Twisted sex allows mirror-image snails to mate face-to-face, research finds

PA 268/17 - A study led by the University of Nottingham has found that differently-coiled types of Japanese land snails should in fact be considered a single species, because - against all odds - they are sometimes able to mate, a result which has implications for the classification of other snails. Although most snails have a right-handed spiralling shell, rare 'mirror-image' individuals have a shell that coils to the left. This inherited condition has attracted attention because the genitals of so-called 'lefty' snails are on the opposite side of the head, and so it had been thought that normal 'face-to-face' mating is difficult or impossible. But the new research by Dr Angus Davison, and Paul Richards, a PhD student in the University of Nottingham's School of Life Sciences, published in the journal Evolution Letters, has revealed instances in a Japanese snail where the two types can overcome this seemingly insurmountable barrier - by twisting their genitals to allow them to mate in a face-to-face position. The study also found evidence of this in their genetic make-up For many years, dextral (right-coiling) Euhadra aomoriensis and sinistral (left-coiling) Euhadra quaesita were believed to be two separate species because their mirror-image anatomy was thought to make it impossible for them to mate. However, the researchers found that the snails are sometimes able to twist their genitals into an appropriate position, and so mate in a normal face-to-face position. The common ancestry of the two types was also borne out by a comparison of the snails' genomes, or their genetic make-up, which also revealed the genetic similarities.