Wednesday, February 13, 2019

A Snail’s Dart of Love (A Guest Post)

By Jenna Miskowic

Snails that shoot darts. Who would have thought? Turns out, snails have a lot of competition for mates. Females of some snail species have evolved ways to select which males they want to be the father of their eggs. One of these strategies is a female can mate with multiple males and store their sperm. The female can then “choose” which sperm she wants to fertilize her eggs. This affects how males compete for mates. Males want to make sure they are the father to the offspring because they want their genes to be passed on. So male snails have developed ways to increase their chances of paternity.

Euhadra quaesita gliding through foliage. Image by Angus Davison
and Satoshi Chiba posted at Wikimedia Commons.

Enter the dart-bearing land snail, Euhadra quaesita. Snails of this species are simultaneous hermaphrodites that use cross-fertilization. Simultaneous hermaphrodites are animals that have both female and male reproductive tissues and systems. Cross-fertilization means that the snails require a mate. So, when two dart-bearing land snails cross paths and decide they want to mate, they will take their love-dart and pierce it into their mating partner. Because the snails are simultaneous hermaphrodites, they both perform this behavior before exchanging their sperm.

Love darts are composed of a crystalline form of calcium carbonite, which is what sea shells are made of, called aragonite. They are very sharp and pointed so that they are able to pierce the other snail. The dart is covered with a secretion from its mucous glands. When the dart pierces into the other snail, mucus is transported from the dart’s glands into the pierced snail’s blood. This mucus helps increase the amount of sperm being stored in the recipient snail and increases the likelihood of the donor snail being the father to the offspring of the recipient snail. Researchers Kazuki Kimura, Kaito Shibuya, and Satoshi Chiba from Tohoku University in Japan hypothesized that the dart’s mucus would also reduce future matings and promote laying eggs, also called oviposition.

Drawing of Euhadra quaesita’s love-dart. Cross-section on the left and lateral view on the right.
Image by Joris M. Koene and Hinrich Schulenburg posted at Wikimedia Commons.

To test these hypotheses, the researchers conducted two separate experiments. The first experiment focused on the effects of dart shooting and future matings of the recipient snail. Individually, non-virgin adult snails were presented with a non-virgin or virgin adult for their initial mating. In this species, non-virgin adults shoot their darts and virgin snails do not shoot their darts while performing the mating behavior. Thus, the subjects paired with a non-virgin adult were pierced with their partner’s love-dart, and the subjects paired with a virgin adult were not pierced with their partner’s love-dart. Then the subjects were offered to mate again with an unfamiliar non-virgin snail with a high mating motivation caused by individual rearing. They recorded how long the snail subject went, in days, before mating again with another individual of the same species. The researchers found that the amount of time between matings was longer in pierced snails than in ones not pierced.

The second experiment focused on the effect of injected artificial mucus on future matings and promotion of oviposition behavior. Researchers dissected an extract of the mucous glands out of adult snails and combined it with saline solution to create the artificial mucus. There were two groups used in this experiment: (1) adult snails injected with the artificial mucus, also known as the treatment group and (2) adult snails injected with only the saline solution, also known as the control group. They recorded the number of hatched eggs and their parentage. They found that artificial mucus-injected snail pairs mated less often than the control pairs. Additionally, they found that the amount of the snails that laid eggs was larger in the snails injected with artificial mucus. These findings support the researchers’ hypotheses that dart mucus can subdue future matings in its recipients.

So what are the benefits to stabbing your partner with a love dart? Well, if an animal has multiple partners, then it is quite advantageous for the partner to make sure that they are the parent. Mating suppression after being injected with the love dart is one way to fight off the competition. So, beware to all who search for Cupid’s arrow this Valentine’s Day. There may be more to an arrow of love than you realize.


References

Kimura, Shibuya, & Chiba. (2013). The mucus of a land snail love-dart suppresses subsequent matings in darted individuals. Animal Behaviour, 85(3), 631-635.

Tuesday, January 29, 2019

Why You Can’t Hibernate the Winter Away

A reposting of an original article from January, 2015.

You open your eyes, slap the alarm, and pull the covers a little tighter around your shoulders. It’s still dark outside and you dread the moment that you step out from under the warm comforter and the cold sucks your breath out. Can’t you just hibernate and sleep the winter away?

A dormouse in his snuggly hibernation state.
Image by Krysztof Dreszer at Wikimedia.
Actually, no. Hibernation and sleep are two completely different physiological processes (shown by studies of brain function). And chances are, you don’t have the physiological bits needed to hibernate safely.

Hibernation has more to do with energy and body temperature than it does with sleep. Hibernation is defined as a process in which an animal allows its body temperature to approximate the environmental temperature for several days or longer. It is a strategy that some animals use during periods of food shortage to conserve the energy that would normally be used to generate body heat. When food is scarce in the winter, the animal will lower its metabolism (the burning of food molecules to create energy and heat), which will result in the animal having less energy (and entering a sleep-like state) and less heat (until the body approaches the environmental temperature). So really, hibernation is the reduction of metabolism when food is scarce. Lack of activity and cold body temperatures are just the by-products.

