A common set of genes may determine whether all sorts of animals – from mice to fish – mate with one partner or many.
Rebecca Young and Hans Hofmann of the University of Texas at Austin and colleagues looked at which genes are turned on in the brains of males in five pairs of closely related species: two mice, two voles, two songbirds, two frogs and two cichlid fish. Each pair included one monogamous species and one non-monogamous species.
They analysed the patterns of gene expression to look for genes that were consistently more active or less active in monogamous species than their non-monogamous relatives.
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Although the 10 species in the study last shared a common ancestor 450 million years ago, the results show that the five species that have evolved monogamy have a similar pattern of gene expression in the brain.
This isn’t too surprising from the point of view of an evolutionary biologist, says Hofmann. “All the things that happen in our bodies have an evolutionary history that leads back to a common ancestor, and there are only so many different ways to solve a problem,” he says.
Meet the parents
For most animals, mating with multiple partners is advantageous, so monogamy is the exception rather than the rule. But for some species, it pays to remain faithful – particularly those that rarely encounter any prospective partners.
One of the species in the study is the mimic poison frog, the first known monogamous amphibian. It raises its offspring in small pools where there is little to eat, so the tadpoles need help from both parents to get enough food to reach adulthood.
Monogamy typically entails a set of related behaviours, including forming pair bonds, sharing some parental duties and defending territory.
The analysis highlights 24 genes that are robustly associated with monogamy, although hundreds more follow a similar pattern. Some of these genes are known to be involved in learning and memory, which makes sense considering monogamous males need to recognise their mate and offspring and form a strong bond. Others have a role in basic molecular processes such as gene activity regulation, with a less obvious link to behaviour.
Cause or consequence
While the results show that some of the same changes in gene activity have occurred in all the monogamous species, they can’t tell us whether the genetic shifts are a cause or a consequence of switching to monogamy. “I think both types of results would be interesting, but I’d like to have a better understanding of which type is represented by these new findings,” says Jenny Tung of Duke University, North Carolina.
One way to test that idea would be to manipulate these genes and see whether the animals’ behaviour changes as predicted.
But first, the team want to gather more data to learn where in the brain these genes are expressed and test more species, so they can make more specific predictions about which genes affect which aspects of behaviour.
Another question that arises is: do humans fit the pattern? Monogamous systems are common across most, but not all human cultures. Chimpanzees would make an ideal non-monogamous comparison species. “We would tentatively expect for humans to share many of the gene expression signatures we find in other monogamous species,” says Hofmann.
We know from studying animals’ physical features, such as limbs, that the same genes control the body’s development in similar ways across a wide range of species. It’s less clear whether the same rules apply to behaviour, but it’s starting to look like they do, says Young.
Other studies have found common genetic patterns related to aggressive behaviour in mice and fish, and learned vocalisations in humans and songbirds. “I suspect that we will find a lot of commonality as we continue to do these kinds of studies,” she says.
PNAS
