The Secret Life of Lobsters (20 page)
Read The Secret Life of Lobsters Online
Authors: Trevor Corson
Given the lobster's ability to project a plume of water forward, or to suck another lobster's plume toward its own nose, Jelle suspected that a peculiar quirk he'd noticed in the lobster's anatomy was more than an evolutionary mishap. The American lobster urinates not from some posterior region of its body, but directly out the front of its face. Two bladders inside the head hold copious amounts of urine, which the lobster squirts through a pair of muscular nozzles below its antennae. These powerful streams mix with the gill outflow and are carried some five feet ahead of the lobster in its plume. Quite possibly, lobsters were sensing each other and sending signalsâ“I beat you up last night, remember?” or “Would you like to mate with me, I'm about to get undressed?”âby pissing in each other's faces.
Finding out, of course, would require a lobster catheter. One of Jelle's students cemented latex tubes to the urine nozzles on a lobster's face with superglue. The two tubes curved over the lobster's shoulders to a Y-connector fastened to the lobster's back. From there a tube ran up to a vial that floated on the surface. Returned to his aquarium and readied for a social encounter with another male, the catheterized lobster wandered the tank, pursued by the floating jar overhead that would collect his urine. The experiment would be akin to sending an angry man into a street-corner altercation with a soundproof hose strapped to his mouth, delivering all his words into a balloon floating above his head.
What the researchers discovered during the ensuing fights was that dueling lobsters accompanied their most punishing blows during combat by intense squirts of piss at the oppo
nent's face. What was more, in scenes akin to a showdown at the OK Corral, the winner of the physical combat almost always turned out to be the lobster that had urinated first. And well after the fight was over, the winner kept pissing. By contrast, the loser shut off his urine valves immediately. In an underwater world navigated by scent instead of sight, the tactic was clearly an attempt to hide.
But what, exactly, were lobsters doing when they peed at each other during fights? One possibility was that the lobsters weren't communicating at all but instead using urine as a kind of chemical weaponâsome insects inject caustic chemicals into their urine and pee at predators as a form of defense. But that seemed unlikely. There were two other possibilities.
Dissections in Jelle's lab had revealed an unexplained gland inside the lobster's head that emptied directly into the urinary tract. Conceivably, the gland was used to produce proteins that registered a unique odor signature for each individual. Indeed, a urine analysis of several different lobsters revealed a unique pattern of molecular weights in the protein content of each animal's pee. Mice are known to employ proteins in urine to convey individual identity, but a similar system has never been shown to exist in invertebrates. Perhaps what lobsters were doing when they squirted urine during fights was simply the equivalent of the angry man on the street corner shouting his own name every time he punched his opponent. “This pain goes with this name,” the lobsters seemed to be saying, “so remember it well.”
The second possibility, even less certain, was that victorious lobsters might be reinforcing their own aggression through increased reception or production of a chemical motivator such as serotonin. The result might be to instill a sense of confidence, so to speak. Chemically, this condition wouldn't be unlike the enhancement a human gets from a cup of coffeeâcaffeine delays the reuptake of serotonin, which makes more of the motivating chemical available in the brain. A dominant lobster with enhanced chemical motivation might exude some sort of chemical clue to the heightened level of aggression in his
urine, which in turn could be detected by the animal's peers and paramours.
Jelle and one of his students designed an experiment to test whether other lobsters could detect something like a sense of confidence exuding from a winning male. First they forced a pair of males of equal size to compete for a single shelter in a tank. As expected, one of them emerged as the dominant animal and the shelter's sole occupant. Meanwhile, at the head of another tank called a flume, the scientists installed two shelters behind a sheet of wire mesh. Jelle's flume was nine feet long, and it had a water current flowing straight through it from one end to the other. The scientists then separated the two shelters with a wall that ran halfway down the flume, creating a pair of parallel waterways that emptied into a single space downstream. One male was then ensconced behind bars in each waterway upstream, at the top of the flume. From a pool of twenty female lobsters, none of whom had encountered either of the males before, the scientists placed one female at a time in the tank downstream, where the waterways converged. The female thus had two streams of scent to choose from, one originating from each of the unfamiliar males.
Initial trials, with the males catheterized, revealed that when a female drew near one of the shelters, the male inside it pissed with vigor out the door at her. When the catheters were removed and the urine could flow freely down the flume, the females spent most of their time trying to push through the bars of the shelter containing the male that had proved himself dominant in the other tank. Since the females hadn't met him before, the only way they could have known of his superior status was by detecting some indication of the sense of confidence he exuded. Presumably, his piss smelled better.
