The Contagious Cancer (A Guest Post)

By Stephanie Stanton

The Tasmanian devil, perhaps more popularly known by its animated counterpart Taz in Warner Bros.’ “Looney Toons,” is a carnivorous marsupial native to Tasmania, an island off the southern coast of Australia. Similar to Taz, the Tasmanian devil lives a violent lifestyle. While a good portion of fights don’t go beyond screaming matches, sometimes (especially during the mating season) fights escalate to full-on biting matches. Unfortunately, it is this aggressive nature that has been linked to the alarming drop in Tasmanian devils’ numbers over the last decade. However, it is not violent wounds acquired during fights that are causing this rapid decline, but rather the Devil Facial Tumor Disease (DFTD), a contagious cancer.

DFTD is a transmissible cancer that operates as its own living entity- it is genetically distinct from its host and lives on its host’s face. Most of these tumors appear on their faces. Coincidentally, this also happens to be where a majority of open wounds are acquired in this species. Because of this, it is believed that DFTD is transferred through open wounds on the skin.

A healthy Tasmanian devil in all his glory. Photo by Chen Wu at Wikimedia Commons.

This cancer has been so successful in spreading throughout the population because of the devils’ small population size and low genetic diversity. Among the genes with low genetic diversity in the population is the Major Histocompatibility Complex (MHC), a collection of genes responsible for a strong immune response in vertebrates. Without a strong immune response, it is difficult to fight off serious threats such as DFTD. Unfortunately for the devils, the tumors growing on their faces do not even register on their limited immune system’s radar- so their bodies don’t even fight back! Because of this, DFTD is in most cases fatal within six to nine months of showing clinical symptoms.

A Tasmanian devil afflicted with DFTD. Photo courtesy of Menna Jones, available at Wikimedia Commons

Three Australian scientists by the names of Rodrigo Hamede, Hamish McCullum, and Menna Jones from the University of Tasmania and Griffith University recognized the alarming decline in the Tasmanian devil population and sought to find a way to better understand and control the spread of the disease. They looked at two separate populations over four seasons, collecting data once every three months by taking counts of bites on individual devils and tracking who got DFTD, when, and on what part of their bodies. They hypothesized that because the tumor was transmissible through open wounds, then the number of open wounds could be used as an early predictor for the onset of DFTD.

And they were right…although perhaps not in the ways they thought they would be. Contrary to what common sense would have everyone believe, devils with the least amount of facial wounds were the most likely to develop the fatal cancer. How could this be?

Simply put, it appears that the disease is getting transferred from devil to devil not because their bodies are exposed to a bite from an infected individual, but because devils are biting the tumors of infected individuals, thereby creating a direct path for the tumor to enter the new host.

The scientists argued that the devils that have the fewest open wounds were better at fighting and also the most aggressive (A side effect of the cancer? Perhaps.) Tasmanian devils are likely to have cuts or scrapes in their mouths because of their aggressive eating style, providing a port for the cancer cells to invade. It was because they were biting the tumors of the infected devils that they were contracting the disease, which also explains the higher occurrence of tumors in the mouth. Less aggressive devils accumulated more injuries to the face, but as long as the cancer cells did not come into contact with open wounds, their likelihood of contracting the disease was slim.

Rodrigo, Hamish and Menna hope that their results along with further research can help reduce the effects of the disease on the shrinking Tasmanian devil population by offering potential solutions to better control its spread. Exciting research published in 2016 is also already offering hope in keeping Taz and his furry counterparts alive for future generations to enjoy.


Want to know more? Check out the original article below:

Hamede, Rodrigo K., McCullum, H., Jones, M. (2013). “Biting injuries and transmission of Tasmanian Devil facial tumour disease. Journal of Animal Ecology. DOI: 10.1111/j.1365-2656.2012.02025.x.

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

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

Are Territory Disputes Between Male Butterflies Influenced by Motivation?

By Nick Gremban

Male speckled wood butterflies will “perch” on leaves
and ends of twigs to look out over their territory for females.
 However, they have been known to be quite aggressive
with any intruding males! Photo by Alvesgaspar at
Wikimedia Commons, modified by Nick Gremban.

