The anomaly P syndrome in green frogs: the history of discovery, morphological features and possible causes

Abstract

The anomaly P in green frogs was firstly found in 1952 in France by French writer and scientist Jean Rostand. Mild form of anomaly P manifestation includes polydactyly, while complex morphological transformations affect the fore and hindlimbs and include combinations of traits: polydactyly, brachymely, hind limb flexion, small additional limbs, bone outgrowths, tumors and edema in the hind limbs. Rostand experimentally showed that this anomaly is not inherited and is caused by some environmental factors. It was recorded only in Western Palearctic green frogs of the genus Pelophylax and was absent in other amphibian species, despite their syntopic occurrence. The severe cases of anomaly P were not found for a long time by researchers and were re-discovered after half a century since its last observation. A new record was made in 2016 in the central part of Russia in the Privolzhskaya Lesostep’ nature reserve. The morphological features of the anomalous frogs in the study area turned out to be similar to those described by Rostand. Symmetric polydactyly, brachymely, hind limb flexion, edema of hind limbs, small additional limbs in thighs, outgrowths, and concomitant anomalies – mandibular hypoplasia, unmoved hind limb, open opercular chamber. The frequency of occurrence of the anomaly in the studied population reached 24.7% (n = 384). Moreover, the “severe forms” of the anomaly P were noted in 4.7% of cases, and the “light” (polydactyly) in 20.0%. Growing tadpoles together with freshwater mollusks allowed us to obtain the anomaly P in the laboratory. It was revealed that the mollusks Planorbarius corneus are the intermediate hosts (vectors) for the “infectious agent” of this anomaly. As the most possible cause of the anomaly, the infection by trematodes species is considered.