New research published in the journal Animal Behaviour shows that male black widow spiders prefer their female mates to be well-fed virgins — a rare example of mate preference by male spiders.
The study, authored by Emily MacLeod, a postdoctoral researcher at the University of Toronto Scarborough, and Maydianne Andrade, a professor in UTSC’s Department of Biological Sciences, found that in the wild and in controlled field studies, black widow males overwhelmingly chose to mate with well-fed, unmated females. They also found that male black widows can tell whether a potential mate is well-fed and unmated by pheromones released by females.
“This near unanimous preference by males for well-fed mates using only phermonal cues has not been documented in any other spider species,” said MacLeod. “These are not visual or auditory cues they are picking up, but smells they are sensing, often from far away.”
Macleod said the reason males show a strong preference for females who smell like they’ve eaten a lot is that mating with a fatter female may result in more offspring than with less well-fed females.
“Females who have been able to eat a lot and obtain a lot of food resources can transfer those resources into egg production,” said MacLeod. “It’s not just that they are healthier but that they are more fertile because they can produce more egg sacks.”
Another reason for male choice may be a simple matter of survival. “It’s important to remember that when a female eats a lot of prey, she’s less likely to eat a potential mate,” said Andrade.
The study focused on Latrodectus hesperus, a species of black widow native to western North America, including parts of Canada. These black widows are not generally cannibalistic, but males are much smaller than females, so if a female is hungry her drive to feed may be greater than her drive to reproduce.
“If you have this little food item dancing on a web, you may as well eat it if you don’t have energy to produce eggs,” said MacLeod.
The existence of male choice in nature is unusual because of the costs associated with being picky. In a lab environment, male spiders can afford to be choosey, but in nature there are risks in spending time, energy, and resources on finding a mate, said Andrade.
The study also shows there may be more involved to mating preference than a mere matter of what’s available.
“It shows that males aren’t just promiscuous sperm packages. In fact, they can go to great lengths to exercise choice in a mate,” said MacLeod.
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