Parasitic Scorpionflies

Fleas are not a separate insect order, as previously thought, and are a lineage of scorpionflies, which evolved when they started feeding on the blood of vertebrates sometime between 290 and 165 million years ago (Permian to Jurassic periods), according to a new genetic analysis of fleas and related insects.

An ancient flea species called Atopopsyllus cionus may carry evidence of an ancestral strain of the bubonic plague (Yersinia pestis). Image credit: George Poinar Jr.

An ancient flea species called Atopopsyllus cionus may carry evidence of an ancestral strain of the bubonic plague (Yersinia pestis). Image credit: George Poinar Jr.

Fleas are medically important blood-feeding insects responsible for spreading pathogens such as plague, typhus, and myxomatosis.

They exhibit one of the most bizarre bodyplans and modes of life among insects. They have a wingless body, siphonate mouthparts, very reduced eyes, and hind legs adapted for jumping.

However, their exact position on the insect tree of life has proven to be one of the most persistent problems in insect evolution and systematics.

“Of all the parasites in the animal kingdom, fleas hold a pre-eminent position,” said study’s first author Erik Tihelka, an undergraduate student in the School of Earth Sciences at the University of Bristol.

“The Black Death, caused by a flea-transmitted bacterium, was the deadliest pandemic in the recorded history of mankind; it claimed the lives of possibly up to 200 million people in the 14th century.”

“Yet despite their medical significance, the placement of fleas on the tree of life represents one of the most persistent enigmas in the evolution of insects.”

In the study, Tihelka and his colleagues tested competing hypotheses on the evolutionary relationships of fleas and related insects using the largest molecular dataset available to date consisting of 1,478 protein-coding genes, a smaller mitogenome and sequence alignment of 16 genes.

They found that the closest living relatives of fleas are the members of the scorpionfly family Nannochoristidae, a rare group with only seven species native New Zealand, southeastern Australia, Tasmania, and Chile.

Unlike the blood-thirsty fleas, adult nannochoristid scorpionflies lead a peaceful existence feeding on nectar.

“It seems that the elongate mouthparts that are specialized for nectar feeding from flowers can become co-opted during the course evolution to enable sucking blood,” said study’s co-author Mattia Giacomelli, a Ph.D. student in the School of Earth Sciences and the School of Life Sciences at the University of Bristol.

“The new results suggest that we may need to revise our entomology textbooks,” said study’s senior author Dr. Chenyang Cai, a researcher at the Nanjing Institute of Geology and Palaeontology and the School of Earth Sciences at the University of Bristol.

“Fleas no longer deserve the status of a separate insect order, but should actually be classified within the scorpionflies.”

“We have exceptionally preserved fossil fleas from the Jurassic and Cretaceous.”

“In particular, some Jurassic fleas from China, about 165 million years old, are truly giant and measure up to 2 cm.”

“They may have fed on dinosaurs, but that is exceedingly difficult to tell.”

“What is more interesting is that these ancient fleas share important characters with modern scorpionflies.”

The study was published in the journal Palaeoentomology.

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Erik Tihelka et al. 2020. Fleas are parasitic scorpionflies. Palaeoentomology 3 (6); doi: 10.11646/palaeoentomology.3.6.16

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