Ducks in evolution's crossfire
Brood parasitic black-headed ducks caught in their host's interspecific arms
race
By Nick Atkinson

Research on brood parasites usually focuses on the evolutionary arms race
between host and parasite, but findings published this week in Nature
highlight the importance of a broader perspective. The paper presents
seemingly paradoxical evidence that even when the parasite imposes a minimal
cost, it still isn't tolerated by the host. The reason lies in an
intraspecific battle being fought within the host species: the parasite is
simply caught in the crossfire.

The black-headed duck Heteronetta atricapilla, a little-known South American
species, is the only obligate brood parasite whose chicks require no more
parental care than incubation as eggs: within a day of hatching, they leave
the host nest and set off for independent life. Despite the apparently
minimal costs of parasitism-limited to incubating an extra egg-the two coot
species that play host to over 80% of the duck's eggs frequently reject them
from their nests.

However, Bruce Lyon and John Eadie, researchers at the University of
California's Davis and Santa Cruz campuses, respectively, discovered another
layer of brood parasitism, operating at the intraspecific level: both coot
host species also lay eggs in conspecific's nests. "Most host-parasite
interactions focus solely on interspecific interactions," Lyon told The
Scientist. "Our study indicates that some of these behaviors, such as the
rejection of duck eggs by coots, might in fact stem from a within-species
evolutionary arms race."

Full Text at The Scientist
http://www.biomedcentral.com/news/20041122/01

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