(ORDO NEWS) — Male birds are not the only animals that lure individuals of the opposite sex through movements and sounds. Male wolf spiders sometimes beat out a rhythm for 45 minutes just to win over a female.
Squeezing their appendages, shaking their abdomens and tapping their front paws, male wolf spiders put on quite a show. And the more sophisticated this representation, the better.
New research on a species of North American wolf spider known as Schizocosa stridulans has shown that the males who create the most complex rhythms are also the most popular with the spider.
And it’s not just good vibrations. Demonstrative visual cues were important factors in female selection, despite how obvious they may appear to a male to predators.
“However, the question of why females are more likely to accept males with more complex display remains open,” the researchers wrote, led by evolutionary biologist Nuri Choi of the University of Nebraska-Lincoln.
“However, despite the presumably higher cost of increasing signal complexity, our data indicate that S. stridulans males can and will actively change their signal complexity, and that this ability may be under direct selection by females.”
During the study, the researchers filmed female and male wolf spiders to see how they react when they meet each other. The dates took place on strips of filter paper, which allowed the researchers to record the animals’ subtle vibrations.
The female spider came first, and while she waited for her suitor for five minutes, she unwound a thread of silk saturated with pheromones, which indicated that she was ready to mate.
When a male appeared, the spiders were allowed to communicate for up to 20 minutes.
In 44 trials, males mated more often and faster if they gave complex courtship signals.
This meant mixing transitions between two sounds – the sound of nails on a rough surface (the so-called “turns”) and the sound of heels on linoleum (the so-called “idle”).
These signals are not only observed by the female spider, but also felt by her in the form of vibrations (after all, spiders do not have ears).
In cases where the female appeared particularly fertile, as evidenced by her body size, successful male spiders stepped up their transitions and began to improvise with sound patterns.
The results obtained indicate that male wolf spiders change the complexity of their signals depending on the feedback from the females.
“We see this in many other animal groups, but people who work with other animal groups are often surprised when they see stories of spiders engaging in such complex behavior,” says behavioral ecologist Eileen Hebets of the University of Nebraska-Lincoln.
“We’ve found this in several studies and it really supports the fact that spiders are just as complex as any other animal when it comes to communication.”
In studies of other types of wolf spiders, scientists have found that males that use different kinds of signals are more successful in mating than those that can only use visual or vibrational signals.
A complex set of signals seems to be a classic example of sexual selection, where the choice of the female helps create increasingly complex means for sex.
The tapping and shaking of the male wolf spider clearly attracts females, but whether these signals convey something deeper is unknown.
In the study, male wolf spiders were not more successful at capturing a female if they were larger. But perhaps the difficulty of touching and shaking tells the female how much the male fits her in some other way.
“Females aren’t necessarily looking for the biggest male, the loudest or the strongest,” says Hebets. “But maybe they’re looking for a male who is really athletic and can coordinate all these different signals in one display.”
Similar disputes are currently being waged over other complex forms of sexual selection in the animal kingdom. Are these complex courtships a sign of high quality mates, a sensory predisposition that males enjoy, or does it just come down to females’ aesthetic preferences?
Perhaps the wolf spider will help us solve this riddle.
Contact us: [email protected]