Pomphorhynchus laevis: An invasive species in the river Rhine?

Abstract

Acanthocephalans of the globally distributed genus Pomphorhynchus have been intensively studied during the past decades. In Europe, Pomphorhynchus species have shown a certain degree of variability in their morphological characteristics and behavior. Nowadays two different Pomphorhynchus species, namely P. laevis and P. tereticollis, have been described for different waterbodies in Western and Central Europe. However, until now it appears that both species do not co-occur at the same time in the same habitat. We assume that due to their very similar morphology some of the individuals that were identified based on their morphological characteristics as either of the two species might have been misidentified in previous studies. To avoid this possible source of error, we used molecular marker (ITS 1, COX genes) to identify Pomphorhynchus individuals from European eels that were sampled within a time period of 12 years from the Rhine River to elucidate the distribution of the two species in Western and Central Europe. Our results together with a re-examination of former studies provide evidence that P. laevis might have been introduced together with potential host species (intermediate, paratenic, and/or definitive) from the Ponto-Caspian region, and that it outcompeted and repelled the endemic P. tereticollis from the mainstream of the river. Our results also provide first evidence on the former coexistence of both Pomphorhynchus species in the river Rhine.