Head and body lice appear to be the same species, genetic study finds
Phys.org
Apr 09, 2012A new study offers compelling genetic evidence that head and body lice are the same species. The finding is of special interest because body lice can transmit deadly bacterial diseases, while head lice do not.
The study appears in the journal Insect Molecular Biology.
Scientists have long debated whether human head and body lice are the same or different species. The head louse (Pediculus humanus capitis) is a persistent nuisance, clinging to and laying its eggs in the hair, digging its mouthparts into the scalp and feeding on blood several times a day. The body louse (Pediculus humanus humanus) tends to be larger than its cranial counterpart, and is a more dangerous parasite. It lays its eggs on clothing, takes bigger blood meals, and can transmit relapsing fever, trench fever and epidemic typhus to its human host.
Previous studies have found that even when they are both present on the same host, head and body lice don't stray into each other's territories. They don't breed with one another in the wild, but they have been shown to successfully reproduce under specific laboratory conditions. The presence of head lice has little to do with human hygiene, but body lice seem to appear out of nowhere when hygiene suffers – in times of war or economic hardship, for example.
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"The differences in their sequences were so minor that if we didn't know they were separate groups, we would have considered them the same species," he said.
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Obviously, the genetic differences are sufficient to compel different behaviors, no matter what their similarities are.
The fact that they can be induced to breed under laboratory conditions does not negate the fact that they are two different species. Clearly, they are still fairly early in the speciation process. Since they do not naturally interbreed, eventually their genomes will drift far enough apart that interbreeding will become impossible even in lab conditions.