Tag / predation

by Roslyn

A microscopic predator-prey chase

In terms of behaviour, animals have plants beat – though some would argue that plants have their own brand of intelligence.

Not all photosynthesizing beasts are firmly planted, though, and many that live in the water can move. Aquatic algae, for instance, often have whip-like structures (called cilia and flagella) that they can use to propel themselves along in the water. Some land plants also produce flagellated sperm that can move on their own volition.

H. akashiwo

A single-celled marine algae with flagella for getting around. From Wikimedia.

In the ocean, the ability to move can be beneficial, allowing algal cells to find food or move to a suitable environment. Motile cells can also avoid their predators by swimming away – something land plants definitely cannot do. Swimming algae incredibly slow, topping out at about half a centimetre per minute – but a new study suggests that the slow race between algae and their predators might be responsible for a far bigger, more dangerous phenomenon.

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by Roslyn

Cuttlefish strike a pose for 3D camouflage

In the game of hide and seek, cuttlefish have the upper hand. These chameleons of the sea are astonishingly good at disappearing: they can instantaneously change the colour of their skin to blend in with the background, matching even the finicky details like the pattern of coloured rocks on the ocean floor.

Divers have long known that cuttlefish are masters of the 3D camouflage game, too, and new research from the Wood’s Hole Oceanographic Institute has revealed how they do it.

Alexandra Barbosa, a graduate student, and Dr. Roger Hanlon were interested in the way cuttlefish strike a pose when trying to hide. After encountering a predator, these octopus-like animals will flee among the corals, rocks and algae, and freeze with their arms contorted into shapes that mimic nearby objects – a feat made all the more impressive by the fact that cuttlefish arms can bend in any direction. Some birds and insects are also known to camouflage themselves with body posture, but few come close to cuttlefish in shape-shifting flexibility (see photos of cephalopod camouflage in the wild here).

To understand just how they do it, Barbosa and her colleagues in Dr. Hanlon’s lab presented captive cuttlefish with some highly unusual surroundings: jailbird stripes, in black and white. In response, the cuttlefish got theatrical, raising their arms roughly parallel to the angle of the stripes. And when the researchers shifted the angle of the background image, the cuttlefish stretched their arms into a new position in an attempt to stay hidden.

Cuttlefish posing on artificial backgrounds

Cuttlefish posing against different backgrounds. Modified from Barbosa et al. 2011 (see Figure 1).

Intriguingly, not all of the ten individuals tested were able to match the angle perfectly all of the time – but these quirks may not be surprising given that cuttlefish camouflage is so complex. After all, in nature cephalopods get to choose their own hiding places, a decision that might involve several different factors. According to the researchers, camouflaged cuttlefish are even known to gently wave their arms to match the movement of the underwater plants they are trying to mimic.

These results are a clear demonstration that cuttlefish use vision to guide their 3D camouflage, since the study animals matched a flat background image. Moreover, Barbosa and Hanlon have shown that shape-shifting cephalopods can easily handle scenarios that would never occur in the environment where these behaviours evolved, and adjust just as flexibly to this artificial environment as they do in their natural habitats.

Captive experiments like this are just the first step in understanding how cuttlefish use visual cues to hide, and some big questions remain. For instance, little is known about how cuttlefish can detect and match colours so well despite the fact that they are, in effect, colourblind – Hanlon has found that giant Australian cuttlefish can take on the colouration of rocks on the ocean floor even in the middle of the night.

These remarkable split-second decisions about where, and how, to hide might also help us understand something bigger. Strategic camouflage is just one aspect of the surprising intelligence of cuttlefish, which have the largest brains for a given body size of any invertebrate – these animals are also able to learn and communicate with one another at a level that rivals many land-based animals. It will be intriguing to see where hide and seek fits in to the history of cephalopod brain evolution.

Further Reading

Barbosa, A. et al. 2011. Proceedings of the Royal Society B. In press.

by Roslyn

How I learned to respect the peahen

Written for the Los Angeles Arboretum.

Meep meep? More like “Honk honk!”

