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Early life stages of exotic gobiids as new hosts for unionid glochidia
Abstract
Introduction of an exotic species has the potential to alter interactions between fish and bivalves; yet our knowledge in this field is limited, not least by lack of studies involving fish early life stages (ELS).
Here, for the first time, we examine glochidial infection of fish ELS by native and exotic bivalves in a system recently colonised by two exotic gobiid species (round goby Neogobius melanostomus , tubenose goby Proterorhinus semilunaris ) and the exotic Chinese pond mussel Anodonta woodiana .
The ELS of native fish were only rarely infected by native glochidia. By contrast, exotic fish displayed significantly higher native glochidia prevalence and mean intensity of infection than native fish (17 versus 2% and 3.3 versus 1.4 respectively), inferring potential for a parasite spillback/dilution effect. Exotic fish also displayed a higher parasitic load for exotic glochidia, inferring potential for invasional meltdown. Compared to native fish, presence of gobiids increased the total number of glochidia transported downstream on drifting fish by approximately 900%.
We show that gobiid ELS are a novel, numerous and ‘attractive’ resource for unionid glochidia. As such, unionids could negatively affect gobiid recruitment through infection‐related mortality of gobiid ELS and/or reinforce downstream unionid populations through transport on drifting gobiid ELS. These implications go beyond what is suggested in studies of older life stages, thereby stressing the importance of an holistic ontogenetic approach in ecological studies.
... If an invasive species can serve as a suitable host (e.g. intermediate, paratenic or final host) for local parasites, these parasites may spill back to other local hosts, thereby increasing their infection rates within the native host populations (Kelly et al., 2009;Šlapanský et al., 2016). In contrast, invasive species might also be responsible for a decrease of the infection risk in the native host populations (e.g. ...
... In contrast, invasive species might also be responsible for a decrease of the infection risk in the native host populations (e.g. Gagne et al., 2016;Šlapanský et al., 2016).This so-called dilution effect occurs if the invaders serve as inappropriate hosts for local parasites, in which the parasites cannot develop further or if they are not favoured as food item by a predatory definitive host (Ostfeld and Keesing, 2000;Johnson et al., 2012). ...
Ponto-Caspian gobies became highly abundant in many regions outside their native distribution range (e.g. in the Rhine River system). In the newly invaded habitats, the parasite communities of the invasive gobies are characterized by a lower species richness compared to their native range. Interestingly, acanthocephalans of the genus Pomphorhynchus are highly abundant, although they do not become mature and mostly remain encapsulated in the abdominal cavity as preadults. Thus, gobiids could either represent a dead-end host for Pomphorhynchus sp. declining its population (dilution effect) or act as a paratenic host that could increase the infection pressure if the infected gobies are preyed upon by appropriate definitive hosts (spill back). To determine which of the 2 scenarios the gobiids contribute to, we conducted 2 infection experiments using smaller and larger individuals of the definitive host chub (Squalius cephalus), infected with preadults of Pomphorhynchus sp. collected from the abdominal cavity of Neogobius melanostomus. The results showed that preadults were able to complete their development and mature in the definitive host with mean recovery rates of 17.9% in smaller and 27.0% in larger chubs. Successful infections were observed in 62.0% and 80.0% of the smaller and larger chubs, respectively. Our study demonstrated that gobies can theoretically serve as a paratenic host for acanthocephalans of the genus Pomphorhynchus, and that infection might spill back into the local fish community if infected gobies are preyed upon by suitable definitive hosts of Pomphorhynchus sp. such as large barbel or chub.
... Nearly no glochidia were attached on the trunk or tail. This also agrees with other studies, which found preferable attachment on the fins and head (e.g., McMahon and Bogan, 2001;Šlapansky et al., 2016;Mineeva and Semenov, 2021a, b). Giusti et al. (1975) concluded that the negligible attachment to the trunk and tail was linked to the scale cover of these body parts. ...
... Others, however, recorded low rates in some gobiid species but a high value in a sympatric goby (e.g., Mierzejewska et al., 2014;Itoh et al., 2016). Again, others found high glochidia burdens (e.g., Antal et al., 2015;Šlapansky et al., 2016). If repeated infection decreases the risk of further infestation by boosting the immune response, this could explain the divergent infestation rates of perennial gobiid fishes. ...
To complete their life cycle, freshwater mussels of the order Unionida depend on fishes as hosts for their obligatory parasitic larval phase, the glochidium. Here we report the first documentation of gobioid fishes as hosts of glochidia of unionid mussels in the wild in Italy and in southern Europe (outside of the Danube drainage area). We also examined the pattern of the attached glochidia. A recent review reported 326 fish species as suitable hosts for unionids, but only eight (2.5%) of these were Gobioidei. Host identification and the documentation of their benefits or threats for the interaction of the mussels with their hosts is important for conservation of freshwater mussels. But the coexistence of mussels with non-native fish species is only poorly understood, including the compatibility of these two groups. Knipowitschia panizzae and Pomatoschistus canestrinii, two translocated sand gobies, were sampled in 2022 at the east shore of Lake Trasimeno (Italy). Two species of anodontine mussels were present at this locality, the native Anodonta anatina and the translocated Sinanodonta woodiana. Genetic data revealed that both sand gobies hosted glochidia only of A. anatina but not of S. woodiana, possibly because of seasonal bias. About 50% of the specimens of both fish species were infested. The paired fins were the most prominent targets. The examined individuals of both sand gobies carried only few glochidia (max. 5). Nevertheless, the two species showed a divergent pattern of glochidia attachment.
... Either way, the invasive species can also serve as an additional appropriate host that might amplify the transmission of native parasites. This so-called parasite spill back results in an increased parasite infestation rate in native host species, which might lead to changes of relative ratios of certain parasite species within the community (Tompkins and Poulin 2006;Kelly et al. 2009;Šlapanský et al. 2016). Furthermore, if non-native parasites are introduced together with their invasive hosts, they could "spill over" to the native host communities and become highly abundant that might lead to a replacement of native and sometimes closely related parasite species (Kelly et al. 2009;Diagne et al. 2016;Hohenadler et al. 2018). ...
... Furthermore, if non-native parasites are introduced together with their invasive hosts, they could "spill over" to the native host communities and become highly abundant that might lead to a replacement of native and sometimes closely related parasite species (Kelly et al. 2009;Diagne et al. 2016;Hohenadler et al. 2018). However, the invasive free-living species might also decrease the infection risk in native host populations, i.e., the so-called dilution effect (Šlapanský et al. 2016;Gagne et al. 2016) if they acquire local parasites but turn out to be an inappropriate host for further parasite development or maturation (so-called dead-end host). ...
Invasive species are a major threat to ecosystems worldwide. Their effects are versatile and mostly well studied. However, not much is known about the impact of invasion on native parasite communities, although parasites are usually important response variables for ecosystem health. To improve the knowledge on how native fish parasite communities and their dynamics are affected by invasive species and how these processes change local host-parasite interactions over time, we studied different host-parasite systems in four German rivers. Three of these rivers (Rhine, Ems, and Elbe) are heavily invaded by different Ponto-Caspian species such as the amphipod Dikerogammarus villosus and various gobiids such as Neogobius melanostomus and Ponticola kessleri that serve as potential hosts for different local parasite species, while the fourth river (Schwentine) was free of any Ponto-Caspian invaders. Due to the lack of additional uninvaded river systems, literature data on parasite communities before invasion were compared with the post invasion status for the rivers Rhine and Elbe. The results showed differences among the parasite communities of different host species from the three invaded rivers when compared to the Schwentine River. Among the local internal parasite communities, especially the acanthocephalan Pomphorhynchus laevis and the nematode Raphidascaris acus have to be considered as key species associated with invasions from the Ponto-Caspian region. As the examined invasive Ponto-Caspian fish species serves as suitable host for both parasite species, the increases in their infection rates in native fish species are examples of parasite spill back (R. acus) and spill over (P. laevis, at least in the river Rhine). These results were further supported by the analysis of literature data on parasite communities of the past 20 years. Consequences for local parasite communities range from decreased prevalence of native parasites towards an extinction of entire parasite species.
