After 15 years of research, scientists reconstruct evolution of groups of flies from dinosaur era
August 18, 2021
By André Julião | Agência FAPESP – Two researchers have spent the last 15 years tracking down a story that is over 100 million years old with the aid of little more than a microscope, a featherweight forceps, and well-trained eyes. After reviewing the scientific literature, traveling the world to collect specimens, and analyzing others held by natural history museums, Sarah Siqueira de Oliveira, currently a professor at the Federal University of Goiás (UFG), and Dalton de Souza Amorim, a professor at the University of Sao Paulo’s Ribeirão Preto School of Philosophy, Sciences and Letters (FFCLRP-USP), in Brazil, have produced the most comprehensive study to date of a subgroup of fungus gnats, insects that belong to the fly order Diptera, occurring around damp, decaying vegetation, algae, and fungi.
The publication, with more than 100 pages and 107 mostly color illustrations, occupies an entire volume of Bulletin of the American Museum of Natural History (BAMNH), a peer-reviewed scientific journal issued since 1881. The research exemplifies the importance of continuous public funding for science, as it has been supported by FAPESP via several projects since 2004.
The study’s innovations include descriptions of new species and a proposed new classification of the family Mycetophilidae, which comprises the bulk of fungus gnat species (the family’s name is Greek for “fungus lovers”). Since their emergence in the Late Jurassic, more than 145 million years ago, they have diversified enormously and are found all over the world. Their larvae feed on mushrooms, puffballs, molds, and other wood-decay (xylophagous) fungi.
The researchers focused most of all on Leiinae, a subfamily originating in the south of the supercontinent Gondwana, which later broke up to form present-day South America, Africa, Antarctica, India, Australia and New Zealand. The subfamily, which coexisted with the dinosaurs, is one of five, and one of the most diverse in the family Mycetophilidae, with more than 600 described species and an estimated 2,000 or more yet to be described. The BAMNH study concludes that the subfamily comprises 37 genera and notes the existence of amber fossil records.
“There was no consensus in the scientific literature as to which groups belong to this subfamily, so we chose to work both on describing and naming species, and on understanding their evolutionary relationships. It’s a highly diverse group, and not much is known about it in the Neotropics,” said Oliveira, who painstakingly studied more than 1,000 specimens as part of the undertaking.
Oliveira began studying insect evolution while she was an undergraduate reading biology at FFCLRP-USP. The FAPESP Research Program on Biodiversity Characterization, Conservation, Restoration and Sustainable Use (BIOTA-FAPESP), launched in 1999, was then in its early years, and there was a large amount of collected material to be identified, offering Oliveira an opportunity to study fungus gnats. This first task was supported by FAPESP via a scientific initiation scholarship for 2005-06.
It was part of a larger project entitled “Geographic limits and causal agents of Diptera endemism in the Atlantic Forest”, supported by a BIOTA Thematic Grant, and with Amorim, her supervisor, as principal investigator. She also completed her master’s and PhD research under the aegis of this project.
While she concentrated as an undergraduate on identifying specimens collected in the Atlantic Rainforest, and her master’s project focused on a particularly diverse genus, she set out in her PhD research to conduct a comprehensive analysis of Leiinae, then one of the least studied subfamilies of fungus gnats. This was the basis for the BAMNH monograph published earlier this year, expanded with the results of her postdoctoral research, which was also supported by FAPESP.
“Insects are very ancient, and many are found worldwide,” Amorim said. “As a research supervisor, therefore, I prefer to choose themes in which students can become world leaders on groups that have few specialists. We chose Leiinae because of the lack of knowledge about this important group, and Sarah has become a leader in the field thanks to this study.”
Becoming an authority on a group of animals found worldwide requires personal analysis of specimens. Many are in natural history museums, whose mission is to preserve the largest and most diverse collections of animals, plants and minerals possible.
During her PhD research, Oliveira went to Australia to analyze the collections of the Australian Museum in Sydney and CSIRO-ANIC in Canberra. On the way back to Brazil, she stopped in South Africa to work at the Kwa-Zulu Natal Museum (NMSA), Iziko South African Museum (SAMC) and Pretoria National Collection of Insects. On another trip, she studied collections in the US and Canada. During her postdoctoral research, part of which was supported by FAPESP via a Research Internship Abroad (RIA) Scholarship, Oliveira spent a period studying the collection of the Natural History Museum in London. While in Europe, she visited collections of museums in France and Germany. Her on-site studies and analysis of material sent by correspondence covered collections in ten countries. Amorim collected specimens in Australia, Brazil, California (USA), Chile, Costa Rica, Nepal and New Zealand.
“An important part of all this research was bringing back to Brazil specimens that had been collected here but didn’t exist in Brazilian collections. They’re very diverse animals from the Neotropics that originated in southern Gondwana and later spread around the world. Historically, however, researchers from countries in the northern hemisphere described many Brazilian species until the 1940s. Now part of the collections has been repatriated,” Oliveira said.
In some of the museums, the agreement allowing Oliveira to pursue her research entailed organizing insect collections that had often been stored away for years without a specialist to identify the specimens.
“Many were single specimens or consisted of only a few units, and they were often very old,” Amorim said. “These factors usually make genetic analysis impossible. However, analysis of morphology using a microscope is sufficient to obtain most of the evidence needed for our work. In addition, genetic analysis of fossils isn’t possible, and morphology is the source of information enabling us to include them in the system.”
One of the principles in the work of taxonomists like Oliveira and Amorim is precisely finding patterns in the sharing of morphological traits such as wings, legs, and other parts that make them unique. In the BAMNH monograph, 128 morphological features are used to differentiate genera, including head, thorax, legs, wings and genitalia.
To create a classification structure with all genera in the subfamily, the researchers added three new tribes to the existing four. The study included 54 species known from fossils in 12 extinct genera. Eight fossils are preserved in amber, a fossilized tree resin made famous by the 1993 movie Jurassic Park. The insect that appears in the movie did not feed on blood as shown, according to Amorim, but is a fungus gnat belonging to the family Keroplatidae.
“Dinosaurs are popular, but few people discuss where they lived, what they ate or what other beings lived around them,” he said. “Our work shows that this group of flies also existed during the same period, swarming at their feet and with larvae that fed on the fungi associated with forests. At the time, the forests consisted mainly of conifers, in contrast with present-day tropical forests. We’re now beginning to see an increasingly complete picture of the flora and fauna of that era.”
The monograph “Phylogeny, classification, Mesozoic fossils, and biogeography of the Leiinae (Diptera: Mycetophilidae)” is at: https://digitallibrary.amnh.org/handle/2246/7256.
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