Sea turtles are less of "righties" and "lefties" than their land-dwelling counterparts. Life in the water and, in particular, the constant need to move the flippers simultaneously, deprived sea turtles of asymmetric reflexes – that is the conclusion of Egor Malashichev, Associate Professor at St. Petersburg State University. The results of the SPbU biologist's study are set forth in an article published in Physiology & Behavior, a scientific journal.

Sea turtles are less of "righties" and "lefties" than their land-dwelling counterparts. Life in the water and, in particular, the constant need to move the flippers simultaneously, deprived sea turtles of asymmetric reflexes – that is the conclusion of Egor Malashichev, Associate Professor at St. Petersburg State University. The results of the SPbU biologist's study are set forth in an article published in Physiology & Behavior, a scientific journal.

It is known that land and freshwater turtles use the so-called diagonal pattern when walking and swimming – that is, they mve their front and hind limbs on opposite sides simultaneously. But sea turtles employ synchronous locomotion, the simultaneous movement of just the front flippers or all four limbs at once. Studying amphibians – toads that walk diagonally and frogs that simultaneously use both hind legs to jump – the SPbU Associate Professor Egor Malashichev suggested that turtles use the same movement pattern. That is, the motor asymmetry is only expressed in those species that move their limbs diagonally.

In February 2015, Egor Malashichev conducted a study on the island f Sri Lanka. The experiment was based on the manifestation of the righting reflex when turning over from the supine position. It allows to easily test the motor asymmetry in vertebrates by noting which side the specimen chooses when turning over. In tailless amphibians, these lateral preferences are also directly related to the degree of use of their limbs while moving in the water or on land.

The hypothesis of a link between the functional asymmetry and the method of locomotion was tested by the biologist on two species of sea turtles: the green sea turtle (Chelonia mydas) and the olive ridley sea turtle (Lepidochelys olivacea). 100 specimens participated in the experiment – 50 representatives of each species. The scientist noted whether a turtle would choose the right or the left side to turn over from the supine position.

In the course of these tests, the subjects exhibited individual and group preferences in choosing sides and in limb use. The species with the most "synchronous" locomotion (the green sea turtle) proved to be more symmetric in exhibiting the righting reflex; that is, the number of specimens that preferred one side to the other was not great. The more "asynchronous" species (the olive ridley sea turtle) proved to be more asymmetrical, with a larger share of lateralised specimens and a smaller number of those that had no preferences in choosing right or left limbs.

"Sea turtles at least have individual righting lateralisation. At the same time, there is a clear trends in the population: they mostly use the right forelimb to push off the surface. Thus, turtles, that had never been studied from this point of view, have demonstrated the same principle found in amphibians (frogs and toads). This may be evidence of a common physiological mechanism linking asynchronous movement and asymmetric nerve (spinal) reflexes," said Egor Malashichev.

The biologist noted that these observations can likely be extended to all vertebrates and suggested that slight asymmetry is typical for all four-legged animals. As for those species that stand on their hind limbs (including humans), their asymmetry has increased due to the new uses of the forelimbs, perhaps related to the asymmetry in other neural mechanisms.

Egor Malashichev is planning to study closely related species of freshwater turtles that have different movement patterns. The results of the righting reflex test will allow to estimate the speed of such evolutionary changes: knowing how long ago the species started to evolve independently, you can find out how much time is enough for the synchronous movement to reflect on the asymmetry of reflexes.

Previously, the scientist studied laterality manifestations in mammals, proving, together with his SPbU colleagues Andrei Gilyov and Karina Karenina, that the true "handedness" is not peculiar to primates only (see Kangaroos and Lefties Have a Lot in Common). The study of kangaroos' forelimb lateralization allowed scientists to understand the causes of a pronounced asymmetry in the use of limbs, typical for humans, for example. The SPbU experts established that the key role in this process was most likely played by the vertical body position, bipedalism and the use of forelimbs to handle objects.