... Nymphalini butterflies [34] Malaria-birds [52] California butterflies [69] Unionid mussels-fish [24] Nematinae sawflies [66] Nematodes-Artiodactyla [51] Spider mites [26] Gyrodactylid gill parasites-fish [78] Lycaena salustius butterfly [70] Trematodes-snakes, turtles etc. [33] Pomphorynchus worm-amphipods [21] Nematodes-birds [49] Platyhelminths-anurans [79] Cospeciation is rare or absent Nymphalid butterflies [34] Malaria-birds [6] Psyllid bugs [71] Nematodes-Artiodactyla [51] Phyllonorycter moths [67] Lice-pocket gophers Box 2 ...
... How can squirrels be reservoirs for bacteria causing leprosy in humans [20]? Another example of the same paradoxical situation is the fact that a species colonizing a new geographical area sooner or later (often sooner) is infected with locally resident parasites or conversely infects local species with its own parasites [21][22][23][24]. Why and how do the parasite species expand from the host to which they are already well adapted, and on which they are supposedly highly specialized? ...
Parasite-host and insect-plant research have divergent traditions despite the fact that most phytophagous insects live parasitically on their host plants. In parasitology it is a traditional assumption that parasites are typically highly specialized; cospeciation between parasites and hosts is a frequently expressed default expectation. Insect-plant theory has been more concerned with host shifts than with cospeciation, and more with hierarchies among hosts than with extreme specialization. We suggest that the divergent assumptions in the respective fields have hidden a fundamental similarity with an important role for potential as well as actual hosts, and hence for host colonizations via ecological fitting. A common research program is proposed which better prepares us for the challenges from introduced species and global change.
... In the freshwater area (lagoons and river systems) related to the Baltic Sea (Ondrackova et al. 2005(Ondrackova et al. , 2009(Ondrackova et al. , 2010(Ondrackova et al. , 2015(Ondrackova et al. , 2021Francova et al. 2011;Mierzejewska et al. 2011;Emde et al. 2012;Slapansky et al. 2016) and in the Great Lakes (Kvach and Stepien 2008;Gendron et al. 2012) round goby parasite communities have been studied more extensively than in the brackish Baltic Sea (Kvach and Skora 2007;Kvach and Winkler 2011;Kornis et al. 2012;Flink et al., 2017). There are some studies on parasites in round goby and other invasive gobies that support the idea of the parasite release hypothesis (in leaning to the predation release hypothesis) when alien species enter new environments, also showing that these species act to a certain extent as vector of new parasites (Kvach and Stepien 2008;Emde et al., 2014;Hohenandler et al., 2018). ...
The aim of the Workshop on Stickleback and Round Goby in the Baltic Sea (WKSTARGATE) was to update, summarize and synthesize the current knowledge of both species with respect to their ecology and potential use in fisheries. Ongoing projects were presented in the mornings of the first two days to inform participants about current research in the respective countries (Annex 5). The group discussed ecological aspects that are relevant to fisheries, such as distribution and abundances, feeding ecology and behaviour. So far, no dedicated monitoring exists for either of the species. However, the Baltic International Acoustic Survey (BIAS), coordinated by ICES, has been used to estimate abundances and biomasses of pelagic stickleback in offshore areas across the Baltic, while the availability and quality of coastal data differs between countries, but is generally scarce. Even less current abundance information is available for round goby. It is only available for areas where it is already commercially exploited like Latvia. Most studies on the ecological impact of these species focus on trophic interactions, and its resulting competition. It became clear, that these ecological impacts depend on the abundance of the species and that the effects therefore vary on a temporal and spatial scale. Estimating the ecological impact of a stickleback or round goby fishery is therefore very speculative without reliable abundance data, why the group decided to describe the known impact of the species on the ecosystem.
Landings of round goby increased significantly in Latvia during the last years, while stickleback landings decreased over the last five decades but most recently show a slight increase. A targeted round goby fishery exists in Latvian waters, while the stickleback is solely taken as bycatch in all Baltic countries. Both fisheries are currently unmanaged and, with the exception of round goby fishery in Latvia, unregulated. In Latvia the round goby fishery is regulated by effort, to reduce
the bycatch of native species. Furthermore, Latvia has initiated work towards a stock assessment of round goby. Efforts for a Baltic-wide stickleback assessment have been undertaken by Sweden, and both, Sweden and Denmark are taking first steps towards a full analytical stock assessment
... Considering parasites with complex life cycles, the parasite fauna of Ponto-Caspian gobies is characterised by a low prevalence of adult forms and a high percentage of larval forms, which tend to be less host-specific and more adaptive in comparison to adults or parasites with direct life cycle (Poulin, 1992 (Kvach & Stepien, 2008). As parasite abundances in their non-native ranges were sometimes several times higher than those their native range (Ondračková et al., 2015;Šlapanský, Jurajda, & Janáč, 2016), this suggests the potential for 'parasite amplification' (see Kelly et al., 2009). On the other hand, gobies translocated to new areas may also play an important role in 'parasite dilution', where non-competent hosts reduce the presence of a parasite in the environment (see Gendron & Marcogliese, 2017). ...
This study provides a comprehensive checklist of parasites reported for native and non-native populations of seven Ponto-Caspian goby species, i.e. Babka gymnotrachelus, Neogobius fluviatilis, N. melanostomus, Ponticola gorlap, P. kessleri, Proterorhinus semilunaris and P. semipellucidus, all of which have recently expanded their natural range, either by transoceanic translocation or along the three main European intracontinental invasion corridors. In some cases, invasion success is facilitated by loss of natural enemies, such as predators and parasites; thus, knowledge of a species natural parasite fauna is essential for assessments of enemy release in the host’s non-native range. The study is based on published literature and personal unpublished data related to parasites of Ponto-Caspian gobiids. A total of 249 parasite taxa have been reported during 1931—2019, with higher numbers reported from native (214) than non-native (151) ranges. This checklist indicates apparent reduction in native parasites in non-native ranges in all goby species, although parasite colonisation in non-native ranges differs between fish species and invasion corridors. Interestingly, the cumulative number of species reported is still gradually increasing in both ranges. Acquisition of high number of local parasite species also indicates competence of Ponto-Caspian gobies to a wide range of generalist parasites.
... Predation on benthic invertebrates, for example, may cause shifts in their assemblage structure (Lederer et al. 2008;Kipp and Ricciardi 2012;Mikl et al. 2017a), with possible consequences for exploiting prey resources and increased competition with native fish. Round goby introduction also has the potential to cause alterations in host-parasite relationships, such as parasite spill-over (Ondračková et al. 2015;Šlapanský et al. 2016) or dilution effects (Poos et al. 2010;Gendron and Marcogliese 2017). Further, round goby dietary preference in combination with goby consumption by native predators could alter nutrient flows through the food web, increasing the risks of contaminant accumulation in higher trophic levels (Marentette et al. 2010;Polačik et al. 2015). ...
The round goby Neogobius melanostomus is a small invasive benthic fish that has caused multiple and variable impacts in freshwaters. One of the most recent round goby introductions occurred in the upper Elbe in 2015. In this case, the new population was isolated from other populations both by land and by at least 600 river km. Monitoring of this population has provided a unique opportunity to describe the characteristics of round gobies naturally spreading from a single introduction point and to examine its effects on native fish. Passive downstream dispersal of early life stages has played a central role in population spread, with the proportion of small fish increasing downstream and decreasing with time. The sex ratio of the novel population was strongly female-biased and with no apparent spatial structure. Round goby introduction appears to have had a negative impact on native 0+ fish abundance and species richness. Relationships with ≥ 1+ fish were more diverse, ranging from a significant decrease in chub Squalius cephalus abundance to a significant increase in European eel Anguilla anguilla abundance as goby abundance increased. As no impacts on these species have been reported before, the study appears to provide further evidence for case-specificity in round goby impact.
... In New Zealand, nonnative fish are more frequently occurring with freshwater mussels in lowland lakes and rivers (Rowe & Wilding, 2012;Collier et al., 2016), and have the potential to disrupt the obligate glochidial larval stage of the unionid life-cycle (Berg et al., 2008;Poos et al., 2010). This can occur directly by providing an unsuitable host in the mussel-fish relationship (Douda et al., 2013;Salonen et al., 2016;Š lapanský et al., 2016), and indirectly through competition and predation of native host-fish populations (Poos et al., 2010). ...
