Calls and Cries from the Digital Jungle (Link round-up, 2/4/11 edition)

- Roland Kays, curator of mammals at the New York State Museum, writes about how snow affects field biologists and animals they study in the New York Times. He also describes the magic of camera traps: “[they’re] like a mix of fishing and Christmas. Finding pictures of common things like deer and squirrels is fun, like catching bluegills, but there’s always a chance of catching the big one — for example, a coyote, fisher or other rare species.”

- highlights some of the conflicts that occur when the worlds of wild macaques and urban humans collide. “Aggressive encounters with macaques are common in urban areas…humans [unintentionally] contribute to the problem by leaving garbage for them to raid.”

- President Obama cracked a joke about the complexity of federal fish regulations during his State of the Union address last week (I missed it because I was, well, gutting fish). Is government oversight of salmon as complicated as he’d have you believe? Slate’s Explainer explains.

- I did some explaining myself the other week at mental_floss, and talked about why we have flat and Phillips head screwdrivers and how the Duck Hunt Zapper works.

- Also at mental_floss, my co-blogger Rob provides an in-depth history of Rescue 911. Can’t wait for him to do one on Cops.

- Brian Switek talks about the armor of glyptodonts, the prehistoric, badass cousins of modern armadillos.

- Ed Yong reports on the spread of facepalming gestures in a group of captive mandrills. The pictures alone will make your day.

- The International Year of Chemistry launched the other day here in Philadelphia. David Kroll has a quick rundown of why the IYC is celebrated and where and when the Philly events are, as well as a shout out to the awesome Chemical Heritage Foundation museum.

-Five words: Baby elephant frolics on beach

- Robert Kurzban wonders why there’s a biased sex ratio in a certain spider species. The answer, as it so often is, is that parasites manipulate everything we do.

- Emperor penguins might use a coat of air bubbles to reduce drag and launch themselves out of the water and onto land.

- When it comes to love, it’s not just humans have to settle for what they can get.

- Conjoined tilapia twins give new meaning to “synchronized swimming.”

- Frog leg mustache!


Deathstalker v. Nightstalker: Bats take down highly venomous prey without a care in the world

There are some 1,400 described species of scorpion in the world, and while only 25 of those have proven they can take down a human being with their venom, many more of them can easily injure and kill smaller creatures. Given that, you’d expect scorpions to be important predators in desert food webs, but you might not expect them to be equally important as prey.

Otonycteris hemprichii

Yes, despite the pincers and the stinger and the venom, plenty of animals – among them, centipedes, tarantulas, lizards, owls,shrews and bats – regularly chow down on scorpions. Hemprich’s long-eared bat (Otonycteris hemprichii, at right), found in deserts in northern Africa, the Middle East and south-central Asia, considers scorpions a major food group, along with beetles, centipedes and spiders. In Israel’s Negev Desert, the proportions of these groups in the bat’s diet changes throughout the year, with scorpion fragments found in only 10% of bat droppings in the early spring and in a whopping 70% in the late summer.

That’s a whole lot of scorpions they’re eating, and while some of those are certainly weakly toxic Large-clawed Scorpions, the bats also prey on the Palestine yellow scorpion (Leiurus quinquestriatus, below). Everything you need to know about L. quinquestriatus can be summed up in its nickname, the deathstalker. These scorpions are considered some of the most dangerous in the world and possess a highly toxic venom that contains a grab bag of neurotoxins. Their sting can cause extreme pain, fever, convulsions, paralysis and death (via heart or respiratory failure), even in humans. These scorpions are also “sit-and-wait predators” that hunt by remaining quiet and still and lashing out at unsuspecting prey that wanders too close.

They certainly sound appetizing, but how do the bats deal with prey that present such a challenge to both detecting and disabling them? Carmi Korine, of Ben-Gurion University of the Negev in Midreshet Ben-Gurion, Israel, and colleagues found that Hemprich’s long-eared bat is what’s known as a gleaner, which means it takes prey from surfaces and not right out of the air, as many bats do. Korine and his team hypothesized that, like gleaning Pallid bats that prey on scorpions in North America, Hemprich’s bat might rely on passive gleaning to find its meals, simply listening for the prey to make noise instead of actively using echolocation to detect it based on its echo signature. The researchers figured that, if that was the way the bats hunted, then they would select prey based on 1) body size (bigger scorpions being easier to detect), and 2) toxicity (less venomous scorpions posing less risk of injury).

