The Coevolution of Lice & Their Hosts

eldavojohn writes "It might be an uncomfortable subject but parasites are an interesting subject when it comes to evolution. Ever wonder if pocket gophers have lice? Well, they do. And most interesting of all is the evolution of these lice mirroring the evolution of gophers. To study the genes of lice may shed just as much light on evolutionary trees as studying the genes of the actual host the lice has evolved to. The most unsettling result from these studies is that human head lice and human pubic lice (crabs) vary so greatly that they are in two separate genera. There were similarities between our pubic lice and the lice found on gorillas. Scientists came to the conclusion, which they published today in BMC Biology, is just as striking as their earlier one about head lice. But it is hardly the same. We did not get pubic lice from other hominids. We got them from the ancestors of gorillas."

Comments

Rather than read a second-hand account...

[GrumpySimon]

Rather than read a second-hand account (although Carl Zimmer is very good), the original article is open access and is available here: http://www.biomedcentral.com/1741-7007/5/7/abstrac t

Conclusion:

Reconciliation analysis determines that there are two alternative explanations that account for the current distribution of anthropoid primate lice. The more parsimonious of the two solutions suggests that a Pthirus species switched from gorillas to humans. This analysis assumes that the divergence between Pediculus and Pthirus was contemporaneous with the split (i.e., a node of cospeciation) between gorillas and the lineage leading to chimpanzees and humans. Divergence date estimates, however, show that the nodes in the host and parasite trees are not contemporaneous. Rather, the shared coevolutionary history of the anthropoid primates and their lice contains a mixture of evolutionary events including cospeciation, parasite duplication, parasite extinction, and host switching. Based on these data, the coevolutionary history of primates and their lice has been anything but parsimonious.

Re:hair shape

[Arker]

It all goes back to the very tight coupling between parasite and host. Even tiny differences between different populations in a host species are mirrored in parasite populations. So lice populations found among hosts of European ancestry have a difficult time with African hair forms. African lice populations, however, do not. Apparently lice populations in North America are mostly of European derivation, but that is far from true in other areas.

Re:Gorilla / Human lovin'?

[radtea]

Anyway, best article linked from /. in ages. Great, thought provoking read.

It's an excellent article, but the summary makes no sense, which at least encouraged me to read the article to figure out what the hell they were talking about. For example, from the summary:

The most unsettling result from these studies is that human head lice and human pubic lice (crabs) vary so greatly that they are in two separate genera.

1) What is "unsettling" about this? Anyone? No prior deeply held beliefs have been overturned. No profound conceptual schemes have been shaken to their very foundations. Parasites are known to be highly specialized. This fact has been published repeatedly for decades, always with great emphasis on how apparently hard it is to believe. After a couple of decades of being routinely reminded that individual species of ticks and fleas and lice are hyper-specialized, do you think we might ask that people stop presenting this fact as something astonishingly new?

2) The statement is contradicted by the article. What the article says is that head lice and pubic lice in humans are so different morphologically that "early taxonimists" assigned them to different genera. The article implies but does not say explicitly that this early assignment was not in fact justified.

In any case, this is an absolutely fascinating, albeit tentative and partial, reconstruction of the hominid evolutionary tree from parasite DNA, and I'm sure that as more data from different parasites becomes available we will be in for some real surprises. Internal parasites that are less likely to be passed between species should provide a record that is clearer than the lice record, where despite the relative paucity of inter-species transfers the record has clearly been muddied several times.