Parasites avoided by controlled hatching
Modifications to laying order and growth of
nestlings, significantly lessen offspring mortality and enables finches to breed
when mites are present.
Biologists have found that female birds can modify the hatching order and
growth of their nestlings in order to protect them against seasonal nest
parasites, illustrating another example of the continual race between host and
Alexander Badyaev and colleagues studied the breeding
of house finches
desert of Arizona
. Desert finches
breed twice a year, in winter,
when nests are parasite free, and in late spring, when most nests are heavily
parasitized by mites. In response to selection pressure from the mites, finches
have evolved two distinct egg-laying strategies.
The team found that mite-free winter conditions favour longer growth of
nestlings, while in the spring, when mites are present, faster nestling growth
is favoured to evade the mites. In spring, but not in winter, finches laid
female eggs first and male eggs last to minimize the exposure of slower-growing
and more vulnerable males to mite infestation. The team says their results show
how evolution can produce precise and complex adaptations.
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