November 26, 2013
Seahorses belong to the genus Hippocampus, which gets its name from the Greek words for “horse” and “sea monster.” With their extreme snouts, weirdly coiled bodies and sluggish movements produced by to two puny little fins, these oddly shaped fish seem like an example of evolution gone terribly awry. And yet, new research published today in Nature Communications shows that it is precisely the seahorse’s uncanny looks and slow motions that allow it to act as one of the most stealthy predators under the sea.
Seahorses, like their close relatives the pipefish and sea dragons, sustain themselves by feasting on elusive, spastic little crustaceans called copepods. To do this, they use a method called pivot feeding: they sneak up on a copepod and then rapidly strike before the animal can escape, much like a person wielding a bug swatter tries to do to take out an irritating but otherwise impossible-to-catch fly. But like that lumbering human, the seahorse will only be successful if it is able to get near enough to its prey to strike at very close range. In the water, however, this is an even greater feat than on land because creatures like copepods are extremely sensitive to any slight hydrodynamic change in the currents around them.
So how do those ungainly little guys manage to feed themselves? As it turns out, the seahorse is a more sophisticated predator than appearance might suggest. In fact, it is precisely its looks that make it an ace in the stealth department. To arrive at this surprising conclusion, researchers from the University of Texas at Austin and the University of Minnesota used holographic and particle image velocimetry–fancy ways of visualizing 3D movements and water flow, respectively–to monitor the hunting patterns of dwarf seahorses in the lab.
In dozens of trials, they found that 84 percent of the seahorses’ approaches successfully managed not to sound the copepod’s retreat alarms. The closer the seahorse could get to its unsuspecting prey and the faster it struck, the greater its odds of success, they observed. Once in range of the copepod, seahorses managed to capture those crustaceans 94 percent of the time. Here, you can see that method of attack, in which the seahorse’s giant head looks like a floating bit of marine sludge drifting toward the blissfully ignorant copepod:
The way the seahorse’s movements and morphology–especially its head–interact with the water particles, the researchers found, likely take the credit for its exceptional hunting skill. The animal’s arched neck acts like a spring for generating an explosive strike, they describe, while the shape of its snout–a thin tube with the mouth positioned at the very end–allows it to drift through the water while creating minimal disturbance.
To emphasize this pinnacle of engineering, the team compared water disruptions caused by seahorses with those of sticklebacks, a relative of the seahorse but with a more traditional fishy look. Thanks to the shape and contours of the seahorse’s head, that predator produced significantly less fluid deformation in the surrounding water than the stickleback. The poor stickleback possesses neither the morphology nor posture to generate “a hydrodynamically quiet zone where strikes occur,” the authors describe. In other words, while the seahorse may appear a bit odd so far as fishes go, evolution was obviously looking out for that funny but deadly animal’s best interests.
November 21, 2013
Over the course of 1700 miles, they sampled the water for small pieces of plastic more than 100 times. Every single time, they found a high concentration of tiny plastic particles. “It doesn’t look like a garbage dump. It looks like beautiful ocean,” Miriam Goldstein, the chief scientist of the vessel sent by Scripps Institution of Oceanography, said afterward. “But then when you put the nets in the water, you see all the little pieces.”
In the years since, a lot of public attention has been justifiably paid to the physical effects of this debris on animals’ bodies. Nearly all of the dead albatrosses sampled on Midway island, for instance, were found to have stomachs filled with plastic objects that likely killed them.
But surprisingly little attention has been paid to the more insidious chemical consequences of this plastic on food webs—including our own. “We’d look over the bow of the boat and try to count how many visible pieces of plastic were there, but eventually, we got to the point that there were so many pieces that we simply couldn’t count them,” says Chelsea Rochman, who was aboard the expedition’s Scripps vessel and is now a PhD student at San Diego State University. “And one time, I was standing there and thinking about how they’re small enough that many organisms can eat them, and the toxins in them, and at that point I suddenly got goosebumps and had to sit down.”
“This problem is completely different from how it’s portrayed,” she remembers thinking. “And, from my perspective, potentially much worse.”
