Mind-Manipulating Slave-Making Ants!

A reposting of an article from October 10, 2012.

An entire colony enslaved by an alien species to care for their young. Slave rebellions quelled by mind manipulation. It sounds like science fiction, right? But it really happens!

Myrmoxenus ravouxi (called M. ravouxi for “short”) is a slave-making ant species in which the queen probably wears a chemical mask, matching the scent of a host species in order to invade their nest without detection. Once inside, she lays her eggs for the host species workers to care for. Armies of M. ravouxi workers then raid these host colonies to steel their brood to become future slave-laborers to serve the needs of the M. ravouxi colony.

A M. ravouxi queen throttling a host queen. Photo by Olivier Delattre.

Enslaved worker ants could rebel: They could destroy the parasite brood or at least not do a good job caring for them. But to selectively harm the parasite brood without harming their own nests’ brood, the host ants would have to be able to tell them apart. Ants learn the smell of their colony in their youth, so any ants born to an already-parasitized colony would likely not be able to tell apart parasite ants from their own species. But what about ants that were born to colonies before they were invaded?

Olivier Delattre, Nicolas Châline, Stéphane Chameron, Emmanuel Lecoutey, and Pierre Jaisson from the Laboratory of Experimental Ethology in France figured that compared to ant species that were never hosts to M. ravouxi colonies, ant species that were commonly hosts of M. ravouxi colonies would be better able to discriminate their own species’ brood from M. ravouxi brood. Host species may even be better at discriminating in general.

The researchers collected ant colonies from near Fontainebleau and Montpellier in France. They collected M. ravouxi colonies and colonies of a species that they commonly parasitize (but were not parasitized at the time): Temnothorax unifasciatus (called T. unifasciatus for “short”). The researchers also collected T. unifasciatus that were parasitized by M. ravouxi at the time. Additionally, they collected colonies of T. nylanderi and T. parvulus, two species that are never parasitized by M. ravouxi. (Sorry guys. All these species go by their scientific names. But really, that just makes them sound all the more mysterious, right?). The researchers took all their ant colonies back to the lab and housed them in specialized plastic boxes (i.e. scientific ant-farms).

On the day of the tests, the scientists removed a single pupa (kind of like an ant-toddler) from one nest and placed it into a different nest of the same species or back in its own nest. They did this for colonies of both non-host species and for colonies of host species T. unifasciatus that were not parasitized at the time. Then they counted how many times the workers bit the pupa (an aggressive behavior) or groomed the pupa (a caring behavior).

Workers from all three species bit the pupa that was not from their colony more than they bit their own colony’s pupa. But the T. unifasciatus (the host species) were even more aggressive to foreign pupa than the other species. And only the T. unifasciatus withheld grooming from the pupa that was not from their colony compared to the one that was from their colony. Although all three species seemed to be able to tell the difference between a pupa from their own nest versus one from another nest, only the species that is regularly enslaved by M. ravouxi decreased care to foreign young. So that is what these ants do when they are not enslaved. How do you think enslaved ants respond to their own species’ young compared to M. ravouxi young?

A 1975 cover of Galaxie/Bis, a French science
fiction magazine, by Philippe Legendre-Kvater.
Image from Wikimedia.

The researchers repeated the study using enslaved T. unifasciatus, placing either a pupa of their own species from a different nest or a M. ravouxi pupa in with their brood. Even though prior to M. ravouxi takeover the T. unifasciatus bit foreign pupa more than their own, after M. ravouxi takeover they didn’t bite foreign pupa of their own species or M. ravouxi pupa very much. Not only that, but they groomed the M. ravouxi pupa more than the pupa of their own species! Ah hah! Mind control!

This, my friends, is the kind of truth that science fiction is made from.

But how might this work? Ants born to an enslaved colony would be exposed to both their own odors and the M. ravouxi odors. Because ants learn the smell of their colony in the first few days after they emerge from their eggs, these enslaved ants would have a broader set of smells that they may perceive as being “within the family”. That would explain why the enslaved T. unifasciatus ants didn’t attack either the foreign-born T. unifasciatus or the M. ravouxi young, but it doesn’t explain why the enslaved ants provided more care to the M. ravouxi than they did to their own species. One possibility is that the M. ravouxi produce more or especially attractive odors to encourage the host workers to take care of them.

