Morphological and molecular data show no evidence of the proposed replacement of endemic Pomphorhynchus tereticollis by invasive P. laevis in salmonids in southern Germany

Abstract

Changes in parasite communities might result in new host-parasite dynamics and may threaten local fish populations. This phenomenon has been suggested for acanthocephalan parasites in the river Rhine and Danube where the species Pomphorhynchus tereticollis is becoming replaced by the Ponto-Caspian P. laevis. Developing knowledge on morphologic, genetic and behavioural differences between such species is important to follow such changes. However, disagreements on the current phylogeny of these two acanthocephalan species are producing conflicts that is affecting their correct identification. This study is offering a clearer morphological and genetic distinction between these two species. As P. tereticollis is found in rhithral tributaries of the Rhine, it was questioned whether the local salmonid populations were hosts for this species and whether P. laevis was expanding into the Rhine watershed as well. In order to test for this, brown trout, Salmo trutta, and grayling, Thymallus thymallus from SouthWestern Germany watersheds have been samples and screened for the occurrence of acanthocephalan parasites. For the first time, both species were confirmed to be hosts for P. tereticollis in continental Europe. P. tereticollis was found to be common, whereas P. leavis was found only at a single location in the Danube. This pattern suggest either that the expansion of P. laevis through salmonid hosts into rhithral rivers has not yet occurred, or that not yet ascertained biotic or abiotic features of rhithral rivers hinder P. laevis to spread into these areas.

Intermediate host patterns of acanthocephalans in the Weser river system: co-invasion vs host capture

“…Phylogenetic comparison of specimen from the Weser river system supports the existence of 3 separate species. Pomphorhynchus tereticollis in our sample was closely related to specimens from southern Germany and the British Isles (Andreou et al ., 2020 ; Ros et al ., 2020 ). Haplotype analysis and the NJ tree revealed that P. laevis belonged to the western-European clade previously described by Perrot-Minnot et al .…”

“…For further phylogenetic analysis, the following NCBI accessions were added to the dataset EF051062–EF051071 (Moret et al ., 2007 ), JN695505–JN695508 (Špakulová et al ., 2011 ), JQ824373 (Pan and Nie, 2012, unpublished), KJ819957–KJ820006 (Vardić Smrzlić et al ., 2015 ), KY075794 (Andreou et al ., 2020 ), KY490045–KY490047 (Li et al ., 2017 ), KY911293–KY911323 (García-Varela et al ., 2017 ), LN994840–LN994853 (Perrot-Minnot et al ., 2018 ), MF563495–MF563527 (David et al ., 2018 ), MK133340–MK133344 (Nedić et al ., 2019 ) and MK612497–MK612545 (Reier et al ., 2019 ), MT216151–MT216172 (Ros et al ., 2020 ) (for more details see the Supplementary material). The total dataset of 316 sequences was edited in MEGA 11 and trimmed to a length of 507 bp.…”

“…For further phylogenetic analysis, the following NCBI accessions were added to the dataset EF051062-EF051071 (Moret et al, 2007), JN695505-JN695508 (Špakulová et al, 2011) et al, 2018), MK133340-MK133344 (Nedić et al, 2019) and MK612497-MK612545 (Reier et al, 2019), MT216151-MT216172 (Ros et al, 2020) (for more details see the Supplementary material). The total dataset of 316 sequences was edited in MEGA 11 and trimmed to a length of 507 bp.…”