Choosing their own mates works best for zebra finches
Fancy flying back to my place?
1 MOST research into how animals choose their mates looks at how partners show preference for certain physical traits, which may well indicate genetic fitness—usually measured as reproductive success. Yet in some species, mating preferences are more individualistic. Zebra finches are one. They are choosy about their mates and there is not a lot of agreement about who is the best catch. Once hitched, zebra finches tend to be monogamous and the fathers share in the child care.
2 Malika Ihle and her colleagues at the Max Planck Institute for Ornithology, in Seewiesen, Germany, wondered what would happen if the finches were prevented from choosing their mates. So they constructed an experiment to discover if birds allowed to pursue life with a chosen mate fared any better than those forced into an arranged union. To do this they studied 160 bachelor zebra finches, putting together groups of 20 males and 20 females in an aviary to get to know each other.
3 Pairs that started grooming each other—a sign of courtship—were deemed couples. Half of those couples got to stay together, but the other half were forced to pair off with someone else’s chosen mate. The reason for this was that the researchers wanted to make sure all the individuals had been found desirable by another finch, even if not by the one they ended up with. This meant that whatever happened next wasn’t because some of the birds were simply losers.
4 All the couples were given their own cages for a few months, to help the forced pairs develop bonds. Then they were released into a group aviary where they started their families. Over the next five months—enough time for the finches to raise three separate broods—the researchers continued to observe them, both directly and with video. The experiment was then repeated with the same birds, this time forcing two-thirds of the couples into arranged matches and allowing only one-third to stay with their chosen mate.
5 The results, published this week in PLoS Biology, showed a clear advantage for birds who had chosen each other over those who had not: they had 37% more surviving young. Those strong-armed into a relationship yielded more eggs that went unfertilised or got lost, and more deaths of hatched chicks. Females in forced couplings were not as interested in sex, and males were less keen to look after the chicks. The males who had their partners chosen for them also did more philandering.
6 Dr Ihle and her colleagues say the evidence supports the idea that zebra finches select their mates based on how well they get along, putting behaviour ahead of seeking genetic compatibility. The researchers argue that if the finches were choosing mates for genetic reasons, they would expect to see more embryos die because of genetic defects caused by a degree of interbreeding between a more limited selection of partners. But they did not see that at all. Instead, the difference in the survival of chicks appeared to depend on the youngsters being looked after well by their parents, whatever they looked like.
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