Almost all species that hibernate are small mammals, including some hamsters, dormice, jumping mice, ground squirrels, marmots, woodchucks, bats, marsupials and monotremes. Bears, common examples of hibernating species, are actually debated by scientists as to whether they should even be considered hibernators due to the fact that their metabolisms and body temperatures do not decline as much as those of other hibernating species. The only bird species known to hibernate is the poorwill.

Each hibernating species has a specific range of body temperatures that their body can endure. Their first line of defense is to find a hibernaculum (a chamber or cavity in which to hibernate that is more insulated than the exposed environment). If the hibernaculum becomes so cold that the animal’s body temperature drops below its minimum endured range, it will either increase its metabolism slightly to raise its body temperature or it will arouse (wake up). Arousal is the process of increasing metabolic heat production to near-normal levels. All hibernating species seem to undergo multiple periods of temporary arousals during hibernation and scientists are still unsure why. Increasing the metabolism and body temperature from lower levels is an energetically costly process (similar to how your car uses more gas to accelerate than to maintain a higher speed). In most hibernating species, the process of increasing the metabolism uses a specialized tissue called brown fat.

Fat cells come in two main types: white fat and brown fat. White fat, the squishy stuff that we constantly try to diet and exercise away, is filled with lipids (fats) that we store to generate energy in the future. Brown fat cells also contains lipids, but they are specialized to break them down faster. Brown fat is found in newborn mammals and adult hibernators and is commonly located on the upper back, neck, chest and belly (like a vest) and around major arteries. Brown fat cells have lots of mitochondria (the metabolic parts of the cell that break down food molecules like lipids to generate energy). Brown fat mitochondria is specialized in that they have a protein called uncoupling protein 1 that causes them to generate heat rather than energy when they break down lipids. When the body becomes stressed, it releases norepinephrine, a stress hormone, which causes brown fat cells to increase the rate at which they break down lipids to generate heat. This heat warms the major arteries and increases blood flow, which then distributes the heat throughout the body.

A PET scan shows brown fat in a human.
Image by Hellerhoff at Wikimedia.
Although humans are born with a fair amount of brown fat, we lose it as we age. More specifically, it converts to white fat. We used to think that we lost it completely, but in recent years we have learned that some lean adults maintain a few pockets of brown fat in their necks and chests that obese people are more likely to lose. Researchers are currently exploring if and how we can convert some of our adult white fat to brown fat in order to increase our metabolisms and potentially combat obesity and diabetes.

So for now, we can’t hibernate the winter away. But continuing research into hibernating animals may hold an important secret to our own health.

Tuesday, January 22, 2019

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

Tuesday, December 18, 2018

Reindeer Games: 8 Surprising Facts About Reindeer

A reposting of an original article from December, 2017.

A Swedish reindeer watches you. Photo by Alexandre Buisse at Wikimedia Commons.

1. Reindeer are caribou (kinda): Reindeer are the same species as caribou (with the scientific name Rangifer tarandus), but the terms are not completely interchangeable. Rangifer tarandus is a species of deer that is native to Northern regions of Europe, Siberia and North America, which includes many different habitat types, like arctic, subarctic, tundra, snow forest and mountains. These variations in harsh environments have led to variations among populations, resulting in multiple subspecies. The Rangifer tarandus subspecies that live in North America are commonly called caribou and the subspecies that live in Europe and Siberia are commonly called reindeer. We also often refer to domesticated populations as reindeer, regardless of where they are.

A map of reindeer and caribou distributions. Image by TBjornstad at Wikimedia Commons.

2. Rudolf’s red nose was an adaptation: Technically, reindeer don’t have red noses, but they do have lots extra blood flow in them. The inside of their noses are twisted and vascularized so the warm blood can heat up the frigid Arctic air before it gets into the lungs.

3. Santa’s reindeer were probably girls: Not only do reindeer have the biggest antlers of all deer species (relative to body size), but they are the only deer species in which both males and females grow antlers. Both males and females use their antlers to scrape through the snow and look for food, but males also use their antlers to compete with one another and impress the ladies during the breeding season. Unlike horns, antlers shed and regrow every year, and this process is regulated by sex hormones. When the new antlers grow in spring, they are made up of cartilage and lots of blood vessels and are covered in a furry skin called velvet. The blood carries lots of calcium into the antlers, which helps them to grow and harden into bone. When testosterone levels drop in males at the end of their breeding season in early December, their antlers fall off. Females, however, generally keep their antlers until March or April. So, if Santa’s reindeer had antlers at the end of December, they were probably female!

4. If you’re going to pick an animal to travel the world in one night, reindeer are a good choice: Some North American caribou migrate over 3,000 miles a year (more than any other land mammal). They can run up to 50 miles per hour and swim over 6 miles per hour. Migration herds can be up to 500,000 animals and baby reindeer learn to run within two hours of birth!

A swimming caribou herd. Photo by Lestar Kovac at Wikimedia Commons.

