Some snails have shells that spiral to the left, while most spiral to the right.
This detail may seem insignificant. Yet in snails, the direction of the spiral also corresponds to a difference in the organization of the body. When two individuals have opposite shell orientations, their organs are not arranged in exactly the same way. This can even complicate their reproduction.
Biologist Angus Davison holds two Japanese snails of the genus Euhadra with opposite shell spirals, one to the left and the other to the right.
Photo: Angus Davison, CC0 1.0.
Researchers studied Japanese snails of the genus Euhadra. In this group, some species naturally have shells that spiral to the left. This is neither a disease nor an accidental deformity: the trait is passed down through generations.
The team compared their DNA with that of snails whose shells spiral in the opposite direction. They identified two ancient versions of the same gene, associated with a protein called myosin. This protein contributes to the movements and forces exerted inside cells.
The difference can act very early, from the first stages of embryo development. As cells begin to organize themselves, small movements help define what will become the left and right sides of the body. A change in the protein could then orient this organization in one direction or the other.
The researchers also discovered that the two versions of the gene had existed for a very long time. And unlike certain mutations studied in other snails, neither appears to cause any particular health problems. Both orientations are therefore part of the natural diversity of these animals.
Why does this discovery interest biologists? Almost all animals have a different organization between their left and right sides. In humans, for example, the heart is generally on the left and the liver more often on the right. But we still do not fully understand how this orientation emerges in the embryo.
Snails offer a rare opportunity to observe both possibilities in nature. Studying them may help us understand how the first cells establish a left-right orientation.