Bird Moms Manipulate Birth Order To Protect Sons
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."And what applies to birds also applies to humans. During late pregnancy miscarriages in humans, the survival rate for males is less than for females, during the miscarriage if the embryonic development is interupted the surviving fetus if it was in the process of becoming male reverts to female.
natural selection may encourage weak mothers to have a disproportionate number of female infants because they are more likely to survive pregnancy, a characteristic that would be particularly valuable in times of hardship. Any biologist will tell you that a pregnancy with a male child has a substantially higher risk of miscarriage and stillbirth, such that the numbers of male to female infants at birth are roughly equal, even though far more male infants are conceived. Further, studies of neonates confirm that premature female infants survive at much higher rates than premature male infants of the same gestational age. Certainly, in lean times, natural selection would encourage the selection of the gender most likely to survive pregnancy and birth, thereby justifying the biological expense of a woman’s pregnancy. Male infants simply don’t fit the bill. A pregnancy with a male fetus is useless if the infant doesn’t survive the pregnancy and birth. Accordingly, a mother in “poor condition” would be “better off” having a girl because a girl is much more likely to survive the pregnancy. In times of abundance, natural selection would also favor a “strong” woman taking to the biological risk of expending energy and resources on a male pregnancy. Because resources are abundant, the investment in a pregnancy that is more likely to end in miscarriage would be less costly.
Find blog posts, photos, events and more off-site about:
birds, biology, male-birds, survival, mites, female-birds, mothering, zoology, gender,