Background: Feather lice are small parasitic insects that attack birds. There ar
ID: 59080 • Letter: B
Question
Background: Feather lice are small parasitic insects that attack birds. There are many species of feather lice, each usually attacking just one or a few species of bird host. Clayton et al. (2013) studied the interaction between pigeons and their feather lice and discovered that preening (running the feathers through the bills to remove debris) is an important defense against the lice. They discovered that larger species of lice were removed by preening, but smaller species of lice fit between the barbs (hair-like branches) of the birds’ flight feathers and remain attached during preening. The smaller lice that stay attached can then parasitize the pigeon.
[1] The amount of space between the barbs in a flight feather scales with the overall length of the feather, and the length of feathers scales with body size. So, larger-bodied pigeon species have more space between their feather barbs. The key finding in the Clayton et al. paper was a strong positive correlation between the body sizes of pigeon species and the body sizes of the lice species that successfully attack them, with larger lice attacking larger birds and smaller lice attacking smaller birds. Could host-parasite co-evolution explain this pattern? If not, why not? If so, how, and what are the host trait and the parasite trait that are evolving?
Explanation / Answer
Yes, the given case truly explains the host-parasite co-evolution. Parasites naturally harm their hots, so natural selection favours the host to get the resistant to parasites. The same natural selection also favours the parasite to overcome this resistance. Thus, hosts and parasites may co-evolve in continuous arms races of defence and counter-defence.
The amount of space between the barbs in a flight feather scales with the overall length of the feather, and the length of feathers scales with body size. And body size of the parasite are co-evolving.
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