Parasites entangled in food webs

Hidden parasite diversity in a European freshwater system

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.

Mesopredatory fishes from the subtropical upwelling region off NW-Africa characterised by their parasite fauna

Eastern boundary upwelling provides the conditions for high marine productivity in the Canary Current System off NW-Africa. Despite its considerable importance to fisheries, knowledge on this marine ecosystem is only limited. Here, parasites were used as indicators to gain insight into the host ecology and food web of two pelagic fish species, the commercially important species Trichiurus lepturus Linnaeus, 1758, and Nealotus tripes Johnson, 1865. Fish specimens of T. lepturus (n = 104) and N. tripes (n = 91), sampled from the Canary Current System off the Senegalese coast and Cape Verde Islands, were examined, collecting data on their biometrics, diet and parasitisation. In this study, the first parasitological data on N. tripes are presented. T. lepturus mainly preyed on small pelagic Crustacea and the diet of N. tripes was dominated by small mesopelagic Teleostei. Both host species were infested by mostly generalist parasites. The parasite fauna of T. lepturus consisted of at least nine different species belonging to six taxonomic groups, with a less diverse fauna of ectoparasites and cestodes in comparison to studies in other coastal ecosystems (Brazil Current and Kuriosho Current). The zoonotic nematode Anisakis pegreffii occurred in 23% of the samples and could pose a risk regarding food safety. The parasite fauna of N. tripes was composed of at least thirteen species from seven different taxonomic groups. Its most common parasites were digenean ovigerous metacercariae, larval cestodes and a monogenean species (Diclidophoridae). The observed patterns of parasitisation in both host species indicate their trophic relationships and are typical for mesopredators from the subtropical epi- and mesopelagic. The parasite fauna, containing few dominant species with a high abundance, represents the typical species composition of an eastern boundary upwelling ecosystem.

Effects of the transmissibility and virulence of pathogens on intraguild predation in fragmented landscapes

It is well known that pathogenic infection can have a profound effect on the outcome of competition and predation, however the role of pathogenic infection in systems where predators and prey also compete for other resources is yet to be explored (i.e. in systems of intraguild predation). Using a cellular automaton model, we here explore the effect of pathogenic infection on the spatial dynamics of species that also engage in intraguild predation (IGP) in a fragmented landscape. First, the shared pathogen by the predator and prey can enhance species coexistence in the IGP system, consistent with results for non-spatial IGP systems. Second, equilibrium population sizes of the predator and prey depend crucially on the pathogen virulence to the predator but are insensitive to the change in the virulence to the prey. This asymmetric response to virulence change is due to the fact that the predator species has to juggle between predation, resource competition and pathogenic infection. Finally, the response of the pathogen to habitat fragmentation is largely determined by its life-history strategy (transmissibility and virulence) and the trophic level of its host. These results enrich our understanding on the role of pathogens in the ecosystem functioning of eco-epidemiological systems.

DNA barcoding increases resolution and changes structure in Canadian boreal shield lake food webs

Food webs are important in understanding the structure, function, and behaviour of ecosystems, but, due to methodological limitations, are often poorly resolved in ways that impact food-web properties. Although DNA barcoding has proven useful in determining the diet of consumers, few studies have used this technique to determine food-web structure. These studies report mixed impacts on various food-web properties, but are limited by their taxonomic focus and their failure to evaluate DNA barcoding for both diet analysis and food-web structure. In this study, we show that, when compared to a morphological approach, DNA barcoding increases foodweb resolution by increasing the number and frequency of prey species identified in the stomach contents of eight species of Canadian boreal shield predatory fishes. In addition, we observed differences in food-web structure, such as increased generalism, habitat coupling, and omnivory, that have strong implications for food-web stability and dynamics. We conclude that DNA barcoding is a powerful tool to evaluate how resolution impacts foodweb properties and can help further our understanding of how food webs are structured by identifying feeding interactions in an unprecedented and highly detailed manner.