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16 June 2010

Let’s Look to the Animal World for Paternal Bonding

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Paternal Bonds, Special and Strange

By NATALIE ANGIER

Published: June 14, 2010

Not long ago, Julia Fischer of the German Primate Center in Göttingen was amused to witness two of her distinguished male colleagues preening about a topic very different from the standard academic peacock points — papers published, grants secured, competitors made to look foolish.

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Stefanie Henkel

STATUS SYMBOL An adult male Barbary macaque at La Forêt des Singes, a zoo in Rocamadour, France, comforts an infant, and impresses his fellow males.

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“One of them said proudly, ‘I have three children,’ ” Dr. Fischer recalled. “The other one replied, ‘Well, I have four children.’

“Some men might talk about their Porsches,” she added. “These men were boasting about their number of children.” And while Dr. Fischer is reluctant to draw facile comparisons between humans and other primates, she couldn’t help thinking of her male Barbary macaques, for whom no display carries higher status, or is more likely to impress the other guys, than to strut around the neighborhood with an infant monkey in tow.

Reporting in the current issue of the journal Animal Behaviour, Dr. Fischer and her co-workers describe how male Barbary macaques use infants as “costly social tools” for the express purpose of bonding with other males and strengthening their social clout. Want to befriend the local potentate? Bring a baby. Need to reinforce an existing male-male alliance, or repair a frayed one? Don’t forget the baby.

It doesn’t matter if the infant is yours or not. Just so long as it has the downy black fur and wrinkly pinkish face that adult male macaques find impossible to resist. “They will hold up the infant like a holy thing, nuzzling it, chattering their teeth,” Dr. Fischer said. “It can be a bit bewildering to see.”

Just in time for Father’s Day come this and other recent studies that reveal surprising, off-road or vaguely unsettling cases of Males Behaving Dadly — attending to the young with an avidity and particularity long thought to be the province of the mother.

Scientists have learned, for example, that the male pipefish — which, like his seahorse relatives, famously becomes pregnant and gives birth to live young — is both more generous and more calculatedly harsh toward his offspring than previously believed, able to fine-tune the flow of nutrients to his gestating babies depending on how he feels about their mother.

In most species of birds, males and females take turns incubating the eggs and fetching insects for the fledglings. But among some large, flightless birds like emus and rheas, the male is often the sole keeper of the nest. Scientists now have evidence that such father-focused child care may represent the primordial avian program, one that dates back to the birds’ storied ancestors, the dinosaurs.

Why do males of some species attend to their offspring prolongedly, while others tend to spring off post-coitally? The reasons vary widely and are not always easy to discern.

In 90 percent of mammalian species, promiscuity is common and paternity uncertain; females gestate the young internally and then provision them with breast milk, and males rarely have any evolutionary incentive to play Ward Cleaver. Yet in that remaining 10 percent, the daddy decile, we find most of the world’s primates.

“Lots of primates are suckers for babies,” said Sarah Hrdy, the primatologist and author of “Mothers and Others” (Harvard University Press, 2009). Consider how the male of two small New World monkey species, the cotton-top tamarin and the common marmoset, reacts to a mate’s pregnancy.

His hormones change, the dendritic connections in his brain begin to change, and he puts on weight — all in preparation for the heavy lifting to come. Female marmosets and tamarins generally give birth to twins, which together weigh about 20 percent of what the father does, and from the moment the babies are born until they reach independence, the male will be expected to carry them most of the time. If he’s sitting, he’ll hold them on his lap. While he’s swinging through the trees, the twins will cling to the comforting thermal pads between his shoulder blades. If he hears the babies crying, he can’t help himself — he must fetch them and pick them up.

In a study that appeared in the American Journal of Primatology, Sofia Refetoff Zahed and her colleagues at the University of Wisconsin compared the responses of experienced fathers and inexperienced males when confronted with the sound of a fussy infant monkey coming from a distant cage.

