The very hungry Caterpillar: 60 Million-year-old Feeding Traces. Sharing of food plants as a driving force for insect diversity

Newswise — Researchers from the Hessian State Museum Darmstadt and the Senckenberg Biodiversity and Climate Research Center Frankfurt have made a significant discovery regarding the factors behind the vast diversity of herbivorous insects. Their findings, published today in the esteemed scientific journal "PNAS," reveal that the diversity of herbivorous insects has evolved primarily due to their shared utilization of food plants over the past 60 million years. To arrive at these insights, the scientists analyzed feeding traces left by arthropods on an impressive collection of over 45,000 fossilized leaves.

Herbivorous insects constitute the most diverse group of multicellular organisms on our planet. Their remarkable variety extends to their mouthparts and feeding behaviors. For instance, there are caterpillars or beetles equipped with powerful, jaw-like mouthparts that chew on leaves, bugs and aphids that pierce plants to access their sap, and creatures that prompt the formation of galls—an excessive tissue growth—within which they find protection and sustenance away from their adversaries. Remarkably, the preserved feeding traces on fossilized leaves provide valuable evidence for identifying the factors that have contributed to the immense diversity of herbivorous insects. Dr. Jörg Albrecht from the Senckenberg Biodiversity and Climate Research Center in Frankfurt elaborates on the significance of these findings.

Albrecht, in collaboration with Prof. Dr. Torsten Wappler from the Hessian State Museum in Darmstadt and other researchers from Senckenberg, conducted a comprehensive study involving the classification of 47,064 fossil leaves belonging to 436 plant species. These leaves were collected from 16 different locations across Central Europe, Iceland, and Norway. The researchers' main focus was to examine these fossilized leaves for any feeding traces left by insects. Remarkably, the fossils covered a wide span of time, encompassing nearly the entire Cenozoic era, spanning from 66 to two million years before the present day. Additionally, the fossilized leaves originated from diverse climate zones, ranging from subtropical to oceanic to humid continental. Prof. Dr. Torsten Wappler further elaborates on the scope and significance of their study.

The research team meticulously scrutinized each well-preserved fossil leaf to identify any indications of insect feeding. Surprisingly, over one-fifth of the examined leaves exhibited clear traces of such activity. "By analyzing this data, we have established that food plants were already being utilized by various herbivorous insects during the early stages of geological history. Furthermore, our in-depth assessment of the feeding traces reveals that the collective utilization of a particular plant species by different groups of herbivorous insects contributed twice as much to their functional diversity in terms of feeding methods as the actual species diversity of the food plants," explains Albrecht.

The findings of the study offer fresh perspectives on the origins of insect diversity and shed light on the principal driver behind the functional diversity of herbivorous insects: the coexistence of numerous specialized insect species on the same plant species. The authors assert that when different insect species share a common food plant, they must adapt their diet and feeding behaviors to avoid direct competition. This adaptive process has unfolded over millions of years, resulting in an astonishing array of mouthpart structures and, ultimately, the emergence of a multitude of insect species.

These insights find resonance in today's tropical forests, where herbivorous insect species predominantly exhibit specialization towards specific plant families, thereby creating an intricate network of interdependence between plants and insects. The diversity observed in the present-day tropical forests mirrors the evolutionary processes that have shaped herbivorous insects over millennia, as they continue to adapt and thrive in their respective niches.

Wappler concludes that our study underscores the valuable role of the fossil record in examining fundamental theories concerning the origins of biodiversity. Moreover, the outcomes of our research serve as a significant reference point for identifying the key factors that influence the diversity of herbivorous insects in modern ecosystems. By delving into the past, we gain essential insights that can inform our understanding of the present-day ecological dynamics and the processes that have contributed to the remarkable diversity of herbivorous insects in the world today.