Becoming promiscuous to ensure reproduction

Date:  October 9, 2018

Source:  Hokkaido University

Females of a socially monogamous passerine, the Japanese great tit (Parus minor), become more promiscuous after hatchings fail in the first breeding attempt -- apparently attempting to ensure successful reproduction.

Many organisms, including human beings, form monogamous relationships. Birds do particularly so, with 90 percent of species exhibiting monogamous relationships. Indeed, a pair of birds conjures up the image of a "happily married couple." Yet after paternity tests based on DNA analyses were introduced in the 1990s, it was discovered that, in more than 75 percent of monogamous bird species, females had mated with other male birds, producing offspring whose genetic father is not the mother's partner -- the phenomenon called extra-pair paternity.

"Universality of extra-pair paternity in monogamous birds was shocking and much research has been performed on extra-pair paternity among various species in the last 30 years. However, how flexibly individual females behave to changing circumstances when selecting mates has been largely unexamined due to the difficulty of controlling conditions in wild populations," explains Itsuro Koizumi, an Associate Professor of Hokkaido University.

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Female birds get drabber when their males fool around

Kai Kupferschmidt 

4 November 2015 1:00 pm

Bird species in which one male can mate with many females tend to have more colorful males. But the promiscuity has an even stronger effect on females, making them drabber. That’s one of the more surprising conclusions in a new study of more than half of all living species of birds, which also reveals that a bird’s size and breeding location has a strong influence on the extravagance of its plumage.

“This paper is one of the most ambitious comparative studies ever conducted,“ says Geoffrey Hill, an ornithologist at Auburn University in Alabama, who was not involved with the work. But Richard Prum, an ornithologist at Yale University, says the paper is flawed because the team relied on pictures of birds in a book rather than observing them in the wild. “You couldn't study animal pheromones with scratch-and-sniff recreations."

Most scientists believe that bright colors signal good health or a great immune system. But why are some bird species more colorful than others? That’s been tough to resolve because it is hard to quantify how colorful a plumage is, says Bart Kempenaers, an ornithologist at the Max Planck Institute for Ornithology in Seewiesen, Germany. “How do you compare bright red with bright blue or yellow? That is the problem we had to solve."

Kempenaers and his colleagues tried a new approach: scanning pictures. The scientists focused on passerine birds, a group that makes up more than half of all known bird species and that is sometimes known as perching birds for their arrangement of toes—three pointing forward, one back. The researchers scanned illustrations in the Handbook of the Birds of the World, the only book covering every known living bird species, and then used a computer program to quantify how colorful each bird’s plumage is.

The tricky part was getting just one number that they could compare across species. For each bird, the scientists looked at six different patches of feathers (nape, crown, forehead, throat, upper breast, lower breast) and then identified the 1% of birds that were closest in color in the same patch. The more males, the higher the score for that patch. The researchers then calculated the average of the six patch scores for each bird. In essence, the scientists measured how "malelike" a bird appeared. But because male birds, in general, tend to be more colorful, that measure also works as a measure of how colorful a bird’s plumage is.

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Promiscuity and Sperm Selection Improves Genetic Quality in Birds

Sep. 3, 2013 — New research from the University of East Anglia has shown that females can maximise the genetic quality of their offspring by being promiscuous.

Researchers studied red junglefowl (the wild ancestor of the domestic chicken) in a collaborative project with the University of Oxford, Stockholm University and Linköping University.

Findings published today in the journalProceedings of the Royal Society Breveal that mating with different males helps females produce offspring that are more resistant to diseases.

This is down to 'cryptic female choice' -- where an internal mechanism in their reproductive tract favours the sperm from males that are most genetically different to them.

The genes in question (Major Histocompatibility Complex; MHC) play a key role in detecting and fighting infections. By biasing fertilisation in favour of MHC-dissimilar males, females increase the diversity of MHC within their offspring, providing them with better disease resistance.

The findings will be important for animal breeders as well as conservation projects because they show that allowing multiple matings will produce the most disease resistant and genetically healthy offspring.

Prof David S Richardson, from UEA's school of Biological Sciences, said: "Our research has shown that the females don't need to choose between males to produce the most healthy offspring. Rather by mating with multiple males, they allow their internal choice mechanism to favour the most genetically different sperm.

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