Hidden parasite diversity in a European freshwater system

Abstract

Parasites comprise a huge part of the biodiversity on earth. However, on a local scale, not much is known about their diversity and community structure. Here, we assess the diversity of larval trematode communities in an interconnected freshwater system of the River Ruhr in Germany and analyse how the parasites are spatially and temporally distributed in the ecosystem. A total of 5347 snail hosts belonging to six species revealed a highly diverse parasite fauna with 36 trematode species. More abundant snail species harboured more species-rich trematode faunas and communities, with the two dominant snail species, Radix auricularia and Gyraulus albus, accounting for almost 90% of the trematode diversity and harbouring spatially and temporally stable parasite communities. The results highlight the important role of stable keystone host populations for trematode transmission, structure and diversity. This local trematode diversity reveals information on definitive host occurrence and trophic interactions within ecosystems.

Figure 1

Graphical representation of the snail species and their trematode fauna in the Ruhr lakes. Each circle represents one host snail species, with the area of each circle corresponding to the total number of snails sampled during the study. Trematode species of a particular host are indicated in the respective circles. Areas where circles overlap indicate shared trematode species; arrows show the position of individual species where space was limited.

Figure 2

Two-dimensional MDS ordination plots of 75 trematode component communities based on the similarity in trematode component community structure (Bray-Curtis index, stress value = 0.11). (a) Ordination plot with indication for lake. (b) Ordination plot with indication for snail host, with ellipses drawn to highlight the communities in the different snail hosts.

Figure 3

Scheme of transmission pathways of the trematode species found in the snail populations in the five studied lakes. Boxes in the middle represent second intermediate hosts or encystment in the aquatic environment and boxes at the top represent definitive host groups. The lines indicate trematode species utilising individual transmission pathways, with the thickness of the lines being proportional to the number of trematode species utilising each transmission pathway. Dotted lines show direct infection of definitive host. Abbreviations: Ba = Baldeneysee; He = Hengsteysee; So = Sorpetalsperre; Hn = Hennetalsperre; Ve = Versetalsperre.

Figure 4

Map of the Ruhr area and the lake system studied. Individual sampling sites are highlighted by red dots. Abbreviations: Ba = Baldeneysee; He = Hengsteysee; So = Sorpetalsperre; Hn = Hennetalsperre; Ve = Versetalsperre.