Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Riverine biodiversity is deteriorating rapidly as a result of multiple interacting anthropogenic pressures. Freshwater species are subject to physico-chemical pollution originating from various sources (e.g. agriculture, industries, households), hydro-morphological alterations (e.g. construction of dams, river calibration), and the introduction of invasive species (e.g. topmouth gudgeon, Chinese mitten crab, round goby in Flanders). Conservation and restoration actions generally focus on protecting freshwater habitats and species, and the assessment of ecological quality is based on the diversity and abundance of species and specific taxa. However, other metrics, such as genetic diversity and the composition of parasite communities, provide important information about environmental and ecological patterns (Chapter 1).In this PhD study, I investigated environmental and spatial patterns of fish communities, fish parasite communities, and genetic structure with a focus on responses to environmental pollution and degradation in Flanders (Belgium). Assessment of parasite communities and genetic patterns focused on three riverine fish species (three-spined stickleback, stone loach, topmouth gudgeon) with contrasting ecology, environmental tolerance, life history traits, dispersal capacity, and invasion history.In Chapter 2, I studied the response of fish communities to environmental pollution and degradation, using a community model based approach. Physico-chemical, hydro-morphological, and ecological quality of freshwater systems in Flanders and many other member states of the European Union remains inadequate. Ecological quality based on fish community structure (e.g. Fish Index in Flanders), in particular, lags behind and only 1% of all waterbodies in Belgium reached sufficient quality by the end of 2015. Hence, successful restoration and conservation practices should be identified and prioritized. I aimed at identifying responses of fish communities to environmental policy targets based on the Flemish implementation of the Water Framework Directive. Responses to both physico-chemical (oxygen, conductivity, chemical oxygen demand, and nitrogen) and hydromorphological (riverbed, profile, flow, longitudinal and lateral continuity) targets were modelled using a joint species distribution model. Species richness responded most strongly to a decrease in conductivity and nitrogen levels, and an increase in riverbed quality. However, responses to current quality standards were weak.Although not directly included in the Water Framework Directive, analysis of parasite communities is important in the assessment of environmental status of rivers, partly because parasites provide a direct indication of biodiversity, and partly because parasite communities can be used as indicators of environmental quality. Nevertheless, processes and factors influencing parasite infection in freshwater fish and the link with pollution are not well understood. To better understand anthropogenic and natural factors driving variation in parasite infection, I studied parasite communities of three-spined stickleback, stone loach, and topmouth gudgeon in the Demer basin. Ectoparasites of three-spined stickleback were positively correlated with nutrient levels (Chapter 3), while the endoparasitic species, depending on trophic ingestion for their transmission, did not appear affected by pollution. Moreover, pollution did not influence body condition of three-spined stickleback, suggesting that other processes are responsible for the increase in ectoparasite abundance. In Chapter 4, I explored variation in parasite communities of the three focal species. Topmouth gudgeon harboured fewer parasites, a pattern often observed in invasive species, while parasite communities of the native species reflected (physico-chemical and host-related) environmental and spatial heterogeneity.The importance of genetic diversity for the persistence of species has been widely recognized, but genetic patterns have not often been included in conservation planning of riverine species. Analysis of genetic diversity highlighted different population genetic patterns (Chapter 5). We observed strong population genetic structure in three-spined stickleback, accompanied by low levels of genetic diversity. Population structure was less pronounced in stone loach and diversity was higher compared to three-spined stickleback. Populations of topmouth gudgeon, however, were less differentiated compared to the native species. Population structure was strongly driven by waterway distances and the presence of migration barriers, while other environmental and spatial factors are likely responsible for the observed population structure in both native species.When comparing patterns of genetic and species diversity (i.e. species-genetic diversity correlations, SGDCs), results show that α- species and genetic diversity are non-congruent in Flemish riverine systems (Chapter 6). Community dissimilarity (β-diversity), on the other hand, correlated to population differentiation in topmouth gudgeon, and to a lesser extent in stone loach. This is likely a result of the response of both species and genetic composition to the presence of migration barriers and other spatial processes.Overall, the results of this PhD indicate that prioritizing locations and areas for conservation and restoration will be challenging as levels of species, genetic, and parasite diversity do not strongly overlap. Although some general drivers could be identified, it is clear that an interplay of complex processes shapes different aspects of riverine diversity and ecosystems in a different manner.

