"Importantly, this indicates that the spiders likely recognized the difference between habitats and the efficacy of signaling via vibrations on leaf litter," said Gordon.
This efficacy of the seismic signaling for mating was measured via a laser vibrometer, a highly sensitive instrument capable of detecting the barely perceptible vibration signals of these tiny animals. The males send out these signals via body bounces and stridulation (rubbing opposing parts of special "file and scraper" organs) on these environmental surface substrates. The measurements found that such movements made atop leaves transmitted significantly more mating signal vibrations vs. those made upon other surfaces (rock, soil, wood). As a consequence, these different substrates can dramatically affect the spiders' ability to communicate.
While the male spiders did continue the leg taps and body bounces on surfaces that transmit faint or no vibrations (wood, soil, stone), the males also altered their communications to produce significantly more visual signals (raising and arching a foreleg) when placed on soil, rock or wood substrates vs. leaf-litter substrate.
Said Uetz, "In other words, when the seismic signals aren't working due to the environment, male wolf spiders have the ability to vary their signals and shift to another communications mode. They then put more effort into another channel, this being visual cues, in order to get the desired response. We can think of it as going to plan B."
He added that, traditionally, such behavioral flexibility has been considered a hallmark of vertebrate animals but not invertebrates: "These findings suggest that invertebrates have more ability to modify their behavior than has been traditionally thought to be the case. This ability enables them to compensate for the impact that an animal's environment has on its ability to communicate."
|Contact: M.B. Reilly|
University of Cincinnati