There is still more to learn about this system: How exactly may the M. ravouxi be hijacking the pheromonal systems of their host species? How are the host species protecting themselves from exploitation? I guess we’ll have to wait for the sequel.

Want to know more? Check this out:

Delattre, O., Chȃline, N., Chameron, S., Lecoutey, E., & Jaisson, P. (2012). Social parasite pressure affects brood discrimination of host species in Temnothorax ants Animal Behaviour, 84, 445-450 DOI: 10.1016/j.anbehav.2012.05.020

Miss Behavior’s Picks of 2012

The "Best in Show" for 2012:
The Top 5 Animal Physiology
and Behavior Blog Posts of 2012.
Photo from freedigitalphotos.net.

‘Tis the season for year-end lists. As we sift through lists of the most downloaded songs, most popular books, best movies, most interesting people, and most embarrassing moments of 2012, I would feel remiss if I did not contribute my own year-end list for the best animal physiology and behavior blog posts. There have been so many great blog posts across the interwebs this year, it was hard to choose. These are my picks for The Top 5 Animal Physiology and Behavior Blog Posts of 2012 (not including The Scorpion and the Frog posts, of course, and in no particular order).

1. Paternal care is rare in the animal kingdom. Males taking care of babies that aren’t even their own is exceptional. Elizabeth Preston in Inkfish talks about the strange case of a snail species in which males don’t just care for their own babies, but other snails’ babies too in Long-Suffering Snail Dads Carry Illegitimate Babies.

2. Jordan Gaines at Gaines, on Brains explains exactly what happens to your cat when you give her that catnip-filled toy in Catnip Fever: Why Your Cat Acts High.

3. Chimpanzees don’t just use tools, but they carefully select them. Jason Goldman at The Thoughtful Animal writes about how scientists discovered this chimpanzee decision-making process in For Chimps, Tool Choice Is A Weighty Matter.

4. Everything you have ever wanted to know about turtle penises (and much, much more) is brilliantly explained in Tetrapod Zoology by Darren Naish at Terrifying Sex Organs of Male Turtles.

5. In Not Exactly Rocket Science, Ed Yong explains how fairy wrens know which babies are theirs in Fairy Wrens Teach Secret Passwords to Their Unborn Chicks to Tell Them Apart From Cuckoo Impostors.

Enjoy!

Mind-Manipulating Slave-Making Ants!

An entire colony enslaved by an alien species to care for their young. Slave rebellions quelled by mind manipulation. It sounds like science fiction, right? But it really happens!

Myrmoxenus ravouxi (called M. ravouxi for “short”) is a slave-making ant species in which the queen probably wears a chemical mask, matching the scent of a host species in order to invade their nest without detection. Once inside, she lays her eggs for the host species workers to care for. Armies of M. ravouxi workers then raid these host colonies to steel their brood to become future slave-laborers to serve the needs of the M. ravouxi colony.

A M. ravouxi queen throttling a host queen. Photo by Olivier Delattre.

Enslaved worker ants could rebel: They could destroy the parasite brood or at least not do a good job caring for them. But to selectively harm the parasite brood without harming their own nests’ brood, the host ants would have to be able to tell them apart. Ants learn the smell of their colony in their youth, so any ants born to an already-parasitized colony would likely not be able to tell apart parasite ants from their own species. But what about ants that were born to colonies before they were invaded?

Olivier Delattre, Nicolas Châline, Stéphane Chameron, Emmanuel Lecoutey, and Pierre Jaisson from the Laboratory of Experimental Ethology in France figured that compared to ant species that were never hosts to M. ravouxi colonies, ant species that were commonly hosts of M. ravouxi colonies would be better able to discriminate their own species’ brood from M. ravouxi brood. Host species may even be better at discriminating in general.

