Why are lice so species-specific?

Submitted by _teadog t3_ykotiz in askscience

Currently treating my pet rats for lice, and while researching if it was something to be concerned about for us or our other pets, I learned that lice are generally very species-specific. But I can't really find a satisfying answer as to why and what evolutionary advantage this provides over something more suited to a wider range of hosts, like fleas.

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viridiformica t1_iuvtrnc wrote

Just found this: https://www.mdpi.com/2075-1729/12/9/1442/pdf

Which suggests that the host specificity in mammalian lice is due to less opportunity for host switching (relative to birds), and closer interaction with the immune system putting them into an evolutionary arms race which requires specialisation

"Birds, mammals, and their lice diversified over similar timescales, with major lineages diversifying around the K–Pg boundary [21], so it seems that there may be fundamental biological or ecological differences between the lice hosted by birds and mammals that could explain these differences. In general, birds have higher dispersal capabilities than mammals, and this dispersal may provide more opportunities for host-switching [33]. The sedentary and asocial nature of pocket gophers, for example, has been used to explain the high level of host-specificity and cospeciation in their lice [5]. Another major difference is that avian feather lice have little interaction with the host immune system because they mainly consume feathers, which are inert, while mammalian lice consume blood or sebum and directly interact with the host immune system [61,62]. This interaction in mammal lice may lead to an evolutionary arms race and more coadaptation between mammals and their lice, making host-switching more difficult."

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Akitiki t1_iuxn936 wrote

One reason I know about is that the lice developed the hooks on their legs for the specific type of hair on certain animals. Even in humans, we have three types of lice that infest specific areas! Head lice, body lice, and pubic lice are very different.

The pubic lice have (relatively speaking) huge hooks/claws for gripping coarse hair. The hair on your head is too thin for them, they wouldn't be able to grip effectively. Head lice have finer hooks, much too small to get a grip on coarser pubic hair! Their bodies are also shaped differently.

I got head lice a lot as a child. To the point I needed prescription stuff as they got resistant to normal treatment. I wondered how they never got into other hair, and researched it!

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