Nature Shapes Faithful and Unfaithful Brains

A reposting of an original article from January 22, 2017.

Among monogamous animals, some individuals are more faithful than others. Could these differences in fidelity be, in part, because of differences in our brains? And if so, why does this diversity in brain and behavior exist?

A snuggly prairie vole family. Photo from theNerdPatrol at Wikimedia Commons.

Prairie voles are small North American rodents that form monogamous pair bonds, share parental duties, and defend their homes. Although prairie voles form monogamous pairs, that does not mean they are sexually exclusive. About a quarter of prairie vole pups are conceived outside of their parents’ union.

Not all male prairie voles cheat on their partners at the same rates. In fact, some males are very sexually faithful. It turns out, there are both costs and benefits to being faithful and to cheating. Mariam Okhovat, Alejandro Berrio, Gerard Wallace, and Steve Phelps from the University of Texas at Austin, and Alex Ophir from Cornell University used radio-telemetry to track male prairie voles for several weeks to explore what some of these costs and benefits might be. Compared to males that only sired offspring with their own partner, unfaithful males had larger home ranges, intruded on more territories of other individuals, and encountered females more often. However, these unfaithful males were also more likely to be cheated on when they were away (probably because they were away more). I guess even rodents live by The Golden Rule.

Maps of how paired male voles in this study used space. The solid red/orange/yellow peaks show where a faithful male (in the left map) and unfaithful male (in the right map) spent their time in relation to where other paired males spent their time (showed by open blue peaks). Image from the Okhovat et al. Science paper (2015).

Vasopressin is a hormone that has been found to affect social behaviors such as aggression and pair bonding when it acts in the brain. Mariam, Alejandro, Gerard, Alex, and Steve all set out to determine how vasopressin in the brain may relate to sexual fidelity in prairie voles. They found that faithful males had lots of a particular type of vasopressin receptor (called V1aR) in certain brain areas involved in spatial memory. Surprisingly, faithful males did not have more V1aR in brain regions typically associated with pair bonding and aggression. A male that has more V1aR in spatial memory regions might better remember where his own mate is and where other males have been aggressive, which would decrease the chances that he would intrude on other territories in search of other females and increase the time that he spends home with his own mate. A male that has less V1aR in spatial memory regions might be less likely to learn from his negative experiences and more likely to sleep around.

Photos of a brain section from a faithful male (left) and unfaithful male (right). The dark shading shows the density of V1aR vasopressin receptors. The arrows show the location of the retrosplenial cortex (RSC), a brain area involved in spatial memory. Faithful males had significantly more V1aR receptors in the RSC compared to unfaithful males. Image from the Okhovat et al. Science paper (2015).

The research team then found genotype variations that related to having lots or not much V1aR in one of these spatial memory regions (called retrosplenial cortex … but we’ll just call it RSC). They confirmed these findings with a breeding study, in which they reared siblings that were genetically similar, but some had the genotype they predicted would result in lots of V1aR in RSC and some had the genotype they predicted would result in very little V1aR in RSC. They confirmed that these genetic variations correspond with the amount of vasopressin receptor in this specific spatial memory area.

The researchers then looked closer at the different versions of this vasopressin receptor gene in the RSC brain region to see if differences in the amount of vasopressin receptors in RSC may be caused by the epigenetic state of the gene (i.e. how active the gene is). They found that the genotype that results in very little V1aR in RSC had many more potential methylation sites, which can repress gene activity.

All of this data together tells a very interesting story. Male prairie voles that have the genotype for more V1aR vasopressin receptors in their RSC part of their brain are more likely to remember where their home and mate are and to remember where other aggressive prairie voles are, which will make them more likely to spend more time with their partner, to be sexually faithful and to have sexually faithful partners. Male prairie voles that have the genotype for less V1aR in their RSC are more likely to forget where their home and mate are and where other aggressive prairie voles are, which will make them more likely to cheat and to be cheated on. Overall, faithful and unfaithful male prairie voles have roughly the same number of offspring, but advantages may emerge with changes in population density. Prairie vole populations vary anywhere from 25 to 600 voles per hectare from year to year. When population densities are high, you (and your partner) are more likely to encounter more potential mates and it may benefit you to cheat (and have a “cheater’s brain”). When population densities are low, you (and your partner) are less likely to encounter more potential mates and it may benefit you to be faithful (and have a “faithful brain”). But when populations fluctuate between high and low densities, both faithful and unfaithful genotypes will get passed along from generation to generation.


Want to know more? Check this out:

Okhovat, M., Berrio, A., Wallace, G., Ophir, A., & Phelps, S. (2015). Sexual fidelity trade-offs promote regulatory variation in the prairie vole brain Science, 350 (6266), 1371-1374 DOI: 10.1126/science.aac5791

Mr. Nanny Makes Mr. Right

A reposting of an original article from November 28, 2012.

Quick! Introduce yourself to this guy before
his baby-high wears off! Photo by David
Castillo Dominici at FreeDigitalPhotos.net. 

What happens if you take a wrestler or action star and force him to babysit obnoxious but lovable kids? Well, if you’ve seen movies like The Pacifier with Vin Diesel, The Tooth Fairy with Dwayne ‘The Rock’ Johnson, Kindergarten Cop with Arnold Schwarzenegger, or The Spy Next Door with Jackie Chan, you know that he will fall madly in love both with his young charges and with the closest available woman. Hollywood is so sure of this phenomenon that they have based a whole genre of family movies on it. Now, scientists are finding that Hollywood may be on to something.

Prairie voles are one of the only 3-5% of mammals that are monogamous and in which both parents help take care of young. In females, maternal care is regulated in part by the hormones associated with pregnancy, birth and lactation. The fact that males don’t do those things and they still provide paternal care is curious. The fact that male prairie voles will often provide care to offspring that aren’t even their own is even more curious.

Will Kenkel, Jim Paredes, Jason Yee, Hossein Pournajafi-Nazarloo, Karen Bales, and Sue Carter at the University of Illinois at Chicago recently explored what happens to male prairie voles when they are exposed to unfamiliar vole pups. Male voles without any experience with females or pups were placed in a new clean cage. Then the researchers put either a pup (that was not related to the male), a dowel rod (an unfamiliar object), or nothing into the cage with them for 10 minutes. Afterwards, they measured oxytocin (a hormone associated with bonding between mothers and their offspring) and corticosterone (a stress hormone) in the males’ blood at different time points. In another study, they also looked at the activity of brain neurons associated with the production of these hormones.

