Invaders, natives and their enemies: distribution patterns of amphipods and their microsporidian parasites in the Ruhr Metropolis, Germany.
BACKGROUND
The amphipod and microsporidian diversity in freshwaters of a heterogeneous urban region in Germany was assessed. Indigenous and non-indigenous host species provide an ideal framework to test general hypotheses on potentially new host-parasite interactions, parasite spillback and spillover in recently invaded urban freshwater communities.


METHODS
Amphipods were sampled in 17 smaller and larger streams belonging to catchments of the four major rivers in the Ruhr Metropolis (Emscher, Lippe, Ruhr, Rhine), including sites invaded and not invaded by non-indigenous amphipods. Species were identified morphologically (hosts only) and via DNA barcoding (hosts and parasites). Prevalence was obtained by newly designed parasite-specific PCR assays.


RESULTS
Three indigenous and five non-indigenous amphipod species were detected. Gammarus pulex was further distinguished into three clades (C, D and E) and G. fossarum more precisely identified as type B. Ten microsporidian lineages were detected, including two new isolates (designated as Microsporidium sp. nov. RR1 and RR2). All microsporidians occurred in at least two different host clades or species. Seven genetically distinct microsporidians were present in non-invaded populations, six of those were also found in invaded assemblages. Only Cucumispora dikerogammari and Dictyocoela berillonum can be unambiguously considered as non-indigenous co-introduced parasites. Both were rare and were not observed in indigenous hosts. Overall, microsporidian prevalence ranged from 50% (in G. roeselii and G. pulex C) to 73% (G. fossarum) in indigenous and from 10% (Dikerogammarus villosus) to 100 % (Echinogammarus trichiatus) in non-indigenous amphipods. The most common microsporidians belonged to the Dictyocoela duebenum- /D. muelleri- complex, found in both indigenous and non-indigenous hosts. Some haplotype clades were inclusive for a certain host lineage.


CONCLUSIONS
The Ruhr Metropolis harbours a high diversity of indigenous and non-indigenous amphipod and microsporidian species, and we found indications for an exchange of parasites between indigenous and non-indigenous hosts. No introduced microsporidians were found in indigenous hosts and prevalence of indigenous parasites in non-indigenous hosts was generally low. Therefore, no indication for parasite spillover or spillback was found. We conclude that non-indigenous microsporidians constitute only a minimal threat to the native amphipod fauna. However, this might change e.g. if C. dikerogammari adapts to indigenous amphipod species or if other hosts and parasites invade.
Aquatic Ecology and Centre for Water and Environmental Research, University of Duisburg-Essen, Universitaetsstr. 5, 45141, Essen, Germany. daniel.grabner@uni-due.de.|Centre for Water and Environmental Research, University of Duisburg-Essen, Universitaetsstr. 5, 45141, Essen, Germany. daniel.grabner@uni-due.de.
Daniel S
DS
Grabner
Department of Animal Ecology, Evolution and Biodiversity, Ruhr-University Bochum, Universitaetsstr. 150, 44801, Bochum, Germany. alexander.weigand@rub.de.
Alexander M
AM
Weigand
Department of Animal Ecology, Evolution and Biodiversity, Ruhr-University Bochum, Universitaetsstr. 150, 44801, Bochum, Germany. florian.leese@rub.de.|Present address: Aquatic Ecosystems Research, University of Duisburg-Essen, Universitaetsstr. 5, 45141, Essen, Germany. florian.leese@rub.de.|Centre for Water and Environmental Research, University of Duisburg-Essen, Universitaetsstr. 5, 45141, Essen, Germany. florian.leese@rub.de.
Florian
F
Leese
Aquatic Ecology and Centre for Water and Environmental Research, University of Duisburg-Essen, Universitaetsstr. 5, 45141, Essen, Germany. caroline.winking@uni-due.de.
Caroline
C
Winking
Aquatic Ecology and Centre for Water and Environmental Research, University of Duisburg-Essen, Universitaetsstr. 5, 45141, Essen, Germany. daniel.hering@uni-due.de.|Centre for Water and Environmental Research, University of Duisburg-Essen, Universitaetsstr. 5, 45141, Essen, Germany. daniel.hering@uni-due.de.
Daniel
D
Hering
Department of Animal Ecology, Evolution and Biodiversity, Ruhr-University Bochum, Universitaetsstr. 150, 44801, Bochum, Germany. tollrian@rub.de.|Centre for Water and Environmental Research, University of Duisburg-Essen, Universitaetsstr. 5, 45141, Essen, Germany. tollrian@rub.de.
Ralph
R
Tollrian
Aquatic Ecology and Centre for Water and Environmental Research, University of Duisburg-Essen, Universitaetsstr. 5, 45141, Essen, Germany. bernd.sures@uni-due.de.|Department of Zoology, University of Johannesburg, PO Box 524, Auckland Park 2006, Johannesburg, South Africa. bernd.sures@uni-due.de.|Centre for Water and Environmental Research, University of Duisburg-Essen, Universitaetsstr. 5, 45141, Essen, Germany. bernd.sures@uni-due.de.
Bernd
B
Sures
D033304:Amphipoda / Q000235:genetics / Q000469:parasitology*; D000818:Animals; D004247:DNA / Q000235:genetics; D058893:DNA Barcoding, Taxonomic; D017753:Ecosystem; D005858:Germany; D006790:Host-Parasite Interactions; D058865:Introduced Species; D016814:Microsporidia / Q000302:isolation & purification / Q000502:physiology*; D010802:Phylogeny; D045483:Rivers; D013045:Species Specificity
D004247:DNA