In the years since, Rochman has shown how plastics can absorb dangerous water-borne toxins, such as industrial byproducts like PCB (a coolant) and PBDE (a flame retardant). Consequently, even plastics that contain no toxic substances themselves, such as polyethylene—the most widely used plastic, found in packaging and tons of other products—can serve as a medium for poisons to coalesce from the marine environment.
But what happens to these toxin-saturated plastics when they’re eaten by small fish? In a study published today in Scientific Reports, Rochman and colleagues fill in the picture, showing that the toxins readily transfer to small fish through plastics they ingest and cause liver stress.This is an unsettling development, given that we already know such pollutants concentrate further the more you move up the food chain, from these fish to the larger predatory fish that we eat on a regular basis.
In the study, researchers soaked small pellets of polyethylene in the waters of San Diego Bay for three months, then tested them and discovered that they’d absorbed toxins leached into the water from nearby industrial and military activities. Next, they put the pollution-soaked pellets in tanks (at concentrations lower than those found in the Great Pacific garbage patch) with a small, roughly one-inch-long species called Japanese rice fish. As a control, they also exposed some of the fish to virgin plastic pellets that hadn’t marinated in the Bay, and a third group of fish got no plastic in their tanks at all.
Researchers still aren’t sure why, but many small fish species will eat these sort of small plastic particles—perhaps because, when covered in bacteria, they resemble food, or perhaps because the fish simply aren’t very selective about what they put in their mouths. In either case, over the course of two months, the fish in the experiment consumed many plastic particles, and their health suffered as a result.
“We saw significantly greater concentrations of many toxic chemicals in the fish that were fed the plastic that had been in the ocean, compared to the fish that got either clean plastic or no plastic at all,” Rochman says. “So, is plastic a vector for these chemicals to transfer to fish or to our food chain? We’re now fairly confident that the answer is yes.”
These chemicals, of course, directly affected the fishes’ health. When the researchers examined the tiny creatures’ livers (which filter out toxins in the blood) they found that the animals exposed to the San Diego Bay-soaked plastic had significantly more indications of physiological stress: 74 percent showed severe depletion of glycogen, an energy store (compared to 46 percent of fish who’d eaten virgin plastic and zero percent of those not exposed to plastic), and 11 percent exhibited widespread death of individual liver cells. By contrast, the fish in the other treatments showed no widespread death of liver cells. One particular plastic-fed fish had even developed a liver tumor during the experimental period.
All this is bad news for the entire food webs that rest upon these small fish, which include us. “If these small fish are eating the plastic directly and getting exposed to these chemicals, and then a bigger fish comes up and eat five of them, they’re getting five times the dose, and then the next fish—say, a tuna—eats five of those and they have twenty-five times the dose,” Rochman explains. “This is called biomagnification, and it’s very well-known and well-understood.”
This is the same reason why the EPA advises people to limit their consumption of large predatory fish like tuna. Plastic pollution, whether found in high concentrations in the Great Pacific garbage patch or in the waters surrounding any coastal city, appears to be central to the problem, serving as a vehicle that carries toxins into the food chain in the first place.
November 19, 2013
The North Pole is losing about 30,000 square miles of sea ice per year. Over the past century, average global temperatures have climbed by 1.5 degrees Fahrenheit. And yet, over the past few years, the sea ice that surround the South Pole has steadily been growing.
This past September, at the end of the Southern Hemisphere’s winter, the extent of Antarctica’s sea ice reached 19.51 million square kilometers, breaking a 35-year record that dated back to the start of data being collected in 1978. (In comparison, from 1981 to 2010, the average extent on the same date was just 18.5 million square miles.)
Why are the Arctic and Antarctic such polar opposites? Climate change deniers have pounced upon the unexpected divergence to argue that the planet’s temperature isn’t actually rising. But new research suggests that a different mechanism—unrelated to climate change—is responsible for the ice growth. The real answer, says University of Washington oceanographer Jinlun Zhang, can be found blowing in the wind.
Specifically, according to a study he and colleagues published in the Journal of Climate, the vortex of winds that swirl around the South Pole has both strengthened and converged, a trend that can explain about 80 percent of the growth in ice extent that has been detected in recent years.