Without exception, the experienced fathers would quickly cross a bridge to reach the source of the distress cry, arriving within 45 seconds. Inexperienced males, by contrast, took their time. A minute, five minutes, wah wah wah! Oh well, guess I’d better see what the problem is. Or not. In half the cases, the inexperienced males never made it to the stimulus cage before the experiment was up.

Marmosets and tamarins become dream daddies because their partners are queen bees of fecundity. A mother monkey can’t possibly handle the energetics of lugging around a pair of growing twins. Not when she is expected both to produce a double dose of milk and to become pregnant again roughly two weeks after giving birth.

“When I first started watching the monkeys, I thought the females were so mean,” said Ms. Zahed, who is working on her doctorate. “The infants would try to get food, to get whatever the mother had, and the mom would grab it back and go away. The dad, on the other hand, would give up his food and let the infants get away with anything.

“Then I got pregnant with my second child while I was still nursing the first,” she added. “Then I understood. You do get grouchy.”

In contrast to the obvious link between paternal care and offspring welfare seen in tamarins and marmosets, a male Barbary macaque’s fascination with infants can look less than kid-friendly. Once abundant throughout North Africa, but now limited to forest patches in Algeria and Morocco, these monkeys live in troops of some 30 animals, a mix of related adult females and unrelated adult males. Females give birth in the spring, and Dr. Fischer said, spring “is high season for infant dealing.”

Within days of being born, every infant is fair game for male pawings. “A male will approach a mother slowly,” Dr. Fischer said, “seize the moment, and take the infant.” He will carry the infant under his belly, or in his arms, and he’ll advance toward one or two other males and start to make nice.

“If they don’t have an infant, they can’t interact,” Dr. Fischer said. “There would be too much tension between them.” A male may hold on to an infant for hours at a stretch. If the baby starts to cry, he may take it back to the mother for a feeding, all the while hanging on to the ankle of his precious networking tool.

The researchers initially assumed that baby handling might have a tranquilizing effect on the males, but on measuring the macaques’ hormone levels, they found the opposite: carrying an infant caused a male’s stress hormones to spike. The scientists now propose that the males use the infants as “battle symbols,” as Dr. Fischer put it, “to show other males that they can bear the stress.”

What better proof of a worthy ally, who will not wilt come breeding season — when males must form coalitions to monopolize fertile females and help spawn the next generation of fuzzy handheld devices?

Nature may never have invented the wheel, but she’s the original wheeler-dealer and hedger of bets. The pouch of a male pipefish was long thought to be a passive incubator in which embryos could develop safely while feasting on yolky nutrients the mother had supplied. Recent research suggests that the male also infuses the pouch with plenty of food, not to mention regulating osmotic pressure, salinity and oxygen flow.

Paternal generosity does have its limits. In a report published in the March 18 issue of Nature, Kimberly A. Paczolt and Adam G. Jones of Texas A&M University showed that the pouch of a gulf pipefish is a staging ground for sexual barters and the occasional war.

Male pipefish like big females, and if they mate with a meaty one, they will lavish her eggs with abundant nutrients of their own. But if a male ends up mating with a lightweight because she was the best he could find, and midway through gestation a fatter female swims by, the male’s pouch knows what to do: abort or reabsorb a few existing embryos to use as food for the new.

Yes, fathers love to take charge, beat the odds, expand the nest. Reporting in the journal Science , David J. Varricchio of Montana State University and his colleagues offered evidence that for at least some species of birdlike carnivorous dinosaurs, fathers may have been the ones who cared for their young.

The researchers argued that to begin with, the repeated discovery of adult dinosaurs in close proximity to egg clutches indicated that dinosaurs didn’t just dump and dash, turtle style, but instead stuck around to protect the nest. What’s more, the total volume of each clutch was impressively large, suggesting input from more than one female.

Finally, the bones of the adults associated with the nests suggested that their owner might well have been male. A male that invited many females to mate with him and lay their heavy treasures in his nest. He was a good father. They had done their part. Now he would do the rest.

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