Owl Monkeys with Single Partners Have More Babies

It is difficult to find monogamy in the animal kingdom; it is a trait that is quite rare. However, researchers have found that staying loyal to a partner can offer animals a lot of benefits.

A new study conducted by researchers at the University of Pennsylvania suggests that monkeys who remain faithful to their primary mate have more offspring than those who change partners frequently.

To prove their hypothesis, they focused on the intense relationship occurring among the owl monkeys and noticed that when an owl monkey leaves its mate, the one who accepts a new partner produces fewer babies than the one who remains with its primary mate.

Owl monkeys, also known as nocturnal monkeys, are socially monogamous and form pair-bonds. They give birth to only one infant each year, as this increases the survival chances of the infant. The researchers highlight the concept of pair-bonding that increases the reproductive fitness of the species. This provides clues on how the human relationship pattern evolved.

The owl monkeys residing in Argentina's Chaco region were carefully monitored by researchers Eduardo Fernandez-Duque and Maren Huck since 1997. They picked clues of these species by noticing their physiological sampling, demographic data and above all, their behavioral patterns.

"We have managed over the years to have quite significant sample sizes for a study of wild non-human primates," Fernandez-Duque an associate professor in Penn's Department of Anthropology said in a press statement. "These findings are possible because we have a combination of intense demographic monitoring year-round that allows us to notice when a male is missing, when a female is missing or when there's a new adult in the group. We couple this with intense behavioural monitoring that allows us to document the details of fights or the whole process of mate replacement."

After 16 years of observation, the researchers state that these nocturnal animals mostly dwell in monogamous groups. It includes a pair-bonding (adult male and female) and their offspring. At the age of 3 or 4, their offspring leaves the group.

But the pair-bonded couple is disturbed by an individual called a 'floater' that disrupts the pair, and it could be either a male or a female. Nearly 27 female and 23 male floaters were observed that broke the pair-bonding. Interestingly, those who remained loyal with one partner produced 25 percent more offspring per decade than those with multiple partners, thereby emphasizing the fact that certain species benefit from monogamy.

What remains a mystery is the significant impact on the reproductive success of the remaining partner. They assumed delay in reproduction could play a role, as females reproduce in March and May and delay occurs as the two need time to assess one another before reproducing.

The study was conducted on 8 owl monkey groups that included a total of 154 animals. The findings have been published in the journal PLoS ONE.