On subsequent trials the scientists compared the attractiveness of two males that were both dominants in their own right in separate tanks. One of them, however, had won a greater number of fights than the other. The females in the flume had no way of knowing that, and yet they consistently preferred the male that had won the greater number of fights.
Jelle remembered the first time he had imagined how lobster mating worked, the female poised to receive suitors in her shelter, emitting a sexy scent and attracting males from downstream. For nearly twenty years Jelle had followed the trail of chemical communication in the sea. He still didn't know exactly what combination of individual identity and general confidence gave a particular lobster its social status. But it was clear that in a natural setting, the basic pattern of lobster mating was just the opposite of what he had first envisioned.
The dominant male waited in his shelter, peeing out the door of his apartment at the females who came calling. A female would poke her head in and pee back at her prospective mate, a love potion in her urine suppressing his bellicosity and putting him in the mood for courtship. He would stand on tiptoe and pulse his swimmerets, drawing her urine in and fanning it appreciatively about the boudoir.
The scents of his dominant masculinity and her seductive femininity would mingle, Jelle supposed, and waft out the back door of his shelter, like an olfactory billboard posted in his backyard. With this billowing advertisement to the females of the neighborhood that his love nest was active, it hardly seemed surprising that a dominant male might develop a sense of confidence.
F
or all of Jelle Atema's efforts, he had yet to truly enter the lobster's
Umwelt
âto sense the world as a lobster did. The problem was that chemical signals were a messy business. Eyes detect light that mostly travels in straight lines at constant velocity. Ears detect acoustic waves that disperse through a medium according to well-established rules. But smell requires the detection of patches of molecules carried by ever-changing eddies inside chaotic plumes of moving air or water.
The first time Jelle had ever dropped a chunk of fish into a lobster's tank, he'd been amazed by the speed with which lobsters could pinpoint an odor source. At the first sign of an attractive scent they flicked their antennules and began to move, walking slowly at first and adjusting their heading with an accuracy that was nearly instantaneous. After a few seconds they were jogging toward the origin of the odor, whether it was a tasty morsel of food or an alluring lobster of the opposite sex. How did they do it?
The lobster's noseâits pair of antennulesâis perhaps a less remarkable organ than its eyes, but the antennules are far more useful underwater. Attached to them are hundreds of sensory hairs with permeable walls. Inside each hair is a dense tuft of some four hundred grasslike neural cells that are attuned to particular combinations of molecules. If a lobster is walking into a current, the animal aims the antennules straight up like rabbit ears, so that water washes against the full length of the sensory-hair array. But if clear reception is interrupted
by confused currents or imperfect orientation, the lobster flicks its antennules downward in swift strokes to obtain a stronger signal. Thus the analogy to sniffing.
Detecting waterborne chemicals is one thing; tracking them to their source is quite another. The question of how lobsters use their antennules to locate the origin of seemingly random splotches of whirling odor had dogged Jelle for decades. He'd spent hours crouched over a drainage gutter in the floor of his basement lab, squirting dye into the flow of seawater in a vain attempt to detect patterns in the plume of swirls. It was an impossible task because he couldn't see the plume from a lobster's point of view.
That changed when Jelle learned of a research project under way in Colorado. A neuroscientist in Denver was working on ways to repair the neurotransmitters of patients with Parkinson's disease. He had developed a miniature electrode for detecting the neurotransmitter dopamine in rat brains. The electrodes were about the same size as the receptors on a lobster's antennules. Jelle guessed that a pair of these detectors might be able to “see” a water current containing dopamine the same way a lobster “saw” a current containing an odor.
Jelle began to collaborate with the neuroscientist and ran an initial trial in his flume tank. He injected a jet of dopamine into the current from a nozzle at the head of the tank. Then he positioned one of the electrodes at sixty successive locations across a grid downstream, recording the fluctuations in dopamine concentration at each location. As water flowed through the tank, it dispersed the dopamine in an increasingly turbulent plume of cascading eddies. But this time Jelle wasn't watching the plume with human eyes. Instead, he was seeing what a lobster standing at different locations in the tank would sense with its antennulesâa series of changes in chemical concentration.
Neurological studies in Jelle's lab had determined the detection frequency, response speed, and acclimation rates of the chemoreceptor cells in a lobster's antennules. Using this data, Jelle calibrated the recordings from the dopamine detector to
match the lobster's own sensory abilities and graphed the results. The effect was stunning. The odor landscape inside a turbulent plume looked to a lobster something like a mountain range of chemical peaks, each following the next in time. Near the source, those peaks would be tall and steep because the patches of chemicals passing across the lobster's antennules were dense and had clearly defined edges. Farther away from the source, or off to the side, the peaks the lobster would perceive were by degrees shorter and gentler in slope, and spaced farther apart, because the patches of chemicals had become fuzzier and more diffuse.
