Ever wondered what in the brain allows animals to say - "You are my one and only!" Listen to experts on the MinM podcast to find out.
Conceived, written and presented by Reham Elsayed, Ralph Levy, Emily Swanekamp
for course BIOL 4585-001 Evolution of mating systems (J-term, 2021)
Class of 2022 (RE and RL) and 2024 (ES), University of Virginia
Transcript of Audio
RALPH: Good morning ladies and gentlemen, welcome to Monogamy in the Morning
today, January 15. My name is Ralph Levy and joining me here at the UVA studio
today are experts Emily Swanekamp and Reham Elsayed to share their recent research findings
Previously on “MinM” we’ve discussed monogamy in species like the long-living wandering albatross. We learned how skewed sex-ratios in isolated Laysan albatrosses caused them to change their rearing strategies by forming female-female nesting pairs. Last week we also discussed with Dr. Olivia J. Tatiana the role of a hormone called vasopressin in Prairie vole species. We dubbed it a “love catalyst. ” Dr. T explained how when these male voles lose their virginity, and how their brain chemistry changes. Vasopressin receptors physiologically set them into the
honeymoon mode.
Today with the help of my distinguished guests we are going to learn more about this love chemical in a different vole species. They’ll share how to tell the difference between the monogamy by choice preferences that the voles are born with, and monogamy by circumstance in sex-skewed populations like the albatross. Some of my listeners may recall that I spent last summer in southern
Australia living among the parrots and studying their behavior of social monogamy. Emily, however, has read the literature and participated in lab studies—she specializes in studying neurological responses and its effects on monogamous behavior. Similarly, Reham’s research out of U.C Berkeley specifically focuses on genetic bases and she will help tease apart genetic and
epigenetic factors. For some of our more layman listeners, Reham could you please explain
what we mean by genetic versus epigenetic?
REHAM: Epigenetics is the study of heritable phenotype changes that do not involve
changes in DNA sequence—these alterations in gene expression arise from
non-genetic environmental influences on gene expression. Genetic monogamy is when genes, not social and behavioral norms, dictate the practice of monogamy
RALPH: Great--now Reham, could you please explain what you’ve learned about some of these chemical and neurological responses and how that’s new from what Dr. Tatiana showed us last week?
REHAM: There are many factors that are associated with monogamy, but I think thatone of the most important factors associated with monogamy is pair bonding. Because without pair-bonding, you cannot really have monogamy. Arginine vasopressin and its V1a receptor subtype (V1aR) are critical for pair-bond formation between adult prairie voles. So, they found that there is high concentration of vasopressin in the reward and enforcement regions of
the brain.
In their study, they confirmed that there are three regions of the brain that are critical sites for vasopressin dependent pair bonding in voles. All three brain regions highly express V1aR in prairie voles, but not in non-monogamous montane voles. One of the region I want to talk about is the ventral pallidal because they were the first to show that vasopressin neurotransmission occurs in the ventral pallidum during mating, and that V1aR activation in this region is necessary for pair bond formation in male prairie voles. In the experiment, they blocked V1aR in ventral pallidal, but I am not going to go into deep detail about that because it is long and complicated for the audience. They found that blockade in the ventral pallidum will prevent partner preference formation meaning that receptors in this region are necessary for pair bonding. This is not an exception—They found that the same thing happening in another monogamous vole species such as the pine vole and actually other monogamous species across distantly related taxa that also show high density of V1aR.
Another example is found in a monogamous marmoset monkey and the monogamous California mouse (Peromyscus californicus), in which both have receptors here, but the non-monogamous rhesus monkey and the non-monogamous white-footed mouse (P. leucopus) do not. Another important aspect that I want to add is that not all regions tested were correlated with partner preference formation. The medial amygdala (experiencing emotion) and the Mediodorsal thalamus (cognitive control and working memory, decision making) actually failed to prevent partner
preference formation, suggesting that V1aR activation in these regions is not necessary for pair bond formation. They hinted that maybe oxytocin receptor and V1aR antagonist should both be used to block partner preference. In particular, social memory formation in the medial amygdala has been shown to require oxytocin receptors in the mouse.
EMILY: agrees and discusses about Taiwan voles….
In the study, researchers compared the distribution of vasopressin and
oxytocin receptors in the brain:
○ Vasopressin receptors in the nucleus accumbens and peripheral cortex region of the brain between monogamous prairie voles and socially monogamous Taiwan voles. Social monogamy refers to a long term or sequential living arrangement between an adult male and female. This pair
bond does not require sexual exclusivity , while genetic or reproductive monogamy refers to two individuals who exclusively reproduce with one another.
