Researchers report a genetic explanation for a distinctive mating tactic in male Australian redback spiders: a deliberate backflip into the female and a constriction of the abdomen that together prolong copulation. The study, led by doctoral candidate Kardelen Özgün Uludağ at the University of Hamburg, used controlled hybrid crosses between the Australian redback (Latrodectus hasselti) and its New Zealand relative, the katipō (Latrodectus katipo), and was published 12 August in Biology Letters. The experiments aimed to separate genetic influence from behavioural and ecological factors by observing hybrids in a noncannibalistic mating context.
The team first mated katipō females with redback males to produce hybrid offspring, then backcrossed those hybrids to generate males with mixed ancestry. Researchers could not pair katipō males with redback females because redback females often consume katipō males before mating, so they instead observed hybrid males paired with katipō females to record mating maneuvers without the confound of cannibalism. Investigators recorded occurrences of the somersaulting backflip, abdominal constriction, and the frequency with which males broke off their pedipalps during copulation.
Analysis showed that the somersaulting backflip displayed a simple inheritance pattern consistent with linkage to the spiders’ sex chromosome and a dominant–recessive relationship between alleles. In contrast, abdominal constriction did not follow a simple Mendelian pattern; it appeared to be polygenic or strongly modulated by female behaviour. Hybrid males exhibited both behaviours together only about half the time, otherwise performing one or the other, indicating the two traits can be genetically uncoupled despite their joint function in prolonged copulation in redbacks.
The findings refine understanding of how dramatic reproductive behaviours can evolve within a genus. Not all widow spiders practise sexual cannibalism; the Australian redback and the Southern black widow (Latrodectus mactans) are notable for it, while other close relatives court without lethal outcomes. The authors recommend broader comparative genomic and behavioural studies across Latrodectus species to map trait evolution and identify specific genetic loci involved, providing a clearer picture of how mating strategies diverge among closely related species.