A potential mechanism of global decline
in freshwater mussel (Unionida: Bivalvia) abundance
and diversity is disruption of their obligate parasitic
life-cycle by non-native fish species, which may
introduce novel interaction pathways that threaten
unionid recruitment. We assessed three non-native fish
(brown bullhead catfish, Ameiurus nebulosus; rudd,
Scardinius erythrophthalmus; and goldfish, Carassius
auratus) as glochidial hosts for the New Zealand
freshwater mussel Echyridella menziesii to test the
hypotheses that (i) non-native fish will have lower
glochidial attachment rates than a native fish (the
common bully Gobiomorphus cotidianus), and (ii)
encystment rate will be lower on non-native species.
We found that the non-native fish had significantly
lower total glochidial attachment than the native
control fish after infestation and did not produce
ecologically significant quantities of juvenile mussels.
This research supports the general assumption that
non-native species are less suitable hosts of native
freshwater mussels. However, confirming our findings
in the field will indicate if removing non-native fish or
enhancing native fish populations is recommended for
conservation of E. menziesii populations in New
Zealand.
... It should also be noted that, while our paper provides a view on direct impact on the nearshore native fish assemblage, round goby also have the potential to affect aquatic ecosystems through other direct or indirect routes. These may, for example, include a negative impact on the invertebrate assemblage (Lederer et al., 2008;Mikl et al., 2017), altering trophic pathways (Rush et al., 2012), pollution recycling (Johnson et al., 2005a;Kornis et al., 2012;Polačik et al., 2015) or parasite spillback/dilution (Poos et al., 2010;Ondračková et al., 2015;Šlapanský et al., 2016). ...
A number of Ponto-Caspian Gobiid species have greatly increased their geographical ranges over recent decades. Most expansion studies to date, however, have focused on navigable waterways. In this study, we present a summary of six-years (2008–2013) monitoring of round goby Neogobius melanostomus expansion along two connected non-navigable rivers. Contiguous range expansion was observed in both rivers, with dispersal rate ranging from 1.2 to 3.2 km/year. Gobies at newly invaded sites ranged from 20 to 117 mm, with both juveniles and adult fish observed. Though the data did not allow us to see any consistent pattern in the first years after detection, there was some evidence for a shift to a female-biased, juvenile-dominated population over time. While the abundance of non-native tubenose goby Proterorhinus semilunaris appeared to be negatively influenced by round goby establishment, diversity of nearshore native fish showed no evidence of dramatic decline attributable to round goby.
... Both species have been described as common paratenic hosts for P. laevis, both in their native and non-native range (Ondračková et al. 2006;Kvach and Skóra 2007). P. laevis usually occurs in high abundances in a larval or pre-adult stage encysted in the abdominal cavity of these invasive gobiid species (Ondračková Table 4 Sequence-comparison of ITS 1 and ITS 2 genes of P. laevis samples from each sampling spot (2003 and 2004) (Prenter et al. 2004;Tompkins and Poulin 2006;Kelly et al. 2009;Peeler et al. 2011;Š lapanský et al. 2016). If the invasive species additionally serves as a suitable host for a native or already established parasite, the number of dispersal pathways and host species for parasites increase, leading to higher infection risks among native communities (spill-back) (Kelly et al. 2009). ...
Acanthocephalans of the globally distributed genus Pomphorhynchus have been intensively studied during the past decades. In Europe, Pomphorhynchus species have shown a certain degree of variability in their morphological characteristics and behavior. Nowadays two different Pomphorhynchus species, namely P. laevis and P. tereticollis, have been described for different waterbodies in Western and Central Europe. However, until now it appears that both species do not co-occur at the same time in the same habitat. We assume that due to their very similar morphology some of the individuals that were identified based on their morphological characteristics as either of the two species might have been misidentified in previous studies. To avoid this possible source of error, we used molecular marker (ITS 1, COX genes) to identify Pomphorhynchus individuals from European eels that were sampled within a time period of 12 years from the Rhine River to elucidate the distribution of the two species in Western and Central Europe. Our results together with a re-examination of former studies provide evidence that P. laevis might have been introduced together with potential host species (intermediate, paratenic, and/or definitive) from the Ponto-Caspian region, and that it outcompeted and repelled the endemic P. tereticollis from the mainstream of the river. Our results also provide first evidence on the former coexistence of both Pomphorhynchus species in the river Rhine.
... As it now dominates the host pool, N. melanostomus are also expected to alter host-parasite relationships (Ondračková et al. 2015;Š lapanský et al. 2016) and to either reduce parasite load in the NFA through a 'dilution effect' or, alternatively, increase parasite loading through 'parasite spillback' (Kelly et al. 2009;Poos et al. 2010). ...
The round goby Neogobius melanostomus has recently invaded several major freshwater systems in Europe and North America. Despite numerous studies predicting an impact on native fish assemblages, few have attempted to demonstrate it. In this case study, we monitored the effect of N. melanostomus colonisation on abundance and habitat utilisation of both young-of-the-year (YOY) native fish and YOY western tubenose goby Proterorhinus semilunaris in a typical, medium-sized European river. Colonisation by N. melanostomus had no apparent effect on either native fish abundance and species richness or P. semilunaris abundance. Moreover, after colonisation, both native fish and P. semilunaris occupied similar niches (i.e. microhabitats) to those occupied before colonisation. While niche use of YOY N. melanostomus and P. semilunaris overlapped significantly, YOY native fish utilised different habitats from the gobiids. We suggest that N. melanostomus did not compete for resources with YOY fish in our study area due to lack of niche overlap and/or surplus resources. As N. melanostomus rapidly dominated the fish assemblage at our site, we further suggest that utilisation of an empty niche, rather than competitive superiority, was the main factor facilitating its success.
The introduction of invasive species has become an increasing environmental problem in freshwater ecosystems due to the high economic and ecological impacts it has generated. This systematic review covers publications from 2010 to 2020, focusing on non-native invasive freshwater bivalves, a particularly relevant and widespread introduced taxonomic group in fresh waters. We collected information on the most studied species, the main objectives of the studies, their geographical location, study duration, and type of research. Furthermore, we focused on assessing the levels of ecological evidence presented, the type of interactions of non-native bivalves with other organisms and the classification of their impacts. A total of 397 publications were retrieved. The studies addressed a total of 17 species of non-native freshwater bivalves; however, most publications focused on the species Corbicula fluminea and Dreissena polymorpha, which are recog-nised for their widespread distribution and extensive negative impacts. Many other non-native invasive bivalve species have been poorly studied. A high geographical bias was also present, with a considerable lack of studies in developing countries. The most frequent studies had shorter temporal periods, smaller spatial extents, and more observational data, were field-based, and usually evaluated possible ecological impacts at the individual and population levels. There were 94 publications documenting discernible impacts according to the Environmental Impact Classification for Alien Taxa (EICAT). However, 41 of these publications did not provide sufficient data to determine an impact. The most common effects of invasive bivalves on ecosystems were structural alterations, and chemical and physical changes, which are anticipated due to their role as ecosystem engineers. Despite a considerable number of studies in the field and advances in our understanding of some species over the past decade, long-term data and large-scale studies are still needed to understand better the impacts, particularly at the community and ecosystem levels and in less-studied geographic regions. The widespread distribution of several non-native freshwater bivalves, their ongoing introductions, and high ecological and economic impacts demand continued research. Systematic reviews such as this are essential for identifying knowledge gaps and guiding future research to enable a more complete understanding of the ecological implications of invasive bivalves, and the development of effective management strategies.
In this review, we synthesize the current knowledge of the biology, ecology, and impact of Sinanodonta freshwater mussels (Bivalvia, Unionidae), native to East Asia, that have successfully invaded Europe, Central America, North Africa, and several Asian regions. The main introduction pathways of Sinanodonta were reconstructed based on DNA sequence data and distribution records. We show that invasive lineages of Sinanodonta belong to three species, namely, S. woodiana s. str. (“temperate invasive” lineage), S. pacifica (“tropical invasive” lineage), and S. lauta. Their generalist fish-dispersed larvae, short life span, high fecundity, use by humans for multiple purposes, and ability to establish populations in anthropogenically disturbed conditions were identified as crucial traits driving their invasions. Information on the consequences is scarcer, but Sinanodonta can impact native species through larval parasitism, host fish/food competition, and parasite transmission. In addition, ecosystem effects through their filtration—biodeposition—excretion activity and the occurrence of massive die-offs were detected. Ecosystem services and disservices have not yet been quantified, even at local scales, and management methods in the invasive range are understudied. A better understanding of Sinanodonta ecology, impacts, and management options is urgently needed to make informed decisions and set realistic and impactful restoration goals.