Dye swirling in a current might appear chaotic to the human eye, but after several hundred million years of tracking odors underwater, a lobster inside a turbulent odor plume surely felt right at home. Most of Jelle's colleagues thought the idea was crazy, but Jelle believed a lobster might be capable of pinpointing its own location in relation to the distant source of the scent simply by the look of the chemical slopes and hills in its immediate vicinity.
The fact that lobsters had not one but two antennules, spaced a body width apart, was also essential to tracking odors. That was all too clear when Jelle snipped one antennule off a lobster and it started walking in circles. One of Jelle's students set about constructing a lobster backpack that contained a submersible amplifier and two dopamine electrodes. When the backpack was attached to a lobster, one electrode sat directly behind each antennule. The lobster was blindfolded and lowered into the downstream end of the flume tank, and a brew of dopamine and squid extract was squirted from a jet upstream. A cable from the lobster's backpack supplied a computer with the electrode readings while another cable supplied the computer with a video feed of the lobster's movements, filmed by an overhead camera. As the lobster tracked the scent of squid up the tank, the computer synchronized the chemical and visual data. The scientists could see the pulses of odor the lobster was experiencing on the right and left sides of its head while it was deciding which direction to turn. As expected, the
lobster turned toward the antennule that detected steeper and higher hills of odor before the other antennule did, enabling the lobster to “climb” the mountain range of the plume to the source, the animal's trajectory growing ever more accurate as the steepness of the peaks increased.
Perhaps it was inevitable that the next experiment would involve mounting two odor-release nozzles on the lobster itself, one pointing at each antennule. Now that Jelle understood how a lobster perceived an odor landscape, it was a simple matter to generate lobster virtual reality. A hungry lobster could be steered through an empty tank at will by squirting bursts of fish-flavored seawater at one antennule or the other.
And after lobster virtual reality, perhaps it was inevitable that lobster artificial intelligence would be the next hurdle. When the diminutive automaton was complete, poised at the downstream end of Jelle's flume tank, it had 256K of RAM and its name was RoboLobster.
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The hurricane warning crackled over Bruce Fernald's radio aboard the
Double Trouble
two days before the end of August 1996. The storm was a monster and approaching Little Cranberry Island quickly. Of Bruce's eight hundred traps, a third were still sitting in shallow water near shore, where a gale could beat them into tangles of wire and twine.
Already, one of those traps had nearly killed him. Bruce had been breaking in a new sternman aboard the
Double Trouble
that yearâa young man who'd never worked on a boat before. Two weeks before Bruce's forty-fifth birthday, the fellow had lost his grip on a brick-laden trap at low tide and let it fall fifteen feet from the wharf to the boat. The trap had missed hitting Bruce by a yard. Bruce was glad to have escaped injury, not least because catches were still on the rise and he couldn't afford to sit out the height of the trapping season. But with a hurricane on the make, Bruce would have to remove his gear from shallow water to ride out the storm.
The next two days passed in a blur of coiled rope and
stacked traps. Aboard the
Double Trouble
Bruce and his sternman, like worshipers of some Pharaoh of lobsters, built pyramid after pyramid of wire-mesh rectangles as they hauled the dripping traps from the water and lugged them in boatloads to land. Little Cranberry's fleet of old pickup trucks came and went from the wharf in a chorus of squeaky springs as the fishermen carted their traps up the road.
The day the hurricane was to arrive a stiff breeze raced across the harbor. The men spent the afternoon hauling small boats out of the water and battening down equipment on the co-op wharfâelectric scales, hundreds of wooden lobster crates, dragnets, and plastic bait trays. After checking the mooring lines to the lobster pens, the lobstermen rowed their skiffs into the harbor and double-checked the mooring lines to their lobster boats, which were too big to pull onto land on short notice.
When the rain came crashing down in leaden sheets across the harbor and the ocean frothed white out of the west, the fishermen knew they were inside the leading edge of the hurricane, and there was nothing more they could do.
Still in their rain slickers and dripping wet, they congregated in the bar at the end of the restaurant wharf to watch the storm come. It was the final day of the restaurant's summer season, when the owners held their customary closing night for the islandersâno tourists allowed. Leftover beer would flow for free until the kegs ran dry. Clutching pints of Harpoon ale and Budweiser, the fishermen sat with their backs to the bar, gazing out through the windows while the rising tempest buffeted the wharf on its pilings and pulled their pitching boats tight on their mooring lines.
