Scott Schrage, July 15, 2022
In plain sound: Noise disrupts, confirms hidden channel of spider courtship
POCKET SCIENCE: EXPLORING THE ‘WHAT,’ ‘SO WHAT’ AND ‘NOW WHAT’ OF HUSKER RESEARCH
Welcome to Pocket Science: a glimpse at recent research from Husker scientists and engineers. For those who want to quickly learn the “What,” “So what” and “Now what” of Husker research.
Though most research into animal communication has focused on signals that target just one sense — visual, auditory, olfactory, tactile — biologists are increasingly investigating communication that can engage multiple senses at once.
Wolf spiders of many species, including Schizocosa retrorsa, are wizards at this communicative multitasking. A male attempting to attract a mate, for instance, may lift and wave a foreleg to catch at least some of a female’s eight eyes before hammering that leg to the ground, sending her what he hopes are good vibrations that signal his fitness to sire spiderlings.
Yet prior experiments have shown that an S. retrorsa male is just as likely to get lucky when courting a female in pitch darkness, while on granite — conditions that nullify his visual and vibratory signals, respectively. Those findings have hinted that the leg-waving might also be communicating via near-field sound: by stirring the movement of air particles that can themselves stir sensory hairs on a female’s legs. To date, though, no study had directly tested the hypothesis.
The team used a microscope to confirm that the sensory hairs, or trichobothria, of a female wolf spider responded to the white noise piped in by a speaker.
Nebraska’s Pallabi Kundu, Eileen Hebets and colleagues conducted experiments that kept the darkness and granite but added a third potential impediment: air particle-animating noise. If S. retrorsa males do court females with near-field sound, the arachnologists figured, then piping in white noise might disrupt their manipulation of air particles enough to lower their odds of persuading females to mate.
That’s what the team found — with a catch. Across two experiments, 21 of the 40 males that courted females without the white noise managed to mate, versus just five of the 40 whose signals were drenched with that noise. Males also waved their forelegs substantially less often in the presence of noise, suggesting that they might be less willing to invest energy in courtship under the less-than-ideal conditions. As Kundu and company expected, more leg-waving corresponded with more mating success when the noise was absent.
But the waving-mating relationship held in the noisy condition, too, seeming to contradict the other findings. The surprising result could mean that noise will delay or challenge, but not totally impede, a female’s ability to sense the near-field sound — a conclusion backed by the fact that females took less time to decide on mating in the no-noise condition. Another, simpler explanation? The frequency of the white noise was higher than that of the near-field sound generated by males’ leg-waving, possibly mitigating the effects of the former.
Remedying that frequency mismatch could help determine whether it contributed to the counterintuitive finding, the researchers said. Arachnologists could also attempt to study the near-field sound in natural environments, where wind, other animals and traffic produce potentially disruptive noise.