Differently-coiled types of Japanese land snails should be considered a single species because - against all odds - these snails are sometimes able to mate, a new study has found.

Although most snails have a right-handed spiraling shell, rare 'mirror-image' individuals have a shell that coils to the left.

This inherited condition has attracted attention because the genitals of 'lefty' snails are on the opposite side of their head, so it was thought normal 'face-to-face' mating was difficult or impossible.

However, new research has revealed instances in a Japanese snail where the two types can overcome this barrier by twisting their genitals to allow them to mate face-to-face.

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Reciprocal mating between sinistral (left-coiling) E. quaesita and dextral (right-coiling) E. peliomphala. Mating between these distantly related species may not produce viable offspring, but illustrates the general point that dextrals and sinistrals are able to mate, rarely

For many years, dextral (right-coiling) Euhadra aomoriensis snails and sinistral (left-coiling) Euhadra quaesita snails were believed to be two separate species because their mirror-image anatomy was thought to make it impossible for them to mate.

However, a new study led by researchers at the University of Nottingham in the UK and the University of Tohoku in Japan 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 researchers also analyzed the snail's genomes and compared them, which revealed common ancestry and their common ancestry and genetic similarities.

'We were surprised to find that different-coiled individual Euhadra snails can sometimes mate, against expectations, and that there is evidence for this in their DNA.

'It was previously supposed that face-to-face mating was impossible between mirror image snails.

LEFTY SNAIL JEREMY STARTS A FAMILY WEEKS BEFORE HE DIES Although most snails have a right-handed spiralling shell, rare 'mirror-image' individuals have a shell that coils to the left. The genitals of 'lefty' snails are on the opposite side of their head, so it was thought normal 'face-to-face' mating was difficult or impossible. However, new research has revealed instances in a Japanese snail where two types can overcome this barrier by twisting their genitals to allow them to mate face-to-face. It was the romantic match that captured the hearts of the world, but for Jeremy the lefty snail, the days of chasing love are sadly over. Jeremy, (pictured), the 'left-coiling' snail with a one in a million genetic anomaly, died in October of 2017 The University of Nottingham's Dr Angus Davison's work on these mutant snails has made international headlines after he led a public campaign to find a left-coiling mate for 'lefty' snail Jeremy - with the hopes he could use any potential offspring to study the inheritance of this rare condition. The campaign ended up being successful - shortly before Jeremy's recent death, he was able to produce offspring with mate Tomeu, which will be studied at Nottingham. Tomeu has recently been preserved as part of a bid to be included in the Sanger Institute's iconic 25 Genomes project, which would potentially help to uncover the DNA blueprint for these left-coiling snails. Advertisement

'We showed that while mating - and the movement of genes - between the two types is certainly a rare event, it occurs sufficiently often that the two types should properly be considered a single species,' said Dr Angus Davison, a researcher at the University of Nottingham and the lead author of the study.

'It turns out that the mating problem is mainly behavioural, requiring a twisting of the genitals, rather than a physical incompatibility.'

Collaborating scientist Professor Satoshi Chiba of Tohoku University said: 'We were really surprised to find these reports from Japanese naturalists, of mating between sinistral and dextral snails, but in evolution even rare events can have quite large impacts on the underlying genes.'

The genitals of rare 'left coiling' snails are on the opposite side of their head, so it was thought that normal 'face-to-face' mating was difficult or impossible. However, to types of snails can overcome this barrier by twisting their genitals to allow them to mate face-to-face

'As snails in general are sometimes classified into separate species based mainly on their shell-coiling, then this work has implications for the classification of other snail species.'

Dr Davison said: 'As it has previously been shown that the same sets of genes that make mirror image snails are also involved in making mirror image bodies in other animals - including humans - further research into the natural variation of snails could offer the chance to develop an understanding of how organs are placed in the body and why this process can sometimes go wrong.'

Chiral (handedness) reversal in the Japanese snail genus Euhadra presents one of the best opportunities for researchers to investigate the possibility of two species having diverged from a single ancestor.

Previously, two separate studies used mitochondrial DNA sequences to investigate the evolutionary history and genetic relationships between the left-coiling and right-coiling Euhadra species - but came up with very different explanations.

For this new study, the researchers used their network of mollusc experts and sources in Japan to investigate the evidence of possible matings between these two partners - uncovering five instances of this behavior.

Pictured is Dr Angus Davison holding snails. Dr Davison is a professor at the School of Life Sciences at University of Nottingham

The researchers also used a powerful DNA scanning method to scan the DNA of left-coiling and right-coiling snails, which revealed that there is movement of genes between the two types.

In future, the researchers would like to use this same method to identify the genes that make the snails mirror images, which may have implications for our understanding of the development of other animals, including ourselves.

Dr Davison's work on these mutant snails has made international headlines after he led a public campaign to find a left-coiling mate for 'lefty' snail Jeremy - with the hopes he could use any potential offspring to study the inheritance of this rare condition.

The campaign ended up being successful - despite a tough where potential mates who were discovered mated with each other and produced offspring.

Shortly before Jeremy's recent death, he was able to produce offspring with mate Tomeu, which will be studied at Nottingham.

Tomeu has recently been preserved as part of a bid to be included in the Sanger Institute's iconic 25 Genomes project, which would potentially help to uncover the DNA blueprint for these left-coiling snails.