Monogamous animals often wind up with unattractive partners

Washington, Feb 2 (ANI): According to previous studies, in monogamous species throughout the animal kingdom, each female has a good chance of pairing with a male that matches her ideal choice of partner.

But a new study has challenged these theories.

In socially monogamous species, from birds to humans, most individuals find partners.

However, a large proportion of females wind up with unattractive males of below-average quality, according to the study, which also found that such less-than-ideal relationships raise female stress levels.

"In socially monogamous animals, very few individuals end up with the perfect partner because, of course, he or she is likely to be paired to someone else," Discovery News quoted lead author Simon Griffith as saying.

"That is, lots of men would like to be married to, say, Angelina Jolie, and lots of women would love to be married to Brad Pitt. But the reality is that they can't and only someone like Brad Pitt is able to marry someone like Angelina Jolie," he added.

"So how does a female respond to her real partner?" Griffith, an associate professor in Macquarie University's Department of Biological Sciences, asked.

"Work over the past few decades has shown that females can actually make a number of subtle strategies to improve their own fitness," he added, explaining that these include sleeping with other males that could improve the genetic fitness of any potential offspring.

To determine what might underlie such behavior, Griffith and colleagues Sarah Pryke and William Buttemer observed partnerships and mating in Gouldian finches.

In these birds, red- and black-headed individuals are partially genetically incompatible with each other. Red-headed Gouldian finches additionally are more aggressive than black-headed males and are not as good at providing parental care.

In one experiment, both types of birds were placed in an aviary where they had the freedom to select the partners of their choice. In a second forced-pairing experiment, 50 red females were individually paired with either a red or black male.

When females paired with males of the same head color, eggs were laid nearly a month earlier than those for mismatched couples. Blood tests determined that females matched with a different colored male had elevated levels of the stress hormone corticosterone that were three to four times higher than levels in females paired with preferred mates.

It's now thought that these hormones may help to drive everything from cheating to break-ups.

The findings are believed to apply to humans as well.

"If a female is stressed by her partner's attractiveness, then it is quite possible that the speed of becoming pregnant and the number of children she has may vary as a result," Griffith explained. "In humans, we can't do these experiments to prove this, but it is completely plausible."

The study has been published in the latest issue of Proceedings of the Royal Society B. (ANI)