A new University of Pennsylvania study found that when an owl monkey pair is severed by an intruding individual, the mate who takes up with a new partner produces fewer offspring than a monkey who sticks with its tried-and-true partner.
The findings underscore how monogamy and pair-bonds - relatively rare social formations among mammals - can benefit certain individuals, with potential implications for understanding how human relationship patterns may have evolved.
Eduardo Fernandez-Duque and Maren Huck report on the research in PLOS ONE. Fernandez-Duque is an associate professor in Penn's Department of Anthropology. Huck completed a postdoctoral fellowship in Fernandez-Duque's laboratory and is now a professor at the University of Derby in the United Kingdom.
The current study amasses data from 16 years of observation of 18 owl monkey groups, a total of 154 animals. Owl monkeys live in monogamous groups consisting of an adult male, an adult female and their offspring. The juveniles disperse from the group around age 3 or 4.
In 2008, Fernandez-Duque and colleagues published a paper reporting, for the first time, the presence of a so-called "floater" individual, which attacked the male in a pair and essentially replaced him as a mate and infant-care provider.
The Penn team now demonstrates that this usurping of mates by both male and female floaters is a common occurrence. The researchers documented 27 female and 23 male replacements in the groups they observed.
The replacements often involved dramatic fights, some of which ended fatally for the evicted individual.
By following pairs and observing replacements, Fernandez-Duque and Huck show that having a partner evicted harms the reproductive success of the remaining mate. Owl monkeys with one partner produced 25 percent more offspring per decade than those with two or more partners.
"What we're showing is that if you manage to stay with the same partner you produce more infants than if you're forced to change partners," Fernandez-Duque said.
The reason for this significant impact on the reproductive success of the remaining partner is not yet completely clear, but the researchers surmise that it may have to do with a delay in reproduction due to the fact that female owl monkeys in Argentina typically only conceive between March and May.
It's also possible the delay occurs because the two individuals take time to assess one another before reproducing, given the significant commitment to infant care that both males and females make.
The results demonstrate that, for owl monkeys, long-term monogamy and pair-bonding improves reproductive fitness. (ANI)