Impress me, or I might eat you. This seems to be the unfortunate case for peacock spiders, whose courtship rituals can sometimes turn sour if the male isn’t putting on a good enough show. And according to new research on the teeny tiny arachnids, the females aren’t easily wooed.
Demonstrating that the flashiest males tend to be the ones that get lucky, this study lends weight to the notion that female preference plays a huge role in the evolution of extremely exaggerated male traits in these spiders. While we knew sexual selection can shape male appearance, experimental evidence for such pressure driving these grandiose displays has been lacking.
To impress the rather drab-looking females, males – which are just a few millimeters in length – do more than simply flash some color. An exceptionally sexually dimorphic genus, meaning males and females show dramatic differences in appearance, male Maratus spiders show off and wave their elaborate abdominal flaps, which are decorated in a variety of bright, iridescent colors and arranged in striking patterns. These, combined with their elongated third legs that they wiggle and jiggle around in an apparently enticing manner, make quite a visual display.
But it doesn’t end there. During their dance show, the males make the females shake at the knees by sending out a variety of vibratory signals, ranging from “crunch-rolls” to “rumble-rumps.” Your guess is as good as ours as to what exactly comprises a rumble-rump. But which signals are more important to the females when it comes to choosing a mate, or are they all needed to maximize the chances of success?
To find out, researchers collected male and female Maratus volans specimens and set up arenas, consisting of a camera-lined, circular frame that the researchers covered with “nylon fabric” (pantyhose, according to National Geographic). This allowed the team to pick up the vibratory signals with little distortion. In total, 64 pairs were put on trial, but if the male didn’t manage to impress or mate within 15 minutes, or the female became aggressive, they were separated. Any female that was wooed was then put through a second trial with a different male.
As described in Proceedings of the Royal Society B, the males had to work extremely hard to win over the females, who more often than not would shun the males’ advances. In fact, only 25 percent of the first trials ended in success, and none of the second round led to mating. Sometimes, the females would give an abdomen shake to warn them their advances were not welcomed. But that’s not the full extent of their aggression: Study author Michael Kasumovic told National Geographic that disinterested females sometimes engage in cannibalism.
“The males can try to impress as much they want, if the female says no, there is nothing he can do,” Jürgen Otto, a peacock spider expert not involved in the current study, told IFLScience. “I believe the environment in which they are in may also have an influence, for example whether they have a suitable place to mate.”
Importantly, the researchers found that while both visual and vibratory signals were important, females were much more likely to mate with males that gave the best visual display. The more visual effort they put in, the less time they spent hesitant, and the more time they spent mating.
According to the researchers, these findings affirm the notion that these elaborate rituals have evolved as a result of strong sexual selection from females, something that has been difficult to confidently show in scientific studies, not just in spiders but extreme cases of sexual dimorphism in general.