If you hadn’t guessed yet, I’m really interest in how parasite consumption affects parasite transmission. One type of parasite consumption that I haven’t talked about yet is grooming.
You’ve probably had some experience with using grooming to reduce parasite transmission if you have kids or if you ever were a kid: the dreaded lice infestation! One recommendation for reducing lice transmission is to avoid sharing hats and combs and the like – to reduce contact/encounter rates – and another is to use those lovely lice shampoos (=grooming).
Presumably, if you’ve had lice, you didn’t eat them. (Your loss.) But, of course, many animals do eat their picked off parasites. Free food!
You might be wondering: when animals groom themselves or each other, does it actually reduce parasite transmission? The answer is YES, and it can even reduce parasite transmission to YOU. I’ve written before about how host biodiversity can reduce parasite transmission if communities with low biodiversity tend to have highly competent hosts. For instance, in the Lyme disease system, white-footed mice are highly competent, resilient hosts, and opossums have low competence, and are less resilient. But why the difference in their host competence? Well, one reason is that opossums are really good at grooming themselves and killing ticks, while white-footed mice are not-so-good at grooming.
Ok, so, grooming can reduce parasite transmission. Does grooming ever increase parasite transmission? Why YES, sometimes it does! For instance, female Japanese macaques of high rank are more likely to be infected with nematodes and have higher parasite loads than females of lesser rank (open access!). While the mechanism is somewhat unclear, the trend appears to be related to the fact that high ranking females are groomed by and groom more individuals than lower ranking females. (In this case, increasing contact/encounter rates.) Neat!
I wonder if early humans groomed each other, and if so, when did that allogrooming behavior stop? Or did it stop?