Samplings—News from Nature

September 2008

Bladderwort trap contains algae. Photo by Thomas Lendl, University of Vienna

Bladderworts, carnivorous plants of the genus Utricularia, live in water or soggy soil. To snare their snacks, bladderworts set ingenious little traps, sometimes in the hundreds, among their waterborne leaves. The traps maintain an internal pressure lower than that outside; when passing prey triggers an exterior hair, a trapdoor snaps open, and inflowing water carries the prey inside to be digested.

     Biologists have long noted algae among the insects, nematodes, and other minute animal prey in bladderwort traps. Are the algae symbionts? Are they swept in accidentally with animals? Or could bladderworts actually eat algae?

     To advance the debate, Marianne Peroutka of the University of Vienna and several colleagues analyzed 1,450 traps from four species of Utricularia. More than half the traps contained algae, often unaccompanied by animal prey. In fact, algae constituted as much as 80 percent of trap contents under certain conditions. Intriguingly, the softer the water the plant inhabited, the more algae its bladders bore. Soft water, low in minerals, supports less animal life than hard water does, and Peroutka thinks bladderworts may compensate for the lack of meat by eating more greens. Indeed, some of the entrapped algae appeared semi-digested, as others have noted.

     A few other carnivorous plants are known to eat plant matter, so perhaps we should start calling them omnivores. (Plant Ecology)

Web Links:

     Cell Physiology & Scientific Film

     University of Vienna

—Ashok Prasad

	A chimpanzee chooses between cooked and raw food. Wobber and colleagues found that great apes preferred cooked to raw food when presented with such a choice. Photo courtesy of the Jane Goodall Institute. All rights reserved: image may not be reproduced, copied, or sold without written permission of the Jane Goodall Institute.

When early humans mastered the use of fire, their immediate rewards were warmth, light, and protection from nocturnal predators. Investigators have assumed that our ancestors also quickly realized the advantages of flame-cooked food—easy chewing and digestion—though clear evidence has been hard to find. A new study bolsters that idea, showing that we share our fondness for cooked grub with our wild cousins, the great apes.

     Victoria Wobber and her graduate advisor at Harvard University, Richard Wrangham, along with a third colleague, gave a choice between cooked and raw food to a number of captive apes. Chimpanzees clearly preferred cooked carrots, sweet potatoes, and beef over the raw alternatives. They did not express any preference in the case of white potatoes and apples—perhaps, the scientists say, because both remain relatively unchanged by cooking. A few bonobos, gorillas, and orangutans were also tested, and except for a penchant for cooked beef, not many expressed a preference, but those that did agreed with the chimps. The findings concur with research showing that cats favor cooked meat and rats opt for cooked starch.

     If animals with no regular access to cooked food nevertheless prefer it, it is plausible that our ancestors would have readily roasted their own victuals once they got the chance—a fine story to tell your guests around the barbecue this evening. (Journal of Human Evolution)

Web Link: The Jane Goodall Institute

—Stéphan Reebs

Common murre chick, an indicator of fish quality in the Baltic Sea Photo by the Baltic Seabird Project

In the Baltic Sea, birds called common murres (guillemots) raise their young on herringlike fish called sprat. In the 1990s, local sprat became unusually abundant after populations of their main predator, cod, plunged because of overfishing and climatic changes. Yet during that time, murre chicks grew poorly. Why?

     The answer may lie in the “junk food hypothesis,” which holds that poor-quality food can hamper the reproductive success of marine predators just as badly as low-quantity food. Henrik Österblom, the biologist from the Baltic Nest Institute at the University of Stockholm who studied the murres, noted that sprat were leaner when they were abundant and had to compete for limited supplies of zooplankton. The lean sprat made less-nutritious meals for the murre chicks. The chicks’ parents tried to compensate by bringing home more sprats, but because they catch and carry just a single fish at a time, it was hard to keep up.

     The murres aren’t alone: recent experiments have shown that many marine fish-eaters, including Steller’s sea lions and kittiwakes, either can’t raise healthy young or can’t maintain their own weight when fed low-energy food, however plentiful. With colleagues, Österblom reviewed all the papers he could find on the subject and concluded that the junk food hypothesis could explain, at least in part, recent cases of breeding failure among marine predators. (Oikos)

Web Link: Baltic Seabird Research Project

—S.R.