Atmospheric scientists had previously observed that these swirling winds had gradually strengthened since the 1970s. Using a computer model, Zhang’s team found that this mechanism drives ice growth—even in the face of rising temperatures—by pushing floating layers of sea ice together, compressing them into thick ridges that are slower to melt.
“Ice ridging increases the amount of open water and areas with thin ice, which are then exposed to cold air in winter, leading to enhanced ice growth,” Zhang says. “Meanwhile, the ridges, driven together by the wind, shrink less during the summer, because thicker ice tends to survive longer.” Based on this mechanism, the model accurately predicted ice growth in the same areas—the Weddell, Bellingshausen, Amundsen and Ross seas—that it’s been most distinctly observed.
Of course, the explanation brings to mind another question: Why is this vortex of swirling winds growing more powerful in the first place? Scientists are still unsure, but a few hypotheses have been put forth.
One possible culprit is the hole in the ozone layer, caused by lingering CFCs that were emitted before their use was phased out by the Montreal Protocol. Because ozone absorbs ultraviolet light from the Sun, missing ozone affects the local balance and transfer of energy, potentially leading to stronger winds. Another possibility is that the strengthened winds can simply be chalked up to natural variability.
Whatever the cause, the observed effect—a growth in Antarctic ice—has been relatively small, especially in comparison to the rapidly melting ice in the Arctic. For now, the winds are causing ice growth, but going forward, that trend is likely to be overwhelmed by a far more potent one: the continued rise in greenhouse gas emissions and the climate change they’re rapidly driving. “If the warming continues, at some point the trend will reverse,” Zhang says.
November 6, 2013
New species of insects, worms and other creepy-crawlers are announced on a monthly basis. Similarly, just last week, two new humpback dolphin species splashed into the headlines. And in October, news broke that early humans may have included fewer species than previously thought. This forces the question: what does it take to be a distinct species?
More than 70 official species definitions exist, of which 48 are widely accepted and used by scientists. And there’s no hard rule that scientists must stick to just one definition; some apply a handful of species definitions when approaching the topic. “I personally go to my lab every day and use five species definitions to conduct research,” says Sergios-Orestis Kolokotronis, a molecular ecologist at Fordham University, and co-author of the new dolphin study, published in Molecular Ecology. “And I sleep just fine amidst this uncertainty.”
Species definitions oftentimes do not translate from one organism to another. Dolphins may become isolated by distance and behavior that prevents them from reproducing, but in other cases–such as bacteria, which reproduce asexually–these distinguishing markers do not apply. Thus, the definition of what constitutes a species varies depending on whether scientists are studying dolphins, monkeys, insects, jellyfish, plants, fungi, bacteria, viruses or other organisms, Kolokotronis explains. And likewise, methods for investigating those species also vary. “Whoever figures out THE unifying species definition across the Domains of Life gets the Crafoord Prize!” Kolokotronis jokes.
In the case of the four dolphin species, each occupy different sections of ocean around the world, including in the Atlantic off West Africa (Sousa teuszii), in the central to western Indo-Pacific (Sousa plumbea), in the eastern Indian and western Pacific (Sousa chinensis) and in northern Australia (researchers are in the process of working on a name for that one–Sousa bazinga, anyone?).
While the humpback dolphins look quite similar, their genetics tells a different story. Researchers collected 235 tissue samples and 180 skulls throughout the animals’ distribution, representing the biggest dataset assembled to date for the animals. The team analyzed mitochondrial and nuclear DNA from the tissue, which revealed significant variations between those four populations. They also compared the skulls for morphological differences.
Although the line between species, sub-species and populations is a blurry one, in this case, the researchers are confident that the four dolphins are divergent enough to warrant the “species” title. The mitochondrial DNA turned up genetic signatures distinct enough to signal a separate species, and likewise, differences in the dolphins skulls supported this divergence. Although the nuclear DNA provided a slightly more confounding picture, it still clearly showed differences between the four species.
“We can confidently say that such strong divergence means these populations are demographically and evolutionarily isolated,” says Martin Mendez, a molecular ecologist at the American Museum of Natural History and lead author of the dolphin paper. “The key is that all the evidence–mitochondrial DNA, nuclear DNA and morphology–exhibited concordant patterns of distinct units,” he continues, which are “usually a must for species proposals.”
