办事指南

Mother's darlings

点击量:   时间:2019-03-07 12:20:17

By Matt Walker FEMALE zebra finches give chicks fathered by their favourite mates a boost when they are still in the egg. The finding could be a headache for biologists, as this kind of trick makes it difficult to tell whether the father’s genes or the mother’s extra help allows offspring to thrive. Several studies of birds have shown that females tend to go for highly ornamented males, and that when they do, their offspring have a better chance of survival. It is generally thought that this is because these males have superior genes. However, testing this has been complicated by the fact that some mothers seem to invest more in raising chicks fathered by good males. Some experiments have controlled for this effect, but evolutionary biologist Diego Gil of the University of Paris in Nanterre suspected that there may be an even bigger problem. Gil and his colleagues at the University of St Andrews had a hunch that females also give chicks from favoured mates a helping hand by depositing more testosterone in the egg. Chicks in eggs with high levels of testosterone are usually the first to hatch, beg more for food and grow faster than the others. The researchers randomly attached either red or green bands to the legs of a number of male zebra finches (Taeniopygia guttata). Females find the lure of the red bands even more attractive than the male’s traditional ornament, its red beak. They then allowed six females to mate with the red males, and six to mate with the greens. The clutches of eggs produced by these liaisons were taken away for hormone analysis. The two groups of females were then swapped around and allowed to mate with males of the other colour. The females deposited significantly more testosterone in all the eggs from the preferred red-banded males (Science, vol 286, p 126). The researchers aren’t sure how this happens, but it could be that the females’ general levels of arousal increased their own hormone levels, which in turn affected the eggs. This doesn’t mean that there is no connection between ornaments and superior genes—but it does make testing the idea a lot harder. “This is a remarkable study—it raises lots of new and exciting questions,