by Richard Sprott, Ph.D.
26 December 2015
Prairie voles are noted, as a species, for strong pair-bonding and raising off-spring together. Vasopressin 1a Receptor (V1aR) varies within the prairie vole population. The amount of receptors is encoded by a gene, called avpr1a. Variations in the gene avpr1a can lead to more receptors or fewer receptors in the brain. The V1aR can be abundant in the part of the brain that is focused on spatial memory. The more abundant vasopressin receptors are in that part of the brain, in an individual male vole, the more likely they are to stay close to home. Fewer V1aR, then the more likely to roam, the more likely to encounter other females, the more likely to sire offspring with those other females. About 25% of the prairie vole males have offspring outside their “monogamous” pair-bondings.
In terms of evolutionary pressure, there is a tension among males between “mate-guarding” and “mate-multiplying” as reproductive strategies. Mate-guarding would correlate, then, more V1aR which would lead to smaller “home ranges” and more likely to guard the home. Mate-multiplying would correlate with less V1aR which would lead to larger “home ranges” but less likely to guard the home.
One possibility (not tested yet) is that population density, then, would tip the scales in terms of which reproductive strategy would be advantageous, thus leading to selection pressure on a particular genetic variation. The more dense the population, the more likely to encounter others, the more advantageous it is for a male to “mate-multiply” than to “mate-guard.” Those with a variation of avpr1a that codes for fewer receptors would soon out-produce those with a variation of avpr1a that codes for more receptors. [the idea of population density affecting monogamous vs. non-monogamous behaviors or strategies is an interesting one, someone might want to investigate that more carefully, in animal models and in humans]
There seems to be a connection between spatial memory and sexual fidelity. What exactly that relationship is, no one is clear yet. For me, this is a piece in the larger picture that connects also “sensation-seeking” and other aspects of personality that favor “exploration.” Exploration as a behavior has strong developmental consequences, and does seem to rely on a number of genetic mechanisms, shaped or intensified by learned/environmental factors. I think that kink and poly behavior is closely related to the personality factors that favor exploration. That seems like a no-brainer to me!
Okhovat, M., Berrio, A., Wallace, G., Ophir, A.G., Phelps, S.M. (2015). Sexual fidelity trade-offs promote regulatory variation in the prairie vole brain. Science, 350, 6266, pages 1371-1374. Doi: 10.1126/science.aac5791