Unionid populations are declining worldwide as they are threatened by anthropogenic habitat alterations, the introduction of invasive alien species and the effects of climate change. Several studies have focused on the habitat preferences of adult mussels but none to date have reported on the importance of the habitat preferences of host fish species. The aim of this study was to determine the habitat preferences of unionid host fish species in the Netherlands, to examine potential differences between native and alien host fish species, and to evaluate the effect of alien host fish species on unionid dispersal. Species sensitivity distributions (SSDs) were constructed for the range of occurrences and laboratory tolerance of host fish species in the Netherlands for water temperature, substrate type, flow velocity, and water depth. A case study was selected to assess the suitability to substrate type, flow velocity and water depth of a novel river habitat along longitudinal training dams in the river Waal. Unionid host fish species in the Netherlands preferred shallow littoral zones (0.1 m) with low flow velocity (0.05 m/s), an average water temperature of the Rhine delta (15°C), and most substrate types (ranging from silt to cobbles). Boulder substrate was the most limiting factor of the abiotic factors assessed for both native and alien host fish species. Management options for unionid populations should include host fish species in their assessments while focusing on creating and maintaining areas with limited boulders and implementing alien host fish species removal measures.
Ponto–Caspian gobies are among Europe's most invasive freshwater fish species. These small freshwater and brackish water fish have spread rapidly since the end of the last century, invading the major European river systems, including the Rivers Danube, Rhine, Moselle, Meuse, Vistula, Elbe, Nemunas, Neva, Volga, while also establishing in streams, dam reservoirs, lakes, and artificial canals in 17 European countries. Two species have also successfully established in North America. The contribution of Ponto–Caspian gobies to local fish assemblages varies, but locally they are abundant or dominant components of fish assemblages in invaded ecosystems. We have considered their invasive distribution, range of occupied aquatic environments, abundance, and frequency of occurrence, and summarised their role and position in the trophic webs of invaded ecosystems. We focused on four goby species: western tubenose goby Proterorhinus semilunaris, bighead goby Ponticola kessleri, racer goby Babka gymnotrachelus and monkey goby Neogobius fluviatilis. Based on our own research and other published studies, we described the habitat preferences of these species and assessed their ecological impact on co-occurring species, both native and non-native, as predators, prey, competitors, and as hosts and vectors of parasites.
The round goby (Neogobius melanostomus) is an invasive species that has become one of the most abundant fish in the St. Lawrence River, Quebec, Canada over the past 15 yr. Since its introduction, the round goby has acquired a number of native parasites, yet little is known about the dynamics of parasite recruitment. To examine this question, young-of-the-year and juvenile round gobies were collected monthly from 2 localities in the river (Îles de la Paix, Île Dorval) from June through November 2012. At Îles de la Paix, round gobies (n = 180) were infected with 3 species of parasites, all larval stages (Diplostomum spp., Tylodelphys scheuringi, Neoechinorhynchus tenellus). Prevalence of the digenean Diplostomum spp. varied from 3.3 to 13.3%, and mean abundance from 0.03 to 0.53 from June through September, with a maximum in August. The digenean T. scheuringi was seen only in August, at a prevalence of 10.0% and a mean abundance of 0.53. The acanthocephalan N. tenellus was observed in June, August, and September, prevalence ranging from 3.3 to 10.0% and mean abundance from 0.03 to 0.27. Maximum infection for all 3 species occurred in August. All infected fish were ≥44 mm in total length (TL). Fish infected with more than 1 parasite species were >60 mm TL. No round goby (n = 178) was infected at Île Dorval. This study demonstrated that the invasive round goby starts to acquire parasite infections in the St. Lawrence River in the first year of life and may contribute to the transmission of some parasites within this ecosystem.
Ponto-Caspian gobies became highly abundant in many regions outside their native distribution range (e.g. Rhine River system). In the newly invaded habitats, the parasite communities of the invasive gobies are characterized by a lower species richness compared to their native range. However, acanthocephalans of the genus Pomphorhynchus are highly abundant, whereas in gobies they do not become mature and mostly remain encapsulated in the abdominal cavity as preadults. Thus, gobiids could either represent a dead-end host leading to a decline of the Pomphorhynchus sp. population (dilution effect) or act as a paratenic host that could increase the infection pressure to the original host community (spill back). To determine the importance of gobiids for one or the other process mentioned, we conducted two infection experiments using smaller and larger individuals of the definitive host chub (Squalius cephalus), which were infected with preadults of P. bosniacus collected from the abdominal cavity of Neogobius melanostomus.
The results showed that preadults obtained from gobiids can develop and mature in the definitive host with mean recovery rates of 17.9 % in smaller and 27.0 % in larger chubs. No infection was observed in 38.0 % and 20.0 % for smaller and larger chubs respectively. Our study clearly demonstrated that gobies serve as a paratenic host for acanthocephalans of genus Pomphorhynchus and thus spill back the infection into the local fish community. However, comparisons with previous experimental studies conducted with cystacanths from intermediate gammarid hosts showed that the preadults have significantly lower recovery rates than cystacanths.
Non-native species are known to escape their parasites following introduction into a new range, but they also often acquire local parasites as a function of time since establishment. We compared the parasite faunas of five non-native Ponto-Caspian gobies (Gobiidae) and local fish species (Perca fluviatilis, Gymnocephalus cernua, Gobio gobio) in three European river systems; the Rivers Rhine, Vistula and Morava, where Ponto-Caspian gobies were introduced 4-13 years prior to the study. Overall parasite species richness was considerably lower in non-native gobies compared to local fish species, and the same result was found at the component and infra-community levels. Both parasite abundance and diversity greatly varied among the regions, with the highest values found in the River Vistula (Wloclawski Reservoir), compared to a relatively impoverished parasite fauna in the River Morava (Danube basin). While only half of parasite species found in local hosts were acquired by non-native gobies, most of the parasites found in gobies were shared with local fish species related either phylogenetically (percids) or ecologically (benthic gudgeon), including the co-introduced monogenean Gyrodactylus proterorhini. As a result, similarity in parasite communities strongly reflected regional affiliation, while phylogenetic distances between fish host species did not play a significant role in parasite community composition. In accordance with other studies, all parasites acquired by gobies in their new range were generalists, all of them infecting fish at the larval/subadult stage, indicating the possible importance of gobies in the life cycle of euryxenous parasites. The absence of adult generalists, particularly ectoparasites with low host specificity, in non-native fish may reflect their generally low abundance in the environment, while an absence of adult endoparasitic generalists was probably related to other factors.
The western tubenose goby Proterorhinus semilunaris, an invasive Ponto-Caspian fish species, has established populations in a wide range of habitat types in the Dyje/Morava river basin (Danube basin; Czech Republic). In this study, we assessed tubenose goby tolerance to environmental variables potentially contributing to its spread and performance in new habitats. Of the seven aquatic habitats examined (lowland rivers, brooks, backwaters, oxbow lakes, borrow pits, reservoirs and carp aquaculture ponds), all except small brooks proved suitable for survival and reproduction, with habitat size the only limiting factor. Diet analysis indicated chironomid larvae as preferred prey, though tubenose gobies were able to switch to other food items under specific conditions (e.g. high macrozoobenthos density), suggesting feeding plasticity. Fish condition was positively correlated with individual diet range, but not with parasite burden. Eighteen metazoan parasite taxa were identified, greatly exceeding the known parasite fauna from the species’ native range. Parasite species richness decreased significantly with fish host dominance. Foraging plasticity, the ability to occupy different habitats and cope with parasitism observed in this study all may have important implications for tubenose goby dispersal success and invasiveness.
1. The survival of affiliate (dependent) species in a changing environment is determined by the interactions between the affiliate species and their available hosts. However, the patterns of spatial and temporal changes in host compatibility are often unknown despite host shifts having direct impact on the persistence of local populations. Bivalves of the order Unionida (freshwater mussels) are a functionally important but declining group of affiliate species, which are dependent on freshwater fish to host their parasitic larvae. The role of local adaptations and host fish resistance in shaping freshwater mussel host relationships remains poorly understood.
