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

Male redback spiders, known for their distinctive black-and-red markings, meet a peculiar end during mating, a dramatic somersault that leads to their demise. This behavior, observed in the Australian redback (Latrodectus hasselti), is linked to a genetic trait identified in a recent study published in Biology Letters. Researchers from the University of Hamburg in Germany discovered that the self-sacrificing mating ritual is encoded in the spider’s DNA, distinguishing it from its non-cannibalistic relative, the New Zealand katipō (Latrodectus katipo). During mating, male redbacks perform a complex sequence of actions designed to prolong their time with the female. They begin by executing a somersault, positioning their large abdomens near the female’s fangs to facilitate the biting action. Once in place, the males constrict their bodies, creating the illusion of being squeezed, which delays their death. This elaborate display allows them to transfer more sperm into the female’s spermatheca, increasing the likelihood of successful reproduction. Female redbacks can store sperm for up to two years, using it to fertilize eggs laid at later dates. The study focused on comparing the mating behaviors of redbacks and katipō, two closely related species that diverged around 100,000 to 200,000 years ago. While redbacks exhibit a monogamous mating system, where males mate with only one female throughout their short lifespan, katipō engage in polygamous relationships, mating repeatedly with multiple partners. This difference in mating strategy appears to be rooted in their genetic makeup. To investigate the genetic basis of the redback’s self-sacrificing behavior, researchers bred male redbacks with female katipō. The resulting offspring exhibited a mix of traits from both species, offering insight into how specific behaviors might be inherited. Dr. Cor Vink, an entomologist at Lincoln University in New Zealand, explained that the redback is considered an invasive species in New Zealand, where it competes with the native katipō. Both species were collected from different locations in New Zealand before being transported to Germany for further analysis. Behavioral ecologist Bruno Alves Buzatto, affiliated with Flinders University, noted that the findings support the theory that male spiders benefit from being eaten during mating. By extending their time with the female, males increase the chance of transferring sufficient sperm to ensure reproductive success. “Being cannibalized can actually provide an evolutionary advantage,” Dr. Buzatto remarked. The redback’s mating ritual has been studied extensively, with early research conducted by scientists at the University of Toronto featured in a 2010 episode of ABC TV’s Catalyst program. Despite the grim nature of the ritual, the redback remains a common sight in Australia, though its bites are no longer life-threatening thanks to the availability of antivenom since the 1960s. The study highlights the complexity of animal behavior and the role of genetics in shaping survival strategies. As researchers continue to explore how such behaviors are encoded in the DNA of invertebrates, they hope to uncover broader insights into evolution and adaptation. For now, the redback’s somersault remains a fascinating example of how nature balances sacrifice with reproductive success.