	Left: Dinosaur bone marked by scavenging dermestid-beetle larvae. Right: A living example of one of the larvae. Photos by Brooks B. Britt

Dermestid beetles are well known in forensic circles: they congregate on corpses to feed and breed, and their presence and life stage can help establish when the victim died. Some species haunt natural history museums, where they can be pests (munching the dead skin of stuffed animals) or helpers (enlisted by curators to clean bits of tendon and muscle off skeletons). Now, new evidence shows that dermestids were recycling carcasses as far back as the Jurassic.

     Working with two collaborators, Brooks B. Britt of Brigham Young University in Provo, Utah, examined the 150-million-year-old fossil of a Camptosaurus dinosaur and observed that most of its bones bear minute pits, grooves, bores, and scratches. Those, the team established, are the telltale signs of dermestid larvae that tried to get at the bone marrow after the putrid dinosaur meat ran out. The marks matched those made by modern-day dermestids and not those of any other insect scavengers, such as termites (which can consume an entire human skeleton), mayfly nymphs, or moth larvae.

     After examining 7,000 fossilized bones in addition to the Camptosaurus’s, Britt says insect marks are common but often go unnoticed. Insect activity could explain some fossil mysteries, such as “dinosaur dentures”—teeth that are found side by side in perfect order but without any supporting jaw. Chances are, scavenging insects ate the whole bone away before it could fossilize. (Ichnos)

—S.R.

A young three-toed sloth hangs out. Photo by Bryson Voirin

Sloths have a reputation for sluggishness, so nobody was surprised when a 1983 study reported that they sleep sixteen hours a day—one of the highest values ever recorded for any species. But the sloths under scrutiny were living in captivity, a necessity given the complex and cumbersome equipment needed to pick up sleeping animals’ brain waves. Now, the development of lightweight recorders has enabled the first field study, which may force a redefinition of the word “slothful.”

     Niels C. Rattenborg of the Max Planck Institute for Ornithology in Seewiesen, Germany, and seven colleagues captured three adult brown-throated three-toed sloths (Bradypus variegatus) in the jungles of Panama. The team fitted small brain-wave and muscular-activity recorders onto the sloths’ heads, then let them go. During the next five days, the scientists were surprised to find, the sloths indulged in just nine and a half hours of sleep daily.

     To elucidate sleep’s still-mysterious function, researchers often compare species, and they try to correlate sleep time with ecological conditions and physiological traits. Rattenborg warns that captivity, with its abundant food, lack of predators, and attendant boredom, may permit animals to be abnormally drowsy, and so may muddy scientists’ understanding of their natural sleeping habits. (Biology Letters)

Web Links:

     Smithsonian Tropical Research Institute

     Automated Radio Telemetry System Initiative

     “Schlaf und Flug bei Vögeln” (in German)

     Sleep and Flight in Birds

—S.R.

	Escherichia coli Images courtesy of Saeed Tavazoie

Gut Reactors

Bacteria may be humble single-celled creatures, but they’re sophisticated enough to anticipate regular events, such as the arrival of day, thanks to their internal circadian clocks. A new study shows that they can also anticipate and prepare for sporadic events, as long as the events are reliably preceded by a signal.

     What kinds of events? Well, to colonize the gut of a mammal, Escherichia coli must first enter the warm-blooded diner’s mouth, where the bacteria experience a temperature rise; a short time later, they end up in the intestines—a place with low oxygen levels, as well as fierce competition from other microscopic settlers. Bacteria would do well to anticipate low-oxygen conditions and begin to adjust metabolically from the moment they enter the mouth.

     Indeed, when Ilias Tagkopoulos, his graduate advisor Saeed Tavazoie, and Yir-Chung Liu, all at Princeton University, cranked up the heat on E. coli in the laboratory from 77 to 98.6 degrees Fahrenheit, the bacteria immediately deactivated genes involved in aerobic respiration (which requires oxygen) and activated genes governing anaerobic respiration (which doesn’t).

     Then the team repeatedly exposed a population of E. coli to a rise in oxygen following a rise in temperature, a sequence unlikely to occur in nature. The bacteria’s native low-oxygen response all but vanished within a hundred generations, confirming that their foresight is flexible and results from natural selection. (Science)

—S.R.