Arboretum regulars will no doubt recognize the call of a startled peahen, but you may not be aware of the clever ways they use it. Not that they try to boast or taunt the enemy, necessarily, but I’m starting to think that the birds at the Arboretum owe a lot to their version of the Road Runner’s call.

How do I know? Some background is in order here: I’m the tall blond woman who has been hanging around the Arboretum morning and night for the past few years, overdressed and hauling a camera, a pair of binoculars, some peanuts and, if I was lucky, a peacock. Working at the park each spring, I often wished I had more time to chat with visitors. But I was preoccupied, and the life of an ornithologist can sometimes feel like that of Wile E. Coyote on a bad day.

For the past four years, I’ve been chasing peafowl across the continent – from Arcadia in February to Winnipeg, Toronto and New York in May and June. Incidentally, the Bronx Zoo is the only place in North America that even comes close to the Arboretum in sheer number of peafowl. Three years into my PhD in biology, and I’ve spent literally hundreds of hours watching these birds.

You may be wondering what got me into this mess.

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by Roslyn

Cultured tastes

Dinner in Shippagan, New Brunswick. Photo by Charlie Croskery.

We drove halfway across the country for the party, but the main course alone was worth the trip. When the pig was finally hauled out by a crew of strapping male relatives, the guests at Anne-Claire and Martin’s wedding converged at the carving table. Small children, I’m told even a Jewish person or two – nobody could resist a taste of warm skin ripped straight off with a knife. Not after seeing (and smelling) the thing turn that entire August afternoon.

I doubt we would have made the cross-country trip if charlem was on the menu. That’s what Vladimir Mironov, an expert in stem cell and tissue science, calls his latest culinary invention. Mironov’s product is grown right in his lab at the Medical University of South Carolina in Charleston – hence the name, short for Charleston engineered meat.

In a handful of labs around the world, scientists like Mironov are working on a curious agricultural problem: how to generate edible meat products without the farm – or the animals1,2. Their solution is to grow meat from animal stem cells. Some use cells taken from embryos, while others, like Mark Post at Eindhoven University in the Netherlands, are looking into the feasibility of growing muscle satellite cells taken from adults1. These can be extracted from domestic pigs or fowl with a quick and painless biopsy, and used to seed in vitro cell cultures.

In the future, this could be an easier way to serve a crowd. Like human cancer cell lines immortalized in a Petri dish, satellite cells can potentially go on multiplying forever in the lab, so long as you give them enough growth medium. Vladimir Mironov sees industry ultimately growing “charlem” – his cultured turkey – in bioreactors the size of football fields that he likes to call “carneries”. He imagines a world where fresh charlem is also grown at your local grocery store, in miniature appliance-size versions of the bioreactor machines3.

His work is, in part, funded by PETA, in an effort to stem the unmeasurable output of animal suffering caused by industrial agriculture. In 2008, the animal rights group also announced their in vitro chicken prize for the first person to develop a commercially viable product and sell it in at least 10 US states. To be eligible, the chicken also has to pass a panel of tasters when breaded and fried. The $1 million dollar reward is still up for grabs3,4.

No doubt this is a noble goal*. Large-scale meat production is an environmental scourge. The North American “meat guzzler”, as Mark Bittman calls it, is not sustainable6. Influential food writers like Bittman and Michael Pollan, and others including star chef David Chang, have been urging us to rethink our eating habits for years7. Environmentally, there’s a lot to be said for the alternatives: we could save a lot of resources by switching to the Asian practice of using small amounts of meat to complement dishes where vegetables and grains are the main event.

According to Nicholas Genovese from Vladimir Mironov’s lab, “Animals require between 3 and 8 pounds of nutrient to make 1 pound of meat. It’s fairly inefficient. Animals consume food and produce waste. Cultured meat doesn’t have a digestive system.”3

He’s right, of course. But his last point also happens to be the very reason charlem will never make it: meat from an animal is more than the sum of its in vitro parts. Want nutrients? We’ll have to add those in at the factory. Vitamin B12 and iron – two of the main nutritional reasons for eating animal protein in the first place – come from gut bacteria and blood1. You can’t get them from muscle tissue in isolation. Want taste? Let me see if we have an additive for that too…

Scientists may figure out how to culture meat efficiently in the lab, but it won’t be a viable solution to our agricultural problems, at least not anytime soon. The trouble with fake meat is that it’s up against evolution on two fronts, and, ironically, morality on a third.

