A variety of insects feeds on plants. These species and their nutritional patterns have developed very early in evolution – much earlier than previously assumed, as can now be used to show food at 165 million year old fossil leaves. Accordingly, it was not the development of flowering plants in the early Cretaceous period that drove the evolution of herbiviting insects. Instead, the selection pressure by parasitic insects could have accelerated the evolution of herbiviting insects in the Jura.
In today’s ecosystems, plants and herbivoring insects form a complex system of mutual interactions. According to a common assumption, their biodiversity and interactions developed in parallel 125 to 90 million years ago, in the sub -line period. At that time the flower plants began to spread and diversify. At the same time, according to the assumption, new forms of plant -eating insects were created. But when and how their development actually went on was unclear.
Insect traces on fossil plants
Biologists around Lifang Xiao from the Guangdong Academy of Sciences have now examined this in more detail. To do this, they analyzed 134 fossil plants of different ages, which come from different regions of the world, as well as three modern forest collections. The researchers searched for feeding damage and other traces on the plants that are left by herbiviting insects. This includes, for example, eating the leaf edges or surface, drilling and eating the interior, piercing and sucking out the plants as well as egg racks. From these traces, the biologists concluded the changing ways of life and nutrition of the insects in the course of the past 305 million years.
The evaluation showed that today’s variety of insects and the plant damage caused by them existed 165 million years ago, in the middle of the Jura era. This was a correspondingly old fossil collection from the Chinese Daohugou, whose fossil leaves showed a pattern similar to the modern plant samples. At the time, insects lived at the time than today, but their diversity led to the same extent of herbent, the team explains. This detection of insect eating is thus dated around 60 million years earlier than the development boom of angiosperms, the covered flowering plants. According to this, the herbivorous insects developed much earlier than before, long before flowering plants dominated the food supply on land.
Enemy instead of food as an evolutionary drive?
But what plants did the early insects eat in the Jura, if not from angiosperms? The fossils from this period come mainly from gymnosperms such as conifers, palm ferns and several extinct plant groups. In contrast to the covered sauces, the seeds of these naked are not enclosed in a ovary. Today’s herbivorous insects rarely infest the naked. But in the past it apparently looked different: “The results point out that the insects’s descent lines previously (165 to 100 million years ago) had a broader spectrum of nutritional styles that restricted itself in modern times,” writes the team. Accordingly, the early types of insects were specialized in certain naked plants, but later species used the covered plants a little more generally.
The researchers conclude that the herbivorous insects did not diversify as previously intended by the parallel development of the plants. Instead of the feed offer as a driving force, the natural enemies of herbivorous insects could have promoted their evolution, as Xiao and her colleagues report. Accordingly, the occurrence of parasitic insects that the herbivorous insects liked, the development of which is probably promoted in the Jura – as an attempt to escape the enemies. Such insects, especially wasps, flies and beetles, experienced an evolutionary boost around 180 million years ago, in the early Jura, as the team explains.
According to Xiao and her colleagues, the findings on past evolution phases could help to understand today’s biodiversity and plant insect interactions. With the knowledge, the insects and their ecosystems could be better protected.
Source: Lifang Xiao (Academy of Sciences Guangdong) et al.; Proceedings of the National Academy of Sciences, DOI: 10.1073/PNAS.2412036122