Protecting her kids from peril is the job of every good mom.

When marauding mites turn up in a house finch's nest, she shelters her sons from the blood-suckers by laying male eggs later than those containing their sturdier sisters, according to new research.

Making sure the vulnerable baby boys are exposed to mites for a shorter period allows both the sons and the daughters to survive long enough to leave the nest.

"Sons are more sensitive to the mites than daughters," said Alexander V. Badyaev of The University of Arizona in Tucson. "Mothers minimize sons' exposure to mites by laying male eggs later than female eggs. As a result, the males are in the nest fewer days."

Even so, the male chicks that grow up during mite season end up just as big as ones from the mite-free time of the year.

It's all mom's doing, Badyaev said.

Once breeding female finches are exposed to mites, their bodies make hormonal changes that affect the order of egg laying and accelerates the development of their sons while they're still in the egg.

"We've found a mechanism by which duration of growth can be adjusted to a changing risk of mortality," said Badyaev, a UA assistant professor of ecology and evolutionary biology. He added that this is the first documentation that maternal manipulation of both ovulation and growth influences the duration of development in birds.

Badyaev and his colleagues' article, "Sex-Biased Maternal Effects Reduce Ectoparasite Induced Mortality in a Passerine Bird," is scheduled to be published in the early online edition of the Proceedings of the National Academy of Sciences the week of Sept. 18.

His co-authors are UA graduate students Terri L. Hamstra and Kevin P. Oh and UA research specialist Dana A. Acevedo Seaman. The David and Lucile Packard Foundation, the National Science Foundation and the Silliman Memorial Research Awards funded the research.

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Contact: Mari N. Jensen
mnjensen@email.arizona.edu
520-626-9635
University of Arizona
18-Sep-2006