The team captured eight O. hemprichii individuals, set them up in a room with a scorpion buffet that included both living and dead Large-clawed Scorpions (Scorpio maurus palmatus), Israeli common scorpions (Buthus occitanus israelis) and, of course, deathstalkers.

When the bats took off to search for food, they spent a few minutes circling the room and dropped down directly onto a scorpion once they noticed it. They only went after the live scorpions, ignoring the dead ones and even walking right over motionless live ones if they missed on their initial divebomb, confirming that they glean passively and rely on prey noises.

Once they landed on a scorpion, the bats immediately started biting the scorpions’ heads. The scorpions did not take this lying down and fought back, stinging the bats on the head and face and, in one case, under the eyelid. The bats made no observable attempts to either avoid or disable the stingers and once they had killed the scorpions they often ate the whole thing, including the stinger and poison gland.

This is how the bats hunted all the scorpions. Contrary to the researchers’ predictions, the bats showed no preference among scorpion species based on either on size or toxicity, diving on their prey immediately after detection without any further inspection and going only on limited acoustic information. In 49% of the test sessions the bats actually went after the more poisonous of the available species (and in 24 direct comparisons, the deathstalker was chosen 50% of the time).

The researchers did not have an explanation for the bats’ indifference to the danger their meals pose, but speculated that either scorpions aren’t able to pierce the bat’s skin, or that the bats have at least a partial tolerance to the venom. Given that the bats regularly ate the stingers and venom glands, it seems more likely that their just tough enough to handle what the deathstalkers can dish out.

For other takes on this study, see Michael Marshall’s post at Zoologger and Zen Faulke’s post at Neuro Dojo .

Reference: Holderied M, Korine C, & Moritz T (2010). Hemprich’s long-eared bat (Otonycteris hemprichii) as a predator of scorpions: whispering echolocation, passive gleaning and prey selection. Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology PMID: 21086132

Images: “Otonycteris hemprichii” by Wikimedia Commons user Charlotte Roemer, used under a Creative Commons license.

“Deathstalker near Tzehelim, Israel” by Wikimedia Commons user Yair Goldstof, used under a Creative Commons license


The werewolf is dead, long live the werewolf, or: The co-existence of lycanthropy and Cotard’s syndrome This post was chosen as an Editor's Selection for
“I speak, breathe and eat but I am dead,” said the patient.

The symptoms had started two years earlier, and his family finally brought the patient, a 32-year-old high school dropout, laborer and family man, to the Kerman Psychiatric Hospital in southern Iran after he refused to go to work for two straight weeks. At first, he just felt restless and sensed a subtle, strange feeling in his body, like a faint electric shock. Soon he felt as if his whole body had changed and, finally, he concluded that he was dead and that his death was caused by his sins during life. He said that after his death, sometimes his jaw moved automatically and concluded that he had been transformed into a dog. His wife had suffered the same fate. His three daughters had also died and were transformed into sheep and the scent of their urine made him restless. He could smell their it even then, in the hospital, far away from his family.

He started having trouble sleeping and then felt no need for it. At night, he laid far away from his family, afraid of sexually assaulting his daughters while they slept. He had, after all, had a sexual relationship with a sheep during his life as a human and still could not get over the guilt from it. He also refused sexual contact with his wife, as he believed his sins were so grave that he should never look at any woman again.

He began to accuse his friends of harming him. When they asked why he thought that and how they had supposedly harmed him, he gave no explanation, but did not worry either. He believed that God protected him, even in death, and that no poisons could hurt him. He explained that his relatives and friends repeatedly poisoned his tea with cyanide but that he had not been harmed.

The man and the beast were dead, but would live forever. Having suffered for their sins, they were now protected by the hand of God.

The man met DSM-IV criteria for mixed-type bipolar mood disorder with psychotic features. In addition, he displayed delusions that DSM-IV criteria could not explain. Lycanthropy in folklore and horror movies is applied to humans who change into wolves. In the psychiatric literature, though, it is a rare belief or delusion that one has transformed into an animal, or the exhibition of behavior suggesting that belief. Cotard’s syndrome is another rare condition in which the afflicted has nihilistic delusions that lead them to deny their own existence or that of the external world. The syndrome also involves the paradoxical ideation of immortality. He presented a typical case of Cotard’s syndrome, having both delusions of being dead and of immortality. His lycanthropy was a rare variant in which both the patient and others were transformed into animals, a delusion reported only once before.