RALPH: However, there is an alternate theory to explain why social monogamy is observed
in these Taiwan voles. In the study there were quantitative differences in receptor binding of
Taiwan voles from two habitats in brain regions where oxytocin and vasopressin signaling have been shown to be involved in partner-preference formation. These areas of the brain are associated with pleasure pathways, so when there are more receptors concentrated in these areas of the brain and they are activated during mating, which could explain monogamous behavior in prairie voles.
Oxytocin receptors in the nucleus accumbens and peripheral cortex region of the brain between monogamous prairie voles and socially monogamous Taiwan voles. When comparing the brains of prairie voles and taiwanese voles in this research study, both vole species had similar levels of oxytocin receptor distribution that is similar in the nucleus accumbens. However, in the prefrontal cortex, prairie voles had a significant increase in the distribution of oxytocin receptor distribution in the prefrontal cortex when compared to taiwan voles.
Significance:
· In vietnam voles, oxytocin receptor binding was detected in the prefrontal
cortex, nucleus accumbens, and other areas of the brain
· Taiwan voles had specific vasopressin binding in the ventral pallidum, and
other regions of the brain that are consistent with those observed in prairie
vole. What is particularly interesting about the oxytocin receptor distribution
patterns in the nucleus accumbens is that it is associated with monogamous
behaviors in certain species, it is also associated with sociality between
species where social monogamy or alloparental behaviour is observed, as
exemplified by naked mole-rats and is most likely also the case in taiwan
voles.
· Radioligands that binding specificity of oxytocin receptor sites showed
binding in the nucleus accumbens was greater in females than males after
exposed to radiology
· There was no difference in oxytocin and vasopressin binding between sex
and habitat for all the analyzed brain region, except for oxytocin binding in
the nucleus accubens .
· Habitat caused these differences seen in oxytocin receptor distribution
between males and females
· There was an increase in the oxytocin binding in the nucleus accumbens in female taiwan voles when they lived in the forest as (opposed to the meadow , which made them more prone to developing depression/withdrawal symptoms
· Lead them to conclude that they tend to form monogamous bonds (ecological factors might affect how sexes express oxytocin which is then reflected in their preferred mating strategies.
· Males however tended to have lower oxytocin binding occurring when they lived in the forest instead of meadows, which is why they seem to participate in extra pair paternities often because they did not have high levels of oxytocin binding in the nucleus accumbens, so they did not experience as severe withdrawal symptoms and can easily switch between mates but nests with one female. Ralph, I know epigenetics is your specialty. Are there any other examples of epigenetic factors influencing social monogamy?
RALPH : Actually, as it turns out epigenetic factors also influence social monogamy. For example in parrots, Sex-biased mortality can lead to altered adult sex ratios (ASRs), which may in turn lead to harassment and lower fitness of the rarer sex and causes changes in the mating system. Female
critically endangered swift parrots ( Lathamus discolor ) suffer high predation while nesting due to an introduced mammalian predator, the sugar glider (Petaurus breviceps ). High predation on females is causing severe population decline alongside strongly biased adult sex ratios (≥73% male). Combining everything we talked about. Here is a study that investigates if genetic or epigenetic factors can explain huddling and cuddling behavior in Californian mice. 2013 study say - “ Non-genomic transmission of paternal behaviour between fathers and sons in the monogamous and biparental California mouse”
· CA mouse is textbook reproductively monogamous.
· No genetic basis (remove thru castration)--if the dad showed love, the kid would show love--shared vs genetic.
· Here, we demonstrate that decreased paternal huddling and grooming behavior (HG) during development influences paternal behaviour in the adult male offspring.
· When the mother is absent from the nest, the sons of castrated fathers perform less HG than the sons of sham-operated fathers and also increase their pup retrieval frequencies.
· Because we were able to randomly assign males to either low or high HG conditions by surgical manipulation, we can infer that the observed similarity between the paternal behaviour of fathers and sons is not solely attributable to shared genetic material, but that the postnatal behavioural environment experienced by offspring also shapes the systems that support paternal behaviour in adulthood.
After a message from our sponsor, we’ll look at another species and break
down whether or not monogamy is in their DNA or if it's just learned and
socially enforced. Thank you.
References
Chappell, A. R., Freeman, S. M., Lin, Y. K., LaPrairie, J. L., Inoue, K., Young, L. J., & Hayes, L. D. (2016). Distributions of oxytocin and vasopressin 1a receptors in the Taiwan vole and their role in social monogamy. Journal of Zoology , 299 (2),106–115. https://doi.org/10.1111/jzo.12332
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M.M Lim, L.J Young, Vasopressin-dependent neural circuits underlying pair bond
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Tokarev, Kirill, et al. “Sexual Dimorphism in Striatal Dopaminergic Responses
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