title: Transcriptome analyses of Anguillicola crassus from native and novel hosts.
abstract: 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.
authors.affiliation: Department for Molecular Parasitology, Institute for Biology, Humboldt University Berlin , Berlin , Germany.
authors.forename: Emanuel
authors.initials: E
authors.lastname: Heitlinger
authors.affiliation: Department of Ecology and Parasitology, Zoological Institute, Karlsruhe Institute for Technology , Karlsruhe , Germany.
authors.forename: Horst
authors.initials: H
authors.lastname: Taraschewski
authors.affiliation: Department of Ecology and Parasitology, Zoological Institute, Karlsruhe Institute for Technology , Karlsruhe , Germany.
authors.forename: Urszula
authors.initials: U
authors.lastname: Weclawski
authors.affiliation: Edinburgh Genomics, The Ashworth Laboratories, The University of Edinburgh , Edinburgh , UK.
authors.forename: Karim
authors.initials: K
authors.lastname: Gharbi
authors.affiliation: Edinburgh Genomics, The Ashworth Laboratories, The University of Edinburgh , Edinburgh , UK ; Institute of Evolutionary Biology, The Ashworth Laboratories, The University of Edinburgh , Edinburgh , UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Blaxter
keywords: Anguilla; Anguillicola crassus; Anguillicoloides crassus; Discriminant analysis of principal components (DAPC); Eel; Gene expression; Invasive parasite; Population differentiation; SNPs; Transcriptome