The genetic data the team collected does not have enough resolution to reveal how long ago the humpback dolphins diverged, and the team has yet to examine the drivers that fueled those speciation events. But Mendez and his colleagues have found that, in some dolphin populations, environmental factors such as currents and temperature play a role in separating populations and encouraging speciation. Different behaviors can help reinforce that separation, too. Most likely, however, geographic isolation plays a significant role in this case. “For populations living a couple hundred kilometers from one another, it’s perfectly possible for them to meet,” Mendez says. “But the distance from Africa to Australia is so great, it’s difficult to imagine those populations would ever be linked.”
Dolphins, Mendez and his colleagues are finding, evolve relatively quickly once isolated from parent populations. New cryptic–or hidden–species have similarly turned up in waters near South America. There may very well be other species of dolphins–or any type of animal, in fact–lurking undetected within an already-discovered species. ”This really applies to most taxa,” Mendez says. Across the board, “we’re adding many more species by looking at genetic data.”
While cryptic species almost certainly await discovery and will increase the head-counts of some organisms, in the case of ancient human ancestors, on the other hand, researchers now suspect that we’ve been too quick to pull the species card. An extremely well-preserved, approximately 1.8 million year-old Homo erectus skull discovered in Georgia alerted scientists to the potential revision. The skull’s odd proportions–large, but with a small brain case–prompted researchers to analyze variation between modern human and chimpanzee skulls, and compare those variations with other known human ancestor species. As the Guardian reports:
They concluded that the variation among them was no greater than that seen at Dmanisi. Rather than being separate species, the human ancestors found in Africa from the same period may simply be normal variants of H erectus.
If the scientists are right, it would trim the base of the human evolutionary tree and spell the end for names such as H rudolfensis, H gautengensis, H ergaster and possibly H habilis.
Ancient humans, of course, are no longer around for us to study their behaviors and mating tendencies, so anatomy has to do. For now, researchers are calling for more specimens to determine where that line will fall.
The line distinguishing two species may be a fuzzy one, but in the case of the dolphins, it is a big deal in terms of conservation. Australia, for example, is planning to design protective legislation for its new dolphin species, and Mendez hopes other countries will do the same.
Nonetheless, pondering the speciation of humans in dolphins in light of these two findings raises lots of questions: Are we fractally subdividing genetic information and brain cavity size to group and regroup organisms, or is there vast genetic diversity in even familiar species that we’ve yet to uncover? What does it mean for a species to gain or lose members of its family tree? The world and its organisms await more research.
October 31, 2013
Octopuses, those whip-smart but bizarre cephalopods, seem to embody everything creepy and mysterious about the sea–the thought of their soft squishy bodies lurking in the oceans’ dark reaches has inspired monsters ranging from the Kraken to the Caribbean Lusca. Their otherworldly forms, heightened by unfurling tentacles, find their way into more modern monsters and villains too–think Disney’s sea witch Ursula or Spider-Man’s Doc Oc. And don’t forget the octopus-themed horror movies!
A new book, Octopus! The Most Mysterious Creature in the Sea, by Katherine Harmon Courage, comes out today. Harmon Courage takes a deep dive into all things octopus, ranging from their culinary use in dishes around the world to their tragic sex lives. Here, we highlight a few of the fascinating points covered in the book.
1) Octopuses are waaay old. The oldest known octopus fossil belongs to an animal that lived some 296 million years ago, during the Carboniferous period. That specimen belongs to a species named Pohlsepia and is on display at the Field Museum in Chicago. Harmon Courage describes it as a “flattened cow patty” or a “globular splat,” but a close examination reveals the tell-tale eight arms and two eyes. Researchers aren’t sure, but possibly there’s an ink sack there, too. In other words, long before life on land had progressed beyond puny pre-dinosaur reptiles, octopuses had already established their shape for the millions of years to come.
2) Octopuses have three hearts. Two of the hearts work exclusively to move blood beyond the animal’s gills, while the third keeps circulation flowing for the organs. The organ heart actually stops beating when the octopus swims, explaining the species’ penchant for crawling rather than swimming, which exhausts them.
