A new study conducted by University of Toronto PhD candidate Luciana Baruffaldi and University of Toronto Scarborough professor Dr. Maydianne Andrade describes the mechanism behind the male black widow spider’s mate selection preference.
From an evolutionary standpoint between male and female species, females have been portrayed to be the pickier sex; males across species must often perform mating rituals and engage in competition against other males through a variety of activities, such as producing the most colourful display, creating the loudest calls, or aggressive altercations.
These are all performed in order to impress the female and win her as a mate. In the case of black widow spiders, however, while it is true that males must invest in courtship rituals to attract their female counterpart, they are also picky when they decide which female is worth the investment in terms of performing their courtship displays.
According to Buruffaldi, the males are able to detect pheromones released by females in the silk they produce, and can ultimately determine how well-fed the female is through those chemical cues alone. From a survival and reproduction standpoint, the male black widow spiders are known to typically prefer mates who are well-fed, as this is a physical manifestation of their fertility.
“We knew that males would react in some way to the pheromones, but we didn’t know exactly what information they were using,” says Buruffaldi, adding, “it was really important to show that these chemical cues alone on a filter paper were enough for the males to tell a difference.”
Baruffaldi and Andrade wanted to determine the reason why the male black widow spiders were specifically seeking well-fed partners. They wanted to address the following specific issues — the isolated effect of pheromones on the male black widow’s mate choice, the desire to mate with a fertile female so as to ensure reproductive success, and the need to avoid mating with a hungry and cannibalistic female (it being an established finding that black widow females are cannibalistic in nature).
The researchers conducted comparative studies on two species of black widow male and female spiders, and their findings strongly suggested that males choose mates out of the need to avoid the situation of mating with hungry cannibalistic females, rather than waiting to ensure reproductive success with a well-fed female.
Baruffaldi and Andrade’s findings took into consideration previous research, which established that one of the species naturally did not avoid mating with cannibalistic females, while the other was keen to avoid them.
With respect to the comparative study of these two species, Baruffaldi says, “Males want to find a female, but some want to successfully mate with that female. One species will avoid the hungry females, the other does not.”
