A study of more than 1,400 protein-coding genes of fleas has resolved one of the longest-standing mysteries by reordering the insect's placement in the tree of life.
The University of Bristol study, published in the journal Palaeoentomology, drew on the largest insect molecular dataset available. The dataset was analyzed using new statistical methods, including more sophisticated algorithms, to test all historically proposed hypotheses about the placement of fleas on the insect tree of life and search for new potential relationships.
The findings overturn previously held theories about fleas, the unusual anatomy of which has meant that they eluded classification in evolutionary terms. According to the authors of the study, fleas are technically scorpionflies, which evolved when they started feeding on the blood of vertebrates sometime between the Permian and Jurassic eras, between 290 and 165 million years ago.
The closest living relatives of fleas are the members of the scorpionfly family Nannochoristidae, a rare group with only seven species native to the southern hemisphere. Unlike the blood-thirsty fleas, adult nannochoristid scorpionflies lead a peaceful existence feeding on nectar. "Despite their medical significance as the cause of the deadliest pandemic in the recorded history of humankind, the placement of fleas on the tree of life represents one of the most persistent enigmas in the evolution of insects, and we can say that we successfully solved it," says lead author Erik Tihelka from the School of Earth Sciences in a report published on the university's website.
The Black Death, caused by a flea-transmitted bacterium, was the deadliest pandemic in the recorded history of humankind; it claimed the lives of possibly up to 200 million people in the 14th century. It used to be thought that all blood-feeding parasitic insects began life as either predators or by living alongside vertebrate hosts in their nests.
Explaining the link between scorpionflies' nectar feeding and fleas' blood feeding, Tihelka said "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."