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Ondanks het verbod op het uitzetten van jachtwild worden er nog steeds patrijzen afkomstig uit kwekerijen waargenomen in Vlaanderen. Om zulke illegale uitzettingen op te sporen werd in 2021 een genetische studie opgestart, waarbij ongeveer 30.000 genetische variaties werden gedetecteerd in de Vlaamse patrijzenpopulatie.

Patrijs (vogel) --- Partridges

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

In this thesis we compare parasite abundance and prevalence among populations of three different fish hosts to assess the effect of a different host composition on parasite-host dynamics. We focus on the effect on parasite-host dynamics caused by a non-indigenous and invasive fish species that was accidently introduced via aquaculture. We will also take a look at the bio-indicator capacity of the parasite taxa for seven environmental parameters, the influence of two host-related factors, and the importance of indirect effects. Three fish species were sampled of which one invasive species (topmouth gudgeon, Pseudorasbora parva) and two native species (three-spined stickleback, Gasterosteus aculeatus; stone loach, Barbatula barbatula). In total 694 fish were caught at 15 locations in the Demer basin (Flanders, Belgium). Fish were dissected and inspected for ecto- and endoparasites, which were identified and counted. A total of 12 parasite taxa were distinguished and four extra categories were made containing unidentified species. Parasite communities differed significantly among all three fish species and may be partly explained through niche differences; the highest parasite species richness was found in stone loach. All three fish species shared parasite species. We propose that the presence of other host species might influence the abundance and prevalence of shared parasite species in some host species. Topmouth gudgeon showed overall fewer infected specimen and experienced a significantly lower parasite diversity compared to the two other native fish species. Parasite-host dynamics seemed to be influenced through the population’s host composition in all three fish species. However, part of the observed variation in parasite abundance and prevalence may be explained through the direct or indirect influence of environmental conditions, host quality, biotic interactions, and possibly the presence of other unsurveyed organisms. Overall, parasites with a free-swimming infective stage in their life cycle and ectoparasites seemed to be more affected by the environmental factors: temperature, pH, conductivity, chemical oxygen demand, O2 saturation, total phosphorus and total nitrogen. This may be an indication that free-swimming parasite and ectoparasite taxa are more suitable for assessing environmental quality based on the above factors. Host related factors (body length, sex) had a significant effect on the abundance and/or prevalence of certain parasite taxa, indicating the importance of host quality. Both the interaction effects of location and host species, and host species and host community assembly on parasites were significant. This may indicate the importance of indirect factors, e.g. fluctuations in host density through competition and/or environmental stress, influencing parasite prevalence and abundances. In the introduction, we discuss the importance of parasites in ecosystems and some of the general categorizations of this polyphyletic group are given. Next, we discuss the overall threats of surface freshwater bodies (SFBs) on a global scale, the main sources and types of pollution, climate change, and the effect on parasites. Finally, we focus on the possible mechanisms by which an introduced species may alter native parasite-host dynamics and provide a short overview of the biology and ecology of the studied fish species.

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

De Chinese muntjak is een kleine hertensoort die door de mens is geïntroduceerd in Europa. Wegens schade aan akkers, tuinen en plantsoenen, en voornamelijk aan bossen, wordt de muntjak beschouwd als een probleemsoort. Sinds 2016 geldt een strikt verbod op de import, kweek en uitwisseling van muntjak. Vlaanderen lijkt momenteel het zwaartepunt te vormen van het voorkomen van muntjak in de Europese Unie. De dynamiek in verspreiding is complex, omdat deze gestuurd wordt door menselijk handelen enerzijds en door natuurlijke processen anderzijds. Om deze processen te kunnen ontrafelen, moet de genetische signatuur van individuen, families en populaties bekend zijn. Het doel van dit rapport is tweedelig. In een eerste fase worden patronen van genetische diversiteit, structuur en onderlinge verwantschappen van muntjak in Vlaanderen bestudeerd. In een tweede fase wordt een protocol ontwikkeld waarmee verwantschappen van nieuwe, in de toekomst aangeleverde stalen kunnen worden onderzocht.