Evolutionary divergence of Anguillicola crassus, an invasive parasitic swim bladder nematode of eels of the genus Anguilla

After its introduction to Europe, Anguillicola crassus, a natural parasite of the Japanese eel, had to face novel conditions that have acted as different selective forces leading to the onset of new phenotypic modifications and genetic adaptations of the parasite. This study revealed that the changes in infectivity, development, reproductive output and morphology observed in the parasite after colonization of the European eel were induced by both genetic adaptation and phenotypic plasticity

Massive encapsulation of larval Anguillicoloides crassus in the intestinal wall of Japanese eels

<p>Abstract</p> <p>Background</p> <p>Within the last 25 years, after the introduction of the swimbladder nematode <it>Anguillicoloides </it>crassus from East-Asia to Europe, a body of work has aggregated on the host parasite interactions in the acquired host <it>Anguilla anguilla</it>. Despite the emerging evolutionary interest there is still a lack of knowledge about host parasite relations of <it>A. crassus </it>in its natural host <it>Anguilla japonica</it>. We examined the <it>Anguillicoloides </it>infections of wild-caught Japanese eels as well as from aquacultured specimens in Taiwan with respect to the fate of migratory L3 larvae and performed infection experiments with Japanese eels.</p> <p>Results</p> <p>Inside the intestinal wall of cultured eels, where the infective pressure was higher than among wild eels, we found large numbers of granuloma-like cysts. In a few eels these cysts contained nematodes still recognizable as L3 larvae of <it>A. crassus</it>, while in most cases the content of these capsules was degraded to amorphous matter. Occurrence of these objects was correlated with the number of encapsulated larvae in the swimbladder wall. We were able to show, that the cysts contained disintegrated L3 larvae by amplification and subsequent sequencing of large subunit ribosomal rRNA. Furthermore we identified repeated infections with high doses of larvae as prerequisites for the processes of encapsulation in infection experiments.</p> <p>Conclusion</p> <p>Under high infective pressure a large percentage of L3 larvae of <it>A. crassus </it>coming from the gut lumen are eliminated by the natural host within its intestinal tissue. It is possible to reproduce this condition in infection experiments. We provide a fast, easy and reliable PCR-based method for identification of encapsulated swimbladder parasites.</p

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

BACKGROUND: 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. 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. RESULTS: Under 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. CONCLUSIONS: The 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

Rapid evolution of Anguillicola crassus in Europe: species diagnostic traits are plastic and evolutionarily labile

Background Since its introduction from Taiwan to Europe around 1980, Anguillicola crassus, a natural parasite of the Japanese eel (Anguilla japonica), has acquired the European eel (Anguilla anguilla) as a novel definitive host. In this host the nematode differs noticeably in its body mass and reproductive capacity from its Asian conspecifics. We conducted a common garden experiment under a reciprocal transplant design to investigate whether differences in species-diagnostic morphological traits exist between two European and one Asian population of A. crassus and if yes whether these have a genetically fixed component. Results We found that worms from Germany, Poland and Taiwan differ in the size and shape of their body, oesophagus and buccal capsule. These changes are induced by both phenotypic plasticity and genetic divergence: in the European eel, nematodes from Europe as well as from Taiwan responded plastically with larger body and oesophagus dimensions compared to infections in the Japanese eel. Interestingly, the oesophagus simultaneously shows a high degree of genetically based changes being largest in the Polish strain kept in A. anguilla. In addition, the size and shape of the buccal capsule has undergone a rapid evolutionary change. Polish nematodes evolved a genetically fixed larger buccal capsule than the German and Taiwanese populations. The German strain had the smallest buccal capsule. Conclusions This study provides evidence for the genetic divergence of morphological traits in A. crassus which evolved over a timescale of about 30 years. Within Europe and in the European eel host these alternations affect characters used as diagnostic markers for species differentiation. Thus we provide an explanation of the discrepancy between morphological and molecular features reported for the parasitic nematode featured here, demanding general caution in morphological diagnosis of parasites discovered in new hosts

Capital market financing of family enterprises

The objective of this study is to identify funding opportunities for family businesses with the capital market instruments, and the risks associated with the implementation of common strategies. A family enterprise activity is guided not only by typical economic objectives, but also by striving for maintaining continuity and ensuring succession of the next generation. Therefore, the preservation of economic independence is of particular importance. Its significant determinant is that the funding to a large extent is based on the equity. A bank loan is traditionally perceived as the primary source of external financing. Bank loans access restrictions, as a result of new prudential regulations, force the family businesses to take into consideration alternative ways of funding. Capital market offers a wide range of financial instruments from debt securities through hybrid instruments to external equity. Each of these instruments, to varying degrees, protects the economic independence of an enterprise. For strategic purposes of family business, particularly well adjusted is funding using the mezzanine capital. It provides funds which features that are similar to the ones of equity, and at the same time reducing the influence of investors on the functioning of an enterprise. Venture capital financing, however, poses the risk of loss of control over the enterprise

Transcriptome analyses of Anguillicola crassus from native and novel hosts

Anguillicola crassus is a swim bladder nematode of eels. The parasite is native to the Asian eel Anguilla japonica, but was introduced to Europe and the European eel Anguilla anguilla in the early 1980s. A Taiwanese source has been proposed for this introduction. In the new host in the recipient area, the parasite appears to be more pathogenic. As a reason for these differences, genetically fixed differences in infectivity and development between Taiwanese and European A.crassus have been described and disentangled from plasticity induced by different host environments. To explore whether transcriptional regulation is involved in these lifecycle differences, we have analysed a “common garden”, cross infection experiment, using deep-sequencing transcriptomics. Surprisingly, in the face of clear phenotypic differences in life history traits, we identified no significant differences in gene expression between parasite populations or between experimental host species. From 120,000 SNPs identified in the transcriptome data we found that European A. crassus were not a genetic subset of the Taiwanese nematodes sampled. The loci that have the major contribution to the European-Taiwanese population differentiation show an enrichment of synonymous and non-coding polymorphism. This argues against positive selection in population differentiation. However, genes involved in protein processing in the endoplasmatic reticulum membrane and genes bearing secretion signal sequences were enriched in the set of genes most differentiated between European and Taiwanese A. crassus. These genes could be a source for the phenotypically visible genetically fixed differences between European and Taiwanese A. crassus