Directed Asymmetry in the Rotifer Keratella quadrata Müller, 1786

Based on scientific monitoring data from freshwater bodies in the Central part of the Russian Federation- in 2023–2024, directional asymmetry in Keratella quadrata populations was demonstrated for the first time. Directional asymmetry is characteristic of populations from all sampling stations: individuals with a longer left spine are present in all samples, but consistently constitute less than half of each sample (ranging from 2 to 40%). The magnitude of the Earth’s magnetic field and geographical latitude show moderate correlations with the difference between the maximum and minimum asymmetry values of spine length. Weaker inverse moderate correlations are observed between the percentage of individuals with a longer left spine and indicators such as the geographical latitude and the total biomass of predators of the genus Asplanchna and the order Cyclopoida. Furthermore, the average spine length moderately correlates with the biomass of cyclopoid crustaceans in the water from which K. quadrata rotifers were collected. It can be hypothesized that predators selectively consume anomalous individuals, for whom more favorable habitat conditions may exist in more southern latitudes. Moreover, longer spines are likely beneficial for defense against predatory Cyclopoida. Further research can confirm or refute these hypotheses.