A male prairie vole is startled to find a baby in his cage...

But then he takes care of it. Video by Will Kenkel.

Both adult and juvenile males exposed to a pup for 10 minutes had higher oxytocin and lower corticosterone compared to the males not exposed to a pup. But this effect was short-lived, as male hormone levels quickly evened out again. Most of these males that were exposed to a pup showed alloparental care (care of a baby that is not their own), like approaching the pup, cuddling with it and grooming it. Males with higher oxytocin and lower corticosterone levels were more attentive towards the pups. Additionally, alloparental males exposed to pups had more activity of oxytocin-producing neurons and less activity of neurons associated with corticosterone-production in a specific brain region called the paraventricular nucleus (or PVN for short).

Oxytocin is strongly associated with pair bonding in prairie voles, particularly in females, and corticosterone affects pair bonding too (generally increasing pair bonding in males and preventing it in females). If exposure to a pup affects these hormones, maybe it affects how the male would interact with adult females. To test this, the researchers put male voles in a new clean cage and put a pup, a dowel rod, or nothing into the cage with them for 20 minutes. Then they put the males with an unfamiliar adult female for 30 minutes. After getting acquainted with the female, the males were put in a “partner preference apparatus”, which has three connected chambers: a neutral center chamber, a connected chamber with the familiar female tethered into it, and a connected chamber with an unfamiliar female tethered into it. The researchers measured how much time the males spent in each of the three chambers and with each of the two females over the next 3 hours.



A prairie vole pair snuggles. Photo from Young,
Gobrogge, Liu and Wang paper in
Frontiers in Neuroendocrinology (2011)

Males that were exposed to a dowel rod or to nothing before they were introduced to a female spent equal amounts of time with each of the two females. But males that were exposed to a pup before they were introduced to a female spent nearly 4 times as much time with that female than with the unfamiliar one. In other words, hanging out with a random pup acted like Love Potion #9 on these bachelor males and made them fall for the next female they encountered! Interestingly, this effect was true not only for the males that acted in an alloparental way towards the pups, but it was also true of males that attacked the pups (The researchers quickly rescued the pups if this occurred). Perhaps, males that were alloparental with the pups had increased oxytocin and males that were aggressive with the pups had increased corticosterone, either of which would make it more likely for them to form a preference for the female they were with.

Hmm… Got your eye on a special someone? Try volunteering him to babysit before your next date.

Want to know more? Check this out:

Kenkel, W., Paredes, J., Yee, J., Pournajafi-Nazarloo, H., Bales, K., & Carter, C. (2012). Neuroendocrine and Behavioural Responses to Exposure to an Infant in Male Prairie Voles Journal of Neuroendocrinology, 24 (6), 874-886 DOI: 10.1111/j.1365-2826.2012.02301.x

The Love Chemical of 2018

Hello and welcome to the Love Chemical Pageant Results Show! The voting results are in, and today we get to crown the Love Chemical of 2018… Vasopressin! Now let’s get to know Vasopressin a little bit better.

Vasopressin (also known as Antidiuretic Hormone) is a molecule that is widely involved in the balance of water and ions (such as salts) in mammals. (Other taxonomic groups have variations of it as well). But this chemical has gone to our heads, influencing behavior as well.

In the brain, vasopressin acts on a specific receptor type, called vasopressin 1a receptor (V1aR). There are lots of V1aR receptors in brain areas that regulate social and emotional behaviors. When vasopressin binds to many of these receptors, it can result in aggression, territoriality, and fight-or-flight responses. It is also involved in the formation of memories that are necessary to avoid danger. Interestingly, males and females usually have different patterns of where in the brain these V1aR receptors are.

Although we often think of love and aggression as opposites, the life-preserving roles of vasopressin have made it well-suited to become an important chemical of love. In animals, pair bonding (the formation of a strong and unique connection between mates of a socially monogamous species) is often accompanied by an increase in aggression towards non-mates. This aggression can serve to protect the mate and family, but also to reject competitive suitors towards either partner.

Photo of a prairie vole pair from Young, Gobrogge, Liu and Wang paper
in Frontiers in Neuroendocrinology (2011)

Researchers often use several closely-related vole species to study how the brain regulates pair bonding; While prairie voles and pine voles are monogamous, raise their offspring with their partners, and defend their homes and families, montane voles and meadow voles are promiscuous and females raise their young by themselves. Oddly, giving monogamous vole species vasopressin increases their preference for spending time with their mate, their parental behaviors, and their selective aggression against outsiders, but giving promiscuous vole species vasopressin does not. Vasopressin is also more likely to increase these monogamous behaviors in males more than in females. Both males and females respond differently to vasopressin depending on their reproductive status.

It turns out, the pattern of V1aR receptors in the brain is similar between the monogamous prairie and pine voles, but different from the promiscuous montane and meadow voles. Genetic factors drive this difference, and if you alter the gene for the V1aR of a promiscuous species to be more like the prairie vole’s version of the gene, the previously promiscuous species behaves in a monogamous way! The reason promiscuous vole species don’t behave in a monogamous way when given vasopressin is because they don’t naturally have the V1aR receptors in certain brain regions to respond to it that way.

We are still learning about the role of vasopressin in pair bonding behaviors. Much of what we know has focused on these vole species, and we know much less about vasopressin’s involvement in pair bonding in other species. We also don’t know as much about the role of vasopressin in females across different reproductive stages. But one thing is for sure: Love wouldn’t be the same without Vasopressin!


Want to know more? Check these out:
Carter, C.S. (2017). The Oxytocin–vasopressin Pathway in the Context of Love and Fear. Frontiers in Endocrinology, 8(356): 1-12.

Phelps, S.M., Okhovat, M. and Berrio, A. (2017). Individual Differences in Social Behavior and Cortical Vasopressin Receptor: Genetics, Epigenetics, and Evolution. Frontiers in Endocrinology, 8(537): 1-12.

Tickerhoof, M.C. and Smith, A.S. (2017). Vasopressinergic Neurocircuitry Regulating Social Attachment in a Monogamous Species. Frontiers in Endocrinology, 8(265): 1-10.