How could these two conditions co-exist in one patient? The man’s caretakers found several ties that bound them to each other. Immortality is a common symptom of both lycanthropy and Cotard’s syndrome. His sins in life, one of them being sexual contact with a sheep, were explained as the cause of his death, and zoophilia and bizarre and chaotic sexuality in general are often expressed in a primitive way by lycanthropes (the prevalence rate of zoophilia – both actual sexual contact and sexual fantasies – is significantly higher among psychiatric patients, 55%, than control groups, 10 and 15%). In addition to the paradoxical pairing of the delusions of being dead and immortal in Cotard’s syndrome, the man’s lycanthropy presented its own paradox. In Persian folklore, the dog is both a symbol of loyalty and a symbol of impureness. The man’s sexual history with sheep, coupled with his desire to protect his sheep-daughters and many dogs’ roles as herders and protectors of flocks, adds another layer of paradox. It was concluded that zoophilic orientation associated with a sense of guilt was a driving factor in causing his delusions.

The man was given medication and six sessions of electro-convulsive therapy and after two weeks, the main symptoms were relieved. The sheep, though…the sheep would never be the same.

(Note: This post has been edited from it’s original version in an effort to make the information in the first two paragraphs flow more easily. Info was moved around and rewritten slightly, but no information was removed, nor additional information added).

Reference: Nejad AG, & Toofani K (2005). Co-existence of lycanthropy and Cotard’s syndrome in a single case. Acta psychiatrica Scandinavica, 111 (3) PMID: 15701110

Image: German woodcut of werewolf, 1722.


Acanthaspis petax and the amazing technicolor corpsecoat

Ed Yong recently reposted his fantastic 2008 post on assassin bug camouflage to keep us entertained while he’s away. I covered the same paper on an old incarnation of my blog, and can’t resist joining in on the reposting fun. Kevin Zelnio of Deep Sea News also has a post about it. Remember that scene in Silence of the Lambs where Hannibal Lecter kills one of his guards, cuts the poor bastard’s face off and then wears it as a mask so he can escape in an ambulance? This great (if only for the appearance of Chris Isaak as a SWAT team captain) movie moment, it turns out, is something of a case of art imitating life.

While disguise and camouflage have a long history in the animal world (stick bugs, chameleons, decorator crabs, etc.), the assassin bug Acanthaspis petax, takes things to a Lecter-esque extreme.

The order of insects called Hemiptera is comprised of some 80,000 species, collectively known as true bugs. The order’s defining characteristic the arrangement of the bugs’ mouthparts: the mandibles and maxillae have evolved into a sheathed proboscis capable of piercing tissue and sucking out liquids. Most hemipterans use their proboscises to suck sap from plants, but the assassin bug prefers to stab them into other insects (usually ants) and inject their prey with paralysis-inducing saliva and digestive enzymes in order to break down and suck up bodily fluids.

A few other types of insect do the same thing. So what? Well, Acanthaspis petax one ups its brethren and sticks the corpse of its meal to its back, which secretes fine, sticky threads. There the corpse sits with others like it, forming a coat of bodies that earlier research suggested might protect the bug from predators.

Robert Jackson and Simon Pollard from the University of Canterbury tested this theory by matching the assassin bugs against jumping spiders in a no-holds-barred insect cage match. Three species of jumping spider which – all stalking, vision-guided predators that wouldn’t be able to detect the assassin bug by smell  - were placed in glass cages with either with naked, unmasked, assassin bugs or bugs bug wearing the bodies of its last few meals.Assassin bugs

All three species of spider went after the uncovered bugs about ten times more than the covered ones (even if the bugs were actually dead and preserved decoys the authors used to control variables associated with using live bugs, like motion, behavior, size etc.).

Jackson and Pollard suggest that the cloak of corpses (or skin coat, if you will) successfully deters predators because the bodies break up the assassin bug’s form into something the spiders don’t recognize. They see a mound distinct from the background, but they dont recognize it as prey.

The remaining question is: why ants? Assassin bugs feed on a variety of other insects they encounter, but their camouflage is consistently composed mostly of ant corpses. Jackson and Pollard suggest the possibility that the spiders avoided the cloaked bugs because ants are formidable prey, using chemical defenses and having a nasty tendency to swarm. The assassin bugs, then, might be using ants in particular as disguises because of their tough guy reputation.

Reference: Jackson, R., & Pollard, S. (2007). Bugs with backpacks deter vision-guided predation by jumping spiders Journal of Zoology, 273 (4), 358-363 DOI: 10.1111/j.1469-7998.2007.00335.x


To gape or not to gape? Some mussels’ choices influence their place in a habitat

ResearchBlogging.orgThe segregation of habitat between native and invasive species often comes down to a competition between their physiological and behavioral abilities. This is especially true in habitats prone to frequent change; as both indigenous and invasive species respond to environmental variations in a habitat, it’s the difference in their responses that can determine their success or failure.