Think about any territorial animal. Now think about its aggressiveness while it is defending its territory. Was your animal a butterfly? No? You mean the colorful wings and the natural association with flowers doesn’t strike a fierce image of aggression in your mind? Well, the truth is some butterflies are very territorial and aggressive toward one another, contrary to what we expect.

Male butterflies do not have physical means to inflict harm to one another when it comes to territorial disputes. Instead, two or more males may stage “contests” with each other which often involve elaborate aerial chases. For example, a male that flies into the territory of another male will set off a pursuit by the resident male, resulting in both flying in circles around each other until one eventually gives up and is chased out of the territory. Normally, winners of the contests are the males that are able to endure the longest flights. An example of what these competitions look like can be seen from this video:

Researchers have been puzzled by what determines which male butterfly wins a contest. Some researchers have thought body size should determine who wins the contest. After all, isn’t being bigger always better? Turns out for many butterflies, it’s quite the opposite, with smaller butterflies of some species winning contests more. What about age? Shouldn’t the most experienced butterflies have better odds at winning? Again, the opposite is often true, with some studies finding younger males having better odds at winning competitions. How about motivation? Could some male butterflies be motivated by something that gets them revved up? Researchers from Stockholm University in Sweden seem to think so!

In a study conducted by Martin Bergman, Martin Olofsson, and Christer Wiklund from Stockholm University, male speckled wood butterflies were tested by observing the number of contest rematches won by males that were subject to a source of motivation: a female speckled wood butterfly. Females are a primary purpose to why males hold territories, so interactions with them before a contest was thought to serve as motivation.

The researchers staged their experiment in a series of steps. The first step consisted of introduced contests between two male speckled wood butterflies over a territory, or in this experiment, a sunspot. In total, 60 pairs of males were used to conduct this experiment. Males that won five consecutive contests were considered “winners” and given the status of being the resident male over the sunspot. Afterwards, winners were temporarily removed from the sunspot they just previously won.

Get out of my sunspot! Photo by Martin Bergman.

All males that lost the contests were considered “losers” and were split in to two groups. The first group was allowed to interact with a female for 30 minutes. Males in the second group were placed alone in a cage for 30 minutes. Afterwards, each male was allowed back to the sunspot, now vacant of the winner. After each of the losing males took over the sunspot, therefore claiming themselves as the new resident male, the winners were then returned to the sunspot. The return of the winners allowed rematches of contests. Researchers recorded contest duration and if the males that lost the first round of contests won their rematches.

Loser males that had the chance to interact with a female won 53% of rematches while loser males placed alone only won 17% of rematches. In other words, males that interacted with a female endured longer flights to win their rematch. Furthermore, these same males were more likely to claim the vacant sunspot.

Male speckled wood butterflies
will “fight” over a female (such
as this one)…doesn’t this
concept sound familiar? Photo by
Mark Colvin at Wikimedia Commons.

Overall, the researchers suggested that the males which had interacted with a female had an increased motivation to fight harder on the rematch to win the sunspot. Just like with many other animals, male butterflies are willing to compete for the girl! The presence of a female may serve as a cue for the males that a particular territory is worth fighting for. After all, isn’t reproduction the name of the game?

Butterflies prove to be more mysterious and complex than we typically expect. Not only can they express territoriality without true physical means to harm each other, but they appear to be influenced by motivation! So, next time you see two butterflies fiercely circling each other in flight, you now know they mean serious business.


References

Bergman, M., Olofsson, M., & Wiklund, C. (2010). Contest outcome in a territorial butterfly: the role of motivation Proceedings of the Royal Society B: Biological Sciences, 277 (1696), 3027-3033 DOI: 10.1098/rspb.2010.0646

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.

Song Battles With Other Species Can Change Your Tune

Many animals defend territories from members of their own species for mating, breeding, and finding food and they often use species-specific vocalizations to do this. Defending a territory can be risky and costly in both energy and time, so even territorial animals generally don’t waste this effort on other species that do not share their same food and breeding needs. But what do you do if you live around another very similar species that has the same needs that you do? Can two species learn to speak each other’s languages to live in territorial harmony?


A common nightingale.
Photo by Frebeck at Wikimedia Commons.

A thrush nightingale.
Photo by Locaguapa at Wikimedia Commons.

Today at Accumulating Glitches, I tell the story of two species of nightingales and how they are learning to sing each other's songs to defend their territories! Check out the article here.

