Using Modern Rainforests to Study Fern-Insect Interactions in the Fossil Record

Fern-Arthropod Interactions from The Modern Upland Southeast Atlantic Rainforest Reveals Arthropod Damage Insights to Fossil Plant-Insect Interactions

Summarized by: Haley Vantoorenburg is a geology major at the University of South Florida. Haley currently researches encrusting organisms on Paleozoic brachiopods and plans to work closely with fossil preparation and preservation studies in the future.

What was the hypothesis being tested (if no hypothesis, what was the question or point of the paper)? Ferns were some of the first plants to have evolved broad leaves (fronds) in the fossil record (the earliest known records are about 360 million years old). These broad leaves allow large areas of insect damage from insects present while the plant was alive to be preserved. Modern and fossil ferns can be compared against one another to understand what insect interactions were present throughout geologic time, and the ways these interactions have either changed or remained constant. 

What data were used?: This study examined 17 types of damage (grouped into categories by the method used to cause the damage or by the area of the leaf affected; see Methods below) caused by insects, using both fossil ferns from multiple collection sites and modern ferns from a rainforest in southern Brazil. Ferns were chosen because, as opposed to other plant types, their broad leaves increase access for insect predation and modern broad-leafed ferns are very similar to some of their fossil relatives. Ferns became abundant in the Carboniferous (359.2–299 Mya). In the Carboniferous, records of arthropod (spider and insect) damage to plants also became more frequent. While insects are often not preserved with the fossil ferns, the types of damage that prehistoric insects caused are very similar to the damage types observed today, even if we don’t know if the types of insects that made the damage are or aren’t similar. Because fossil ferns are so similar to their living relatives, and because ferns are one of the first broad-leaved plants, scientists can use modern ferns as models to study the oldest plant-arthropod interactions. 

Methods: This study used an area of rainforest with high humidity, many fern species, and high fern density to study modern ferns. A census of the ferns present and any records of insect-fern interactions were collected over a transitional area from the lower broad-leaf forest to the upland grassland. The damage type, richness per leaf, and damage size were recorded using hand lenses, calipers, and macroscopic and microscopic photography. Functional feeding groups (FFG) were made to categorize the types of insect damage. Damage from egg-laying and traces were also recorded. Damage was recorded using a damage type guide that described 413 different damage types. This was compared to compiled fossil fern data from many sites. 

Results: Even with 413 pre-established damage types, one new damage type was discovered in this study. This new damage type is a sub-type of surface feeding that features a series of rounded damage marks that was observed in both modern ferns and in multiple fossil ferns. Some types of damage were found rarely in modern ferns, but never in fossil ferns (hole feeding – the creation of separate holes in the leaf tissue – and galling – the development of waxy or swollen layers). Margin feeding (consuming only the edges of a leaf) was found in both fossil and modern ferns and included the most common damage types (46% of the damage observed). Surface feeding (damaging but not completely breaking through the leaf tissue) was recorded on both fossil and modern ferns (10%). Some types were found in modern and fossil plants, but some types were only found in angiosperms (i.e., flowering plants) in the fossil record and not fossil ferns (piercing and sucking, small points of damage or swollen leaf sections, 15%, and mining, creating subsurface damage, 8%). 

A bar chart with the number of observed instances on the left y-axis to match the bars and the types of functional feeding groups on the x-axis. It is overlain by a line representing the cumulative percentage. From left to right: Margin feeding, 220 instances and 46% of the total. Piercing-and-sucking, 73 instances, the cumulative total 61%. Hole feeding, unlabeled but about 52 instances, 72% the cumulative total. Surface feeding, 50 instances and 83% of the cumulative total. Mining, unlabeled but around 40 instances, 91% of the cumulative total. Hole feeding, 34 instances, 98% of the cumulative total. Galling, nine instances, 100% of the cumulative total.
Figure: A bar chart of the recorded damage types by functional feeding group, showing the dominance of margin feeding in the modern ferns in the Sao Francisco de Paula National Forest, municipality of Sao Francisco de Paula, Rio Grande do Sul, southern Brazil.

Why is this study important?: This study showed that modern ferns can provide a better understanding of the marks that different insect feeding methods cause and of the fossil record of these marks on similar ferns. Researchers found that the levels of precipitation impacted the amount and types of fern-insect interactions in modern ferns. This means that studying modern ferns can create models for studying past environmental conditions using fossil fern data. Additionally, there are fossil and modern instances of insect interactions that show a specialized association with specific ferns.

Broader Implications beyond this study: The similar rates of predation by insects on both modern and fossil plants show that ferns were important to herbivorous (plant-eating) arthropods throughout history. All FFGs identified in the fossil record were found in modern ferns, so understanding interactions in modern environments can be used to determine the environmental conditions of different fossil assemblages, such as the projected precipitation level of their environment. The prevalence of fern-arthropod interactions throughout history means that it can be used to study changes in these fern-arthropod relationships in geologic time and we may be able to use them to model the influence of climate change. 

