Search

In most tropical regions, the Nile tilapia (Oreochromis niloticus, Cichlidae) has been introduced for aquaculture purposes, making it one of the most widely-introduced species. Adversely, it has escaped aquaculture and became invasive in many places with detrimental effects on the local fauna. It is a fast grower and aggressive species that can hybridize with indigenous cichlids and indigenous cichlid species decline after introduction of Nile tilapia. However, little is known of the detrimental effects of co-introduction of parasites from Nile tilapia and possible parasite spillover and spillback to and from indigenous cichlids. Parasites can strongly influence the fitness and competitiveness of infected individuals and species. Therefore, it is important to monitor host switching between native and invasive fish species. The most prevalent gill parasites on Nile tilapia are Monogenea (Platyhelminthes). These are obligate parasites which have a direct lifecycle (no intermediate hosts), are species rich and generally host-specific. They mainly infect gills or skin of fish. These aspects make Monogenea ideal candidates for host switching, because they only require a single host species in the invasive area and are easily transferred. Also, because monogeneans are host-specific each host species hosts its own unique fauna of parasites, thus providing a distinguishable character between host species. The goal of this research is to trace co-introduction of Nile tilapia parasites and subsequent host switching to indigenous cichlids. To trace this, the pre-introduction (or native) parasite fauna is reconstructed by sampling hosts stored in museum collections (baseline data). Contemporary samples from the same localities are compared with the collected baseline data, which allows for a reliable tracing of host switching events. We present results from two ecoregions, Bas-Congo and Bangwuelu-Mweru, both within the Democratic Republic of the Congo. Belspo

In most tropical regions, the Nile tilapia ($Oreochromis niloticus£, Cichlidae) is introduced for aquaculture, making it one of the major species in culture worldwide. However, it has become invasive in many places with detrimental effects on the local fauna. The literature reports a decline of indigenous cichlid species after the introduction of Nile tilapia in several African regions. Here, Nile tilapia is in direct competition and can hybridize with indigenous cichlids. However, in these studies the effect of parasite co-introduction and thus of introducing additional pest species remains underexplored. Parasite co-introduction can influence the fitness and therefore the competitiveness of both invasive and native species. Also parasite spillover and spillback effects (host-switching) may occur, which can impact competition, fitness, mortality, fecundity, trophic ecology, co-evolution and biodiversity. We focus on monogenean gill parasites ($Cichlidogyrus£, $Gyrodactylus£ and $Scutogyrus£) because they are host-specific, have a high prevalence and a direct lifecycle. Furthermore, we focus predominantly on the Congo Basin because here the monogenean fauna remains largely unstudied. In addition Nile tilapia is introduced multiple times across the Congo Basin, but these introductions received little scientific attention. Studying this through regional case-studies will result in a better understanding of the potential for parasite transfer and the impact of invasive species, which will aid in conserving the native fauna. We will present a contribution to the biogeography and host range of these parasites in Haut-Katanga. In total, 13 cichlid and 19 parasite species were collected of which one cichlid and 6 parasite species are new to science and 3 need redescription. For 9 native hosts, this is the first record of their gill monogeneans. On Nile tilapia we found 5 of the 7 $Cichlidogyrus£ species known to infect this host. These 5 species also occur on the native $Oreochromis£ species in recent and historical samplings, so were already present in the basin before introduction of Nile tilapia. Furthermore, $Cichlidogyrus dossoui£ and $C. papernastrema£ were found to occur both on mouth-brooding and substrate-brooding cichlids which refutes the hypothesis of a strictly separate gill parasite fauna between mouth-brooders and substrate-brooders. BELSPO

Heterogeneous exposure to parasites may contribute to host species differentiation. Hosts often harbour multiple parasite species which may interact and thus modify each other’s effects on host fitness. Antagonistic or synergistic interactions between parasites may be detectable as niche segregation within hosts. Consequently, the within-host distribution of different parasite taxa may constitute an important axis of infection variation among host populations and species. We investigated the microhabitat distributions and species interactions of gill parasites (four genera) infecting 14 sympatric cichlid species in Lake Victoria, Tanzania. We found that the two most abundant ectoparasite genera (the monogenean Cichlidogyrus spp. and the copepod Lamproglena monodi) were non-randomly distributed across the host gills and their spatial distribution differed between host species. This may indicate microhabitat selection by the parasites and cryptic differences in the host–parasite interaction among host species. Relationships among ectoparasite genera were synergistic: the abundances of Cichlidogyrus spp. and the copepods L. monodi and Ergasilus lamellifer tended to be positively correlated. In contrast, relationships among morphospecies of Cichlidogyrus were antagonistic: the abundances of morphospecies were negatively correlated. Together with niche overlap, this suggests competition among morphospecies of Cichlidogyrus. We also assessed the reproductive activity of the copepod species (the proportion of individuals carrying egg clutches), as it may be affected by the presence of other parasites and provide another indicator of the species specificity of the host–parasite relationship. Copepod reproductive activity did not differ between host species and was not associated with the presence or abundance of other parasites, suggesting that these are generalist parasites, thriving in all cichlid species examined from Lake Victoria.

Parasites may have strong eco-evolutionary interactions with their hosts. Consequently, they may contribute to host diversification. The radiation of cichlid fish in Lake Victoria provides a good model to study the role of parasites in the early stages of speciation. We investigated patterns of macroparasite infection in a community of 17 sympatric cichlids from a recent radiation and 2 older species from 2 nonradiating lineages, to explore the opportunity for parasite-mediated speciation. Host species had different parasite infection profiles, which were only partially explained by ecological factors (diet, water depth). This may indicate that differences in infection are not simply the result of differences in exposure, but that hosts evolved species-specific resistance, consistent with parasite-mediated divergent selection. Infection was similar between sampling years, indicating that the direction of parasite-mediated selection is stable through time. We morphologically identified 6 Cichlidogyrus species, a gill parasite that is considered a good candidate for driving parasite-mediated speciation, because it is host species-specific and has radiated elsewhere in Africa. Species composition of Cichlidogyrus infection was similar among the most closely related host species (members of the Lake Victoria radiation), but two more distantly related species (belonging to nonradiating sister lineages) showed distinct infection profiles. This is inconsistent with a role for Cichlidogyrus in the early stages of divergence. To conclude, we find significant interspecific variation in parasite infection profiles, which is temporally consistent. We found no evidence that Cichlidogyrus-mediated selection contributes to the early stages of speciation. Instead, our findings indicate that species differences in infection accumulate after speciation.