Background: Feather lice are small parasitic insects that attack birds. There ar

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. Suppose pigeons in a particular area suffer a nutritional deficiency that means their beaks don’t develop normally. They can still eat and perform the basic necessary functions of life, but they can no longer effectively preen. How do you think this change would alter the selection pressures acting on feather lice? What subsequent evolutionary changes in the lice populations would you expect? If Clayton et al. redid their study on this population, do you think they would still find a positive correlation between host and parasite body sizes?

Explanation / Answer

Yes, if the beaks of the pigeons are smaller and cannot preen, the lice do not hvae the selection pressure to be small in size. They can be larger in size since the bird cannot preen. Hence, evolutionary changes will be seen in lice populations where the population might be more of the bigger size and less of the smaller size.

A positive correlation between host and parasitic body sizes would not be seen as the factor of preening does not occur in the scenario at all.

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