The study solves the position of fleas on the tree of life

A study of more than 1,400 flea genes encoding proteins solved one of the longest-running mysteries in the evolution of insects, rearranging their placement in the tree of life and identifying who their closest relatives are.

University of Bristol study, published in the journal Paleoentomologie, was based on the largest set of molecular insect data available. The data set was analyzed using new statistical methods, including more sophisticated algorithms, to test all historically proposed hypotheses about flea placement on the insect tree of life and the search for new potential relationships.

The findings overturned previously held theories about fleas, whose unusual anatomy meant that they avoided classification in evolutionary terms. According to the study’s authors, contrary to popular belief, fleas are technically scorpions, which evolved when they began feeding on vertebrate blood sometime between the Permian and Jurassic, between 290 and 165 million years ago.

The closest living relatives of fleas are members of the scorpionfly family Nannochoristidae, a rare group with only seven species native to the southern hemisphere. Unlike bloodthirsty fleas, adult nannocoristid scorpions lead a peaceful existence by feeding on nectar.

“Of all the parasites in the animal kingdom, fleas have a preeminent position. The Black Death, caused by a flea-borne bacterium, was the deadliest pandemic in human history; millions of people in the 14th century, “says lead author and student Erik Tihelka of the School of Earth Sciences.

“However, despite their medical significance, the placement of fleas on the tree of life is one of the most persistent puzzles in the evolution of insects.”

It was believed that all the parasitic insects that fed on blood started life either as predators or living with vertebrate hosts in nests. In fact, the blood supply may evolve into groups that initially fed on nectar and other plant secretions.

“It seems that elongated mouthpieces, which specialize in feeding on flower nectar, can be co-opted during the course to allow for blood sucking,” says Mattia Giacomelli, a doctor. student at the University of Bristol who participated in the study.

Previous studies had suggested a link between fleas and unusual anatomical groups of scorpions, but their exact relationships remained unresolved. The mystery has been prolonged by the fact that flea genomes have undergone rapid evolution, which makes it difficult to reconstruct ancient evolutionary relationships. Moreover, nanochoristids are a rather rare and little-studied group that occurs only in New Zealand, southeastern Australia, Tasmania, and Chile, so they are easy to overlook.

“The new results suggest that we may need to revise our entomology textbooks. Fleas no longer deserve separate insect status, but should actually be included in scorpionflies,” says Chenyang Cai, an associate professor at the Institute of Geology and Nanjing. Paleontology (NIGP) and a researcher at the University of Bristol, specializing in Mesozoic insects.

“We have exceptionally preserved fossil fleas from the Jurassic and Cretaceous. In particular, some Jurassic fleas in China, about 165 million years old, are truly gigantic and measure up to two centimeters. It may have fed on dinosaurs, but this is extremely difficult. What’s more interesting is that these ancient fleas share important characters with modern scorpions. ”