Exploring the Evolution of Cicadas Preserved in Amber

Your stay at the Faculty of Science was funded by an international mobility project and you stayed in Prague for seven months. Why did you choose Charles University? Were you previously in contact with anyone from the University?

When I finished my PhD I was looking for doctoral positions and while I was googling available positions I found a short-term mobility project of the Charles University which said I will know the result within a month. So I thought “I’ve never been to Prague and Charles University is the best university in the Czech Republic”. I also knew that the palaeontology research at Charles University has a long history and is excellent and well-known around the world. It seemed to be a great opportunity and I sent my application directly, without contacting anyone from the Institute of Geology and Palaeontology. Luckily it worked, and I stayed at Charles University for seven months thanks to the mobility project and two additional months as a guest scientist, and had a wonderful research experience at Charles University.

During your stay in Prague, you collaborated with Charles University and National Museum. Did you establish some long-term collaborations and projects?

The professors and colleagues at the Faculty of Science were very nice, they provided me with opportunities and supported me in establishing research cooperations. Professor Katarína Holcová helped me with contacting other research institutions, for example the National Museum, where I gave a presentation about my research and established a collaboration with Dr. Jana Bruthansová. During my stay I cooperated with Dr. Lucia Šmídová, and together we visited Messel fossil site in Germany with Dr. Sonja Wedmann. I also visited Brno University of Technology and Masaryk University and established cooperations there.

In your research you focus on insect fossils preserved in amber. Your article on Mesozoic evolution of cicadas was recently published in Nature Communications. The main aim of the study was to unravel the evolution of cicadas. How many fossil samples did you study and which methods did you use to answer your research questions?

For this study we had eleven fossil samples that belong to the superfamily Cicadoidea, which included both nymphs and adults. We were interested in the evolution of their morphology, behaviors, and life cycle, and wanted to obtain some Mesozoic ecological implications from these samples.

We applied different methods in order to get a more comprehensive picture of the samples. First, we checked them with optical microscopes. Next, we used micro-CT  to get X-ray-like photos of the samples, and then we put the images together using an advanced software to create a reconstruction of the species, which enabled us to visualize the cicadas without damaging the samples and get more detailed 3D anatomical structures. To analyse morphological feature data, we conducted phylogenetic analyses to explore the relationships between the studied samples preserved in amber and the extant species of cicadas. Additionally, we conducted analyses of morphological disparity to explore macroevolutionary changes in specific body parts and compared these findings with phylogenetic results.

Cicada nymph preserved in amber, archive of Hui Jiang

Extant cicadas form two quite distinct groups (Cicadidae, Tettigarctidae), what are the biggest differences between these two groups?

Firstly, they are distinct morphologically. Tettigarctidae, which are also called hairy cicadas, have a big pronotum (the first segment of the thorax, in dorsal view), which conceals most of the mesonotum (the middle segment of the thorax, in dorsal view). The singing cicadas, Cicadidae, on the other hand, have a relatively large exposed mesonotum. This difference may be related to the evolution of their flight muscles and flight abilities. Both groups also differ in the shape and the venation of their wings. The emergence of these differences in evolution was one of the main research questions in our study.

There are also notable differences ecology and their distribution between these two cicada groups. The Cicadidae is widespread globally, comprising over three thousand species. In contrast, Tettigarctidae consists of just one genus with two species, both only found in Australia. A fascinating ecological feature is likely their varied sound-producing abilities. The singing cicadas, typically males, generate sound using tymbal mechanisms located in their abdomen, which is then amplified by their abdominal resonator chamber. This can reach levels of up to 120 decibels at maximum. The hairy cicadas, Tettigarctidae, cannot produce loud sounds. Instead, they create vibrations and transfer them through solid substrates (e.g., branches, leaves), with the sound received through their legs.

What did your results reveal about the ecology of the mid-Cretaceous cicadas and the divergence between the two groups?

Our results suggest that the ecology of these species living in the mid-Cretaceous period was similar to the extant cicadas. As nymphs they most likely lived underground (their forelegs suggest excellent digging abilities) and fed on xylem sap from the roots of the plants. During the Cretaceous period they were likely undergoing a profound transformation in their way of life, such as changes in the feeding and flight abilities of the adults, due to changes in the surrounding vegetation – this change occurred around the same time when gymnosperms gave way to angiosperms and the structure of the vegetation changed profoundly. The cicadas may have to change their body plan to adapt to the newly emerging forests during this period.

Based on the results of our morphometric analyses we hypothesise, that the differences in their heads (e.g., mouthparts, distance between eyes), thoraxes (e.g., the relative differences in the pronotum, mesonotum, and forewing) have co-evolved their feeding and flight abilities, and that both of these changes may occur hand in hand with the changes in the surrounding environments.

Eunotalia emeryi cicada and uncovering its mineralized structures, both photos are from Hui Jiang

Was the work on this article a part of your research programme while staying at Charles University? What do you focus on now?

This article is part of the work I began during my PhD in China and Germany, At Charles University, I had the chance to supplement some optical photos with the new microscope equipment. I must say, the imaging results were very impressive. I refined some micro-CT data here, completed the final manuscript, and submitted it to the journal.

My research at that time focused more on amber taphonomy (study of how organisms become fossilized in amber or otherwise preserved in palaeontological record) which is a subject I still focus on until today. This month I will go to the Senckenberg Museum in Germany to conduct further research on some cicada fossils. I also plan to visit Prague and continue in our cooperation. I really liked it in Prague so maybe I will apply for some other project at the Charles University in the future. After graduation it is important to visit different universities and research institutions, establish new collaborations and experience work at different facilities. Some short-term mobilities and programmes are great for these experiences, of course, it's also important to make decisions carefully, considering individual's situations and needs. I've been fortunate to establish collaborations with scientist from many institutions and hopefully, together, we may collectively generate innovative ideas.

For the original study see this link