Monogamous Species Share Deep Genetic Similarities

Pigeons form lifelong pairs. (Photo: Jeanne Menjoulet, Flickr)

Regardless of your opinion on monogamy, it’s a trait found across many species, from songbirds to fish to many humans. But surprisingly, there are plenty of examples in which members of one species will form lifelong pairs, but those of a closely related species won’t. An international team of researchers performed a genetic analysis to attempt to understand what the monogamous species had in common.

The scientists report finding genes associated with monogamy shared between many disparate species, according to a new paper.

“As scientists, we were interested in monogamy as a good example of a complex trait that has evolved a number of times, not only in vertebrates as we study, but also there are cases of invertebrate animals with monogamous mating systems,” Rebecca Young, research associate at the University of Texas at Austin, told Gizmodo. She and her team wondered whether the trait had a similar genetic basis across various species.

Finding the monogamy-associated genes required understanding the genes that the brain cells were using by analysing the transcriptomes. Transcriptomes are sort of like genomes, but rather than catalogue the genetic encyclopedia or DNA, they focus on the RNA, the DNA that the cell is actually using.

They compared the transcriptomes of brain tissue in reproductive males from two closely related species of mice, voles, perching bird, frog, and cichlid fish—from each animal category, they looked at one monogamous and one non-monogamous species.

The researchers identified 24 groups of genes that seem to be associated with monogamy across the species. These genes were involved in activities like neural development, learning and memory, and cognitive function. The expressed genes had more in common than would be expected by chance alone, according to the paper published in the Proceedings of the National Academy of Sciences.

Though the results sound provocative, the researchers were careful not to oversell them. Young stressed that correlation is not the same as causation, so it’s unclear whether the groups share the expressed genes because they’re monogamous or if they’re monogamous due to the shared genes. They also pointed out that the study doesn’t take into account variation among members of the same species.

While the study’s authors were hesitant to generalize the results to humans, senior author Hans Hofman from the University of Texas at Austin told Gizmodo that it should “remind us that we’re a larger part of evolutionary history.”

As to why monogamy evolved, Young speculated perhaps it had to do with the scarcity of mates, or that the young were especially susceptible to predators such that they needed the attention of two parents.

Other researchers not involved in the study were impressed with the work. “This group of scientists took a very novel approach by comparing disparate species who show monogamy, not making any assumptions about whether they evolved monogamy separately or inherited it,” Gene Robinson, the paper’s editor and director of the University of Illinois’ Carl R. Woese Institute for Genomic Biology, told Gizmodo.

“They were just looking at the underlying molecular underpinning, the genetic roots of it, and found these strong connections.”

Robinson and Hofman both told Gizmodo that the study could use more species. Hofman said he’d like to do the study on 200 different species, but that would be quite challenge due to the amount of work involved.

Still, this paper joins the growing body of literature showing deep connections between vastly different animals when it comes to certain behaviours.

And though it might sound like a splashy result, Young remains cautious, because that’s what science is all about. “We were excited about the prospect of what we were seeing, but it takes an extraordinary amount of time and second guessing,” she said.

“It required a careful self-critique to get to this point. It takes the initial, vague excitement away, but I’m excited by biology every day, not just because of one specific result that comes off of the computer.”

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