Tuesday, December 12, 2006

Fight or flight: Could interspecific competition trigger phoresis by feather lice?

Sarah E. Bush, bush@biology.utah.edu, Jael R Malenke, malemke@biology.utah.edu, and Dale H. Clayton, clayton@biology.utah.edu. University of Utah, Department of Biology, 257 South 1400 East, Salt Lake City, UT

Feather lice are permanent ectoparasitic insects known to hitch rides phoretically on more mobile parasites like Hippoboscid flies. Intriguingly, Rock Pigeons (Columba livia) are commonly parasitized by two different types of feather lice (Ischnocera) known as “wing” lice and “body” lice. Although these two types of lice are ecological replicates in many respects, wing lice are often phoretic, whereas body lice are not. What prompts an obligate, permanent parasite to leave one host and hitch a ride to another host? One ecological factor that may trigger phoresis is interspecific competition. Interspecific competition is typically asymmetrical, with one species being an inferior competitor. The “loser,” however, may evade competition by moving to another host individual. To test the impact of interspecific competition on feather lice we experimentally manipulated wing and body louse populations on Rock Pigeons. Birds were infested with only wing lice, only body lice or both lice together. We measured louse population size and resource use for 10 louse generations. We found that both types of lice eat the same feather resources, and the competition for these resources is asymmetric. Specifically, wing louse populations suffer in the presence of body lice. In contrast, body louse populations are not affected by the presence of wing lice. Under these competitive circumstances, moving to other host individuals would be particularly beneficial for wing lice. Indeed, competition may be one factor triggering phoresis among wing lice.

Species 1: Phthiraptera Philopteridae Columbicola columbae (slender pigeon louse)
Species 2: Phthiraptera Philopteridae Campanulotes compar (golden feather louse)