In South Africa, the indigenous mussel Perna perna (below, left) seems to have the odds stacked against it. Its coastal ecosystem is under heavy fire from invasive species, it’s subjected to variable, extreme environmental conditions in its intertidal home and its behavioral repertoire is more than a little limited. What’s a mussel to do? Really, the only thing it can do: open and close its shell (“gaping”). Turns out that this simple behavior has a strong influence on the outcome of the mussels’ turf war.

19066_perna-pernaThe Mediterranean mussel Mytilus galloprovincialis (below, right) is one of the world’s most widespread marine invasive species andcan be found all over the northern and southern hemispheres’ temperate zones. Having found its way to South Africa in the late 1970s, it slowly branched out along the entire west coast and has now spread along 800-900 km of the south coast, too. There, it shows partial habitat segregation with the P. perna in the lower eulittoral zone, or mussel zone, where P. perna typically dominates the lower zone and M. galloprovincialis dominates the higher mussel zone, with some overlap.

The bivalves are regularly covered and uncovered by the changing tide and endurea steady rhythm of wet and dry conditions. When the outgoing tide leaves them high and dry, the mussels have two choices. They can keep their valves closed, which minimizes water loss, but requires them to use anaerobic metabolism (a way for an organism to produce usable energy in the form of ATP without the involvement of oxygen; it’s basically respiration without oxygen). Alternately, they can open and close their valves, which maintains a more efficient aerobic metabolism (energy creation that uses oxygen), but opens them up to (no pun intended) to water loss and the risk of drying out.


Mussels of each species and from each zone were exposed to air at two different temperatures by Katy Nicastro, Gerardo Zardi (CCMAR, CIMAR-Laboratorio Associado at Universidade do Algarve in Portugal), Christopher McQuaid (Department of Zoology & Entomology at Rhodes University in South Africa), Linda Stephens, Gregory Blatch (Department of Biochemistry, Microbiology & Biotechnology at Rhodes University) and Sarah Radlof (Department of Statistics at Rhodes University) in three experiments conducted to observe gaping behavior, water loss and mortality due to dessication. The two species took very different approaches to air exposure. M. galloprovincialis did not show gaping behavior at either temperature, while P. perna showed gaping at both temperatures, with an increased number of gaping individuals and of number of gapes per hour at the higher temperature. Consequently, water loss rates were higher for P. perna than for M. galloprovincialis (average loss of 21% and 4% of total body water, respectively) and while water loss was greater for both species at the higher temperature, P. perna’s water loss rate was much steeper when the temperature was increased. P. perna likewise had higher mortality rates in the desiccation experiment than M. galloprovincialis, but the invasive mussels did show a greater production of stress proteins related to anoxic stress.

Gaping, as simple as it seems, has a profound effect on the segregation of habitat between the native and invasive mussels. While gaping may relegate P. perna to the lower area of the mussel zone, it doesn’t exactly get stuck with a raw deal. It’s greater attachment strength allows it to withstand greater hydrodynamic stress than the invasive mussels that might venture into the zone. P. perna initially aids the survival of M. galloprovincialis in the lower zone by providing protection against waves, but eventually excludes it competitively in the long run and takes the lower zone all for itself. Meanwhile, keeping their traps shut condemns the invasive M. galloprovincialis to more stress and a less efficient metabolism (the end products of which can be toxic or lethal if left to accumulate), but minimizes water loss and allows it to make itself at home in the upper mussel zone, where gaping P. perna can’t survive or compete with it. Territory gets divvied up and both invaders and natives find a niche for themselves based on the simple act of opening up, or not.

Reference: Nicastro KR, Zardi GI, McQuaid CD, Stephens L, Radloff S, & Blatch GL (2010). The role of gaping behaviour in habitat partitioning between coexisting intertidal mussels. BMC ecology, 10 PMID: 20624310

Images: Mytilus galloprovincialis with Symplegma reptans living on it, by Flikr user Jay Vavra. Perna perna from Collection Georges Declercq, via the World Register of Marine Species. Both used under a Creative Commons license.


