Strigea robusta(Digenea: Strigeidae) infection effects on the gonadal structure and limb malformation in toad early development

Abstract

The anomaly P is a mass morphological anomaly reported in some water frog populations across Europe. It was found that polydactyly is only a mild attenuated form of heavy cases of the anomaly P syndrome, which have strong deformations of the hindlimbs and, partly, forelimbs. It was shown that the anomaly P is caused by the trematode Strigea robusta and this syndrome can be considered as a special case of strigeosis in amphibians. The anomaly P for a long time considered to be specific for water frogs of the genus Pelophylax. Herein, we describe polydactyly and heavy forms of the anomaly P syndrome in toads of the genera Bufo and Bufotes, as a result of exposure to S. robusta cercariae. A total of 150 tadpoles of Bufo bufo, 60 tadpoles of Bufotes viridis, and 60 tadpoles of Bufotes baturae were divided into five experimental and four control groups (30 tadpoles in each group). All anomalies in the toads were similar to those observed in water frogs. The survival of tadpoles in the experimental groups was 76%. The anomaly P was observed in 57.9% of toad tadpoles (51.8% of mild forms and 6.1% of heavy forms). The occurrence of the anomaly P varied among groups from 19% to 78%. Heavy forms of the anomaly P were found in all experimental groups. We described rare asymmetrical cases of the anomaly P. According to severe modification of limb morphology, we supposed changes of gonadal morphology (any modifications of the germ and somatic cells).The gonadal development of infected tadpoles was however the same as in uninfected toad tadpoles, and heterochromatin distribution within gonocytes had no differences as well. It seems like the parasite doesn't have any effect on the gonadal development of the toads. The lack of heavy forms in natural populations of toads, as well as a development of gonads were discussed.

Diversity of trematodes from the amphibian anomaly P hotspot: Role of planorbid snails

“…robusta cercariae from Pl . corneus inhabited Ostrovtsovskaya Lesostep’ has been repeatedly shown in experiments with laboratory-reared tadpoles of water frogs and toads [ 37 , 69 , 70 ].…”

“…The manipulation of the parasite is similar to Ribeiroia: tadpoles with the anomalies are less mobile and often become prey for near-water birds (in the case of S. robusta, ducks serve as the final host) [37]. The range of this parasite and, as a result, the place of appearance of the anomaly is much wider than it was previously known: in recent studies, they were found not only in the Penza Region of Russia, but also in the north of the Middle Volga region [69]. It has also been shown that even a small dose of cercariae can cause deformities in water frogs [70].…”