Male spiders who are cannibalized by females are pickier than males who expect to survive the mating process. In an exceptional example of sexual role reversal, these males are coy and the females are seductive. The findings are published in PLOS One this week.
In the animal kingdom, males typically compete for females. That’s because sperm is usually smaller, cheaper to make, and more abundant than eggs. Males are promiscuous and females are choosy. But for many species, males are the ones that exercise mate choice, even when they don’t stick around to take care of their offspring.
Colonial orb-weaving spiders (Cyrtophora citricola) have high rates of sexual cannibalism. They also live in dense colonies of thousands of individuals, so mature spiders are very likely to encounter multiple potential mates. But while females can reenter the mating pool, dead males can’t. With that much to lose, it makes sense for males to be picky about the females they mate with.
Copulation and sexual cannibalism in Cyrtophora citricola. (A) The final approach of the male before he inserts his sperm delivery organ (called the pedipalp) into the genital opening of the female (B). The female bites the abdomen of the male while his pedipalp is still attached (C). Yip et al., PLOS One 2016
To see if males are pickier given their single mate choice, a team led by Eric Yip from Ben-Gurion University of the Negev collected colonial orb-weaving spiders from six different sites in Israel. They paired males and females of varying ages and statuses (virgins, mated, fed, or hungry, for example) to see which sex is more selective and what characters they select for.
Females are “readily polyandrous” and they don’t seem to pick male partners based on factors like age or nutritional state. Males are choosier than females, and they’re twice as likely to copulate with females who are well-fed. Not being hungry doesn’t necessarily mean that she would be more likely to spare him; rather, it’s a proxy for fertility.
"With over 80 percent of males cannibalized after their first copulation, males need to make their one shot at paternity count," Yip explained in a statement. "In a colony, males are likely to encounter multiple receptive females, and we found that males prefer to court and mate with younger, fatter, and therefore potentially more fecund females." Together, group living and sexual cannibalism may promote the evolution of male mate choice.