Abused become abusers
A common explanation for human child abuse—that the abuser was mistreated as a child him—also applies to Nazca boobies nesting on Española Island in the Galápagos, according to new research published in the October issue of The Auk. Chicks that are bitten and pecked by neighboring birds grow up to be abusers themselves. The study provides some of the first evidence that this "cycle of violence" exists in wild animals.
The sea birds' chick abuse is "one of the first things you notice; it's that obvious and disturbing," David Anderson, an evolutionary ecologist at Wake Forest University in Winston-Salem, North Carolina, told ScienceNOW. To understand the consequences of this behavior, Anderson, who has been observing the boobies since the mid-1980s, and his colleagues observed the treatment of 24 chicks, then tagged them and watched their behavior as adults. Sure enough, those individuals that were abused as nestlings grew into worse abusers as adults, much like patterns seen in human behavior. But unlike humans, who are usually related to the children they abuse, the boobies attack unrelated chicks. Furthermore, behavioral biologist Dario Maestripieri of the University of Chicago in Illinois told ScienceNOW, “what happens in humans is pathological, whereas the birds are programmed to attack each other."
Baby beetles befuddle frogs
Two recently discovered ground beetles (Epomis dejeani and E. circumscriptus) breed worm-like offspring that kill and eat amphibians much larger than the fingertip-sized larvae. The beetle larvae appear to trick the amphibians into attacking them, according to new research published last month in PLoS ONE. Specifically, the larvae wave their antennae around as they approach their amphibian prey, sometimes opening and closing their mandibles as well. This elaborate display lures the amphibians into attacking the larvae. The larvae then dodge the attack, and latch onto the unsuspecting frog or salamander’s skin and suck it dry. On the rare occasion that the amphibians take the larvae into their mouths, they quickly spit them out, and the larvae then succeed in killing their prey. One larva that was swallowed into the amphibian’s stomach was eventually thrown up and able to kill and eat the amphibian.
This type of hunting behavior is highly unusual, entomologist Gil Wizen of the University of Toronto told Wired Science. While some 10 percent of predators take down larger prey, this is the only known example of a smaller creature luring a bigger animal to its doom. “The amphibians don’t stand a chance,” Wizen said. “Normally amphibians eat small larvae, so the larvae seem to be taking their revenge here.”
Big koalas = deeper bellows
Koalas are notoriously lazy animals, sleeping 19 hours each day and eating for more than half of the hours they are awake. But during mating season, male koalas break their lethargic routine, projecting low, booming calls known as bellows across the treetops. New research, published in the Journal of Experimental Biology, suggests that these bellows, which could help attract females and ward other males, are an indicator of the male’s size.
Benjamin Charlton from the University of Vienna, Austria, and his colleagues examined the koala’s vocal tract and discovered that the larynx was quite descended, not high up in the throat like many mammals. Additionally, the muscle connecting the larynx to the sternum, called the sternothyroid muscle, was anchored surprising deep in chest, possibly serving to retract the larynx even further. These findings suggest that male koalas have strikingly long vocal tracts, allowing them to create their baritone calls. Sure enough, the larger the male (and the longer the vocal tract), the lower the resonance of their calls. Analyzing the calls, Charlton found that the koalas could make themselves sound even bigger than they were—even bigger than bison—stretching their vocal tracts to nearly the length of their entire body.
“Individuals that could elongate their vocal tracts by lowering the larynx may have gained advantages during sexual competition by sounding larger,” Charlton said in a press release, “and this would drive the evolution of laryngeal descent.”
Grass-cutting ants are renowned for the impressive underground cities they build, housing up to seven million insects that tend to their fungal gardens where food for the young is farmed. New research published in the Journal of Insect Behaviour reveals how the ants maintain the proper temperature in their nests to promote fungal growth. The key lies in specialized structures called turrets that ventilate the nests.
Marcela Cosarinsky from the Argentinian Museum of Natural Sciences, Bernardino Rivadavia, in Buenos Aires, and her colleagues housed a colony of ants in the lab and provided them with variable amounts of three different materials—clay, coarse sand, and fine sand—and observed the nest-making process. The researchers found that regardless of material, the ants constructed the turret walls in a highly porous manner. “The ants construct the turrets by stacking sand grains and little balls of clay that they mould with their [jaws],” Cosarinsky told BBC News. When the team poured water on the nests to simulate rain, the pores collapsed, and the ants immediately set to work repairing the porous structure.
The findings confirm previous suspicions that the turrets are built by the ants specifically to ventilate their nests, and are not simply byproducts of the excavation process. “They don't simply result from a passive deposition of excavated soil, as is the case in many other ant species,” Cosarinsky said.
Calls of the predatory piranha
Underwater recordings of red-bellied piranhas, which have a reputation as vicious predators, suggest that the fish may be more bark than bite, according to a study published in the Journal of Experimental Biology. Indeed, the fish have three different calls, each linked to a different behavior—a repetitive grunt often led to a visual face-off, potentially signaling "get away from me;" a low thud appeared tied to circling and fighting behaviors; and the sound of gnashing teeth, which occurred when the first two “warning” calls didn’t successfully scare off the intruder.
The grunts and thuds were generated by a fast-twitching muscle near the piranha's swim bladder, the researchers showed. "We knew piranhas were able to make sounds but were not satisfied with the explanation for how they do it," biologist Eric Parmentier of the Université de Liège in Belgium told National Geographic. "We wanted to know how they do this and what these sounds might mean to other fish."
(See a piranha video from National Geographic.)