Citation: Cenci, R., & Horodyski, R. S. (2022). Fern-Arthropod Interactions from the Modern Upland Southeast Atlantic Rainforest Reveals Arthropod Damage Insights to Fossil Plant-Insect Interactions. Palaios, 37(7), 349–367.

Interning at a Paleontology Lab

Haley here –

A Busycon coactatum, or Turnip Whelk, specimen.

I recently started interning with Dr. Sarah Sheffield (one of Time Scavenger’s collaborators and USF professor) at the University of South Florida (USF)! As a high school senior, this has been an extremely influential experience to me. With Dr. Sheffield, I have been learning how to catalog fossils, and I have been slowly (but surely!) entering the USF collections to an online database (MyFossil). Along with learning how to photograph and catalog fossils, I have been able to learn about graduate and undergraduate research, sit in on a college level course, learn about fossil identification and photography (1), and meet some amazing people.

I was able to have this internship experience through a class called Executive Internship that is offered to seniors at the high school I attend. This class spends the first nine weeks teaching career skills like writing a resume and cover letter, interview etiquette, and effective communication. Throughout the first nine weeks, we are encouraged to research various career paths that interest us and speak with people working in those careers. By the end of the nine weeks, we are expected to have secured an internship. The school partners with various businesses (such as the Florida Aquarium) in order to ensure that students have options. Some students use these connections, while others choose to intern with businesses they have been to before or reach out to family and friends for suggestions. Others -like myself- email everyone they can think of to see what they would think about having a high school intern. I was fortunate enough that one of the people I reached out to suggested that I speak with Dr. Sheffield, and I was even more fortunate that Dr. Sheffield found a project that she wanted to start and was willing to allow me to help. After everyone has secured an internship and we have completed the first nine weeks of class, all of the interns are given permission to sign out of school instead of attending Executive Internship class. In exchange for essentially leaving a class before school ends, all of the interns are required to record an average of five hours per week in our internship and complete a weekly log. Other than the hour requirement and log, internship schedules and tasks vary for each student.

I can not say when I first became interested in paleontology and geology, but this internship experience has only helped my interest grow. When trying to explain why I wanted to study those fields, my mom helpfully explained that I had “always been a rock girl” which sums it up pretty well. From family trips to North Carolina when I was in elementary school, I became fascinated by the variety of gems and minerals you could find. As I took more science classes, I learned about crystal structures and how various formations occur. In a public speaking class, I was able to pick any topic I wanted and ended up falling into a rabbit hole of the history and changes of paleo-illustration. I think part of what draws me to these fields is how seamlessly they integrate with so many other fields. From chemistry and biology, to history or art, there are so many aspects of paleontology and geology that can combine with other fields. In any case, there is always something new to learn and something to dig deeper into that can reveal so much. This is only highlighted by my experience sitting in on Dr. Sheffield’s class. The class addresses the evolution of life on Earth, but reaches implications of what we truly define as Homo sapiens, the history of paleontology in the United States, biomechanics (how organisms move), and much more.

Bryozoan encrusting on a Busycon carica (Knobbed Whelk) specimen.

When I started my internship, I was unsure what to expect. I am a high schooler, and I was going to be working with a college professor to begin a new project. I was excited to learn, but I can say that I definitely did not expect to come home and tell my parents that I wished there were more Anadara (2) specimens because they were the most fun to photograph. I learned the conventional lighting angles to use for fossil photography, how to measure various shells, and the information needed to catalog fossils. Properly labeled fossils soon became a valued commodity after some specimens only had labels like “bivalve”, “east coast”, or “recent” specimens. To catalog the specimens, I have been using the MyFossil database. It is an extraordinary website that allows museums and researchers to share their specimens so that they are available world-wide. It is amazing to know that I can catalog a specimen and see it appear online next to a trilobite specimen from China and a shark tooth from California. MyFossil has an important feature that allows specimens with detailed information (classification, dimensions, geochronology, and locality) to be marked research grade. This allows MyFossil to function as both a free online museum and as a valuable tool to researchers.

Learning how to catalog fossils entails learning about fossils just from exposure. I have learned about the variety of features of shells and how they function for each species. In order to revise some entries to make them research grade, I have used a website called Macrostrat. By looking up geochronology based on lithostratigraphy or formation, I have begun to recognize the common  rock units of various sites in Florida. I have been able to learn more about fossil features by asking how to denote various characteristics like boring. A notable specimen of snail had a bryozoan encrusting (3). By cataloging fossils and asking about them as I do, I have learned much more than what I expected to learn from the cataloging labels.

This internship has been a great learning experience. I was admittedly unsure of what I wanted to do in college, other than the fact that I wanted to do something with geology and fossils. Interning has allowed me to learn, discuss projects with others, and see the sheer variety of research within the USF School of Geosciences. This, paired with everyone’s enthusiasm for their research, has helped me see the kind of environment that I want to be a part of. It has been an opportunity that has allowed me to gain a better understanding of the college experience, and it has allowed me to have hands-on research experience in the field that I love. I look forward to expanding what I have learned even more through the rest of my internship!