Eavesdropping ungulates use baboon alarms to avoid predators

ResearchBlogging.org362258071_111a8114d8To borrow from Jonah Lehrer (in turn, giving a nod to Hobbes Hobbes), “baboons are nasty, brutish and short.” They’re noisy little brutes, at that. When they encounter predators, females and juveniles produce harsh single-syllable barks (turn your volume up a little). During baboon-on-baboon fights or dominance contests, the women and children scream. In both situations, males produce two-syllable “wahoos.” All the ruckus doesn’t necessarily make them bad to have around, though. Many animals respond, often appropriately, to alarm calls produced by other species. This, “eavesdropping” behavior has been observed both within taxonomic groups (among birds, marmots and squirrels) and between them (some mammals and reptiles, vervet monkeys, red squirrels, Gunther’s dik-diks, banded mongooses and Galápagos marine iguanas among them, respond to bird calls; hornbills can discriminate among different primate alarm calls). If species that live in proximity to baboons have gotten the hang of telling alarm calls from contest ones and learned to associate alarm calls with predators, they might avoid becoming lunch thanks to their noisy neighbors.

On the Okavango Delta in northwestern Botswana, impala, tsessebe, zebra and wildebeest are all abundant, all hear baboon calls often and all respond to the baboons’ alarm calls. Although all four ungulates come into contact with baboons, only impala regularly intermingle with the apes at close range, likely because of their overlapping diet and habitat preferences. Baboons and impala also share a vulnerability to predation by leopards and lions, while the larger ungulates only have to worry about the lions. Impala, therefore, are more likely to experience a close juxtaposition of baboon alarm calls and appearance of predators and have more opportunity to associate the two.

To test what seems like the impala’s edge over the other species, Dawn Kitchen, James R. Nicholson (Ohio State University), Thore Bergman (University of Michigan), Dorothy Cheney and Robert Seyfarth (University of Pennsylvania) broadcasted four unique pairs of baboon call sequences – each pair consisted of one sequence of alarm calls recorded during a lion encounter and one sequence of calls recorded during a male-male altercation that involved the chasing of females and juveniles – in the presence of groups of the four ungulate species. All four species showed stronger responses (responses measured were latency to orient toward the speaker, duration of looking toward the speaker, latency to move at least 1 m and rate of moving) to the alarm call sequences than to the contest sequences (even though both sequence types were similar in pattern, amplitude and duration). The impala, though, had stronger response scores than all other species combined in both the alarm and contest conditions and demonstrated the strongest discrimination between the two call sequence types. Specifically, the impala observed showed shorter latencies to orient toward the speaker, looked toward the speaker for a longer duration, began moving sooner, and moved at faster rates after the playback of alarm calls than contest calls.

Do these ungulates possess an innate skill for telling the difference between baboon alarm calls and other calls, or do they learn, over time, to separate the signal from the noise? Were the ability innate in any of the species, the researchers say, it could be explained by an acoustic convergence between baboon alarm calls and the alarm calls of the ungulates. However, their alarm calls are made up primarily of snorts that have little in common with the baboons’ barks and wahoos. Instead of natural talent, the researchers think the ungulates learn to discriminate between baboon calls, given the impala’s strong response difference to the two baboon call sequences, the species exposure to baboons and available opportunity to associate alarm calls with danger. The researchers suggest that the ungulates’ responses were guided primarily by the alarm calls of the females and juveniles, which are easier to differentiate from other calls than the males’ alarm and contest wahoos (although, female baboons can differentiate male calls and there is some evidence that birds can parse the subtle differences, humans can’t discriminate the calls by ear). Familiarity and social learning have been implicated as mechanisms for interspecies call recognition in other research. Juvenile vervet monkeys residing in groups that regularly hear the alarm calls of superb starlings responded appropriately to playback of starling calls at a younger age than juvenile vervets living in groups with lower rates of exposure. To further test their hypothesis, Kitchen and her co-authors suggest a similar series of playback tests conducted on young ungulates with varying levels of exposure to baboons and their vocalizations.

Reference: Kitchen DM, Bergman TJ, Cheney DL, Nicholson JR, & Seyfarth RM (2010). Comparing responses of four ungulate species to playbacks of baboon alarm calls. Animal cognition PMID: 20607576

Image: “Chacma Baboon – Papio ursinus” by Flickr user Arno & Louise Wildlife


Fish Market: Competition gets clients better treatment from cleaner fish

ResearchBlogging.orgGame theory models based on repeated interactions between two individuals have often been the framework for understanding cooperative interactions in humans, but these models rarely apply in nature. Non-human animals, after all, rarely find themselves in situations like the “prisoner’s dilemma.”

