in these remains were formed during the Triassic-Jurassic transition, about 200 million years ago. That is, Lepidoptera insects have appeared on Earth at least 200 million years ago, while flowering plants only began to grow on land 140 million years ago, and primitive butterflies and moths have appeared 60 million years before the appearance of flowering plants, or angiosperms.
What did these primordial butterflies eat before the flowers appeared?
Before the fossil discovery of the wings of primitive Lepidoptera insects, the general view among scientists was that insect mouthparts such as butterflies and moths appeared to adapt to the evolution of nectar consumption.
But if butterflies and moths with mouthparts appear before flowering plants, what do they feed on? What is it that makes them start to survive by sucking nectar?
Considering that the weather on the earth at that time was much hot and dryer than it is now, the surface area of insects such as butterflies and moths was relatively large, and the water in the body was easy to lose, one of the conjectures of scientists was that in order to adapt to the hot and dry climate at that time, primitive insects evolved a siphon-like beak, which was convenient for effective intake of fluids and replenishing rapidly lost water. That is, the beaks of early butterflies and moths were used to "drink water".
Initially, they may have survived by sucking water droplets and exudates from broken leaves and trunks.
To this day, there are still a few butterflies that retain this original trait. For example, the dead leaf butterfly and the glazed butterfly feed mainly on sap from the wounds of decaying fruits or leaf trunk insect borers.
Dead leaf butterfly/Image source: Wikipedia
After the emergence of gymnosperms, primitive butterflies and moths then discovered the highly nutritious liquid secreted by the immature seeds of primitive pines such as pine cypresses - pollinator drops. Pollinators contain a variety of sugars, including fructose, glucose, and sucrose, and butterflies soon fall in love with the sweetness of the nutrient-rich pollinator drops.
After the emergence of flowering plants, insects are attracted to the nectar, and while sucking the nectar, they also help the flowers pollinate, and the two sides eventually form a mutually beneficial relationship and co-evolve.
Finally, it is important to note that while the evidence so far confirmed suggests that flowers have only existed for 140 million years, some environmental evidence suggests that they may have been around for a longer period of time. After all, we can't go back to the time when flowering plants began to appear, and the origin of angiosperms can only be understood through fossils or existing molecular techniques.
Perhaps, in the future, we will be lucky to find new fossil evidence. Or as technology continues to evolve, we can find flowering plants that have existed longer, and the relationship between flowering plants and insects will be redefined.
Isn't science such a repetitive process of discovery, constant proof, and constant overthrow?
bibliography:
[1] First ever flower, 140 million years ago, looked like a magnolia. By Mario Vallejo-Marin, University of Stirling
[2] Sauquet, H., von Balthazar, M., Magallón, S. et al. The ancestral flower of angiosperms and its early diversification. Nat Commun 8, 16047 (2017).
[3] Van Eldijk T J B , Wappler T , Strother P K , et al. A Triassic-Jurassic window into the evolution of Lepidoptera[J]. Science Advances, 2018, 4(1):e1701568.