One of their fellow fishermen had been running last-minute errands on the mainland, and they wondered whether he would attempt to return to the island. Not long afterward, through the gray dusk they noticed his boat approaching from the north, plumes of spray flying. The fishermen stood up from their barstools and strode to the rattling windows, their pints of beer forgotten, while a part of them, a descendant of the great cod
fisherman Sam Hadlock and one-fifteenth of the whole that made up the island fleet, plunged laboriously toward home. He was half a mile away in jagged peaks of surf.
Suddenly the boat turned east and headed out to sea. They knew what the man was doing. He was afraid the boat might roll on its beam and swamp, so he would try to surf the waves downwind on an angle, find a trough where he could gun the engine and spin the boat back to the southwest, and pound upwind into the oncoming walls of water, splitting them with his bow and making a slow, zigzag kind of progress until he found the harbor. It took him half an hour to cover that half mile, but he managed to reach his mooring and put the boat on its tether. When he walked into the bar he was soaked to the skin, but he had a big grin on his face. A cheer went up and a beer made its way into his hand.
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Little known to the general public, in a nondescript building on the northern fringe of the campus of the Massachusetts Institute of Technology is a small laboratory where research has been funded in part by the U.S. Navy. Inside, scientists have constructed torpedoes that can all but think for themselves. They are called AUVs, or autonomous underwater vehicles, and they disappear into the sea and carry out missions without remote control. Oceanographic research and oil exploration are among the civilian applications of these devices, but close cousins of these machines now assist the U.S. military in amphibious assault operations as well. During Operation Iraqi Freedom several were dropped overboard in the port of Umm Qasr. On dives that could last twelve hours or more, they swam free on their own recognizance, hunting antiship mines.
Thomas Consi, a member of the AUV group of researchers at MIT, was a biologist by training but he liked having little robots walking across his desk. After a day designing intelligent torpedoes Tom would stop by a toy store and hunt for inanimate objects he could bring to life. When MIT hosted its
first Artificial-Intelligence Olympics, Tom fielded a toy army tank that he'd taught to follow a beam of light.
The term for this sort of work, and for the projects under way in the AUV lab, is biomimeticsâthe mimicking of natural physical and behavioral structures using artificial devices and algorithms. The goal isn't only to create useful robots but also to gain insights into the biology of living organisms. Some of Tom's colleagues were constructing a beast called RoboTuna. The purpose of the project was to understand the complex hydrodynamics involved in how a real tuna swims.
When Tom heard about Jelle Atema's plume-tracking project with lobsters, he invited Jelle to MIT, and the concept for RoboLobster was born. Working alongside the intelligent torpedoes in the AUV lab, Tom and a colleague machined, assembled, and programmed the device, and soon the lobster-sized robot had made its way into Jelle's nine-foot flume tank in Woods Hole.
RoboLobster sat poised like a jet fighter on a runway, ready to attack the oncoming current. His watertight body was a shiny cylindrical hull that housed an onboard computer with a 20-megabyte hard drive and sixteen AA batteries. Like an airplane, RoboLobster's fuselage was topped with blinking red lights. A pair of direct-current motors powered his little rubber wheels and provided steering. Protruding straight up from RoboLobster's head were two stainless-steel wiresâa pair of metallic antennules that served as conductivity electrodes. Fresh water was running through the flume instead of salt water, and instead of dopamine or fish juice, RoboLobster would be tracking the scent of a salt-and-ethanol mixture injected into the current.
The brain of a real lobster consists of several nerve ganglions strung together, and nearly half of their volume is dedicated to processing the signals collected by the animal's sense of smell. RoboLobster's brain was far simpler, and the only thing he had to process was smell. He was programmed to turn right or left depending on which electrode detected a higher concentration of salt in the water, to travel in a straight line if
the concentration was similar on both sides, and to move backward if he lost the scent.
Inside the flume RoboLobster managed to track down the source of the salt about 25 percent of the time. Compared to the swift efficiency of a lobster, the paths RoboLobster traveled were torturous. Still, RoboLobster was a start, and Tom was proud of him. RoboLobster was one of the first biomimetic automatons to function successfully underwater. And what was perhaps most startling was how “biological” RoboLobster's performances looked. When plotted on paper, the robot's tracks reflected more the fluid complexity of nature than the programmatic code inside RoboLobster's microchip head. The implication was clear. A real lobster didn't have to be very smart to find its way around inside the currents in the ocean. It just had to be equipped with the proper detectors.