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by Roslyn

I can haz toxoplasmosis

In which you will learn why online cats are so attractive, and discover a new way to lose hours to the internet.

First, the cats. Charlie and I were hashing out the finer points of Facebook, memes and internet superstars, when, in frustration, I brought up his most hated animal.

“Look. Cute baby videos and LOLcats are popular because people send links to their friends. Nobody sits down and says, ‘Well it’s quarter to 10, the same time I always drink my coffee and look for the latest cute cat photos on the–’ ”

Self defeat and laughter mid-sentence, when I remembered living with my friend Jessica in Toronto. She had a brutal job in psychiatric research north of the city. After a hard day, that was exactly what she did. Nothing cheered this woman up like online cat research.

Felis catus is a polarizing species. Some people despise them. Ancient Egyptians and cat ladies have made a religion out of them. The story goes that wild cats were first domesticated in ancient Egypt for useful things like keeping rats out of grain stores and killing poisonous snakes, but this might be more myth than reality. Cats were probably kept around as tame rat-catchers much earlier, certainly before recorded history, and very likely around the beginning of agriculture itself. People were depicting cats on pottery 10,000 years ago1. Cyprus can boast the first Stone Age cat lover. A 9,500 year old burial site on the island is the earliest evidence of humans bonding with these animals, since a cat was intentionally buried alongside a human body there2. The fact that the cat was not butchered, and the inclusion of decorative seashells and stones in the grave, prove that cats had achieved cultural importance beyond their agricultural utility back then.

European wildcat

The European wildcat Felis silvestris is a close relative of the earliest domesticated species. Photo by Péter Csonka from Wikimedia Commons.

But could the cat haters be right – is there something off about feline love? After all, cats aren’t really that useful, at least not when compared to dogs. Dog people might be pleased to hear that when you consider all living and extinct canid and felid species, dogs have bigger brains than cats – probably because they tend to be the more social animals3. Indeed, dogs adapted readily in response to domestication, evolving a number of cognitive abilities that make them particularly good at understanding human gestures – much better, even, than chimpanzees4. Naïve 4-month old puppies will quickly learn what it means when a human points, without any training or close contact with humans beforehand5. Cats can do this too, but they require a lot more effort to learn how6. Dogs can detect certain forms of cancer in humans by smell, and they are often the first ones to notice that something is wrong with their owners7. I have yet to find any high profile studies on feline pathologists. Which raises the question: if cats could do it, would they care enough to try?

And in a bizarre twist, there’s reason to think that our magnetic attraction to cats might be the result of a real parasitic disease.

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by Roslyn

Identity evolves

“Everyone is special.” The paradoxical refrain of baby boomer parents to their millenial offspring is true, so long as you’re a rodent living in a large, stable group of good communicators.

I recently wrote about the phenomenon of identity signals in animals, where variable colours and patchy-looking patterns can provide signatures of individuality, much like the human face. These are not limited to the visual domain. Think of how easily you can recognize a person’s voice – even someone you don’t know very well – from just a few lines of speech, like when a celebrity turns up in an animated movie.

But I didn’t have a chance to cover the latest news on this topic. In some very plain looking rodents, we now have evidence that individuality evolves1. Some of the plainest looking critters, like the Belding’s ground squirrel shown below, have the most distinctive snarfs and grumbles – and it all has to do with the number of group-mates they typically interact with.

Belding's ground squirrel pups

Two Belding’s ground squirrel pups peek out of a burrow. Photo by Alan Vernon from Wikimedia Commons.

The new results came out this month in the high profile journal Current Biology. Previously, researchers had looked for the evolution of individuality in a handful of bird and bat species. The prior studies examined distinctiveness in the begging calls offspring make to their parents, contrasting pairs of closely-related species that vary in the number of offspring in shared “crèche” or communal nest sites2,3. But nobody had tackled the evolution of individuality in a broad context.

