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Sick Dads Are the Best

24 March 2006 (All day)
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Claudio Contreras Koob / SEMARNAT

Nothing to lose.
When blue-footed boobies get old and sick, they double their efforts to raise offspring.

Sick fathers aren't much fun. But a study of birds suggests that sometimes ill dads make better parents, especially when they fear they don't have much longer to live.

According to one evolutionary theory, males from long-lived animal species are careful investors when it comes to reproduction. When deciding how much effort to put into taking care of themselves versus being a good father, they consider their future prospects. If the future looks good, with many years of potential mating ahead, then it pays to keep their own health top priority. But when animals reach their golden years, it makes more sense to disregard illness and invest more time and effort in caring for offspring. This strategy would boost the chances that the animal's genes are passed on to the next generation. But do animals really keep track of their future prospects so carefully?

A team led by Roxana Torres, a biologist at the Mexican National Autonomous University in Mexico City, used the blue-footed booby as a test case. The birds usually live for about 15 years, and their chicks require a long investment--6 months of baby-sitting from both mother and father. The researchers captured 50 males from a booby colony 2 weeks before their mates were due to lay eggs. Then, to put the fathers between a rock and a hard place, the researchers injected the birds with a molecule from the cell wall of Escherichia coli bacteria. The molecule poses no threat to health, but it causes the immune system to go on red alert, bringing all the symptoms of a bacterial infection. As a control, they injected some birds with the buffering solution alone.

The good dad/bad dad theory predicts that the offspring of sick young males should fair poorly because papa will spend more time on himself, while those of old males should do better as the sick males redouble their parental efforts. The booby results seem to bear this out. Relative to controls, 18% fewer fledglings were produced from young immune-challenged fathers, between the age of 3 and 9. But when older males over the age of 10 felt sick, they turned into super-dads, with a 98% boost in the number of successful fledglings, the team reports online 22 March in Proceedings of the Royal Society B.

"The study is quite neat," says Hanna Kokko, a biologist at the University of Helsinki, Finland, but it does not yet clinch the theory for her. What is needed now, she says, is to take such studies a step further and keep track of the subsequent survival and reproductive rates of the offspring, which is the ultimate aim of evolutionary strategies.

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