2. We used an invasive East Asian bivalve, Sinanodonta woodiana (Lea 1834), and its potential host fishes to study the mechanisms shaping fish-mussel coevolution using a combination of laboratory cross-exposure methods and field-collected data. We tested whether generalist host use of S. woodiana is pertinent to native host species, with special attention to bitterling fishes (Acheilognathinae) that are characterized by a mutual association with freshwater mussels. We also tested whether the pattern of the parasite-host association varies temporally (between areas of ancient and recent sympatry) and spatially (at a sub-basin level in its native range).
3. Results revealed the ability of S. woodiana to widely exploit non-bitterling host fishes at a global scale. In contrast, the ability of S. woodiana to exploit closely associated bitterling fishes was low in its native range (with ancient sympatry). In areas of recent sympatry (non-native S. woodiana range in Europe), S. woodiana glochidia were demonstrated to readily parasitize local, evolutionarily naive bitterling species at high density.
4. The results of a population-level experiment with three native populations of S. woodiana and rose bitterling, Rhodeus ocellatus, from various sub-basins of the River Yangtze confirmed that mussel populations vary in their compatibility with particular host populations. However, there was no evidence of population-specific adaptive coevolution.
5. This study provides the first evidence for a role of fish counter-adaptations against freshwater mussel glochidia, and documents the importance of population-level variation in shaping compatibility between glochidia and their host fishes. This outcome can inform predictions on the impact of biotic homogenization on endangered affiliate species in general and freshwater mussels in particular.
Inedit field report of three freshwater/ limnic mollusk forms (two bivalves & one gastropod) for the Ariranha River Basin in the Municipality of Arvoredo, Western region of Santa Catarina State/ SC (see pp. 40-41) ...............
New confirmed occurrence (field record) of the little invasive neartic freshwater pulmonate snail Lymnaea columella (Say, 1817) for the Canoas River Basin, in the Highlands malacological region of Santa Catarina State/ SC (see pp. 38-40) ..........
Round goby, Neogobius melanostomus (Pallas, 1814), an invasive Ponto-Caspian fish species, were registered in the upper Elbe for the first time in 2015, near the City of Ústí-nad-Labem (Czech Republic), apparently introduced by shipping. We sampled 53 individuals from this newly introduced population on May 18 (spring) and October 21 (autumn) 2016 in order to assess parasite load. Seven taxa were recorded, comprising two ciliates, one digenean (metacercariae), one acanthocephalan (cystacanth), two nematodes (larvae) and mollusc glochidia. No specific parasites were registered. Only the acanthocephalan Pomphorhynchus tereticollis was found in high numbers and occurred in both seasons, all other parasites occurring sporadically. Such a low parasite load is typical for Ponto-Caspian gobiids introduced far from their host range, and complies with the predictions of the ‘enemy release hypothesis’. All parasite species were probably acquired in the upper Elbe itself. According to the ‘parasite spillback’ concept, round goby could potentially play an important role in P. tereticollis distribution in the Elbe.
Direct and potentially damaging effects of invasive alien species can remain unnoticed or insufficiently quantified, resulting in a lack of stakeholder awareness. We report for the first time that parasitic larvae (glochidia) of the invasive freshwater mussel Sinanodonta (Anodonta) woodiana (Unionidae, Bivalvia) cause an unexpected reduction in the condition factor of parasitized native fish species. The reduction in the body mass and condition factor of experimentally infested European chub (Squalius cephalus) was associated with changes in several physiological parameters measured in host fish plasma. Ion concentrations (potassium, chloride) and enzymes activities (aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, alkaline phosphatase) were significantly affected; hence, the results reveal the complex effects of non-native glochidia on the homeostasis of the individually tested fish. Changes in host physiology and condition status were recorded also in environmentally relevant infestation intensities (mean of 3.02±0.51 glochidia gram-1). Despite intensive concern regarding the negative biodiversity and ecosystem impacts of the adult stage of S. woodiana among conservationists and natural resource managers, potential effects of its larval stage have been neglected until now. Because fish hosts are an obligatory part of the reproductive cycle of the mussel and the main vector for spreading, documentation of this direct and easily quantifiable impact on fish has great potential to influence the key community of stakeholders in fisheries and aquaculture sectors and to serve as a strong motivating factor for invasive species control. We argue for more careful consideration of potential multiple life-stage effects of S. woodiana and of other invasive alien species as well, as different life stages can have highly specific impacts and corresponding relevance for key stakeholder groups.
The Chinese sleeper (Perccottus glenii), an invasive Asian fish, was first registered in Germany in 2009 (westernmost extent of its invasive range). We sampled Chinese sleepers from two localities on the Bücherlgraben creek (a tributary of the River Naab) in south-eastern Germany in November 2015 and examined them for parasite infection. Twelve taxa were registered, including ciliates (unidentified Trichodina), a monogenean, three cestode species, two digenean taxa, two acanthocephalan species, two nematode species and one mollusc glochidia. Infracommunities consisted of 1–5 species, with 10% of fish uninfected. Three parasite species (Acanthocephalus anguillae, Gyrodactylus luciopercae and Pseudocapillaria tomentosa) were recorded on Chinese sleepers for the first time. The results highlight the important role of the Chinese sleeper as a second intermediate host in the life cycle of heron and grebe parasites. The Chinese sleeper parasite community displayed low homogeneity at both localities sampled, with allogenic parasites (metacercariae and mesocercoids) mostly shared. Differences between localities were mainly caused by autogenic parasites. No invasive parasites associated with the Chinese sleeper were observed in the study area, all parasites being representatives of European fauna. This supports the hypothesis of introduction via the aquarium trade or through transport with commercial fish.
The tubenose goby (Proterorhinus semilunaris) is one of a number of gobiid species currently extending their area of distribution over Europe. We studied inter-annual dynamics and habitat use of 0+ tubenose gobies in the very first years of expansion (1999-2004) in the connected rivers Dyje and Morava (Danube basin). Rapid downstream colonization in the River Dyje (peak in the second year followed by equilibrium) contrasted with slow upstream colonization in the River Morava. 0+ tubenose gobies preferred medium-sized stones (10-30 cm) and avoided fine substrates (silt, sand, gravel). Goby presence also increased in habitats with a larger amount of vegetation or ligneous structures, slower currents, and shallower depths; smallest individuals preferring more homogeneous areas with vegetation and without water currents.
Alien species (those carried outside their original ranges by human activities) have strongly affected the distribution and abundance of mollusks in many North American fresh waters. The best known of these aliens in North America is the zebra mussel (Dreissena polymorpha), which has nearly extirpated native unionid clams from infested lakes and rivers by fouling their shells and outcompeting them for food. Zebra mussels also have reduced populations of native sphaeriid clams, and both increased and reduced populations of snails. The effects of the other well-known alien bivalve in North America, Corbicula fluminea, are surprisingly poorly known. Corbicula probably caused some populations of native bivalves to decline, but other native populations seem to coexist with Corbicula. Several plausible mechanisms of interaction between Corbicula and the native biota have been proposed, but not demonstrated. Other aliens, including the recently arrived snail Potamopyrgus antipodarum, probably compete strongly with native freshwater mollusks under some circumstances. Several alien species, such as round goby and some sunfishes and crayfishes introduced outside their native ranges in North America, are effective predators on native mollusks and have strong effects on their distribution and abundance. Other aliens (particularly aquatic plants) affect mollusks by altering the food base or the physicochemical environment. Alien species can affect water quality, cycling of contaminants, and performance of biological indices of water quality. Because of ineffective control of aliens in North America, they may be an increasingly important factor in molluscan distribution as new species arrive from other continents and established species spread throughout the continent.
The European bitterling Rhodeus sericeus Pallas is a freshwater fish belonging to the Acheilognathinae, a subfamily that has an unusual spawning symbiosis with freshwater mussels. Female bitterling possess long ovipositors that they use to place their eggs onto the gills of a mussel through the mussels' exhalant siphon. Males fertilize the eggs by releasing sperm into the inhalant siphon of the mussel. The embryos develop inside the mussel for approximately a month, eventually leaving the mussel as actively swimming larvae. Because they use a discrete spawning site that can be readily manipulated they have recently been used in studies to understand oviposition choice with respect to mate and spawning site quality, host–parasite coevolution, alternative male mating tactics, and linking behavioural decisions with population dynamics. The current state of knowledge of bitterling reproductive ecology is reviewed and synthesized, and future directions for research on this species are proposed.