3) The plural of octopus is octopuses. The world “octopus” comes from the Greek, októpus, meaning “eight foot.” The word’s Greek roots means it’s pluralized as a Greek word, too, which depends on both a noun’s gender and the last letter it ends with. In this case, an -es is simply tacked on. So no octopi, octopodes or octopussies, Harmon Courage points out.
4) Aristotle thought octopuses were dumb. In his History of Animals, written in 350 BC, the Greek philosopher wrote that ”The octopus is a stupid creature, for it will approach a man’s hand if it be lowered in the water; but it is neat and thrifty in its habits: that is, it lays up stores in its nest, and, after eating up all that is eatable, it ejects the shells and sheaths of crabs and shell-fish, and the skeletons of little fishes.” After describing a few more quirks of octopus life history–it ejects ink for self-defense, it’s slimy, it can crawl on land–he flippantly signs off, “So much for the mollusca.” However, the big-brained cephalopod can navigate through mazes, solve problems and remember solutions, and take things apart for fun–they even have distinct personalities.
5) Octopus tentacles have a mind of their own. Two-thirds of an octopus’ neurons reside in its tentacles, not its head. As a result, the tentacles can problem solve how to open a shellfish while their owners are busy doing something else, like checking out a cave for more edible goodies. The tentacles can even react after they’ve been completely severed. In one experiment, severed tentacles jerked away in pain when researchers pinched them.
6) Octopus ink doesn’t just hide the animal. The ink also physically harms enemies. It contains a compound called tyrosinase, which, in humans, helps to control the production of the natural pigment melanin. But when sprayed in a predator’s eyes, tyrosinase causes a blinding irritation. It also garbles creatures’ sense of smell and taste. The defensive concoction is so potent, in fact, that octopuses that do not escape their own ink cloud can die.
7) Octopuses have blue blood. To survive in the deep ocean, octopuses evolved a copper rather than iron-based blood called hemocyanin, which turns its blood blue. This copper base is more efficient at transporting oxygen then hemoglobin when water temperature is very low and not much oxygen is around. But this system also causes them to be extremely sensitive to changes in acidity. If the surrounding water’s pH dips too low, octopuses can’t circulate enough oxygen. As such, researchers worry about what will happen to the animals as a result of climate change-induced ocean acidification.
8) Octopuses, to some, are erotic muses. Japan’s notorious “tentacle erotica” traces back to an 1814 woodblock print (potentially NSFW) titled Tako to Ama, or “Octopus and the Shell Diver.” According to Courage, the image takes inspiration from a legend about a female shell diver who is chased by sea creatures, included octopuses, after attracting the eye of a sea dragon god.
9) After mating, it’s game over for octopuses. Mating and parenthood are brief affairs for octopuses, who die shortly after. The species practices external fertilization. Multiple males either insert their spermatophores directly into a tubular funnel that the female uses to breathe, or else literally hand her the sperm, which she always accepts with one of her right tentacles (researchers do not know why). Afterwards, males wander off to die. As for the females, they can lay up to 400,000 eggs, which they obsessively guard and tend to. Prioritizing their motherly duties, females stop eating. But she doesn’t starve to death–rather, when the eggs hatch, the female’s body turns on her. Her body undertakes a cascade of cellular suicide, starting from the optic glands and rippling outward through her tissues and organs until she dies.
10) Most octopus for human consumption comes from North and West Africa. Octopus has been a popular food item in East Asia, Spain, Greece and other countries for centuries, and recently, it has gained popularity in the U.S. and beyond. Today, Koreans consume the most octopus. But that popularity has had an impact on octopus stocks in oceans around the world. In Japan, for example, octopus catches plummeted by 50 percent between the 1960s and the 1980s. The international demand for octopus inspired North and West African fisheries to start targeting the animals in the 80s, although recently demand has taken a toll on those waters as well, shifting fisheries from Morocco to Mauritania and, more recently, Senegal. According to the U.N. Food and Agriculture Organization, around 270,000 tons of octopus is imported by various countries around the world each year.