Instead, partner choice and competition are emerging as the framework for understanding cooperation in the natural world. Some mutualisms (biological interactions between organisms where each individual derives a fitness benefit) can be described as “biological markets,” where organisms exchange goods or services. These markets and the animals that participate in them share some similarities with humans and our markets: animals preferentially interact with partners that provide the highest-quality goods or services; animals sometimes cheat each other; competition is often a good thing, and threatening to take your business elsewhere can lead to more cooperative behavior from your partner.

In many cleaner mutualisms among fish, cleaner fish occupy cleaner “stations” where they remove parasites from cooperating client fish. Buyer beware, though, because clients often have to wait for service from a cleaner and when it’s finally their turn, they may be cheated by cleaners that feed on tissue or mucous instead of parasites. Clients don’t have many options for ensuring good service. They can’t demand their mucous back or complain to management. What they can do is go get cleaned somewhere else.

Thomas C. Adam, a graduate student at the Department of Ecology, Evolution, and Marine Biology at the University of California, Santa Barbara, investigated cleaner-client interactions involving the territorial butterflyfish Chaetodon ornatissimus . In the Maharepa lagoon on the north shore of Moorea, French Polynesia, C. ornatissimus (at left) is the preferred client of bluestreak cleaner wrasse (at right), but has the option of partnering with several other species of cleaners common to the area. Snorkelers mapped the territorial boundaries of C. ornatissimus and conducted hour-long observations of their interactions with their cleaners (in total, individual fish in 32 territories were observed for 43 hours).

client copycleaner copy

The results of the study indicate that not only do bluestreak cleaner wrasse compete for access to their butterflyfish clients (the amount of time cleaners had access to clients was negatively associated with the number of cleaner stations in a territory and individual butterflyfish with access to multiple cleaner stations did, indeed, shop around and were less likely to return to a cleaner station for their next cleaning than individuals with access to just one cleaner station), but the ability of butterflyfish to take their business elsewhere got them higher-quality service from cleaners. To wit, (1) the observed clients were never ignored by cleaners (at left) when they had more than one cleaner station in their territory (in contrast, five of 11 fish with a single cleaner station in their territory were observed being ignored), (2) while there was no evidence that clients with access to multiple cleaner stations were cheated less frequently than clients without access, the clients with their choice of partners were less likely have interactions terminated early by cleaners and were inspected for significantly longer during each cleaning session.
See? The free market does work sometimes.

Reference: Adam, T. (2010). Competition encourages cooperation: client fish receive higher-quality service when cleaner fish compete Animal Behaviour, 79 (6), 1183-1189 DOI: 10.1016/j.anbehav.2010.02.023


This is a test. Keep calm and carry on.



Shell Games: The social and behavioral aspects of hermit crab real estate

ResearchBlogging.orgThis post was chosen as an Editor's Selection for ResearchBlogging.orgI recently took part in what social scientists call a “vacancy chain” (a social structure through which vacancies in discrete, reusable, and limited resources propagate through a population) and all I needed was a moving truck, a few helpful relatives, a case of beer and a few pizzas. You see, when my girlfriend and I moved into a new house in May, we filled a vacancy left by the previous tenants. When we moved, someone moved into our old apartment and filled the vacancy we left. Their apartment, in turn, was filled by someone else, and their apartment was moved in to by someone else and so on and so forth. Somewhere (further up the chain than me), a vacancy was created and propagated down the socioeconomic order through a series of interdependent events and resulted in many individuals acquiring new, sometimes better (we have a patio, but no central air, so the jury is still out), resources and benefiting from them.

hermitcrab1 copy

Hermit crabs, for whom really nice shells to call home are a scarce commodity, have evolved their own sorts of vacancy chains as way for optimizing shell acquisition and occupancy. While these shell vacancy chains have been described (and shown to provide aggregate benefits that are distributed across many participants) for several hermit crab species in previous research, not much was known about the behaviorial and ecological factors that lead to and influence them.

Cue the arrival of Randi Rotjan, Jeffrey R. Chabot and Sara M. Lewis (from the New England Aquarium in Boston, the Pfizer Research Technology Center in Cambridge, MA and the Department of Biology at Tufts University, respectively) at Carrie Bow Cay, a ¾-acre island located near the Belizean barrier reef that is home to Eighty-four palm trees and 1,084 purple-clawed hermit crabs of the terrestrial species Coenobita clypeatus.While the biologists were there study parrotfish, bad weather made the water too rough for diving, so they used their time to better understand shell vacancy chains. The researchers marked 20 locations around the island, set out a single vacant shell at dusk at each one and monitored them. Over the course of 24 hours they observed a total of 16 vacancy chains of two different types, asynchronous and synchronous.