Five Gobiid fish species have recently increased their ranges along the Danube/Rhine
river corridor. Studies to date, however, have tended to be local, site specific and
reactive, examining just one or few species. As such, overall range has tended to be
assumed based on a summary of patchy, and sometimes contradictory, data. This study
provides an up-to-date literature review of first records of occurrence for all five
species along their expansion route. In addition, available shipping data are examined to
identify possible proximal causes of introduction. Three main discontinuous population
centres were identified; all at or near important container ports: Vienna, Duisburg and
Rotterdam. Shipping is confirmed as an important factor in the rapid national and
international expansion of Ponto-Caspian Gobiids, with downstream drift, rip-rap and heavy
boat traffic contributing to rapid spread on the Rhine. Geopolitical factors, however,
such as the fall of communism and the Balkan conflict, have been key in influencing where,
when, and by which route gobies first appear. Rapid expansion of Gobiids in the Rhine
raises the possibility of establishment throughout mainland Europe via
two new potential invasion corridors across Germany/Poland and France.
Freshwater mussel larval parasitism of fish is unique among bivalves. The relationship is primarily phoretic rather than nutritive; only the smallest glochidia and the haustorial larva grow substantially while on the host. Growth of the smallest larvae suggests a lower functional size limit of ~150 microns for the juvenile stage. Most Ambleminae, the most diverse North American clade, infect host gills by attracting feeding fish. Many species of Pleurobemini and some Lampsilini release conglutinates of eggs and larvae that resemble host food items. Many Lampsilini and a few Quadrulini use mantle modifications to attract host fish to the female. The mantle of some Quadrulini forms a posterior chamber that holds glochidia for immediate release in response to host fish. In many Lampsilini, mantle flap lures and a protrusible marsupium promote attack by the host fish and direct extraction of glochidia from the marsupium by the host. Host extraction of glochidia from the brooding female might have favored the evolution of long-term brooding in Lampsilini because glochidia need not be released by the female to encounter the host. A remarkable derivative of the host extraction strategy evolved in Epioblasma, which catch fish between the valves and release glochidia directly to the trapped host before releasing it. Host specificity is a critical feature of the evolutionary diversification and conservation biology of Unionoida. As temporary parasites, mussels must primarily evade the innate immune responses of the host, rather than the adaptive (acquired) responses. Evolution of host specificity is associated with selective encounter of host taxa, either because of host attraction strategies or because of dominance of particular host species in the habitat. The intricate relationships between mussels and fish are easily disrupted and, thus, contribute to the imperilment of many mussel species, yet they also fascinate us and compel conservation efforts.
We examined the distribution and abundance of glochidia of the freshwater mussel Anodonta kennerlyi Lea, 1860 on local fishes in three temperate rain forest lakes near Bamfield, on the west coast of Vancouver Island, British Columbia. Fishes involved in the life cycle of the mussel were the prickly sculpin (Cottus asper Richardson, 1836), threespine stickleback (Gasterosteus aculeatus L., 1758), Dolly Varden (Salvelinus malma (Walbaum, 1792)), and cutthroat trout (Oncorhynchus clarkii (Richardson, 1836)). For each lake, we assessed which fish was the most important for larval propagation and recruitment of the mussel by considering the fish's primary habitat, the percentage of fish in a sample with glochidia, and the abundance of glochidia on sampled fish. Also, an alternative method for quantifying the glochidia's "preference" for a host consisted of measuring the number of glochidia per unit area of fish body surface (larval density). We digitized the surface area of fins and head, i.e., the areas used by glochidia for settlement. Every fish species in each lake dispersed the glochidia. There was, however, a sharp gradient in the intensity of the fish–mussel linkage among fishes. Fishes that co-occurred most often with mussels, such as sculpins and sticklebacks, had the highest density of glochidia. Larval density on fishes also revealed the existence of between-lake differences in glochidia preference.
Invertebrate species represent more than 99% of animal diversity; however, they receive much less publicity and attract disproportionately minor research effort relative to vertebrates. Nonmarine mollusks (i.e., terrestrial and freshwater) are one of the most diverse and imperiled groups of animals, although not many people other than a few specialists who study the group seem to be aware of their plight. Nonmarine mollusks include a number of phylogenetically disparate lineages and species-rich assemblages that represent two molluscan classes, Bivalvia (clams and mussels) and Gastropoda (snails, slugs, and limpets). In this article we provide an overview of global nonmarine molluscan biodiversity and conservation status, including several case studies documenting the diversity and global decline of nonmarine mollusks. We conclude with a discussion of the roles that mollusks and malacologists should play in conservation, including research, conservation management strategies, and education and outreach.
a b s t r a c t. over the past 150 years, the waters of the Czech Republic were experimentally stocked or invaded by a total of 41 alien (non-native) fish species. The following species have become fully naturalized and produced self-sustained populations: Carassiusgibelio, Pseudorasboraparva, Ameiurus nebulosus and Gasterosteus aculeatus, which produced stable populations in several spatially limited localities. In some cases Oncorhynchus mykiss, Salvelinus fontinalis and Coregonus maraena will produce instable temporary populations based on released material obtained from fish farms and ponds. The occurrence of the remaining acclimatized alien species (Coregonuspeled,Ctenopharyngodonidella, Hypophthalmichthys molitrix, Aristichthys nobilis) in natural ecosystems and fishponds depends on stocking fish obtained from artificial spawning and cultures. The documented annual average production of alien species fit for human consumption amounts to around 2 000 tonnes, i.e. 8.2 % of the annual average production of marketable fish cultures in the Czech Republic. a significant negative impact of the introduced species on native ichthyofauna has been ascertained as regards its ecological, biological properties, biodiversity and health. Considered a typical invasive alien species,Carassiusgibelio heavily depressed the occurrence and numbers of indigenous Carassiuscarassiuspopulations and also contributed to the decreased numbers of Tincatinca,Leucaspiusdelineatus and other native cyprinid fish. P.parvaand A.nebulosus show a much weaker and limited impact. The introduction of C.idella was accompanied by the introduction of the tapeworm species, Bothriocephalusgowkongensis, which subsequently caused heavy losses in cultures of Cyprinuscarpio. In 2008, Neogobiusmelanostomus was recorded for the first time in this country at the confluence of the Morava and Dyje rivers.
Freshwater mussels (superfamily Unionoidea) are in serious global decline and in urgent need of protection and conservation. The declines have been attributed to a wide array of human activities resulting in pollution and water-quality degradation, and habitat destruction and alteration. Linkages among poor water quality, pollutant sources, and mussel decline in rivers and streams have been associated with results of laboratory-based tests of specific pollutants. However, uncertainties remain about the relationship of laboratory data to actual contaminant exposure routes for various mussel species, life stages, and in the habitats occupied during these exposures. We evaluated the pathways of exposure to environmental pollutants for all 4 life stages (free glochidia, encysted glochidia, juveniles, adults) of unionoidean mussels and found that each life stage has both common and unique characteristics that contribute to observed differences in exposure and sensitivity. Free glochidia typically are exposed only briefly (e.g., seconds to days) through surface water, whereas adults sustain exposure over years to decades through surface water, pore water, sediment, and diet. Juveniles live largely burrowed in the sediment for the first 0 to 4 y of life. Thus, sediment, pore water, and diet are the predominant exposure routes for this life stage, but surface water also might contribute to exposure during certain periods and environmental conditions. The obligate parasitic stage (encysted glochidia stage) on a host fish might be exposed from surface water while partially encysted or from toxicants in host-fish tissue while fully encysted. Laboratory methods for testing for acute and chronic exposures in water have advanced, and toxicant-specific information has increased in recent years. However, additional research is needed to understand interactions of life history, habitat, and long-term exposure to contaminants through water, pore water, sediment, and diet so that the risks of environmental exposures can be properly assessed and managed.