War and Peace



A group of Gelada baboons in Ethiopia.
Photo by A. Davey at Wikimedia Commons.

Syria and Iraq. Ukraine. The Gaza Strip. People are dying in large numbers at the hands of other humans, and for what? Land and resources? Is it really worth it? It is often said that humans are the only species so horrific as to kill its own species in war. But the fact is, we are not alone in what was previously thought to be a uniquely human trait. In many animal groups, individuals will band together in collective defense of territory and resources.

This week at Accumulating Glitches I talk about how group size influences the ability of primate groups to hold their territories. Check it out here.

And to learn more, check this out:

Willems, E.P. Hellriegel, B. and van Schaik, C.P. The collective action problem in primate territory economics, Proceedings of the Royal Society B, 280: 20130081 (2013). DOI: 10.1098/rspb.2013.0081.

The Craptastic Conversations of the Black Rhinoceros

What are you saying with your smells? Image by freedigitalphotos.net.

Animals communicate in all kinds of ways: with vocalizations, body language, vibrations, and even odors. In fact, compared to most species, we are pathetic in our abilities to communicate with body odor. With just a whiff of eau de crotch, many animals can decipher that individual’s species, sex, age, health status, reproductive status, emotional state, and dietary history. Some species can go so far as to make out that individual’s exact identity (*Sniff Sniff* Oh! Hi Mike!).

There are a lot of advantages to using odors to communicate. For one thing, messages sent by smell are more likely to be honest than messages sent by other means. (You might be able to do a pretty good Shakira impersonation, but you can’t hide the fact that you had a tuna sandwich for lunch and haven’t brushed your teeth since). Another advantage is that unlike other signal types, an odor signal can be left behind, kind of like those sticky-notes you leave on your food in the fridge.

How do scientists know which species use odors to communicate and what information these signals contain? This investigatory process involves a lot of reasoning.

A solitary black rhino. Photo by John and Karen Hollingsworth
at the US Fish and Wildlife Service.

Wayne Linklater, Katha Mayer and Ron Swaisgood, an international team of researchers associated with Victoria University of Wellington in New Zealand, Nelson Mandela Metropolitan University in South Africa, University of Potsdam in Germany, and the San Diego Zoo Institute for Conservation Research in California, set out to test whether black rhinoceros use odor to communicate. Although rhinos lack the specialized scent glands that many smell-communicating species have, there are many reasons to suggest that they are a likely species to communicate this way.

A photo of field assistant Brayden
Crocker with rhino dung scrape mark.
Photo by Wayne Linklater.

Black rhinos are solitary. Females often have overlapping ranges, but males’ territories only overlap at their boundaries. This means that they would rarely encounter one another and would benefit from a means to leave “sticky-notes” behind to indicate where their territories are. Furthermore, despite their poor eyesight, male black rhinos have a poop-ritual in which they scrape at the ground and spread their dung. Although female rhinos don’t spread their poo, they do spray their pee when they are ready to mate.

Between 2004 and 2006, the Ezemvelo KwaZulu-Natal Wildlife Veterinary and Game-Capture Team captured a number of black rhinoceros from the Ezemvelo KwaZulu-Natal Wildlife Reserves in South Africa in order to relocate them to other reserves for conservation purposes. At this time, Wayne, Katha, and Ron collected dung from rhinos with known sexes and ages. They stored the dung in labeled plastic bags and froze them to preserve the odor freshness for a series of experiments to explore the extent of the black rhinos’ abilities to communicate with their bodily waste.

In one experiment, the researchers asked whether black rhinos could differentiate between the dung of males and females and between the dung of adults and immature subadults. They presented rhinos with the dung of young males, young females, adult males and adult females, and then measured how many times they sniffed each and how long they spent sniffing. The rhinos spent more time sniffing male dung than female dung. This means that rhino poop likely communicates the sex of the pooper. Rhinos also responded differently to adult and subadult poop, suggesting that they can tell whether the pooper is an adult or not.

In order to test whether rhinos may be able to tell the individual identity of the pooper, they did a habituation-dishabituation test. Habituation is when an animal gets used to something that happens repeatedly and stops responding to it. For example, the first time you heard Gangnam Style, you probably stopped what you were doing and maybe even learned the dance. But now it has been so ridiculously over-played that when you hear it, you just ignore it. Dishabituation happens when an animal is exposed to something slightly different and has a heightened response again. Kind of like the excitement over Psy’s new song, Gentleman, even though it sucks.

