Mouse fidelity comes down to the genes

While birds tend to be at least nominally monogamous, this is not the case with mammals. This strikes some people as strange because humans seem to be monogamous, at least socially, and often we take ourselves to be typically mammalian. But of course we’re not. Like many primates we’re visual creatures, rather than relying in smell and hearing. Obviously we’re also bipedal, which is not typical for mammals. And, our sociality scales up to massive agglomerations of individuals.

How monogamous we are is up for debate. Desmond Morris, who is well known to many from his roles in television documentaries, has been a major promoter of the idea that humans are monogamous, with a focus on pair-bonds. In contrast, other researchers have highlighted our polygamous tendencies. In The Mating Mind Geoffrey Miller argues for polygamy, and suggests that pair-bonds in a pre-modern environment were often temporary, rather than lifetime (Miller is now writing a book on polyamory).

The fact that in many societies high status males seem to engage in polygamy, despite monogamy being more common, is one phenomenon which confounds attempts to quickly generalize about the disposition of our species. What is preferred may not always be what is practiced, and the external social adherence to norms may be quite violated in private.

Adducing behavior is simpler in many other organisms, because their range of behavior is more delimited. When it comes to studying mating patterns in mammals voles have long been of interest as a model. There are vole species which are monogamous, and others which are not. Comparing the diverged lineages could presumably give insight as to the evolutionary genetic pathways relevant to the differences.

But North American deer mice, Peromyscus, may turn to be an even better bet: there are two lineages which exhibit different mating patterns which are phylogenetically close enough to the point where they can interbreed. That is crucial, because it allows one to generate crosses and see how the characteristics distribute themselves across subsequent generations. Basically, it allows for genetic analysis.

And that’s what a new paper in Nature does, The genetic basis of parental care evolution in monogamous mice. In figure 3 you can see the distribution of behaviors in parental generations, F1 hybrids, and the F2, which is a cross of F1 individuals. The widespread distribution of F2 individuals is likely indicative of a polygenic architecture of the traits. Additionally, they found that some traits are correlated with each other in the F2 generation (probably due to pleiotropy, the same gene having multiple effects), while others were independent.

With the F2 generation they ran a genetic analysis which looked for associations between traits and regions of the genome. They found 12 quantitative trait loci (QTLs), basically zones of the genome associated with variation on one or more of the six traits. From this analysis they immediately realized there was sexual dimorphism in terms of the genetic architecture; the same locus might have a different effect in the opposite sex. This is evolutionarily interesting.

Because the QTLs are rather large in terms of physical genomic units the authors looked to see which were plausible candidates in terms of function. One of their hits was vasopressin, which should be familiar to many from vole work, as well as some human studies. Though the QTL work as well as their pup-switching experiment (which I did not describe) is persuasive, the fact that a gene you’d expect shows up as a candidate really makes it an open and shut case.

The extent of the variation explained by any given QTL seems modest. In the extended figures you can see it’s mostly in the 1 to 5 percent range. In Carl Zimmer’s excellent write up he ends:

But Dr. Bendesky cautioned that the vasopressin gene would probably turn out to be just one of many that influence oldfield mice. Though it is strongly linked to parental behavior, the vasopressin gene accounts for 6.7 percent of the variation in nest building among males, and only 2.9 percent among females.

The genetic landscape of human parenting will turn out to be even more rugged, Dr. Bendesky predicted.

“You cannot do a 23andMe test and find out if your partner is going to be a good father,” he said.

Sort of. The genetic architecture above is polygenic…but not incredibly diffuse. The proportion of variation explained by the largest effect allele is more than for height, and far more than for education. If human research follows up on this, I wouldn’t be surprised if you could develop a polygenic risk score.

But I don’t have a good intuition on how much variation in humans there really is for these sorts of traits that are heritable. I assume some. But I don’t know how much. And how much of the variance in behavior might be explained by human QTLs? Humans don’t lick or build nests, or retrieve pups. Also, as one knows from Genetics and Analysis of Quantitative Traits sexually dimorphic traits take a long time to evolve. These are two deer mice species. Within humans there may not have been enough time for this sort of heritable complexity of behavior to evolve.

There are a lot of philosophical issues here about translating to a human context.

Nevertheless, this research shows that ingenious animal models can powerfully elucidate the biological basis of behavior.

Citation: The genetic basis of parental care evolution in monogamous mice. Nature (2017) doi:10.1038/nature22074

6 thoughts on “Mouse fidelity comes down to the genes

  1. Given the duplicity that appears to be baked into human species’ reproductive strategy, I can certainly see why spectrum-y guys with low ability to percieve, much less gracefully pierce, the bio-cultural veil of feints surrounding pair-fidelity, just throw up their hands and await to transfer their intelligence into non-hormonal, unconflicted Machine replacements.

    Now there’ll also be in a not-too-distant, pre-Singularity future –detection, selection, and engineering for fidelity? Coming to a future near you: in addition to all their other expensive bio-engineered “perfections”, Pure Lineage Wealthies will have uncomprehending contempt for the uncontrolled lusts of the poly-mongrel Lower Orders.

    1. RE: duplicity. my review of the genetic data tells me that paternity uncertainty has traditionally been very low in human societies. though perhaps there was an arms race and the current equilibrium of high confidence is the end point of a process.

      1. I saw that paternity piece of yours awhile back, but thinking a moment more on it, did that data involve possibility of abortion skewing away from total inferred infidelitous acts? Birthed vs. the stand-alone, ah, procreative act?

        Unrelated: I just sent my brother a copy of “Oak: The Frame of Civilization”. I would have bought it through you, but it’s not on your sidebar, or did I overlook in haste? Have you seen the book, is it decent scholarship? Also, have you heard of “Debt: the First 5,000 Years” which I hear is rather a polemic, but perhaps useful despite.

        1. there’s too much evidence from different societies with paternal lineage systems and surnames. a ~1 percent rate seems common, at least across much of eurasia.

          looks like an interesting book.

          re: ‘buying through me’, if you click any link and then use the search bar i still get a click (or use the search option top right). seems like more ppl are buying through amazon right now though since i asked for that. so thanks.

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