Until Kim Pollard, that is. Pollard, a recent PhD graduate from UCLA, and her supervisor Dan Blumstein decided to look at this question in the social marmots. You might remember Blumstein from another recent post; his interests range from mammal conservation and environmental education to the bioacoustics of movie soundtracks.

For Kim Pollard’s study of identity signalling, marmots were an ideal choice. Marmota is a large genus of 14 different species in the squirrel family, all social, and all with their own alarm calls that they use to warn neighbours and family members about nearby predators. Species like the yellow-bellied marmot and Richardson’s ground squirrel also have the ability to recognize each other based on the unique sound of these calls4,5.

Crucially for Pollard and Blumstein, social group size also varies in the genus, ranging from about 5 to 15 individuals per clan or family group. This allowed the authors to test the hypothesis that group size has been an important factor in the evolution of distinctiveness, since, as they put it, “The bigger the crowd, the more it takes to stand out.”

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by Roslyn

To kill bias, gather good data

I hate myself for this: I have the worst sense of direction.

For the entire year when I was living in my first apartment in Kingston, I would take a circuitous route along King Street and then up Princess on my way home from the Kingston Yacht Club. Nearly two kilometers, when walking up West Street would have got me home in half the time. As Charlie said when I revealed this to him, “Two sides of a triangle is always greater than one.”

It’s not that I didn’t know grade school geometry, or that I wanted a more scenic route. I just stuck to the path I knew would get me there.

I felt a bit triumphant when I realized how long it can take Charlie when you ask him to pick up the milk. The last time I dragged him to the grocery store, I left him alone for a few minutes to use the bathroom, and returned to find him loading pineapple after pineapple after pineapple – painfully slowly, into the cart. We laughed, but I don’t ask him to come with me anymore. Alone, I can collect a week’s worth of food in less than 20 minutes.

I’m not ashamed to admit my navigational failings, either. My field assistant Myra and I happily agreed that our best strategy driving around Los Angeles was that we should always do the opposite of whatever we both thought was correct. It worked.

What I hate is my sneaking suspicion that I’m just a lame stereotype. Maybe I’m a terrible navigator because of biology; female brains are just not suited for getting around.

Hunter, gatherer

Modified from this cartoon. Original source unknown.

Recently, psychologists looked at this sex difference in what seemed like a neat field study of human foraging behaviour – in a grocery store1. Joshua New from Yale University, and his coauthors from UC Santa Barbara, set up a unique experiment in a California farmers’ market: they led men and women around the market, giving them samples like apples, fennel, almonds and honey. Then they brought the subjects back to a central location and asked them to point in the direction of those same food items.

These researchers wanted to test the idea that women outperform men at certain kinds of spatial tasks: while men are thought to be better at vector-based navigation, women might excel at remembering the locations of objects, because of the way foraging roles were divided up when our brains were evolving. It’s thought that in our hunter-gatherer past, big game hunting meant that men had to figure out how to bring heavy prey home by the most direct route. Women foraging closer to home needed a much different set of spatial adaptations2. It’s not that men are better at spatial reasoning in general, you just have to choose the right task3.

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by Roslyn

Backpedalling on backwards evolution

In a recent post I wrote about irreversible colour changes in morning glory flowers, and how this was promoted as evidence that evolution does not work in reverse1. This is called Dollo’s Law, after the 19th century Belgian paleontologist Louis Dollo. He spent most of his life digging up and reconstructing Iguanodons, but his name lives on in our concept of evolutionary trees. In linguistics, for example, the “stochastic Dollo” model refers to the scenario where words can only arise once in a family of languages2.

Louis Dollo supervising the reconstruction of an Iguanodon

Louis Dollo supervising the reconstruction of an Iguanodon. From Wikimedia Commons.

And the reason Dollo’s name is forever tied to the idea of history not repeating? He wrote that “an organism is unable to return, even partially, to a previous stage already realized in the ranks of its ancestors.”3

Frogs might prove Dollo wrong. A new study by John Wiens, a herpetologist at Stony Brook University, proves that a South American frog re-evolved the long lost bottom teeth of its ancestors, after going more than 200 million years without them4.

