Brown widow males prefer older females even though their chances of surviving mating are lower

Males of the brown widow prefer to mate with older and less fertile females, although there is a 50% risk that the end of such mating will actually be the end of the male being eaten by the female, according to a team of Israeli researchers in a new study published in the journal Animal Behavior.

Males of the brown widow prefer to mate with older and less fertile females, although there is a 50% risk that the end of such mating will actually be the end of the male being eaten by the female, according to a team of Israeli researchers in a new study published in the journal Animal Behavior.

Researchers at Ben-Gurion University of the Negev, the Hebrew University of Jerusalem and the Volcanic Institute collected male and female brown widow spiders from central and southern Israel and set up an experiment in which the males had the option of choosing which spider to approach - young or old. Young females are able to mate and store sperm as subadults and produce eggs, fertilizing them only after the final transition to full maturity.

"Originally we thought that the males would prefer the young females, since they are more fertile and the chance that they will eat at the end of mating is smaller. We were surprised to see that most of the males were actually attracted to the mature females" said the researchers.

Next they investigated whether the male simply blocked the female's pair of genital openings by leaving part of each of his pair of pedipalps (an organ used to transfer the sperm to the female) inside the females. By blocking the openings, the male tries to prevent the female from mating again with another male. If more cases of blocking The mating openings were held after mating with an adult female than with a young female, so, a male that mated with an adult female would benefit from more offspring due to the lack of competition with other males. However, no difference was found in the frequency of closure of the genital openings after mating with an old female or a young female.

"It seems that the males who mate with older females do not act in their own interest and as a result they will suffer twice - they will have fewer offspring and they will not have the opportunity to mate with another female," say the researchers. "There are several possible explanations for this: it is possible that older females secrete a stronger smell (pheromone) and "deceive" the males, and it is possible that the young females are less interested in mating at this stage in their lives, and are less attractive to the males. These hypotheses require further research."

This research is part of the master's thesis of Shavi Wanner from the Hebrew University of Jerusalem, under the joint supervision of Prof. Uzi Motro from the Department of Ecology, Evolution and Behavior, and from the Federman Center for the Study of Rationality at the Hebrew University of Jerusalem, Prof. Yael Lubin from the Marco and Louise Mitrani Department of Desert Ecology at the University of Jerusalem. Ben-Gurion in the Negev and Prof. Eli Harari from the Department of Entomology from the Volcani Center.

The Federman Center for the Study of Rationality at the Hebrew University of Jerusalem supported the research.