Male brown widow spiders prefer sex with older females
When it comes to brown widow spiders, the females are the stronger sex and cannibals at that, while males seem to be suicidal.
According to Ben-Gurion University, the Hebrew University and the Volcani Center researchers, male brown widow spiders want to mate with older, less-fertile females who are 50% more likely to eat them after sex.
The scientists presented their findings in the new issue of the journal Animal Behaviour.
Researchers at BGU in Beersheba, Hebrew University in Jerusalem and Volcani in Rishon Lezion collected the male and female spiders from central and southern Israel and then positioned the females in a way that gave the males the choice of which to approach – immature (sub-adult) or mature (old) females – while they observed the interactions. Immature females are able to mate, store sperm and produce eggs after the final molt to adult stage.
“We originally thought the males would prefer the sub-adult females, as they are more fertile and far less likely to cannibalize them, but we were surprised to discover that was not the case,” the researchers said.
The study is part of the master’s of science degree thesis of Hebrew University’s Shevy Waner, whose adviser was Prof. Uzi Motro from the ecology, evolution and behavior department and the Federmann Center for the Study of Rationality; Prof. Yael Lubin from the Marco and BGU’s desert ecology department; and Prof. Ally Harari of the entomology department at Volcani.
The team subsequently investigated whether the males had plugged the genital openings of the females by leaving part of their pedipalps (the male copulatory organs) inside the females. By plugging the openings, a male may discourage the female from mating again with another male. But that was not the case.
“Males don’t seem to be behaving in their own self-interest and suffer a two-fold cost – fewer offspring and no opportunity to mate with another female,” the researchers said. One possible explanation is that older females are manipulating the males by using strong signals to attract them, a hypothesis that remains to be tested.”