A photo of rhino performing flehmen, a behavior that helps
waft odors for better odor detection. Photo by Wayne Linklater.

Wayne, Katha, and Ron exposed rhinos to the same individual’s dung three times to see if their interest in it waned. With each presentation, the rhinos spent a little less time sniffing it. When the researchers put poop from a different rhino (that was the same sex and age as the first pooper) in front of them, their interest returned. This suggests that rhinos can tell the individual identity of the pooper from his/her poop.

But can rhinos use their poop like “sticky-notes”? The researchers aged dung for 1, 4, 16 and 32 days and put them in front of rhinos to smell. Their response was the same, no matter how old the dung was. This indicates that rhinos can spread their poop to leave an “I was here” message for at least a month.

As fun as it may be to spend years studying rhinoceros poop, there are some important uses for research like this. Black rhinos are critically endangered, largely due to hunting, poaching and habitat loss. In fact, Mozambique's Limpopo National Park declared the last of their rhino population killed as recently as last month. Conservation efforts such as captive breeding programs and reintroductions have helped in several areas, but have not been enough to sustain the populations. Conservationists could apply this knowledge of how rhinoceros use dung odors to communicate to these breeding and reintroduction efforts in order to make them considerably more successful.


Want to know more? Check this out:

Linklater, W., Mayer, K., & Swaisgood, R. (2013). Chemical signals of age, sex and identity in black rhinoceros Animal Behaviour, 85 (3), 671-677 DOI: 10.1016/j.anbehav.2012.12.034

Competitive Females

Paula Broadwell, the aggressive competitor.
Photo from her Facebook page.

By now, you’ve probably heard all about Paula Broadwell, the woman that seduced the notoriously disciplined CIA director, four-star US Army general, husband and father, General David Petraeus. What kind of a woman might be able to sway a man that has such admirable self-control? Broadwell was Petraeus’ biographer, a West Point graduate with a Harvard graduate degree, an Army Reservist thrice recalled to active duty, a fitness champion, Ironman triathlete and even a machine gun model. Her accomplishments are clearly impressive, but maybe the key comes down to her competitive nature. I mean, she did send several threatening e-mails to an attractive socialite and Petraeus family friend, warning her to stay away from her (other) man.

When we think about competing for mates, we generally think about males competing for females and breeding territories with horns to duke it out, or elaborate feathers to show off, or dance-offs to demonstrate their physical abilities. But females often have to compete for the high-quality males and breeding territories too. And many of the concepts that apply to males competing for females have been found to also apply to females competing for males.

A dark-eyed junco thinking
"What you lookin' at?".
Photo by Kristal Cain.

As much as we know about males competing with one another, we know surprisingly little about females competing with one another, although they clearly do. Kristal Cain and Ellen Ketterson at Indiana University sought out to shed light on female competition and its effect on breeding success. They did this with female Carolina dark-eyed juncos, a socially monogamous songbird species in which both parents care for the young. They were curious whether more aggressive females would also have other competitive traits, like large body size. They also wondered whether aggressive females would have better breeding success.

The researchers caught female juncos to measure and put identifying leg bands on them. They then released them and spent their nesting season looking for their nests. When they found a nest, they identified whose nest it was by the female’s leg bands. The researchers tested how aggressive females were towards competing females by placing a caged female within 3 meters of a subject’s nest and watching to see if she swooped at the caged female. Then they kept an eye on the nest to see if the chicks all survived until they fledged (left the nest on their own) or if the nest was destroyed (usually by a predator) before the chicks fledged.

A female junco in full-on attack mode. Photo by Kristal Cain.

Females that were more aggressive towards “competing” females tended to be bigger and had chicks that were more likely to fledge. Now, if this were a story about competitive males, we might think big aggressive males with more successful chicks might have higher testosterone. Alternatively, low testosterone is often found in males that are better fathers. But these are females… Does it even make sense to talk about testosterone in females? Of course it does! Turns out, males don’t have a monopoly on testosterone; females have it too.

The researchers drew blood from the females and then gave them a “testosterone challenge” by injecting them with a hormone called gonadotropin-releasing hormone (or GnRH for short). GnRH is a trigger that causes a series of biological events that result in the gonads producing more hormones, including testosterone. The researchers then drew a second blood sample to measure how much testosterone levels changed in response to the GnRH injection.