The Love Chemical Pageant of 2018

A modified repost of an original article from February 15, 2012.

Hello and welcome to the Love Chemical Pageant of 2018! I’m your host, Miss Behavior, and YOU are the judges.

Since the beginning of…well, social animals, many hormones and neurotransmitters have been quietly working in their own ways to fill our world with love. Lately (over the last few decades), some of them have been brought out of the background and into the limelight, credited with every crush, passionate longing, parental hug, embrace among friends, and cuddle between spouses. But who truly deserves the title of The Love Chemical?

Let’s meet our contestants!

Let’s first meet our reining title-holder, Dopamine! Dopamine is a neurotransmitter produced in the brain. Sex increases dopamine levels in both males and females and blocking its effects during sex can prevent prairie voles (a monogamous species often used to test questions on pair bonding) from forming preferences for their own partner. Dopamine also plays a role in maternal and paternal behaviors.

But dopamine is not just involved in love. It has a wide range of known functions in the brain, involved in everything from voluntary movement, mood, motivation, punishment and reward, cognition, memory, learning, aggression, pain perception and sleep. Abnormally high levels of dopamine have been linked to schizophrenia and psychosis. And dopamine is especially well-known for its role in addiction... in fact, many researchers believe that we may even be addicted to our own romantic partners.

Now let’s meet Dopamine’s partner, Opioids! When natural opioids are released in the brain, they can cause a rewarding feeling that often cause us to seek more of it. When prairie voles are given drugs that prevent opioids from acting on a particular opioid receptor type (mu-opioid receptors) in a particular brain region (the caudate-putamen), they do not form pair bonds with sexual partners. Interestingly, people that see the faces of their loved ones experience lots of activity in the caudate-putamen region of the brain, especially if they rate their relationship with that person as very romantic and passionate. The caudate-putamen region of the brain also uses dopamine, so the two chemicals appear to work together there to promote the feelings of romantic love.

Please welcome Oxytocin! Oxytocin is a peptide hormone, most of which is made in the brain. Some of this oxytocin is released into the blood and affects body organs, such as the uterus and cervix during child birth and the mammary glands during breast feeding. But some of it stays in the brain and spinal cord, acting on neurons with oxytocin receptors to affect a number of behaviors. Released during child birth and nursing, oxytocin is important for helping mammalian mothers behave like moms and in species in which both parents raise young, it helps fathers behave like dads. Also released during sex, oxytocin plays an important role in pair bonding in prairie voles (particularly in the female of the pair). In humans, people given oxytocin nasal sprays have been reported to have less fear, more financial trust in strangers, increased generosity, improved memory for faces, improved recognition of social cues, and increased empathy.

But before you fall head-over-heels for oxytocin, you should know a few more things. For one thing, oxytocin isn’t exclusively linked with feel-good emotions; It has also been associated with territoriality, aggressive defense of offspring, and forming racist associations. Also, oxytocin doesn’t work alone. It has been shown to interact with vasopressin, dopamine, adrenaline and corticosterone and all these interactions affect pair bonding.

Next up is Vasopressin! Vasopressin is closely related to oxytocin. Like oxytocin receptors, vasopressin receptors are expressed in different patterns in the brains of monogamous vole species compared to promiscuous vole species. Released during sex, vasopressin plays an important role in pair bonding in monogamous prairie voles (particularly in the male of the pair). If you block vasopressin in the brain of a paired male prairie vole, he will be more likely to prefer spending time around a new female rather than his mate. On the flip side, if you increase vasopressin activity in specific brain regions of an unpaired male prairie vole or even a promiscuous male meadow vole and introduce him to a female, he will prefer spending time with her than other females. Vasopressin may also make male prairie voles more paternal.

But vasopressin does a lot of things. In the body, its primary function is to regulate water retention. In the brain, it plays a role in memory formation and territorial aggression. And even its role in monogamy is not exclusive: Vasopressin interacts with oxytocin and testosterone when working to regulate pair bonding and parental behavior.

Look out for Cortisol! Cortisol is produced by the adrenal glands (on top of the kidneys) and is involved in stress responses in humans and primates. Both men and women have increased cortisol levels when they report that they have recently fallen in love. Many studies have also found relationships between cortisol and maternal behavior in primates, but sometimes they show that cortisol increases maternal behavior and sometimes it prevents it. In rodents, where corticosterone is similar to cortisol, the story is also not very clear. Corticosterone appears to be necessary for male prairie voles to form pair bonds and it plays a role in maintaining pair bonds and promoting paternal behavior. But in female prairie voles, the opposite seems to be true! Corticosterone in females appears to prevent preference for spending time with their partner and pair bond formation.

Put your hands together for Testosterone! Testosterone is a steroid hormone and is primarily secreted from the gonads (testes in males and ovaries in females). Frequently referred to as “the male hormone”, both males and females have it and use it, although maybe a little differently. Testosterone is associated with sex drive in both men and women. But men who have recently fallen in love have lower testosterone levels than do single males, whereas women who have recently fallen in love have higher testosterone than single gals.

This is Estrogen! Estrogen is another steroid hormone, frequently referred to as “the female hormone”, although again, both males and females have it. Estrogen also seems to play a role in sex drive in both men and women. The combination of high estrogen levels and dropping progesterone levels (another steroid hormone) is critical for the development of maternal behavior in primates, sheep and rodents. But look closer and you will find that the activation of estrogen receptors in particular brain regions is associated with less sexual receptivity, parental behavior, and the preference for spending time with the mate.

So let’s have a round of applause for this year’s contenders in The Love Chemical Pageant! Now it is your turn to voice your opinion in the comments section below. Vote for the neurochemical you believe deserves the title The Love Chemical. Or suggest an alternative pageant result!


Want to know more? Check these out:

Burkett, J.P. and Young, L.J. (2012). The behavioral, anatomical and pharmacological parallels between social attachment, love and addiction. Psychopharmacology, 224:1-26.

Fisher, H.E. (1998). Lust, attraction, and attachment in mammalian reproduction. Human Nature, 9(1) 23-52.

Marazziti, D. and Canale, D. (2004). Hormonal changes when falling in love. Psychoneuroendocrinology, 29, 931-936.