Guenther’s marsupial frog lives in the tropical forests of Colombia and Ecuador. It is the only frog we know of among thousands of species with true teeth in its lower jaw. Nearly all frogs have teeth, but only on the upper mandible. They use their single set for grasping prey items that they swallow whole, rather than chewing. The closest amphibian relatives to frogs, salamanders and worm-like caecilians, have maintained upper and lower teeth. This means that somewhere along the line, early frogs lost their bottom set.

As the odd one out, Guenther’s marsupial frog was originally placed in its own family within the taxonomic order Anura. But early studies of tadpole development and immunological proteins suggested that something was off5. In some ways, the marsupial frog was similar to typical tree frogs in the family Hylidae.

John Wiens’ latest results provide a more comprehensive picture of the early amphibian family tree than ever before. He compiled genetic data from 170 species of frogs, salamanders and caecilians. The new phylogeny firmly places Guenther’s marsupial frog in the family Hemiphractidae, and, by calibrating the new tree with evidence from the fossil record, Wiens can pin down the timing of events in amphibian history. His results show that frogs evolved from a salamander-like ancestor and lost their bottom teeth over 230 million years ago – and Guenther’s marsupial frog regained them quite recently, within the last 17 million years.

Hoatzin chick

The marsupial frog is just the latest in a long line of putative exceptions to Dollo’s Law. Others include fossil ammonites that have lost and regained the coiled form of their shells several times3, and modern slipper limpets that regained the coiled shells of their snail-like ancestors6. Some lizards have re-evolved long lost fingers and toes7. The strange bird known as the hoatzin, which has claws on its wings that are used for climbing until its wings are fully developed for flight, might have re-evolved this feature from its dinosaur ancestry. These examples have led some authors to argue that Dollo’s Law has outlived its usefulness8. Should it go the way of chewing teeth in hens and (most) frogs?

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by Roslyn

Honed

We brought home a new kitchen knife from my parents last month. The knife block was full, but Charlie exchanged the new one for what was previously our smallest and dullest. He wasted no time wrapping the old one up in plastic and hiding it from me. My hand naturally gravitates towards whichever tool will fit nicely inside it, even when I’m cutting a monster squash. We have a good arrangement: Charlie keeps the knives sharp, I keep my fingers, and I toss him the odd carrot slice in return.

But could he eventually be replaced by a sea urchin? A new study in the journal Advanced Functional Materials explains how sea urchin teeth never dull or break. In fact, they get sharper with use1.

Most people are probably familiar with sea urchins as the spiny little balls one occasionally encounters on the beach. Evil looking, but mostly harmless, so long as you avoid stepping on them. Sea urchins live in shallow tidal pools, eating algae and other plant material. So why do they need such sharp teeth? Much like their spines, the teeth probably serve a protective function. The urchins use them to chew burrows, often in solid rock, where they can take shelter from predators and waves.

In the current study, a group of physicists and biologists used an arsenal of sophisticated imaging, chemical and nano-scale stress test procedures to investigate the teeth of the California purple sea urchin (Strongylocentrotus purpuratus). Like starfish and sea cucumbers, urchins are members of a group of animals known for their penta-radial, or five-fold, symmetry. They have five teeth arranged in what is known as Aristotle’s lantern.

Aristotle's lantern

Aristotle’s lantern, as viewed from below with teeth closed. From Killian et al. 20111.

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by Roslyn

Deep archives: Lek perspective

Scene from a lek at the Bronx Zoo

Males display in the “Wild Asia” exhibit at the Bronx Zoo, which can only be seen by riding the zoo monorail. The structure behind the birds is the monorail track.

I’ve had some success on this trip after all. The weather was perfect for my model experiments yesterday (sunny, warm, not too much wind), and although I wasn’t able to fit in quite as many trials as I was hoping for, the ones that I was able to accomplish worked perfectly. Of 16 successful trials (i.e. ones where the male danced for the model), 6 ended in a copulation attempt. In California, 3 of 22 trials ended in such an attempt. This apparent geographical difference in Penelope’s popularity is a bit of a mystery (it could be because a number of my California trials were at the end of the breeding season, when males were somewhat less motivated and harder to trick). Nevertheless, it’s safe to say that overall she was a hit.

