Sunday, January 22, 2017

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

Tuesday, November 15, 2016

More To Come In January

The Scorpion and the Frog is going on a short break until after the New Year. Check back in 2017 for more animal stories.
MMMMMMMMM.... Take some time to meditate about animal behavior.

Tuesday, November 8, 2016

Anybody else feeling totally overwhelmed today? Today I am a flustered desert rain frog:

Tuesday, November 1, 2016

Animal Break

We are all pretty stressed out these days. Let's all take an animal-break - Pick a video to make you smile:

Animals Dancing



Animals Being Jerks



Animals Being Happy


Tuesday, October 25, 2016

True Blood: Vampires Among Us

A reposting of an article from October, 2012.

Who is your favorite vampire? Are you a fan of Edward Cullen, Bill Compton or Stefan Salvatore? Or do you prefer the classic Dracula, elegant Lestat, or butt-kicking Selene?

Vampires have fascinated us since the Middle Ages, when a hysteria of vampire sightings spread across Eastern Europe. We now know that many of these “vampires” were actually victims of diseases like tuberculosis or bubonic plague that cause bleeding in the lungs (and elsewhere), resulting in the disturbing effect of blood appearing at the lips. Add this attribute to the already poorly understood physiology of decomposing corpses and the cases in which people mistakenly buried alive got up and left their graves, and voila! Vampire mythology is born. So vampires don’t really exist… Or do they?

Actually, there are many animals that feed on blood. So many in fact, that there is a scientific term for blood-eating, hematophagy. And why not? Blood is fluid tissue, chock full of nutritious proteins and lipids and a source of water to boot. And if you don’t kill your prey to feed, the food supply replenishes itself. Here are just some of these animal vampires living among us:

Vampire bat


A vampire bat smiles for the camera
from his Peruvian cave. Photo from Wikimedia.
Vampire bats are our most famous animal vampires, and the ones that most resemble our vampiric lore. There are three species of vampire bats that live from Mexico down through Argentina. Two of them, the hairy-legged and white-winged vampire bats, feed mostly on birds. The common vampire bat feeds more on mammals, like cows, horses, and the occasional human. Their razor sharp teeth cut a tiny incision in their victims and their anticoagulant saliva keeps the blood flowing. Like Dracula, vampire bats sleep by day and hunt by night. But these vampires are not loners like Dracula: They live in colonies of about 100 animals, and in hard times will share their blood-harvest and care for one another’s young.

Vampire finch


The Galapagos Islands are the famous home to numerous finch species, each one with a beak shape specially adapted to their preferred food source. For most of these finches, their food of choice is a type of seed or nut that is appropriately sized for their beak shape and strength. But the vampire finch (also called the sharp-beaked ground finch for obvious reasons) uses its long sharp beak to feed on blood. Their most common victims are their booby neighbors (named for less obvious reasons).

Candirú

A tiny candirú catfish (being measured in cm) strikes
terror into the souls of Amazonian fishermen.
Photo by Dr. Peter Henderson at PISCES
Conservation LTD. Photo at Wikimedia.
The tiny Amazonian candirú catfish is legendary for one documented case (and several undocumented ones) in which a candirú swam up a local man’s urine stream into his penis, where it attached to feed on his blood. Although terrifying, this is not typical candirú behavior. Actually, it was all just a misunderstanding. You see, candirú catfish do feed on blood, but they usually feed from the highly vascularized gills of other Amazonian fish. The gills of freshwater fish release high quantities of urea, a major component of urine. So to a hungry candirú, your pee smells an awful lot like a fish-gill blood dinner. Just another reason to not pee where you swim.

Lamprey

Notice the sharp-toothed sucker mouth of the river
lamprey. Photo by M. Buschmann at Wikimedia.
Lampreys are species of jawless fish. With their eel-like bodies and disc-shaped mouths filled with circles of razor-sharp teeth, they look like something from science fiction horror. Although some lamprey species are filter feeders, others latch onto the sides of other fish, boring into their flesh and feeding on their blood. Once attached, they can hitch a ride on their victim for days or even weeks.

Leech

A European medicinal leech.
Photo by H. Krisp at Wikimedia.
Leeches are the earthworm’s bloodsucking cousins. With three blade-like mouthparts, they slice into their victims, leaving a Y-shaped incision. They produce anticoagulants to prevent premature clotting of their bloodmeals, which can weigh up to five times as much as the leach itself. The bloodletting and anticoagulant abilities of leeches have led them to be used medicinally in ancient India and Greece as well as in modern medicine.

Female mosquito

A female mosquito getting her blood meal.
Photo by at Wikimedia.
Most of the time, mosquitos use their syringe-like mouthparts to feed on flower nectar. But when the female is ready to reproduce, she seeks out a blood meal to provide the additional protein she will need to produce and lay her eggs. Although their bites only cause minor itching, these lady vampires are truly something to be feared: They kill more people than any other animal due to the wide range of deadly diseases they spread.

There are many other examples of animals that feed on blood. But unlike their mythological counterparts, none of them come back from the dead to do so… Or do they?

Happy Halloween!

Want to know more? Check these out:

1. SCHLUTER, D., & GRANT, P.R. (1984). ECOLOGICAL CORRELATES OF MORPHOLOGICAL EVOLUTION IN A DARWINS FINCH, GEOSPIZA-DIFFICILIS EVOLUTION, 38 (4), 856-869

2. Francischetti, I. (2010). Platelet aggregation inhibitors from hematophagous animals Toxicon, 56 (7), 1130-1144 DOI: 10.1016/j.toxicon.2009.12.003