Van Anders, S.M. and Watson, N.V. (2006). Social neuroendocrinology: Effects of social contexts and behaviors on sex steroids in humans. Human Nature, 17(2), 212-237.

Young, K.A., Gobrogge, K.L., Liu, Y. and Wang, Z. (2011). The neurobiology of pair bonding: Insights from a socially monogamous rodent. Frontiers in Neuroendocrinology, 32(2011), 53-69.

Addicted to Love

Image from imagerymajestic at FreeDigitalPhotos.net.

Early exposure creates a sense of euphoria, a heightening of senses, a rush of pleasure. In order to recreate and further heighten the experience, more is sought, but the euphoric effect eventually starts to wear off. Craving and palpable longing intensifies in its absence, but the effect of exposure is now a calm relief rather than a euphoric high. And once cut off abruptly and completely, desperation, grief, pain and depression set in. The pull to return to it is (almost) insurmountable.

This describes the phases of substance addiction, listed by the DSM-5, the latest version of the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association. These phases include consumption (taking the substance), reinforcement learning (intense pleasure associated with consuming the substance), seeking more of the substance, developing a tolerance (intense pleasure is replaced with avoidance of discomfort), withdrawal (psychological and physical discomfort associated with not consuming the substance), and relapse (returning to consume the substance, even in the face of large costs of doing so).

Now re-read the first paragraph, but instead of imagining the development of a substance addiction, imagine the process of falling in love.

It sounds the same, doesn’t it? According to one theory, it sounds the same because it is the same. In essence, falling in love is the process of becoming addicted to another individual.

There are undeniable similarities between how the brain responds to substance addiction and how the brain responds to falling in love. Both substances of addiction and individuals we are attracted to cause the brain to release dopamine, a neurotransmitter, into a brain region called the nucleus accumbens. Dopamine acting in this region helps us learn to associate cues with rewarding feelings. However, dopamine acts on two different types of receptors, called D1-receptors and D2-receptors, in complex ways. Activation of D2-receptors promotes bonding with a partner; it also promotes the reward value of a substance. Activation of D1-receptors reduces bonding with a partner; it also reduces the reward value of a substance. During this time early on in a romantic relationship or early exposure to an addictive substance, dopamine is primarily acting on D2 receptors, heightening our senses and focusing our attention on the cues of our next encounter… developing our craving, our longing, our drive for the next meeting.

When we are in the early obsessive stages of love, every encounter (and especially sexual encounters) cause a pleasurable release of not just dopamine, but also natural opioids. These two brain chemicals work together in the brain to continually strengthen the association of the stimulus (the one you are falling in love with) with intense positive feelings. This will cause you to seek more and more of these interactions, craving them intensely in the times in between. These same chemicals act on the same receptors in the same way during the process of forming an addiction to a substance, causing the person to seek more and more of it.

With time, the brain adapts. Repeated encounters no longer cause the same euphoria they once did, but rather, a sense of calm contentment. The dopamine that is released before and during these encounters is now activating more of the D1-receptors, which result in less of a feeling of pleasure, and more agitation and aggression. In terms of relationships, it is thought that this transition actually helps maintain a pair bond with one individual, because in this stage you are less driven to seek a competing pair bond and you are more likely to aggressively defend the pair bond you have already established. In terms of substance abuse, this phase is called tolerance. (I know, this perspective really takes the romance out of long-term marriages, but...)

During this tolerance phase, lack of exposure to the object of your addiction (whether it is a person or a substance) results in a lack of dopamine and opioid release and an increase in stress hormone release. If we are talking about addiction to a substance, we call this withdrawal. If we are talking about a relationship, we call this separation anxiety or even heartbreak. To avoid these horrible feelings, we often relapse… right back into the arms of our addiction.

Love is not listed as a psychological disorder in the DSM-5, nor do we think of it as one. But in a true physiological sense, we may actually be addicted to the ones we love.


Want to know more? Check these out:

Burkett, J.P. and Young, L.J. (2012). The behavioral, anatomical and pharmacological parallels between social attachment, love and addiction. Psychopharmacology, 224:1-26.

Potenza, M.N. (2014). Non-substance addictive behaviors in the context of DSM-5. Addictive Behaviors, 39(1): 1-2.

Nature Shapes Faithful and Unfaithful Brains

Among monogamous animals, some individuals are more faithful than others. Could these differences in fidelity be, in part, because of differences in our brains? And if so, why does this diversity in brain and behavior exist?

A snuggly prairie vole family. Photo from theNerdPatrol at Wikimedia Commons.

Prairie voles are small North American rodents that form monogamous pair bonds, share parental duties, and defend their homes. Although prairie voles form monogamous pairs, that does not mean they are sexually exclusive. About a quarter of prairie vole pups are conceived outside of their parents’ union.

Not all male prairie voles cheat on their partners at the same rates. In fact, some males are very sexually faithful. It turns out, there are both costs and benefits to being faithful and to cheating. Mariam Okhovat, Alejandro Berrio, Gerard Wallace, and Steve Phelps from the University of Texas at Austin, and Alex Ophir from Cornell University used radio-telemetry to track male prairie voles for several weeks to explore what some of these costs and benefits might be. Compared to males that only sired offspring with their own partner, unfaithful males had larger home ranges, intruded on more territories of other individuals, and encountered females more often. However, these unfaithful males were also more likely to be cheated on when they were away (probably because they were away more). I guess even rodents live by The Golden Rule.

Maps of how paired male voles in this study used space. The solid red/orange/yellow peaks show where a faithful male (in the left map) and unfaithful male (in the right map) spent their time in relation to where other paired males spent their time (showed by open blue peaks). Image from the Okhovat et al. Science paper (2015).

Vasopressin is a hormone that has been found to affect social behaviors such as aggression and pair bonding when it acts in the brain. Mariam, Alejandro, Gerard, Alex, and Steve all set out to determine how vasopressin in the brain may relate to sexual fidelity in prairie voles. They found that faithful males had lots of a particular type of vasopressin receptor (called V1aR) in certain brain areas involved in spatial memory. Surprisingly, faithful males did not have more V1aR in brain regions typically associated with pair bonding and aggression. A male that has more V1aR in spatial memory regions might better remember where his own mate is and where other males have been aggressive, which would decrease the chances that he would intrude on other territories in search of other females and increase the time that he spends home with his own mate. A male that has less V1aR in spatial memory regions might be less likely to learn from his negative experiences and more likely to sleep around.