One reason I didn’t get as many trials as I could have was that the Bronx peacocks were the most skittish ones I’ve encountered so far. When I stepped into the nyala enclosure at 7 am yesterday, I had about 2 hours to collect as much data as I could (as many as 20 five-minute trials, I figured). But it took a long time for the males to get used to me being in there. I spent the first hour waiting quietly (and nervously) for one of them to make a move, while they did the same – watching me carefully and no doubt waiting for me to leave. This stand-off shouldn’t be too surprising, though, since the Bronx Zoo birds have enough space to live their entire lives away from people.

This morning, I moved across the Bronx River to work in “Wild Asia”, and the birds there were even more difficult. Happily, though, I was able to get a video of a male reacting positively to Penelope, which will be excellent for illustrating exactly how she worked.

I also made a trip to the “World of Birds” exhibit. They have some pretty amazing animals there – here is a picture of another lek-breeding bird, the lesser bird of paradise:

Juvenile male lesser bird of paradise

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by Roslyn

Language Instincts: “Run, run as fast as you can, you can’t catch me…”

Motmot

From October 5, 2006

What does the racquet-shaped tail of a turquoise-browed motmot (the bird seen at right) have in common with the tail of a deer and the rhyming gingerbread man of fairy tale fame?

They are all important signals in the communication with predators.

The turquoise-browed motmot has a strange looking tail. The two central tail feathers are elongated and designed with weaker barbs towards the ends of the feathers. These barbs wear away to give the feathers an unmistakable tennis-racket shape. When faced with a predator, the motmot will repeatedly wag its tail from side to side in an exaggerated, pendulum-like way (see video of a related motmot species performing the wag display here). Bold move, you might think – and you would be right. The wag display will often draw the one’s eye to a motmot that might not have been seen otherwise, and no doubt it has the same attention-grabbing effect on predators. So why do it?

A researcher from Cornell University, Troy G. Murphy, recently looked into this problem, studying motmot colonies that nest in abandoned quarries and wells in Mexico. He developed several hypotheses to explain the tail wagging behaviour, and then performed careful observations of the context of over 100 wag displays to discriminate between the explanations.

His hypotheses were as follows: (i) The motmot wags its tail as a warning alarm signal to other motmots, alerting them to the presence of the predator. This means that the signal would be beneficial to nearby individuals (such as kin or mates) even though it might be dangerous for the signaler to draw attention to himself. (ii) The motmot wags its tail as a self-preservation alarm signal. The signal should still be directed to other motmots, but instead of being dangerous for the signaler it might benefit him by encouraging other nearby motmots to move closer together or even mob (attack) the predator. (iii) The motmot wags its tail as a pursuit-deterrent signal directed at the predator itself. Much like the gingerbread man, the tail wag would say, “Run, run as fast as you can, you can’t catch me…” This kind of predator-prey communication would actually benefit both adversaries: the prey gets to stay where he is while the predator avoids wasting energy on what would probably be futile chase.

Murphy found that when presented with a predator, the turquoise-browed motmot will perform the wag display even if it is alone and not within sight of other motmots. He also found that motmots are just as likely to tail-wag when they are alone as when they are near their mate, or near any other motmots. These observations allow us to reject (i) since the display is obviously not intended for motmot receivers. Murphy was also able to reject (ii) since the birds do not move closer together or mob when a predator approaches.

From this evidence we can conclude that the tail wagging must be a signal to the predator, communicating that the motmot has spotted the threat and is ready to escape. Interestingly, the tail of many ungulates has a similar pursuit-deterrence function. For example, some white-tailed deer will signal to chasing predators by flagging their conspicuous tails. Pursuit-deterrence signals have also been observed in lizards (arm-waving to deter predators) and fish (swimming right up and inspecting predators directly to deter them). Too bad for the gingerbread man – if he had stayed in one place and relied on his signaling he might not have been eaten after all.