to the pigmented Strep B had prob- LIFE & EVOLUTION lems. Four went into preterm labor; the fifth had an emergency C-section after Jumping spider hears distant sounds researchers found discolored amniotic Arachnid can detect airborne noise from across a room fluid indicating an infection. Neutrophils flooded the sites of infec- BY SUSAN MILIUS coauthor now at Harvard, started clap- tion, but to no avail. Strep B’s pigment, a Accidental chair squeaks in a lab have ping hands, backing away from the spider chain of fat attracted to cell membranes, tipped off researchers to a new world of and clapping again. The claps didn’t seem poked holes in the neutrophils. The pig- eavesdroppers. earthshaking, but the spider’s brain regis- ment “inserts in random places, disfig- Spiders don’t have eardrums, though tered clapping even when the researchers uring the membrane,” Rajagopal says. their exquisitely sensitive leg hairs pick had backed out into the hallway. Neutrophils normally expel their innards, up vibrations humming through solids Clapping or other test sounds might ensnaring invaders in a mess of DNA and like web silk. Biologists thought airborne confound the experiment by sending chromatin, but the traps were ineffective sounds more than a few centimeters away vibrations through equipment holding against the pigmented bacteria. would be inaudible. But the first record- the spider. So the researchers did their Maria Gloria Dominguez-Bello of the ings of auditory nerve cells firing inside a neuron observations on a table pro- New York University School of Medi- spider brain suggest that the Phidippus tected from vibrations. They also took cine says that this “beautiful, elegant audax jumping spider picks up airborne the setup to an echo-dampened cham- study” raises a lot of questions, such as sounds from at least three meters away, ber in the lab of coauthor Ronald Miles how Strep B can go from harmless to says Ronald Hoy of Cornell University. at Binghamton University in New York. dangerous. During early sessions of spider brain Tests revealed a narrow, low-pitched Other recent work found that some recordings, Hoy’s colleagues saw bursts range of special sensitivity for the spi- Strep B strains emit toxic sacs that of nerve cell, or neuron, activity when a ders. They pick up rumbly tones pitched are associated with stillbirth in mice chair moved. Systematic experiments around 70 to 200 hertz, Hoy says; people (SN: 10/1/16, p. 11). But the pigment seems then showed that from several meters hear best between 500 and 1,000 hertz. to be the bacteria’s primary weapon, the away, the spiders detected relatively quiet Spiders may hear low rumbles much authors of the new paper argue. s tones at levels comparable to human as they do web vibes: with specialized leg conversation. In a hearing test based on hairs, Hoy and colleagues propose. They behavior, the spiders also clearly noticed found that making a hair twitch could Krupenye’s team shows for the first when researchers broadcast a low dron- cause a sound-responsive neuron to fire. time that a nonhuman animal can track ing like the wing sound of a predatory “There seems to be no physical reason others’ false beliefs, says psycholo- wasp. In an instant, the spiders hunkered why a hair could not listen,” says Jérôme gist Amanda Seed of the University of down motionless, the researchers report Casas of the University of Tours in St. Andrews in Fife, Scotland. But it has online October 13 in Current Biology. France. When monitoring nerve response yet to be demonstrated that apes, like Jumping spiders have brains about the from hairs on cricket legs, he’s tracked humans, can act on such knowledge, say, size of a poppy seed. Hoy credits the suc- airplanes flying overhead. Hoy’s team cal- by hiding food from others, she says. cess of probing even tinier spots inside culates that an 80 hertz tone the spiders Laurie Santos, a psychologist at Yale these (anesthetized) brains to coauthor responded to would cause air velocities of University, isn’t so sure apes track Gil Menda, also of Cornell. When Menda only 0.13 millimeters a second if broad- false beliefs. Previous research has realized the spider brain reacted to a cast at 65 decibels three meters away. consistently indicated that no non chair squeak, he and Paul Shamble, a That’s hardly a sigh of a breeze. Yet it’s human animals monitor others’ beliefs, above the threshold for leg hair response, even on tasks similar to those used by says Friedrich Barth of the University of Krupenye’s team, Santos says. In the new Vienna, who studies spider senses. study, she adds, apes may have realized Eons of attacks from wasps might have that an observer was ignorant about been an evolutionary pressure favoring an object’s new location but not that such sensitivity, Hoy says. If detecting he had false expectations about where wasp wing drone turns out to have been to find it. important in the evolution of hearing, Krupenye disagrees: “The apes spe- other spiders vulnerable to wasps might cifically anticipated that the actor in do long-distance eavesdropping, too, the video would search for an object says Ximena Nelson of the University Jumping spiders (Phidippus audax, shown) can where we humans know the actor falsely hear airborne sounds from several meters of Canterbury in Christchurch,
G. MENDA/HOY LAB AT CORNELL LAB AT G. MENDA/HOY believed the object to be.” s away, new experiments suggest. New Zealand. s
Watch a spider respond to threatening sounds at bit.ly/SN_jumpingspider www.sciencenews.org | November 12 , 2016 9