Photos of a brain section from a faithful male (left) and unfaithful male (right). The dark shading shows the density of V1aR vasopressin receptors. The arrows show the location of the retrosplenial cortex (RSC), a brain area involved in spatial memory. Faithful males had significantly more V1aR receptors in the RSC compared to unfaithful males. Image from the Okhovat et al. Science paper (2015).

The research team then found genotype variations that related to having lots or not much V1aR in one of these spatial memory regions (called retrosplenial cortex … but we’ll just call it RSC). They confirmed these findings with a breeding study, in which they reared siblings that were genetically similar, but some had the genotype they predicted would result in lots of V1aR in RSC and some had the genotype they predicted would result in very little V1aR in RSC. They confirmed that these genetic variations correspond with the amount of vasopressin receptor in this specific spatial memory area.

The researchers then looked closer at the different versions of this vasopressin receptor gene in the RSC brain region to see if differences in the amount of vasopressin receptors in RSC may be caused by the epigenetic state of the gene (i.e. how active the gene is). They found that the genotype that results in very little V1aR in RSC had many more potential methylation sites, which can repress gene activity.

All of this data together tells a very interesting story. Male prairie voles that have the genotype for more V1aR vasopressin receptors in their RSC part of their brain are more likely to remember where their home and mate are and to remember where other aggressive prairie voles are, which will make them more likely to spend more time with their partner, to be sexually faithful and to have sexually faithful partners. Male prairie voles that have the genotype for less V1aR in their RSC are more likely to forget where their home and mate are and where other aggressive prairie voles are, which will make them more likely to cheat and to be cheated on. Overall, faithful and unfaithful male prairie voles have roughly the same number of offspring, but advantages may emerge with changes in population density. Prairie vole populations vary anywhere from 25 to 600 voles per hectare from year to year. When population densities are high, you (and your partner) are more likely to encounter more potential mates and it may benefit you to cheat (and have a “cheater’s brain”). When population densities are low, you (and your partner) are less likely to encounter more potential mates and it may benefit you to be faithful (and have a “faithful brain”). But when populations fluctuate between high and low densities, both faithful and unfaithful genotypes will get passed along from generation to generation.


Want to know more? Check this out:

Okhovat, M., Berrio, A., Wallace, G., Ophir, A., & Phelps, S. (2015). Sexual fidelity trade-offs promote regulatory variation in the prairie vole brain Science, 350 (6266), 1371-1374 DOI: 10.1126/science.aac5791

Love, War and Genital Shape

The size and shape of your junk may depend on how much sex your ancestors had… that is, at least, if you are a burying beetle.

Buring beetles caught in the act. Photo by Jena Johnson.

Burying beetles are unusual among insects in that they provide parental care and are often monogamous. When burying beetle pairs find a small dead bird or rodent, they pluck it bald, coat it in antibacterial and antifungal body secretions, and dig a hole around it. The female lays her eggs around the carcass-ball, so that their newly hatched babies can feast on it, as well as additional food that the devoted the parents bring them. In this system, mothers are capable of taking care of their babies by themselves, but they do better if fathers stick around. This has led to sexual conflict in these species: after mating, many males will climb to a high perch to release pheromones to attract additional females… but if his partner catches him, she’ll knock him off his perch.

A nurturing burying beetle mom feeding her young. Photo by Paul Hopwood.

Male and female burying beetles also differ over how much sex to have. Males are better off when they have lots of sex, because this increases their chances of fathering more young. However, females are better off when they have less sex, because they don’t need a lot of sex to fertilize their eggs and too much sex reduces their ability to provide maternal care. In this battle of the sexes, genitals can become a specialized weapon.

A research team from the University of Exeter in the United Kingdom, including Paul Hopwood, Megan Head, Eleanor Jordan, Mauricio Carter, Emma Davey, Allen Moore, and Nick Royle, hypothesized that selectively breeding burying beetles who have more or less sex could lead to changes in genital structures over multiple generations. They randomly assigned burying beetles a monogamous partner and measured how much sex they had. They then bred the offspring of the high-sex parents together to create high-sex genetic lines, they bred the offspring of the low-sex parents together to create low-sex genetic lines, and they bred offspring from random parents together to create control genetic lines. They continued these high-sex, low-sex and control lines for ten generations. They then measured and compared the genitals of these 10th generation offspring.

Porno pictures of burying beetle genitals. Images A and B are male genitals from the top and side views. Images C and D are female genitals from the top and bottom views. The blue and pink dots are the landmarks the researchers used for measuring genital size and shape. Image from the Hopwood et al. 2016 paper in Evolution.

The selective breeding program changed genital shape in both males and females after only ten generations. Males from the high-sex genetic lines had longer and straighter penis-like structures with shorter sensory hairs, whereas males from the low-sex genetic lines had shorter penis-like structures with longer sensory hairs. Perhaps these long sword-like penis-like structures help males overcome females that resist male sexual advances by wrestling, kicking and curling their abdomens away. Females, on the other hand, had shorter vulvas and thicker genital claws (yes, these girls have developed genital claws for this sex war) in both the high-sex and the low-sex genetic lines compared to the control genetic lines. Furthermore, the genetic lines in which males developed longer penis-like structures had females that developed more narrow-set genital claws, showing that these traits were changing together from generation to generation.

There is a tremendous diversity of genital shapes across the animal kingdom. We often think of this genital diversity as coming from the compatibility of the sexes, like a lock and key, when the truth is that love is a battlefield and genitals are weapons of war.


Want to know more? Check this out:

Hopwood, P., Head, M., Jordan, E., Carter, M., Davey, E., Moore, A., & Royle, N. (2016). Selection on an antagonistic behavioral trait can drive rapid genital coevolution in the burying beetle, Evolution DOI: 10.1111/evo.12938

The Harm of Verbal Promiscuity

Eastern chimpanzees don't want to be judged. Image by Ikiwaner at Wikimedia.com.

