Left and right snails

Scientists from the University of Nottingham and the University of Tokhok in the Japanese city of Sindai found that ground snails, the sinks of which are twisted in different directions, can nevertheless mate with each other. Previously, the difference in the structure seemed to a scientist an insurmountable obstacle to mating, so snails, which differed in this sign and identical in everything else, were attributed to different types.

The spiral shell of the belly -legged mollusks can be twisted clockwise (to the right) or against (left). Usually the direction of the spiral is the same for the species. Indeed, in individuals with the opposite direction of the sink, all other organs of the body are also located in a mirror display. This prevents the mating of snails, since the genitals of individuals with different directions of the spiral are on different sides of the body. For example, all grape snails ( Helix Pomatia ) - "right -handed". As a result of rare mutations, individuals appear among them, the sink of which is twisted in the opposite direction, but they cannot leave offspring in nature.

Marying Helix Pomatia. Photo: Silke Baron/Flickr

Cases when the arrangement of the organs of the body is mirrored from the usual one in humans. In medicine, they bear the Latin name Situs Inversus and are found in about one out of ten thousand. The heart and stomach of these people are on the right side of the longitudinal axis of the body, and the liver on the left. Their right lung consists of two shares, and the left of three (usually everything is the other way around). The intestines, blood vessels, nerves - all other organs - are also oriented mirror. Among such people, the famous singer Enrique Iglesias and Canadian-American actress Katherine O'Hara. Popular in the 1970s, singer Donnie Osmond almost died due to the mirror arrangement of organs. He had appendicitis, but doctors who did not suspect the unusual structure of his body could not make the correct diagnosis for a long time.

A significant part of people with a mirror arrangement of organs does not experience health problems. For example, the basketball player Randy Foyu, such a feature did not stop making a career in NBA. Such people can (unlike snails) and leave offspring in marriages with ordinary people. In some cases, the transposition of organs is accompanied by heart defects due to the difference in the location of the blood vessels. In approximately 25 % of cases, the mirror arrangement of human organs is associated with the genetic syndrome of primary ciliary discinesia . The cells in their body do not move cilia. In this case, the Situs Inversus is accompanied by chronic sinusitis and bronchial diseases (due to the immobility of the cilia, the cleansing of the lungs of mucus is disturbed), as well as male infertility (sperm ponytails are also motionless).

But back to the snails. The story of a grape snail named Jeremy recently became widely known. She was found in South London near the compost heap of a pensioner who previously worked at the Museum of Natural History, so he drew attention to the unusual appearance of the snail. Jeremy had the same mutation that is found among grape snails once a million: his sink was twisted to the left. As a result, Jeremy settled in the Angus Davison laboratory at the University of Nottingham. Scientists have found out with what changes in the genome are associated with the shape of its sink. And also did not leave hope to find a couple for Jeremy.

They were able to do this by organizing a flash mob on Twitter with a hashtag #snailove. Thousands of people were published by the tweets with a request to find a “snail-lavsh”. And such snails were found, even six pieces. Two of them were delivered to Nottingham as candidates for mating with Jeremy. A snail named Lefti lived with an animal lover from Ipswich, and the Tomeu snail arrived from the island of Mallorca. Snails were settled together, but at first Lefti and Tomeu preferred each other and in May of this year more than a hundred descendants were born . Then they made two more masonry. At the same time, Tomeu acted twice as a mother, and once - Left (snails hermaphrodites and when mating can play the role of both a male and a female). Jeremy remained out of work. Only recently Tomeu posted 56 eggs, whose father was Jeremy. Just a few days after that, October 11, 2017, Jeremy died, since his age was already senile by the standards of grape snails.

Interestingly, the children of Jeremy, Lefti and Tomeu turned out to be quite ordinary grape snails with a sink, twisted to the right. Angus Davison explained this: “The fact that the kids developed sinks, twisted to the right, it is possible, possibly because the mother has both dominant and recessive versions of genes that determine the direction of the sink. The asymmetry of the body in snails is inherited similarly to the color of the shell of bird eggs - only the mother’s genes determine the direction of twisting the sink or the color of the bird egg. Most likely, we will see that offspring with a left -handed sink will appear in the next generation or even later. ”

Angus Davison took up the clarification of the genetic foundations of the asymmetry of the body in the belly mollusks long before meeting Jeremy. In 2016, his article was published in the journal Current Biology, where he, together with colleagues from the UK, Germany, Belgium, the USA and Japan, indicated one of the genes that determine the left or right twisting of the ordinary prince ( Lymnaea Stagnalis ). It turned out that in frogs this gene is also responsible for the asymmetry of internal organs.

The current study was also conducted under the leadership of Davison. This time, the attention of scientists was attracted by land snails from the Euhadra clan, common in Japan and Korea. It is believed that this is 22 species, of which the 17 sinks were twisted to the right, and in five - to the left. Moreover, some of them are very close to each other, for example, Euhadra Aomoriensis (humanly -swirling view) and Euhadra Quaesita (left -bred form). All researchers believed that the difference in the position of the genitals provides these mollusks with reliable reproductive insulation.

Euhadra quaesita. Photo: Angus Davison, Satoshi Chiba

However, now Davison and his colleagues found that sometimes the snails twist their body so that the genitals when mating two “multidirectional” snails are in the right position and fertilization successfully occurs. The community of these two types was confirmed in the study of genomes of both species.

Scientists managed to record five cases of such mating, and four between Euhadra Aomoriensis (a humanly -swirling view) and Euhadra Quaesita , and even between the more distant Euhadra Quaesita and Euhadra Senckenbergiana . “We were surprised to find that in different ways the twisted individuals of the euhadra snails sometimes mate, contrary to all expectations, and that this is evidence in their DNA. It was previously assumed that mating in the position of “face to face”, ordinary for these snails, in the case of different twisting. We showed that mating and, accordingly, the exchange of genes, although, of course, is a rare event, but still occurs quite often so that these two varieties can be recognized as one species. It turns out that the problem of mating is mainly behavioral, requiring twisting genitals, and not physical incompatibility, ”says Engus Davison.

The conclusions made by researchers are also important for the classification of other belly -legged ones, since species that differ in the direction of twisting of the sink are not only in the kind of Euhadra , but also in other births.

The study is published in the journal Evolution Letters.