More aggressive females produced more testosterone in response to the GnRH injection than did less aggressive females. This same effect has also been shown to be true of males behaving aggressively towards each other. I guess males and females really aren’t all that different, eh? But interestingly, females that produced more testosterone in response to the GnRH challenge also had more successful nests.

It’s important to keep in mind that these results are correlational. Maybe testosterone makes females bigger and more aggressive and better mothers. Or perhaps having a temper increases your testosterone production. Or maybe some other hormone that increases in response to GnRH (there are many) is responsible for the effects. In any case, females that are bigger and more aggressive and have more successful offspring also produce more testosterone in response to a GnRH injection.

Paula Broadwell shows off her aggressive abilities in this KRISS ARMS video
(gif'd by Michael Pakradooni).

As far as we know, no one has given Paula Broadwell a testosterone challenge, but she undoubtedly has a number of correlated competitive traits. Paula Broadwell is a competitive, physically fit, attractive parent who has shown that she can out-compete the spouses of high-quality mates… But then again, so is David Petraeus.

Want to know more? Check this out:

Cain, K., & Ketterson, E. (2011). Competitive females are successful females; phenotype, mechanism, and selection in a common songbird Behavioral Ecology and Sociobiology, 66 (2), 241-252 DOI: 10.1007/s00265-011-1272-5

Mmm… The Scent of a Stud

Your smell can say a lot about you… How often you bathe, for example. But in many species, smells can communicate much more… What else might they be saying? And how do you ask them?

What secrets do we hide
when we put on deodorant
and perfume? Image by
freedigitalphotos.net.

Field crickets are one of many species that use pheromones, compounds released by an animal that affect the physiology and/or behavior of others of the same species. Female field crickets can recognize individual males by the pheromones they produce… That is pretty specific information! If females can smell who a male is, what else can she tell about him based on his pheromones?

Male field crickets fight for and defend both females and shelters. Furthermore, females are very picky about what males they mate with and tend to go for males who are better fighters. Raine Kortet and Ann Hedrick at the University of California at Davis asked female field crickets whether they could smell the difference between winners and losers.

Raine and Ann took pairs of male crickets that were the same age and size and placed each one on a separate piece of filter paper in a petri dish for 24 hours. This process infuses each filter paper with that particular crickets’ pheromones. Then they put each of the two pheromone-infused filter papers, plus a third clean filter paper, into an arena. They placed a female in the arena and timed how long she spent on each of the three filter papers. Then they repeated the whole process again with another 58 pairs of males.

Next, Raine and Ann put the size-matched pairs of males together in the same arena and allowed them to compete. Cricket fights generally involve wrestling and biting and then one of the crickets will retreat and avoid his dominant competitor. At this point, they were assigned the ranks of “dominant” (winner) and “subordinate” (loser).

This drawing by Edward Julius Detmold from the 1921 book
Fabre's Book of Insects depicts a dominant cricket defending his
shelter while a subordinate cricket retreats. Image from Wikimedia.

Females spent way more time on the pheromone-infused filter papers than on the clean filter papers. But even more fascinating, the females spent more time on the filter papers infused with the dominant male smell than the papers that smelled like losers. Remember, this was before the males even competed. So now female crickets can predict the future?! …Yeah, kinda. Females can smell which males will win.

But maybe this isn’t as mysterious as it looks at first glance. Pheromones are chemical compounds created by the body – the very same body that wins or loses fights. Bodies that are not in good shape may not be able to produce high-quality pheromones. Another possibility is that the same hormones that influence dominant behavior and fighting ability may also influence pheromones. Or maybe males that are more energetic simply move around more and deposit more scent on the paper. In any case, by picking up the scent of the dominant male, females may be able to choose a mate that is a good fighter, in good physical health, and who may pass these traits on to her offspring.

When you think about it that way, smells can contain a lot of information… So be careful what signals you’re putting out there.

Want to know more? Check this out:

Kortet, R., & Hedrick, A. (2005). The scent of dominance: female field crickets use odour to predict the outcome of male competition Behavioral Ecology and Sociobiology, 59, 77-83 DOI: 10.1007/s00265-005-0011-1

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