Whether they have one true love for life, multiple partners, or are free-loving, animals have many different mating systems. We have different scientific terms for these different mating systems, and most of these terms have very specific meanings. An animal is socially monogamous when it has one exclusive mating relationship, but maybe has sex with others outside of that relationship. It is sexually monogamous when it has one exclusive sexual relationship and is sexually faithful to that partner. Animals are polygamous when they have multiple sexual relationships. Polygamous animals can be polygynous (when one male has a mating relationship with multiple females), polyandrous (when one female has a mating relationship with multiple males) or polygynandrous (when multiple males and multiple females all have a mating relationship). However, one mating system term has been used much more loosely: promiscuous. In some scientific papers, promiscuous is used to describe animals that aren’t choosy about whom they mate with. Others use promiscuous to describe animals that don’t form mating relationships. But promiscuous is also misused by many people, including scientists, to refer to polygamous animals. This loose use of terminology can be damaging to both our scientific understanding and our society.

Scientific terms generally come from common language, but are then are given more specific definitions for their scientific use. When we confuse scientific terms for their common-use meanings, society can be harmed. For example, the Merriam-Webster Dictionary includes a dozen different definitions of “theory” that all include strong elements of uncertainty (such as “an unproved assumption” and “an idea that is suggested or presented as possibly true but that is not known or proven to be true”). In contrast, the scientific term theory refers only to scientific explanations that have been substantiated through such a large amount of rigorous scientific testing and evidence that we are almost certain they are true (because scientists are supposed to never be completely certain). When the scientific term theory is confused with the common word “theory”, then concepts regarded essentially as fact among informed scientists are disregarded by politicians and many of the general public as “just a theory”.

Promiscuity is one of those scientific terms that was originally borrowed from common language and is now confused with its common-word counterpart. The Merriam-Webster Dictionary defines “promiscuous” as “having or involving many sexual partners”, which is almost exactly the scientific definition of polygamous. Thus, “promiscuous” is often misused, even by scientific researchers, when polygamous, polygynous, polyandrous, or polygynandrous are more accurate. Misidentifying the mating system of a species can obscure meaningful connections between behavior and ecology and can negatively impact conservation, captive breeding efforts, and medical and psychological advances.

Image from freedigitalphotos.net

Mark Elgar and Therésa Jones from the University of Melbourne and Kathryn McNamara from The University of Western Australia found that when “promiscuous” is misused in research, scientists are much more likely to use it to refer to polyandrous females than to polygynous males. This biased misuse of the word reflects our moral judgments and causes us additional harm as a society. The common word “promiscuous” has pejorative connotations and evokes negative emotions, especially when applied to women. Our human cultures generally have expectations that women will be faithful to one partner, while we are more understanding of the infidelities of men. When applied to animals, and especially primates, promiscuity has an anthropomorphic nature that places our human expectations and interpretations on other species. It’s bad enough when we judge each other – let’s try not to judge animals too.


Want to know more? Check this out:

Elgar, M., Jones, T., & McNamara, K. (2013). Promiscuous words Frontiers in Zoology, 10 (1) DOI: 10.1186/1742-9994-10-66

Cooperating for Selfish Reasons

An Ethiopian Wolf photographed by Gert Vankrunkelsven.
Image available at Wikimedia.

If you were a young adult Ethiopian wolf, you would have a choice to make: Should you be a member of a monogamous breeding pair or a helper to an already established breeding pair (who are probably your parents)? The choice seems obvious, right? I mean, who wants to be a helper? Why should you forgo all the glory and status of being part of the breeding pair to be a babysitter?

Today I am revisiting my thoughts on the motivations to cooperate from an article I wrote in the early days of The Scorpion and the Frog. You can read the article in it's entirety here.

Your Picks of 2012

This has been a wild first year for The Scorpion and the Frog. I have enjoyed sharing the world of animal physiology and behavior research with you. But even more, I have enjoyed hearing from you about your experiences, thoughts and perspectives.

I gathered data on page visits, comments, and social media attention for The Scorpion and the Frog posts and have determined your top five posts of the year. Here are Your Favorite The Scorpion and the Frog Posts of 2012 (in no particular order).

1. The “Love Hormone” Pageant pits six hormones against one another in a contest for the title of the “Love Hormone”. The "Love Hormone" of 2012 focuses on the big winner (as determined by reader votes), Dopamine!

2. Scientists put the philosophical question, “What Do Animals Think of Their Dead?” to the test. Their results may surprise you!

3. In Snakes Deceive to Get a Little Snuggle, we learn about boy snakes pretending to be sexy girl snakes, all in the hopes of a good cuddle.

4. Male nursery web spiders give silk-wrapped gifts to the girls that catch their eyes. But why waste a perfectly good present when a piece of junk in clever packaging will do? Sex, Lies and Spider Silk tells the story of these deceptive gift-givers.

5. Don’t Challenge a Fruit-Eating Bat to a Drinking Contest. Just don’t. Here’s why.

Thank you for your support and participation over the year. Next year should be full of new wacky animal stories. (And if you’d like to see my 2012 picks for my favorite animal physiology and behavior blog posts at other sites, click here).

Mr. Nanny Makes Mr. Right

Quick! Introduce yourself to this guy before
his baby-high wears off! Photo by David
Castillo Dominici at FreeDigitalPhotos.net. 

What happens if you take a wrestler or action star and force him to babysit obnoxious but lovable kids? Well, if you’ve seen movies like The Pacifier with Vin Diesel, The Tooth Fairy with Dwayne ‘The Rock’ Johnson, Kindergarten Cop with Arnold Schwarzenegger, or The Spy Next Door with Jackie Chan, you know that he will fall madly in love both with his young charges and with the closest available woman. Hollywood is so sure of this phenomenon that they have based a whole genre of family movies on it. Now, scientists are finding that Hollywood may be on to something.

Prairie voles are one of the only 3-5% of mammals that are monogamous and in which both parents help take care of young. In females, maternal care is regulated in part by the hormones associated with pregnancy, birth and lactation. The fact that males don’t do those things and they still provide paternal care is curious. The fact that male prairie voles will often provide care to offspring that aren’t even their own is even more curious.

