St Petersburg University biologists together with colleagues from the Institute of Experimental Medicine and the Papanin Institute for Biology of Inland Waters Russian Academy of Sciences conducted a series of experiments involving axolotls - larvae of the Mexican salamander.


With the help of mirror aquariums, scientists found that amphibians grow slowly if they see relatives around them. However, the competitive conditions force their left hemisphere to develop faster, which allows the axolotls to better recognise food. The results of the work are published in the journal Biological Communications.

"It is known that the visual stimulus can influence the growth of tadpoles (larvae of frogs)," explained Egor Malashichev, an Associate Professor of St Petersburg University. “There is a hypothesis that when they see their relatives as competitors, they begin to look more actively for food, which means spending more energy, and as a result their development slows down. We decided to see what would happen in such conditions with axolotls, which are predators and unlike tadpoles do not form large groups in nature. "

The study was conducted on the basis of the resource centre of the Research Park of St Petersburg University "Observatory of Ecological Safety".

To do this, scientists placed the salamander larvae in both ordinary aquariums and aquariums with mirror walls. They were fed the same number of crustaceans, and sometimes they reversed the positions of the aquariums to minimise the influence of other external factors (temperature, light, etc.). Such comparison made it possible to exclude, among other things, the effect of metabolites (metabolic products) that other individual axolotls would discharge and which could also affect the growth and development of the animals, as in the experiment, real competitors were replaced by "mirror copies" of axolotls.

"Although initially we assumed that such conditions will not affect the growth of axolotls, it turned out that these amphibians also depend on the impact of visual stimuli," said Egor Malashichev. “Individual axolotls in mirror aquaria grew more slowly, and the growth curves show an increasing discrepancy in the course of the experiment. In addition, we noticed regularity: the asymmetry of the reaction to food of the axolotls from the mirror aquariums increased. "

The fact is that the left hemisphere of the brain and hence the right eye is responsible for the ability to distinguish food from non-food.  Three-week-old axolotls from the mirror aquariums, when their ability to distinguish food has already formed, began eating the crustaceans mainly on their right side. This tendency developed with age. They learned this technique much faster than relatives from aquariums with transparent walls.

The study is supported by the current grant of the RSF No. 14-14-00284.

"Thanks to these results, we realised that the presence of large numbers of the same species in the field of view is enough to stimulate the growth inhibition in different species of animals that do not necessarily form large groups in nature," the associate professor of St Petersburg University explained. “This hypothesis can now be tested on fish, and then on mammals. Perhaps this phenomenon is more common in natural populations than we used to think."