Unionid mussels are highly imperiled and the survival of their local populations is linked to the availability and dispersal
potential of their host fish. We examined the displacement distance of logperch (Percina caprodes), which are obligate host fish for endangered snuffbox mussels (Epioblasma triquetra), to determine the dispersal potential by fish. Logperch in the Sydenham River, Ontario, Canada, were electrofished and marked
with visible implant elastomer on five sampling dates during the gravid period of E. triquetra. The majority of all recaptures (82%) of P. caprodes occurred within 30m of their original capture location, with a mean displacement distance of 13±3m (mean±standard error,
n=28). These results were consistent with a review of movement studies of small benthic host fish (i.e., darters and sculpins),
which revealed average fish displacement distances of 37±19m (n=14 species; range: 4–275m). However, significantly greater movement distances were also found and the maximum displacement
distance increased significantly with the spatial extent of the study and with the duration of the study. These results indicate
that many P. caprodes remain in a small area, which could restrict the dispersal and (re)colonization potential of E. triquetra. Further studies are needed to determine the dispersal potential of mussels via host fish, which may be important for maintaining
the connectivity among unionid populations.
KeywordsFreshwater mussel–
Percina caprodes
–
Epioblasma triquetra
–Unionidae–Connectivity–Small benthic fish
The round goby (Neogobius melanostomus) first invaded North America in 1990 when it was discovered in the St. Clair River. Despite more than 15years of potential
invasion, many Great Lakes’ lotic systems remained uninvaded. Recently, we captured the round goby from several Great Lakes
tributaries known as species-at-risk hotspots. With a combination of field sampling of round gobies and literature review
of the impact of round gobies on native taxa, we assess the potential impacts of the secondary invasion to native species
using three mechanisms: competition; predation; and indirect impacts from the loss of obligate mussel hosts. We estimate that
89% (17/19) of benthic fishes and 17% (6/36) of mussels that occur in these systems are either known or suspected to be impacted
by the secondary invasion of round goby. In particular, we note that the distribution of potential impacts of round goby invasion
was largely associated with species with a conservation designation, including seven endangered species (1 fish, 6 mussels).
As these recent captures of round goby represent novel occurrences in high diversity watersheds, understanding the potential
impacts of secondary invasion to native biota is fundamental to prevent species declines and to allow early mitigation.
KeywordsEndangered species-
Neogobius melanostomus
-Round goby-Secondary invasion-Great Lakes-Ecological impact-Species at risk-Invasive species
The impact of multiple invading species can be magnified owing to mutual facilitation--termed 'invasional meltdown'--but invasive species can also be adversely affected by their interactions with other invaders. Using a unique reciprocal host-parasite relationship between a bitterling fish (Rhodeus amarus) and unionid mussels, we show that an invasive mussel reverses the roles in the relationship. Bitterling lay their eggs into mussel gills, and mussel larvae parasitize fish. Bitterling recently colonized Europe and parasitize all sympatric European mussels, but are unable to use a recently invasive mussel, Anodonta woodiana. The parasitic larvae of A. woodiana successfully develop on R. amarus, whereas larvae of European mussels are rejected by bitterling. This demonstrates that invading species may temporarily benefit from a coevolutionary lag by exploiting evolutionarily naive hosts, but the resulting relaxed selection may facilitate its exploitation by subsequent invading species, leading to unexpected consequences for established interspecific relationships.
The round goby Neogobius melanostomus is one of the most wide-ranging invasive fish on earth, with substantial introduced populations within the Laurentian Great Lakes watershed, the Baltic Sea and several major European rivers. Rapid expansion and deleterious ecosystem effects have motivated extensive research on this species; here this research is synthesized. Maps of the global distribution are provided and the invasion history of N. melanostomus, which spread more rapidly at first in North America, but has undergone substantial expansion over the past decade in the Baltic Sea, is summarized. Meta-analyses comparing their size at age, diet, competitors and predators in North American and European ecosystems are provided. Size at age is region specific, with saline habitats typically supporting larger and faster growing individuals than fresh water. Neogobius melanostomus prey differs substantially between regions, demonstrating a capacity to adapt to locally abundant food sources. Neogobius melanostomus comprise at least 50% of the diet of eight taxa in at least one site or life stage; in total, 16 predator taxa are documented from the Laurentian Great Lakes v. five from Eurasia. Invasive N. melanostomus are the only common forage fish to heavily exploit mussels in the Laurentian Great Lakes and the Baltic Sea, facilitating the transfer of energy from mussels to higher trophic levels in both systems. Neogobius melanostomus morphology, life history, reproduction, habitat preferences, environmental tolerances, parasites, environmental effects, sampling strategies and management are also discussed. Neogobius melanostomus inhabit a wide range of temperate freshwater and brackish-water ecosystems and will probably continue to spread via ballast water, accidental bait release and natural dispersal worldwide. Climate change will probably enhance N. melanostomus expansion by elevating water temperatures closer to its energetic optimum of 26° C. Future research needs are presented; most pressing are evaluating the economic effects of N. melanostomus invasion, determining long-term population level effects of egg predation on game-fish recruitment and comparing several variables (density, ecological effects morphology and life history) among invaded ecosystems. This review provides a central reference as researchers continue studying N. melanostomus, often as examples for advancing basic ecology and invasion biology.
Several freshwater mussel species represent some of the most problematic invasive species and have considerably altered ecosystems worldwide. Their invasion potential has been partially attributed to their free-living larvae, which have a high dispersal capability. We investigated the invasion potential of Anodonta (Sinanodonta) woodiana, a species of East Asian unionid mussel established worldwide despite having an obligatory parasitic stage (glochidium), which must encyst on host fish. The invasion success of A. woodiana has been attributed to the success of worldwide introductions of its sympatric fish hosts. We experimentally found, however, that A. woodiana is a broad host generalist, which can complete its development on all eight fish species tested, both coinvasive and native. Subsequently, we used a data on the occurrence and relative abundance of potential hosts in river habitats in the Czech Republic to project scenarios of the effect of host availability on A. woodiana invasion. We found th
Freshwater mussels are important constituents of freshwater ecosystems, yet much of their basic biology remains to be examined. The behavior of 3 species of unionid mussels (Unio tumidus, Unio pictorum, and Anodonta anatina) was examined in the lowland River Spree (Germany). Mussels were marked individually, and their positions on the sediment surface and depth below the sediment surface were recorded weekly between May and October 2004. The average rate of horizontal movement was 11 6 15 cm/wk (mean 6 1 SD). The direction of the movements seemed erratic; however, a significant net shoreward displacement of ;17 cm, possibly caused by rising water levels, was observed during the study. A surprisingly high percentage of the mussels (74 6 7%) was burrowed entirely in the sediment to depths as great as 20 cm during the summer. Smaller mussels and individuals not infested by the zebra mussel, Dreissena polymorpha, burrowed deeper in the sediments than larger or infested mussels. Burrowing reduced infestation densities in a laboratory experiment. Significantly more U. tumidus individuals were found on the sediment surface during the reproductive period in early summer than in late summer, suggesting that reproductive activity may influence burrowing. Burrowing was significantly related to current velocity (discharge), day length, and water temperature (multiple linear regression, R2¼ 0.74, p , 0.001), but current velocity appeared to be the dominant factor driving vertical movements (R2¼ 0.53, p , 0.01). We propose that movement behaviors are important adaptations of unionid mussel populations to the flow and food conditions in rivers. Movement behavior also may help unionids escape predators and control infestation by D. polymorpha.
1. Life histories of the highly diverse and endangered North American freshwater mussel fauna are poorly known. We investigated reproductive traits of eight riverine mussel species in Alabama and Mississippi, U.S.A.: Amblema plicata, Elliptio arca, Fusconaia cerina, Lampsilis ornata, Obliquaria reflexa, Pleurobema decisum, Quadrula asperata and Q. pustulosa, and compare our results with existing life history information for other species.
2. These eight species had reproductive traits characteristic of large, outcrossing populations: hermaphrodites were rare, we found no evidence of protandry, and sex ratios were even or slightly male-biased.
3. Age at sexual maturity varied among species, ranging from <1 to 2 years for L. ornata to 3–9 years for Q. asperata. In all species, most mature females participated in reproduction and fertilisation success was high.
5. Fecundity was related positively to both length and age, but length was the best predictor. In six species, fecundity increased exponentially with increasing size; in two species the rate of increase in fecundity declined in larger animals. In four species, fecundity declined in older animals. These latter results indicate weak reproductive senescence; however, in all species, older individuals continued to produce large numbers of offspring. Mean annual fecundity differed widely among species ranging from 9647 to 325 709. Within-species differences in fecundity were found among rivers and among populations within a river.
