Thursday, 7 January 2010

An unwelcome bug

I usually enjoy having the chance to write BugBlog posts. Not today. As a parent of school age children, I have had occasionally to deal with lice infestations. One of these was apparent on one of my children during the holidays. A combnitting session today yielded shocking results. Tens of nits (eggs) and a fat adult louse. I couldn't resist the photo opportunity. This is the first adult lice I have seen. In previously infestations I could only see nits. I hope this is the only adult louse and that we can clear it quickly.
The louse clinging to hair. Its dark stomach indicates a recent feed of blood
Anyway, despite my dread of live lice, they are fascinating creatures on their own right. Lice are apterous bloodsucking insects (order Phthiraptera) that are adapted to clinging to hair - hence, they are found only in mammals. They lay their eggs gluing them in a shaft to individual hairs, close to the scalp. The newborn lice are nymphs, they are smaller and simpler than adults and metamorphose slowly into adults in three stages. Individuals live for a month or so and females can lay several hundreds of eggs in their lifetime. The study of such species-specific ectoparasites can provide information on the evolution of their hosts. Humans are the host of two species of lice (wingless insects of the order Anoplura), the pubic louse and the hair/body lice complex. In the past hair and body lice were thought to belong to different species, one adapted to lay their eggs on hair, the other on clothing. It was thought that body lice had evolved with the invention of clothing into a separate species. Molecular analysis have revealed, though that the body louse has evolved several times and that they do not form a monophyletic unit separate from head lice. These studies have revealed more intriguingly that there are three old genetic lineages of lice (only one of them includes body lice) and the authors hypothesized that one of such lineages might have evolved in Homo erectus, and been transferred to modern humans when they met. A fascinating hypothesis that has proven to be difficult to test due to the lack of good calibrations for lice DNA.

1 comment:

Ted C. MacRae said...

How about the even-more intriguing idea that human pubic lice originated by horizontal transfer from gorillas (Reed et al. 2007)!