In a mixed-species hive, a European honeybee (blue) gives directions to its Asiatic (green) and fellow European (red) hivemates. Photo by Songkun Su and Shenglu Chen, Zhejiang University

Honeybees are clever little creatures. They can form abstract concepts, such as symmetry versus asymmetry, and they use symbolic language—the celebrated waggle dance—to direct their hivemates to flower patches. New reports suggest that they can also communicate across species, and can count—up to a point.

     With colleagues, Songkun Su of Zhejiang University in Hangzhou, China, and Shaowu Zhang of the Australian National University in Canberra managed to overcome the apian impulse to kill intruders and cultivated the first mixed-species colonies, made up of European honeybees, Apis mellifera, and Asiatic honeybees, A. cerana. The researchers confirmed that the two species have their own dialects: foraging in identical environments, the bees signaled the distance to a food source with dances of different durations. Remarkably, despite the communication barrier, A. cerana decoded A. mellifera’s dance and found the food.

     Also at the Australian National University, Marie Dacke and Mandyam V. Srinivasan trained European honeybees to pass a particular number of colored stripes in a tunnel to get a food reward, which was placed by a stripe. When they removed the food, the bees still returned to the same stripe. Next, they mixed things up on the bees: they varied the spacing of the stripes, and even replaced stripes with unfamiliar markers. The insects consistently passed the same number of markers to approach the former reward site, demonstrating that they could count, up to four.

     The studies burnish the impressive list of honeybees’ known cognitive abilities, all achieved with a brain the size of a sand grain. (PLoS One, Animal Cognition)

—Graciela Flores

	East Antarctic ice stream Image by NASA/Goddard Space Flight Center Scientific Visualization Studio

Wide rivers of ice, called ice streams, flow through relatively slow-moving polar ice sheets, en route to the sea. Glaciologists had assumed that ice streams just creep steadily along—until one was recently shown to pack a powerful one-two punch, generating seismic waves twice a day.

    The seismic signals from Antarctica’s sixty-mile-wide Whillans Ice Stream are as strong as those of a magnitude-seven earthquake, which could cause major damage in a developed area. But, whereas an earthquake of magnitude seven might last ten seconds, the Whillans signals continue for ten minutes or longer. They resemble earthquakes at glacial speed, says Douglas A. Wiens of Washington University in St. Louis.

    Wiens, with three colleagues, discovered the signals after analyzing recordings from seismographs located 600 miles from the ice stream. To pinpoint the signals’ cause, they embedded GPS antennae on and near Whillans. It’s the ice stream advancing abruptly, by about eighteen inches, that causes the signals, the team discovered. In turn, the advances are caused by a combination of ocean tides—which lift and lower floating ice at the stream’s outlet—and pressure from ice upstream. One of the daily slips is triggered by high tide, with a second following five to twelve hours later. (Nature)

—Harvey Leifert

The Warming Earth

A recently regenerated arm of the brittlestar Amphiura filiformis. At this stage the regenerated (regrown) section is distinguishable by a lighter color and thinner appearance than the established arm. Photo by Hannah L. Wood

The oceans absorb about half the carbon dioxide humankind releases into the atmosphere, and seawater is consequently acidifying. That’s a big problem for shellfish, corals, and certain other calcareous creatures, because lowered pH dissolves their shells and skeletons. Echinoderms—starfish and their relatives—have calcium-based skeletons, too, and so researchers have assumed they are likewise subject to slow dissolution.

    Hannah L. Wood of the Plymouth Marine Laboratory in England and two co-workers decided to check. They took brittlestars (Amphiura filiformis), removed an arm or two, and then, to test how acidity affected regeneration of the lost arms, exposed the animals to seawater that was either normal (pH 8.0) or acidified (pH 7.7—the standard worst-case prediction for the year 2100—and pH 7.3). To Wood’s surprise, the brittlestars actually regenerated their arms faster in the acidified seawater than in the normal stuff, showing that they could lay down calcium effectively even under adverse conditions.

    But there was a hidden cost. Both intact and regenerated arms had considerably less muscle mass in acidified seawater than they did in normal seawater. The low-pH animals consumed extra oxygen, so they were working hard, and Wood thinks they had to burn muscle to fuel the laborious regeneration. Weakened arms would undoubtedly affect feeding and reproduction. Thus, even if it doesn’t affect their calcification, low pH still costs echinoderms an arm and a leg. (Proceedings of the Royal Society B)

Web Link: Plymouth Marine Laboratory

—S.R.

Copyright © Natural History Magazine, Inc., 2008