An asynchronous chain occurs when one crab moves into a new, empty shell and abandons its old one to be found by another crab, which abandons its own for another crab to find, etc. With this type of chain, shell switching is sequential and the crabs experience little to no interference or competition. They have the opportunity to investigate any vacant shells they find and can directly compare their current shell with a new shell by switching back and forth between the two. The down side is that individual crabs aren’t very likely to just stumble upon a vacant shell that meets their specific size and quality requirements. It’s like if I told you that you could wander around your town, go into any unoccupied houses you wanted, check them out and pick your dream home, but you’d have to find the one with two bedrooms, a dishwasher and a fireplace on your own by chance, without the aid of Craigslist.

Synchronous shell vacancy chains are more social and much more interesting. They start off with “waiters,” crabs that hang around a shell that’s too big for them, and wait for a bigger crab to come along so that if the big crab moves in to the vacant shell, the waiter can grab their more appropriately-sized hand-me-down shell (the researchers note that the decision to wait, and how long to wait, based on previous experience, provides some evidence that the crabs are smarter than we thought). The chains that the researchers observed began with one to 20 waiters who spent anywhere from a few minutes to an hour-plus loitering around empty shells. As a crowd gathers, the crabs queue up by size, from largest to smallest, and once largest crab switches into the vacant shell, each crab climbs into a new shell as it’s vacated by the slightly larger crab ahead of it, quickly shuffling vacancies (literally) down the chain. In both chain types, the fun stops when the last shell vacated is so low in quality (too small or damaged) that all the crabs reject it.

A Synchronous Chain in Action

In addition to the waiting that kicks off synchronous chains, the researchers observed other unique shell acquisition behaviors that the crabs only exhibited in social contexts and appeared to be associated with the vacancy chains. At almost half of the observed locations, when the waiting crabs were all too small for they vacant shell they had gathered around, some would “piggyback,” or form lines with each crab grasping the shell of another crab from behind and frequently moving in and out of the line to jockey for a better positions. The researchers hypothesize that piggybacking may be help establish a dominance hierarchy among the waiting crabs and/or allow them to investigate some of the shells they might be able to move into. Theses piggyback lines often transformed into queues upon the arrival of crabs that were appropriately sized for the vacant shell.

At some of the locations, multiple queues formed when there were many similarly sized waiters, and the crabs in these queues appeared to engage in a “tug-of-war” for control of the vacant shell. The smallest crabs, positioned at the end of each queue, frequently switched back and forth between the lines in a possible attempt to stake its place in the winning line.

So what sets these theatrics off in the first place? Population density seems to be a key factor determining the length and type of vacancy chains. Using modeling software, the researchers created a simulated habitat space and a population of crabs of varying sizes. Rules for shell switches that realistically reflected hermit crab behavior were established and, after a while, a vacant shell appropriately sized for the largest crab in the population was placed the center of the habitat and the simulation was continued. During 100 model runs were at each combination of 2 parameters: population density (8 levels, from 10 to 900 crabs) and maximum waiting times for the waiters (2 levels), vacancy chain lengths increased along with population density at the highest population density, almost half of the shell switches that occurred were part of synchronous vacancy chains. How word about an available shell gets out among the crabs in the first place is still unknown, though. The researchers plan to address the question in a future study and speculate that the waiters may use aural or chemical signals to draw attention to the vacancy.

Reference: Rotjan, R., Chabot, J., & Lewis, S. (2010). Social context of shell acquisition in Coenobita clypeatus hermit crabs Behavioral Ecology, 21 (3), 639-646 DOI: 10.1093/beheco/arq027

Image: “Caribbean hermit crab (coenobita clypeatus)” by ZooFari, via Wikimedia.


Watch where you sit, the things you touch affect your decisions and judgment

ResearchBlogging.orgHow you think you assess and explore new things? You might assume that you do it primarily through sight, right? If I have a cool new gadget, the first words out of your mouth would likely be, “Can I see it?” Chances are, though, that when you say that, you’ll also extend your arm and open your hand. Seeing isn’t all there is. You want to touch, feel, hold and manipulate unfamiliar things.

The way those objects feel in your hands have a significant influence on the judgments you form about them. Past research has shown that shoppers understand and form impressions more readily about products with which they can physically interact and that tactile sensations can influence their perceptions and opinions of products’ quality. This happens even when touching a product doesn’t give any clues about its quality, like when shoppers said that water from a firm bottle seemed to taste better than water from a flimsy bottle. Findings like this have led psychologists to suggest that touch experiences might create a “scaffold” for the development of conceptual knowledge. In other words, mental action may be grounded in physical action, and sensory and motor processes are fundamental to some aspects of cognition.

creation of adam hands

In a study recently published in Science, researchers tested how three tactile sensations – weight, texture and hardness – influence perceptions, judgments and decisions of and about unrelated situations, people and objects. They found that touching objects can trigger a “haptic [relating to or based on the sense of touch] mindset” and cause people to apply concepts related to those sensations (texture and someone being “rough around the edges,” for example) to interpersonal interactions.