Will Kenkel, Jim Paredes, Jason Yee, Hossein Pournajafi-Nazarloo, Karen Bales, and Sue Carter at the University of Illinois at Chicago recently explored what happens to male prairie voles when they are exposed to unfamiliar vole pups. Male voles without any experience with females or pups were placed in a new clean cage. Then the researchers put either a pup (that was not related to the male), a dowel rod (an unfamiliar object), or nothing into the cage with them for 10 minutes. Afterwards, they measured oxytocin (a hormone associated with bonding between mothers and their offspring) and corticosterone (a stress hormone) in the males’ blood at different time points. In another study, they also looked at the activity of brain neurons associated with the production of these hormones.

A male prairie vole is startled to find a baby in his cage...
But then he takes care of it. Video by Will Kenkel.

Both adult and juvenile males exposed to a pup for 10 minutes had higher oxytocin and lower corticosterone compared to the males not exposed to a pup. But this effect was short-lived, as male hormone levels quickly evened out again. Most of these males that were exposed to a pup showed alloparental care (care of a baby that is not their own), like approaching the pup, cuddling with it and grooming it. Males with higher oxytocin and lower corticosterone levels were more attentive towards the pups. Additionally, alloparental males exposed to pups had more activity of oxytocin-producing neurons and less activity of neurons associated with corticosterone-production in a specific brain region called the paraventricular nucleus (or PVN for short).

Oxytocin is strongly associated with pair bonding in prairie voles, particularly in females, and corticosterone affects pair bonding too (generally increasing pair bonding in males and preventing it in females). If exposure to a pup affects these hormones, maybe it affects how the male would interact with adult females. To test this, the researchers put male voles in a new clean cage and put a pup, a dowel rod, or nothing into the cage with them for 20 minutes. Then they put the males with an unfamiliar adult female for 30 minutes. After getting acquainted with the female, the males were put in a “partner preference apparatus”, which has three connected chambers: a neutral center chamber, a connected chamber with the familiar female tethered into it, and a connected chamber with an unfamiliar female tethered into it. The researchers measured how much time the males spent in each of the three chambers and with each of the two females over the next 3 hours.



A prairie vole pair snuggles. Photo from Young,
Gobrogge, Liu and Wang paper in
Frontiers in Neuroendocrinology (2011)

Males that were exposed to a dowel rod or to nothing before they were introduced to a female spent equal amounts of time with each of the two females. But males that were exposed to a pup before they were introduced to a female spent nearly 4 times as much time with that female than with the unfamiliar one. In other words, hanging out with a random pup acted like Love Potion #9 on these bachelor males and made them fall for the next female they encountered! Interestingly, this effect was true not only for the males that acted in an alloparental way towards the pups, but it was also true of males that attacked the pups (The researchers quickly rescued the pups if this occurred). Perhaps, males that were alloparental with the pups had increased oxytocin and males that were aggressive with the pups had increased corticosterone, either of which would make it more likely for them to form a preference for the female they were with.

Hmm… Got your eye on a special someone? Try volunteering him to babysit before your next date.

Want to know more? Check this out:

Kenkel, W., Paredes, J., Yee, J., Pournajafi-Nazarloo, H., Bales, K., & Carter, C. (2012). Neuroendocrine and Behavioural Responses to Exposure to an Infant in Male Prairie Voles Journal of Neuroendocrinology, 24 (6), 874-886 DOI: 10.1111/j.1365-2826.2012.02301.x

Cooperating For Selfish Reasons

If you were a young adult Ethiopian wolf, you would have a choice to make: Should you be a member of a monogamous breeding pair or a helper to an already established breeding pair (who are probably your parents)? The choice seems obvious, right? I mean, who wants to be a helper? Why should you forgo all the glory and status of being part of the breeding pair to be a babysitter? 

The Governess painted by Rebecca Solomon in 1851 shows a modestly-dressed
Victorian era governess (in black) who diligently cares for the education needs of
her employer's young children, while the well-dressed employer is free to flirt.
Image provided by Wikimedia.

But Ethiopian wolves often do make that choice. These wolves are territorial rodent hunters and their survival and success depends on how many giant mole rats (their favorite food) and Murinae rats (a second-choice food-option) are available in the territory. In territories with fewer rodents, Ethiopian wolf families are likely to consist of a mother, a father, and their pup born that season. However, in territories with lots of rodents available, wolf families also include some of the older siblings from previous years. Why do they stick around?

An Ethiopian Wolf photographed
by Gert Vankrunkelsven.
Image available at Wikimedia.

Jorgelina Marino, Claudio Sillero-Zubiri, Paul Johnson, and David Macdonald from the University of Oxford in the U.K., set out to ask this question. They collected data on 17 wolf packs in the Bale Mountains of southern Ethiopia for 13 years. They did this by following the packs on foot or on horseback and watching them with binoculars. The researchers also mapped the quality of the habitats to estimate the number of giant mole rats and Murinae rats available.

These wolf packs included 13 wolf packs with territories in optimal rodent-hunting areas (high-quality habitat in the Web Valley-Sanetti area) and 4 packs with territories with very few rodents (poor-quality habitat in the Tullu Deemtu area). The packs in the high-quality habitat had from 3-13 wolves, usually including the breeding pair, their pup, their adult sons from previous years and some of their adult daughters from previous years (Adult daughters were more likely to set out on their own than the sons). The packs in the poor-quality habitat only had 2-3 wolves, including the breeding pair and maybe their pup.

The researchers discovered that the small packs generally had large but poor-quality territories. The wolf packs in high-quality habitats had smaller habitats, but the bigger the pack, the bigger their territory and the more high-quality habitat they had on their territory. This may be because for each additional wolf in the pack, the more hunting territory is needed to support it. But the researchers discovered that these large wolf packs had more high-quality territory per wolf than the smaller packs had. So if you were a young adult Ethiopian wolf, you would have more high-quality hunting territory for you if you were to choose to stay home with mom and dad and your other siblings than if you were to seek a mate of your own.

Wolves that lived in the Tullu Deemtu area had small groups and large territories, but the
territories did not have a lot of access to food. Wolves that lived in the Web Valley-Sanetti
area had more access to food and could live in larger groups on smaller territories. The more
wolves in the pack in the Web Valley-Sanetti area, the more territory they could defend
per wolf.  Figure from Marino, Sillero-Zubiri, Johnson, and Macdonald's 2012 Behavioral
Ecology and Sociobiology paper.

The researchers also explored other possible advantages of group living, but didn’t find much. These animals hunt alone, so larger groups do not hunt more effectively than smaller groups. And the helpers were not all that helpful as babysitters either: The breeding pair did not have more pups, and pups were not more likely to survive, in families that had more helpers.

