Study of Flea Genetics Points their Position on Tree of Life and Closest Relatives

A new study analyzed more than 1,400 protein-coding genes of fleas - addressing some of the persisting questions in insect evolution about the flea.

The latest study, from the University of Bristol, pinpoints the flea's position in the tree of life as well as its closest relatives. It draws on the largest dataset available, with researchers using statistical methods and specialized algorithms, challenging historically proposed hypotheses regarding the fleas' position in the insect tree of life.

Technically Scorpionflies

Researchers found a different result compared to previous theories, with the insect's unusual anatomy being a reason for the species eluding previous attempts at evolutionary classification. According to their study, published in the journal Palaeoentomology, fleas are technically "parasitic scorpionflies." They have started evolving shortly after feeding on vertebrate blood sometime between the Permian and Jurassic periods, between 290 and 165 million years ago.

With this report, fleas' closest living relatives are fellow scorpionflies under the family Nannochoristidae, a small and rare group of only seven species - mostly native to the southern hemisphere. Also, unlike fleas, the other nannochoristids feed on nectar instead of blood.

"Of all the parasites in the animal kingdom, fleas hold a pre-eminent position," explained Erik Tihelka, lead author of the study and an undergraduate student from Bristol's School of Earth Sciences, in a news article from the University.

"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," Tihelka added.

Previous theories postulate that all blood-feeding parasitic insects, such as fleas, trace their origins as predators or through co-existing with vertebrate hosts in their nests. Additionally, feeding on others' blood has been hypothesized to evolve from species that previously fed on nectar and other plant-based fluids.

"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," added Mattia Giacomelli, a Ph.D. student and a co-author in the study.

Answering the Questions from Previous Studies

Researchers also noted that previous research has already suggested the links between anatomical uncommon groups of scorpionflies and fleas but cannot establish the exact connection between the two species. This mystery was further left unsolved despite discovering the flea genome's rapid evolution, which made evolutionary reconstruction more difficult. The nannochoristids on the other end of the link are rare and endemic to New Zealand, southeastern Australia, Tasmania, and Chile.

"The new results suggest that we may need to revise our entomology textbooks," said Chenyang Cai, a research fellow at the University of Bristol and an associate professor at the Nanjing Institute of Geology and Palaeontology. She explains that fleas no longer belong to insects' separate order, warranting their reclassification with the scorpionflies.

Cai further explains the presence of flea fossils that date back from the Jurassic and Cretaceous periods. Specifically, those found in China and estimated to be 165 million years old are "giants" by today's standards and measure up to two centimeters. "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."

Check out more news and information on Flea Genetics Science Times.