Male redback's bizarre death somersault during sex is in its genes

Male redback spiders engage in a dramatic and fatal somersault during mating, a behavior that appears to encourage their female partners to cannibalize them. New research published in Biology Letters indicates that this self-sacrificing ritual is rooted in the spiders' genetics, providing males with an evolutionary advantage despite their demise.

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It supports the idea that being killed during copulation and cannibalised can actually lead to the male's advantage.

The study, conducted by researchers at the University of Hamburg, compared the Australian redback spider with its close relative, the New Zealand katipō. Unlike the redback, the katipō does not practice sexual cannibalism. By breeding the two species, scientists aimed to uncover the genetic basis for the redback's unique mating behavior.

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The process of being cannibalised increases the time that they mate with the female. Being able to transfer more sperm to the female's spermatheca, which is the organ that the females use to store sperm, provides an advantage.

Bruno Alves Buzatto, a behavioral ecologist at Flinders University, described the findings as "very striking." He noted that being killed and cannibalized during copulation can benefit the male by increasing the duration of mating. This prolonged contact allows for greater sperm transfer, enhancing the male's chances of siring offspring. Female redbacks can store sperm for up to two years, making successful fertilization crucial.

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In that small amount of time, that whole behaviour is lost.

Cor Vink, an entomologist at Lincoln University in New Zealand, explained that the katipō spider evolved from redbacks approximately 100,000 to 200,000 years ago. "In that small amount of time, that whole behaviour is lost," Vink commented, highlighting how quickly such complex behaviors can disappear in evolutionary terms. The research continues to explore how behaviors are encoded in invertebrate DNA.

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It's really interesting when behaviours like that can be lost. We don't know enough about how behaviours are coded in the DNA of invertebrates.