So the main advantage for a young adult Ethiopian wolf to stay home with mom and dad a bit longer seems to be more access to better hunting grounds. Why would this be? Ethiopian wolves patrol the boundaries of their territories and pee on them to mark their territory. More wolves in the pack means more patrols and more pee. In this way, larger packs are more able to defend more and better-quality territory. This benefits each of the young adults that stay with the family, and even mom, dad and pup too… to a point. Once the pack reaches a size of 8 adults, the benefits per wolf decline. Packs larger than 8 are more likely to split into multiple smaller packs, each with its own breeding pair. One more benefit of being in a larger group: When young adults split off from the family pack to establish their own breeding pair, they often get to inherit some of their natal territory.

If you find yourself living with mom and dad later than you may have anticipated, it may just be worth it as long as the refrigerator stays stocked and the diggs are comfortable. And if you find yourself a mom or dad with an adult child living with you later than you may have anticipated, it may just be worth it as long as they help stock the fridge and keep the place clean. But as soon as the arrangement stops being beneficial for everyone, it is time to strike out on your own.

Want to know more? Check this out:

Marino, J., Sillero-Zubiri, C., Johnson, P.J., & Macdonald, D.W. (2012). Ecological bases of philopatry and cooperation in Ethiopian wolves Behavioral Ecology and Sociobiology, 66, 1005-1015 DOI: 10.1007/s00265-012-1348-x

Uncontrollable Love: A Guest Post

By Yunhan Zhao

Image from Freedigitalphotos.net

What is love? Under Shakespeare’s leather pen, love is the tragedy of Romeo and Juliet. In the poet’s eyes, love is the courage of Paris to elope with Helen and stand against the world. In Pretty Woman love doesn’t care about social status or wealth. When people fall in love the whole world feels brighter and more vibrant. Orpheus and Eurydice, Jane Eyre and Rochester, Darcy and Elizabeth…thousands of romantic stories, poems and songs illustrate the countless versions of love tales. Now scientists have revealed their scientific version of the love tale. They say love is comprised of magic chemicals interacting with our brains.

Photo of a prairie vole pair from Young,
Gobrogge, Liu and Wang paper in
Frontiers in Neuroendocrinology (2011)

In 1999, researchers Mary M. Cho, Courtney De Vries, Jessie Williams and Sue Carter at the University of Maryland conducted NIMH funded research aimed to unlock the secret behind ‘love.’ By using the monogamous prairie vole (Microtus ochrogaster) as subjects, they investigated the important neurophysiological events that contribute to the development and maintenance of pair bonding between heterosexual adults. Here they designed an experiment to test the hypothesis that oxytocin and vasopressin (chemicals that are released in the brain during sexual behavior) facilitate the development of partner preference.

In their experiments, the researchers randomly assigned prairie voles to three different dose groups of oxytocin, three different dose groups of vasopressin and a control group which used cerebrospinal fluid. After receiving injections directly to their brains, each prairie vole was housed with an opposite sex partner for one hour (referred as cohabitation below). Then partner preference was assessed immediately by measuring the time spent in physical contact with either the familiar partner or a stranger vole.

Researchers found that the test subjects made stronger partner preferences depending on which kind of injection they received. As expected, results showed that in male prairie voles, almost all the vasopressin and oxytocin treatments (except the lowest dose of oxytocin) led to a loyal choice for the cohabiting partners over an unacquainted female. In females, however, only the highest dose of vasopressin and oxytocin treatments resulted in a loyal choice. In contrast, with the cerebrospinal fluid control treatment in both genders of voles, the test voles were always equally attracted to their previous partners and the unacquainted strangers.

Partner preferences of male (left) and female (right) after receiving different injections.
OT = oxytocin, AVP = vasopressin, CTL = cerebrospinal fluid. Figure from Cho, M.,
DeVries, A., Williams, J., & Carter, C. (1999). The effects of oxytocin and vasopressin
on partner preferences in male and female prairie voles (Microtus ochrogaster).
Behavioral Neuroscience, 113(5), 1071-1079.

This experiment found that high doses of both vasopressin and oxytocin may indeed associate with high partner fidelity in both gender of prairie voles. However, are these two chemicals the love elements in humans as well? Does it mean in the near future people can prevent divorces with only a few chemical injections to their spouses? The answer is still not clear. Especially since scientists have recently revealed that vasopressin and oxytocin may relate to distress in pair-bonded human relationships.

Shelly Taylor, Shimon Saphire-Bernstein and Teresa Seeman from the University of California, Los Angeles assessed 85 young adults in committed relationships. They asked participants to complete a series of self-reported questionnaires which included items like “how often they argue with you,” “how often they criticize you,” and “how often they get on your nerves”. Additionally, they also had the participants’ blood drawn within a week of finishing the assessments.

Image from Freedigitalphotos.net

Analysis showed that the elevated plasma oxytocin levels were associated with relationship distress in women while the increased plasma vasopressin levels were associated with relationship distress in men. But what should be noticed is that the direction of such effects remains unknown. Although no evidence revealed the exact relationship between humans’ plasma vasopressin and oxytocin levels and relationship distress, it appears that these two chemicals may be associated with very different emotional effects in voles and humans. However, an alternative explanation could also be that oxytocin and vasopressin contribute differently in different stages or contexts of romantic relationships.

Love seems uncontrollable even in the scientific world. Prairie voles crave emotional and sexual union after being injected with a high level of oxytocin and vasopressin into their brains, but people with the high presence of the same chemicals become vulnerable to relationship problems. So what is the key here?

References

1. Cho, M., DeVries, A., Williams, J., & Carter, C. (1999). The effects of oxytocin and vasopressin on partner preferences in male and female prairie voles (Microtus ochrogaster) Behavioral Neuroscience, 113 (5), 1071-1079 DOI: 10.1037//0735-7044.113.5.1071

2. Taylor, S.E., Saphire-Bernstein, S., & Seeman, T.E. (2009). Are Plasma Oxytocin in Women and Plasma Vasopressin in Men Biomarkers of Distressed Pair-Bond Relationships? Psychological Science, 2010 (21), 3-7 DOI: 10.1177/0956797609356507