Evolutionary divergence of the swim bladder nematode Anguillicola crassus after colonization of a novel host, Anguilla anguilla

Bernhard Klar,Horst Taraschewski,Urszula Weclawski,Tobias Baust,Emanuel G Heitlinger,Trevor Petney,Yu San Han

doi:10.1186/1471-2148-13-78

Bernhard Klar, Horst Taraschewski + Show 5 more

Open Access

https://doi.org/10.1186/1471-2148-13-78

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Abstract

BackgroundAnguillicola crassus, a swim bladder nematode naturally parasitizing the Japanese eel, was introduced about 30 years ago from East Asia into Europe where it colonized almost all populations of the European eel. We conducted a common garden experiment under a reciprocal transfer design infecting both European and Japanese eels with populations of A. crassus from Germany, Poland and Taiwan. We tested, whether differences in infectivity, developmental dynamics and reproductive output between the European and Asian parasite populations occur while harboured in the specimens of native and colonized eel host, and if these differences are genetically based or are plastic responses to the new environment.ResultsUnder common garden conditions an evolutionary change in the both European parasite populations of A. crassus compared with their Taiwanese conspecifics was observed for infectivity and developmental dynamics, but not for reproductive output. When infecting the European eel, current European populations of the parasite were less infective and developed faster than their Taiwanese conspecifics. In the reciprocally infected Japanese eel the genetically induced differences between the parasite strains were less apparent than in the European eel but higher infectivity, faster development and higher larval mortality of the European parasite populations could be inferred.ConclusionsThe differences in infectivity and developmental dynamics between European and Taiwanese populations of A. crassus found in our study suggest rapid genetic divergence of this parasite after a successful host switch in Europe.

Highlights

Anguillicola crassus, a swim bladder nematode naturally parasitizing the Japanese eel, was introduced about 30 years ago from East Asia into Europe where it colonized almost all populations of the European eel
The major difference in the developmental dynamics between the European and Taiwanese nematode populations in the European eel was related to the persistently higher densities of L3 larvae for the Taiwanese parasites, while the European parasites never reached such high numbers of L3 (Table 1 and Additional file 2: Model 2; Figure 3)
The lower recovery was Discussion Our common garden experiment revealed that populations of A. crassus have undergone genetic divergence in terms of infectivity and developmental dynamics, while the reproductive output was characterized by a high degree of phenotypic plasticity

Summary

Introduction

Anguillicola crassus, a swim bladder nematode naturally parasitizing the Japanese eel, was introduced about 30 years ago from East Asia into Europe where it colonized almost all populations of the European eel. Many of them have been shown to European eel Anguilla anguilla, an immunologically naive novel host [7,8] As this parasite uses only one final host species under natural conditions, the adaptations driving its population dynamics should be very specific [9]. Further advantages of this host-parasite system are its well established experimental design allowing observation of the developmental cycle of the parasite [10] and the thoroughly studied dispersal of the parasite after its introduction to Europe [8,11]. The parasite was transferred to the genus Anguillicoloides [14], but more recent molecular studies strongly suggest that the new genus is paraphyletic and the original generic name is more appropriate [15]

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