Suchergebnisse

AbstractCrustacean amphipods serve as intermediate hosts for parasites and are at the same time sensitive indicators of environmental pollution in aquatic ecosystems. The extent to which interaction with the parasite influences their persistence in polluted ecosystems is poorly understood. Here, we compared infections of Gammarus roeselii with two species of Acanthocephala, Pomphorhynchus laevis, and Polymorphus minutus, along a pollution gradient in the Rhine-Main metropolitan region of Frankfurt am Main, Germany. Prevalence of P. laevis was very low at the unpolluted upstream reaches (P ≤ 3%), while higher prevalence (P ≤ 73%) and intensities of up to 9 individuals were found further downstream—close to an effluent of a large wastewater treatment plant (WWTP). Co-infections of P. minutus and P. laevis occurred in 11 individuals. Highest prevalence of P. minutus was P ≤ 9% and one parasite per amphipod host was the maximum intensity recorded. In order to assess whether the infection affects survival in the polluted habitats, we tested the sensitivity of infected and uninfected amphipods towards the pyrethroide insecticide deltamethrin. We found an infection-dependent difference in sensitivity within the first 72 h, with an effect concentration (24 h EC50) of 49.8 ng/l and 26.6 ng/l for infected and uninfected G. roeselii, respectively. Whereas final host abundance might partially explain the high prevalence of P. laevis in G. roeselii, the results of the acute toxicity test suggest a beneficial effect of acanthocephalan infection for G. roeselii at polluted sites. A strong accumulation of pollutants in the parasite could serve as a sink for pesticide exposure of the host. Due to the lack of a co-evolutionary history between parasite and host and a lack of behavioral manipulation (unlike in co-evolved gammarids), the predation risk by fish remains the same, explaining high local prevalence. Thus, our study exemplifies how organismic interaction can favor the persistence of a species under chemical pollution.

AbstractCentral European riverine networks are subject to widely varying local anthropogenic pressures, forcing species with limited dispersal abilities to adapt or become locally extinct. Previous catchment-wide studies have shown that some invertebrates tend to have pronounced population structuring throughout mountainous river networks, raising the question of whether this also translates into small-scale phenotypic differentiation and adaptation to local stressors. One such species is the headwater crustacean species Gammarus fossarum clade 11 (or lineage B), which we restudied in terms of population structure four years after first assessment. Our aim was not only to document the temporal stability/dynamics of the population structure, but we asked whether a small-scale genetic structuring also results in phenotypic differentiation and different susceptibility to a commonly applied pesticide. Therefore, we re-assessed population structure based on COI haplotypes and their frequencies, and quantified key parameters related to morphological and life-history differentiation. Furthermore, we examined the difference in sensitivity towards the pyrethroid insecticide deltamethrin. COI haplotype patterns were found to be stable over time and confirmed the small-scale population structuring within the catchment, with isolated headwater populations and connected downstream populations. While little life-history differentiation was observed, marked differences in susceptibility to the pyrethroid insecticide were found. Populations from pristine sites responded significantly more tolerant than populations from anthropogenically impacted sites—showing that prior exposure to a spectrum of stressors does not automatically increase tolerance to a specific stressor. Therefore, our study demonstrates that limited dispersal capacity is reflected not only in population structure, but also in small-scale variation in susceptibility to anthropogenic disturbance. The system thus provides a suitable experimental landscape to test the impact of further stressors (e.g., other novel entities, including pesticides with other modes of action) on locally isolated populations. Based on these findings, important recommendations for the protection of riverine species and their intraspecific genetic variation can be developed.