The researchers collected ant colonies from near Fontainebleau and Montpellier in France. They collected M. ravouxi colonies and colonies of a species that they commonly parasitize (but were not parasitized at the time): Temnothorax unifasciatus (called T. unifasciatus for “short”). The researchers also collected T. unifasciatus that were parasitized by M. ravouxi at the time. Additionally, they collected colonies of T. nylanderi and T. parvulus, two species that are never parasitized by M. ravouxi. (Sorry guys. All these species go by their scientific names. But really, that just makes them sound all the more mysterious, right?). The researchers took all their ant colonies back to the lab and housed them in specialized plastic boxes (i.e. scientific ant-farms).

On the day of the tests, the scientists removed a single pupa (kind of like an ant-toddler) from one nest and placed it into a different nest of the same species or back in its own nest. They did this for colonies of both non-host species and for colonies of host species T. unifasciatus that were not parasitized at the time. Then they counted how many times the workers bit the pupa (an aggressive behavior) or groomed the pupa (a caring behavior).

Workers from all three species bit the pupa that was not from their colony more than they bit their own colony’s pupa. But the T. unifasciatus (the host species) were even more aggressive to foreign pupa than the other species. And only the T. unifasciatus withheld grooming from the pupa that was not from their colony compared to the one that was from their colony. Although all three species seemed to be able to tell the difference between a pupa from their own nest versus one from another nest, only the species that is regularly enslaved by M. ravouxi decreased care to foreign young. So that is what these ants do when they are not enslaved. How do you think enslaved ants respond to their own species’ young compared to M. ravouxi young?

A 1975 cover of Galaxie/Bis, a
French science fiction magazine,
by Philippe Legendre-Kvater.
Image from Wikimedia.

The researchers repeated the study using enslaved T. unifasciatus, placing either a pupa of their own species from a different nest or a M. ravouxi pupa in with their brood. Even though prior to M. ravouxi takeover the T. unifasciatus bit foreign pupa more than their own, after M. ravouxi takeover they didn’t bite foreign pupa of their own species or M. ravouxi pupa very much. Not only that, but they groomed the M. ravouxi pupa more than the pupa of their own species! Ah hah! Mind control!

This, my friends, is the kind of truth that science fiction is made from.

But how might this work? Ants born to an enslaved colony would be exposed to both their own odors and the M. ravouxi odors. Because ants learn the smell of their colony in the first few days after they emerge from their eggs, these enslaved ants would have a broader set of smells that they may perceive as being “within the family”. That would explain why the enslaved T. unifasciatus ants didn’t attack either the foreign-born T. unifasciatus or the M. ravouxi young, but it doesn’t explain why the enslaved ants provided more care to the M. ravouxi than they did to their own species. One possibility is that the M. ravouxi produce more or especially attractive odors to encourage the host workers to take care of them.

There is still more to learn about this system: How exactly may the M. ravouxi be hijacking the pheromonal systems of their host species? How are the host species protecting themselves from exploitation? I guess we’ll have to wait for the sequel.

Want to know more? Check this out:

Delattre, O., Chȃline, N., Chameron, S., Lecoutey, E., & Jaisson, P. (2012). Social parasite pressure affects brood discrimination of host species in Temnothorax ants Animal Behaviour, 84, 445-450 DOI: 10.1016/j.anbehav.2012.05.020

It Doesn’t Always Pay to Kill Your Siblings

A mother reed warbler feeding her "adoptive"
murderous cuckoo chick. Does she really think
this is her child? Photo by Per Harald Olsen
on Wikimedia Commons.

A woman, driven to not raise her own child, leaves her baby in another woman’s nursery, killing another baby that is there and replacing it with her own. As soon as the transplanted baby is strong enough, it slowly, methodically kills all the other children in the nursery, hording all of the adoptive mother’s attention for itself. With time, it grows needier and more demanding, running the poor adoptive mother ragged trying to care for the monstrous child that had murdered all her own children.