Joshua Ackerman, Christopher Nocera and John Bargh (from MIT, Harvard and Yale, respectively) conducted six experiments to see how weight, texture and hardness affected decision making and the formation of social impressions in people they met on the street. In one of the weight-related experiments, 54 passersby were asked to evaluate a job candidate by reviewing resumes on either light (3/4 lb) or heavy (4 1/2 lb) clipboards. Weight is associated seriousness and importance, a la “weighty matters” and the “gravity of the situation.” Sure enough, the people who reviewed the resume on the heavy clipboard 1) rated the the candidate as better suited for the position 2) said the candidate displayed more serious interest and 3) rated their own accuracy on the task as more important than the participants using the light clipboard did.

In the texture experiment, 64 people read a description of an ambiguous social interaction and were asked about the nature of the interaction, specifically, whether it was adversarial or friendly. Before they read the story, though, the participants completed a puzzle, the pieces of which were covered either with sandpaper or left bare. The participants who completed the sandpaper-covered puzzle rated the interaction as more adversarial and harsh than the participants who completed the smooth puzzle, consistent with rough textures’ metaphorical relationship harshness and difficulty (“a rough day,” “coarse language”).

To see if texture affected people’s social decisions, 42 participants first completed either the smooth or rough puzzle and then played an Ultimatum game where they received 10 tickets for a $50 lottery and could choose any of the tickets to an anonymous participant. If the other person accepted the ticket offer, great; if not, all the tickets were forfeited. Participants who completed the rough puzzle offered more lottery tickets than those who did the smooth puzzle, suggesting that they were primed for difficult social interaction and hence used compensatory bargaining behavior.

The last two experiments focused on hardness, which is associated with stability and rigidity (“he’s my rock” and “hard-hearted”). In one experiment, 49 people were asked to watch a magic act and then guess the secret. First, though, they got to examine the object to be used – either a soft piece of blanket or a hard block of wood – and verify that there wasn’t anything odd unusual about them. The act was then postponed indefinitely while the participants read a description of an interaction between a boss and an employee and evaluated the employee’s rigidity/strictness. Those who felt the wooden block rated the employee as more rigid/strict than those who felt the blanket.

throneThe final experiment tested whether or not passive touch experiences could affect decision-making like active manipulation of objects had. Eighty-six participants were “primed by the seat of their pants” and sat in either hard wooden chairs or soft cushioned one while completing an impression formation task similar to the previous experiment and a negotiation task. This negotiation had participants pretending to shop for a new car (sticker price $16,500) and making two offers on the car (the second assuming that the dealer rejected the first offer). Comparable to the previous experiment, people who sat in the hard chairs said the employee was more stable than did participants who sat in the soft chairs. In the negotiation, hard chair participants changed their price between the two offers by a lesser amount than the soft chair participants did, suggesting that a haptic mindset can be triggered even when touch occur in body parts beside the hands and even when an object is not being actively manipulated.

It’s sort of the opposite of what Funkadelic would have you believe: free your ass and your mind will follow. While the idea of your butt or your hands or your feet having such power over your brain might seem a little odd, researchers in the field of embodied cognition have spent decades chipping away at the idea that mind and body are so separate from each other. Past studies have demonstrated that kids who use their hands while solving math problems have an easier time of it, that actors can remember lines more easily when moving and that holding a warm cup of coffee makes you more generous.

If physical sensation and movement has such a strong influence on our thoughts, though, is manipulating the mind as easy as buying heavier clipboards and upholstering the furniture? While the study might provide some lessons for job candidates, pollsters and car salesmen on manipulating their environment to bend social interactions in their favor, the authors note that this sort of exploitation is only easy when people are distracted and that paying attention to your surroundings diminishes the effects of these tactile cues. In other words, you’d do well to watch where you sit.

Reference: Ackerman JM, Nocera CC, & Bargh JA (2010). Incidental haptic sensations influence social judgments and decisions. Science (New York, N.Y.), 328 (5986), 1712-5 PMID: 20576894

Image: Anthony Redmile Carved Armchair with Malachite Bone and Horn via Boing Boing