Females at risk: sexual cannibalism the other way round

In the animal kingdom, as a rule it is the female who chooses carefully a suitable male.Masaryk University scientists have discovered a hitherto unknown form of sexual cannibalism in spiders of the species Micaria sociabilis. Until now we thought that only male spiders became victims of their choosy potential partners. But the new study has shown that females are at risk, too. News of the research was published in the high-prestige journal Behavioral Ecology and Sociobiology.

In the animal kingdom, as a rule it is the female who chooses carefully a suitable male, while the male does everything it can to show itself as the best choice. In choosing the ideal partner the female sometimes devours lower-quality males. So why do males of the species Micaria sociabilis sometimes kill females instead of mating with them?

The study by Lenka Sentenská and Stano Pekár of the MU Faculty of Science offers a possible explanation for this unusual behaviour. Sentenská, a postgraduate student at the Department of Botany and Zoology, summarizes it thus: “We assume that this reverse sexual cannibalism is founded in fastidiousness on the part of the male, based on the age of the female."

How did the scientists reach this conclusion? Over a period of three years they monitored the behaviour of the spiders in laboratory conditions, providing them with sufficient food so as to rule out hunger as a possible cause of cannibalism. Males were offered females of various qualities, as indicated by their size, mating history and age. Within a year there were two generations, which in part overlapped.

Laboratory experiments revealed that cannibalism occurred shortly after first contact. The males killed the females without regard to size and number of previous partners. The most important factor for the determining of the probability of cannibalism, was age. It occurred most often in July, when very young, second-generation males encountered older females.

“The results represent a significant departure from the traditional notion of non-discriminating, diligent males from which females pick their partners in a somewhat indiscriminate manner," explains Stano Pekár.

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