It may sound like the plotline of a horror flick, but it happens every year among several egg-laying species (granted, maybe without quite so much anthropomorphism and drama). Animals that lay their eggs among the egg clutches of other species and benefit from the “hosts” parenting their young are called obligate brood parasites. Like the creepy narrative above, the still-naked, recently-hatched offspring of many obligate brood parasites attack and kill the offspring of their hosts to ensure more parental attention.

Cuckoo chicks are well known to kill their “step-siblings” (the nestmates that are the chicks of their host parents) by pushing them out of the nest. Caution: Watching this BBC video can have emotional consequences:
 

The researchers observed the nests of two common shiny cowbird host species: the house wren, a much smaller host than the cowbird, and the chalk-browed mockingbird, a larger host than the cowbird. For each nest, they either placed a combination of one cowbird egg and a few host eggs, or one cowbird egg and a few artificial eggs. When the eggs hatched, this resulted in some cowbirds having host “step-siblings” and other cowbirds being “only children”. When the chicks were 4 days old and 8 days old, the researchers videotaped each nest, and measured how much food each chick was getting fed and each chick’s weight and tarsus length (that’s the length of one of the leg bones and gives a good method to compare body sizes in birds).

This is a picture of begging chicks in a parasitized nest of a
chalk-browed mockingbird, taken from a video. The chick with
the smaller, redder gape at the top of the image is the cowbird.
The other larger gapes belong to the mockingbird's own chicks.
Photo by Ros Gloag.

Overall, cowbirds grew to similar sizes at similar rates regardless of whether they were raised by mockingbird or house wren parents. But the presence or absence of nestmates had an interesting effect. Among cowbirds raised in mockingbird nests, cowbirds raised with nestmates faired far worse than cowbirds raised alone. Although mockingbird parents worked much harder and brought back more food to nests with more chicks (probably because the begging coming from the nest as a whole was much more rambunctious), cowbirds with mockingbird step-siblings had to share the provisions, whereas lone cowbird chicks got to eat everything the parents returned with. To make things worse, the mockingbird chicks grew faster than the cowbird chicks and they quickly outcompeted them. By the eighth day, cowbirds raised alone were larger and had higher survival rates than cowbirds raised with mockingbird step-siblings.


This graph shows how much food the parents gave to the shiny cowbird chick, depending on whether the chick had mockingbird or wren parents and on whether it had nestmates (mixed) or was alone. The dashed bars show the total amount of food brought back to the nest for nests with nestmates. Notice that although nests with nestmates had the most food brought to the nest (dashed bars) in all cases, the shiny cowbird chicks with mockingbird parents got more food on day 8 if they were alone than if they had nestmates (solid bars) and the shiny cowbird chicks with wren parents got more food on day 8 if they had nestmates than if they were alone (solid bars). Graph from Gloag, et. al 2011 Behavioral Ecology paper.

However, among cowbirds raised in house wren nests, cowbirds raised with wren step-siblings faired far better than cowbirds raised alone. As did the mockingbird parents, wren parents worked much harder and brought back more food to nests with more chicks. The cowbird chicks grew faster than the wren chicks, and so the cowbirds managed to eat more than their fair share of provisions. Additionally, sharing a nest with nestmates can have other benefits as well, such as helping to keep warm. As a result, cowbirds raised with wren step-siblings grew larger than cowbirds raised without wren step-siblings.

We don’t yet know whether obligate brood parasite chicks with multiple host species adjust their strategy (kill or tolerate) depending on the size of the host chicks, but this study suggests that they might. If you are interested in science, this may be a topic you could explore.

At any rate, killing your siblings or step-siblings probably isn’t a wise thing to do. They can help encourage our parents to do more for us, they can keep us warm, and when they’re not looking we can “borrow” their stuff. Besides, birds don’t have the same morals, ethics and court systems that we do.


Want to know more? Check this out:

Gloag, R., Tuero, D., Fiorini, V., Reboreda, J., & Kacelnik, A. (2011). The economics of nestmate killing in avian brood parasites: a provisions trade-off Behavioral Ecology, 23 (1), 132-140 DOI: 10.1093/beheco/arr166