5. Reindeer eat weird stuff: Like cows, reindeer are ruminants, which means their stomachs have multiple compartments, some of which specialize in maintaining microbial communities to help them digest. Unlike cows, reindeer predominantly eat lichen, which are combinations of algae and fungi that are typically high in carbohydrates and low in proteins. To make up for this low amount of protein in their diet, reindeer may occasionally eat rodents and bird eggs.

6. They have the coolest feet: Their hooves have four toes: two that splay out like snow shoes and two dew claws. Their hooves have sharp edges to dig for food and are paddle-shaped for swimming. Their hooves even change with the seasons to provide the best traction, being softer in the summer when the ground is soft and hard in the winter to walk on slippery snow and ice.

7. Some reindeer use clicking knees to communicate: Some subspecies have knees that click when tendons slip over bone extensions in their feet. They use this sound to stay with their herd, even when weather conditions limit visibility. But because larger reindeer have larger legs and therefore make louder knee-clicks, they also use these sounds to establish dominance.

8. Reindeer are the only mammals that can see UV light: They have a reflective layer in the back of their eyes that is golden in summer and blue in winter. When it is blue, this allows reindeer to see contrasts in UV light, such as lichen (which absorbs UV) versus snow (which reflects UV).

Tuesday, December 11, 2018

Not Fair! Even Dogs Know the Importance of Gift-Equity

A repost of an original article from December 2012.

Don't leave out your best friend when
gift-giving this holiday season!
Photo by Ohsaywhat at Wikimedia.
When I was a child, I think one of the things that stressed my mom out most about the holidays was making sure that all of us kids got Christmas gifts worth the exact same amount. Why all the fuss? Because if the value of the gifts wasn’t equal, we were guaranteed to spend our holidays in a chorus of “Not fair!” cries rather than appreciating the holiday bounty and cheer around us.

As a species, we have a pretty developed sense of fairness. This sense of fairness is central to our ability to cooperate to achieve goals that are too difficult for one person to accomplish alone. But we’re not the only social species that cooperates… and it turns out, we’re not the only ones with a sense of fairness, either.

Domestic dogs and their wild relatives, like wolves and African wild dogs, are very social and have cooperative hunting, territory defense, and parental care. Friederike Range, Lisa Horn, Zsófia Viranyi, and Ludwig Huber from the University of Vienna, Konrad Lorenz Institute, and Wolf Science Center, all in Austria, sought out to test whether domesticated dogs have a sense of fairness.

The researchers tested pairs of dogs who had lived together in the same household for at least a year. All of these dogs had been previously trained to give their paw on command, as if giving a handshake. Each pair of dogs was asked to sit in front of an experimenter (one dog was designated the “subject” and the other was the “partner”). In this position, the willingness of the subject dog to shake paws with the experimenter was tested under six different situations.

An experimenter asks two dog-buddies to each give her a paw and they wait
to see who gets rewarded. Photo from Range et al., PNAS, 2009.
In the basic situation, both dogs were asked to give a paw, and both dogs were rewarded with a “low-value” reward (a piece of bread). This happened repeatedly and the researchers measured how many times the subject dogs would give their paw.

In another situation, both dogs were asked to give a paw, but the subject dog was rewarded with a “low-value” reward (a piece of bread) while its buddy was rewarded with a “high-value” reward (a piece of sausage).

In a third situation, both dogs were asked to give a paw, but only the partner dog was rewarded with a piece of bread (the subject dog got nothing).

In the fourth situation, only the subject dog was asked to give a paw, but both dogs were rewarded with a piece of bread.

In the fifth situation, the experimenter measured how many times the subject dog would give its paw for a piece of bread if his doggy-buddy wasn’t around.

In the last situation, the experimenter measured how many times the subject dog would give its paw for no reward if his doggy-buddy wasn’t around.

When both dogs received bread, they were happy to keep giving the experimenter their paw for as long as they were asked to. But when dogs saw their buddy get a piece of bread when they got nothing, they soon refused to give their paw to the experimenter (and started showing signs of stress). You may think this is just what happens when you stop rewarding a dog for doing what you ask, but something different was going on here. The dogs that never got a reward gave their paw to the experimenter for longer when their buddy wasn’t around than if their buddy was around and getting bread treats. Clearly, even dogs know that equal work for unequal pay is not fair.

But the doggy-sense-of-fairness is limited. As long as they got their bread when they gave their paw, they really didn’t seem to care (or notice) if their buddy got bread or sausage, or even whether their buddy had to perform the same trick or not.

So this holiday season, don’t forget to get a present for your four-legged friend so he doesn’t feel left out. But don’t worry about getting something expensive – He doesn’t care anyway. For him, it’s the gesture that counts.

Want to know more? Check these out:

1. Range F, Horn L, Viranyi Z, & Huber L (2009). The absence of reward induces inequity aversion in dogs. Proceedings of the National Academy of Sciences of the United States of America, 106 (1), 340-5 PMID: 19064923

2. Range, F., Leitner, K., & Virányi, Z. (2012). The Influence of the Relationship and Motivation on Inequity Aversion in Dogs Social Justice Research, 25 (2), 170-194 DOI: 10.1007/s11211-012-0155-x