6. The wide variation in reproductive traits among species indicates the existence of widely divergent life history strategies in freshwater mussels.
The ecological role of parasites in the early life-history stages of coral reef fish is far from clear. Parasitism in larval, recently settled and juvenile stages of a coral reef fish damselfish (Pomacentridae) was therefore investigated by quantifying the ontogenetic change in parasite load and comparing the growth rates of parasitized juvenile fish to those of unparasitized ones. Parasite prevalence in two lunar pulses of Pomacentrus moluccensis was 4 and 0% for larval stage fish, 34 and 56% for recently settled fish and 42 and 49% for juveniles. A significant increase in parasite prevalence with age group was found; the most marked increase occurred immediately after larval fish had settled. Standard length did not model prevalence well; as length is a proxy for age, this indicates that the higher prevalence in recently settled and juvenile fish compared with larvae was not a simple result of parasites accumulating with age. In one of three cohorts, there was some evidence that parasitism affected the growth rate of juveniles, as measured by otolith width. The study suggests that settling on the reef exposes young fish to potentially harmful parasites. This supports the idea that the pelagic phase may have the effect of reducing the exposure of young fish to the debilitating effects of parasites.
1. Animal malformations engender wide public and scientific concern because of associated environmental health risks. This is highlighted by increased incidence of limb malformations in amphibians associated with trematode infections and disturbance. Malformations may signal new emerging disease threats, but whether the phenomenon is broadly applicable across taxa, or has population-scale impacts, is unknown.
2. Malformations are widely reported in fish and, until now, have been attributed mainly to contaminants. We tested whether the trematode Telogaster opisthorchis caused severe malformations, leading to population effects, in Galaxias anomalus, a threatened New Zealand freshwater fish.
3. Experimental infection of larval fish caused increasing spinal malformation and mortality with infection intensity that closely matched field patterns. Field malformation frequency peaked in January (65%), before declining sharply in February (25%) and remaining low thereafter.
4. The peak occurred during a ‘critical window’ of larval development, with the decline coincident with a population crash, indicating that malformation was causing mortality in the field.
5. The occurrence of such critical developmental windows may explain why this mechanism of population impact has been overlooked. With global environmental stressors predicted to enhance trematode infections, our results show that parasite-induced malformation, and its population-scale impacts, could be more widespread than previously considered.
Glochidia from gravid females of Villosa iris (Lea, 1829) and Actinonalas pectorosa (Conrad, 1834) were extracted from marsupia and tested for viability over several days. Glochidia that were flushed from the gill and those retained in the excised gill marsupium were tested at three holding temperatures: 0°, 10°, and 25°C. Viability was tested by exposing glochidia to a sodium chloride solution, and then confirmed by infesting known host fish with glochidia at 1 week and 2 weeks post-extraction from the female mussel. Results indicate that extracted glochidia remained viable for significantly longer than excised intra-marsupial glochidia. There was no significant difference in viability of glochidia between 0° and 10°C in extracted treatments (p > 0.05). Extracted glochidia of V. iris maintained >75% viability for 180, 192, and 46 hr at 0°, 10°, and 25°C, respectively. Similarly, glochidia extracted from A. pectorosa maintained >75% viability for 345, 310, and 108 hr at 0°, 10°, and 25°C, respectively. Long-term viability of glochidia would promote downstream dispersal and has practical applications in captive propagation.
Early developmental stages and ecotone utilisation of the non-indigenous Round Goby, Neogobius melanostomus (Pallas, 1811), are described and illustrated. Fish (5-40 mm) were collected in coarse gravel, rocks and debris in the St. Clair River/Lake system, Ontario, in 1994-2000. The Round Goby hatches at about 5 mm with black eyes, flexed urostyle, and developed fins and digestive system. Distinguishing characters include large head, dorsolateral eyes, large fan-shaped pectoral fins, two dorsal fins, fused thoracic pelvic fins and a distinct black spot on the posterior of the spinous dorsal fin. Modal counts for preanal, postanal, and total myomeres were 12, 19, and 31, respectively.
Two unionid clams, Anodonta grandis and A. imbecilis, and their potential fish hosts were collected from two sites in Michigan. Fish were checked for natural infections with the glochidia of these clams. Experimental laboratory infections were carried out to confirm natural infection data as well as to discover other potential hosts. Based on these experiments, 14 new hosts for A. grandis are reported. Artificial infections with A. imbecilis demonstrated successful metamorphosis on five unreported host fish species. The availability of a large variety of potential host fish, coupled with a broad ecological tolerance, helps to explain the persistence and widespread distribution of A. grandis and A. imbecilis in North America.
Human activity has caused a wide range of impacts upon river ecosystems with, perhaps, the most far reaching being the modification of river channel form and discharge, resulting in the loss of lateral diversity and channel -riparian zone connectivity (Boon 1992; Swales 1994; Zalewski et al. 1994). The rivers of the European continent represent the most regulated rivers in the world (Swales 1994). Hence, it is not surprising that many studies have reported a decline in both the quantity (biomass) and quality (diversity) of the ichthyofauna of these rivers. For example, in the River Danube, out of 52 long-established species, 30 are considered to be endangered or vulnerable, primarily as a result of the loss of specialised biotopes (Schiemer et al. 1991; Schiemer & Waidbacher 1992). Similarly, the fish fauna of the River Morava (Czech Republic) has undergone considerable changes in the relative importance of different species with, currently, an ichthyofauna dominated by a small number of generalist species (Jurajda & Penaz 1994). This appears to be a common result of river regulation and has been reported in the River Rhone (Copp 1992a), the River Great Ouse (Copp 1990a, 1992b) and in the Rivers Elbe and Rhine (Lelek 1976). In North America, habitat degradation has been linked to ca. 70% of all extinctions of freshwater fish species (Miller et al. 1989). Surprisingly, no species of riverine fishes have become extinct in Europe, unlike the North American continent, yet localised extinctions are common (Miller et al. 1989; Maitland & Campbell 1992).
Several Ponto-Caspian gobiid species have recently expanded their ranges in Europe and North America. This is the first study to demonstrate passive downstream dispersal (drift) of the round goby (Neogobius melanostomus) and tubenose goby (Proterorhinus semilunaris) in newly colonised areas (River Dyje, Danube basin), a factor that could play an important role in their dispersal. Drift duration (i.e. number of dates on which the species was caught) in round goby was longer than that of both native species and tubenose goby, providing a possible advantage. Size of drifting fish was restricted to a narrow range of 6–8 mm and 5–8 mm for round and tubenose goby, respectively. Drift in both species occurred almost completely during hours of darkness (
1. Biotic resistance is the ability of communities to inhibit the establishment, spread or impact of novel species. However, the interactions that underlie biotic resistance depend heavily on the contexts in which species interact. Consequently, studies of biotic resistance that consider single processes, patches, species or life-history stages may provide an incomplete picture of the capacity for communities to resist invasion.
2. Many organisms have multiphasic life cycles, where individuals can occupy distinct niches at different stages of the life history. Generally, studies of biotic resistance focus on interactions within a single life-history stage, and interactions at other life-history stages are overlooked. Here, we demonstrate that different mechanisms of biotic resistance occur across the life history and together limit the invasion success of an introduced marine invertebrate (Ciona intestinalis) in Northern California.
3. We tested the role of interactions (competition and predation) with the resident community in limiting the abundance of Ciona through experiments conducted on fertilization, larval survival, settlement, early postsettlement survival, and the survival of juveniles and adults.
4. Under some circumstances, Ciona became abundant in mid-successional stages and showed more rapid growth rates than a morphologically similar native species, Ascidia ceratodes. However, predators reduced Ciona abundance much more than that of Ascidia at several life stages. Furthermore, Ciona appeared to be a weaker competitor at the adult stage. Early life-history interactions with other sessile species at the fertilization, larval and recruit stages had modest to no effects on Ciona abundance.
5. The presence of biotic resistance mechanisms acting at multiple life stages, and potentially under different conditions, suggests that different components of biotic resistance interact to enhance the resident community's resistance to invasion.
Freshwater mussels have decreased dramatically in Iberia over the last decades. These animals are responsible for important ecosystem services such as recycling nutrients and improving water clarity. Under this view a better knowledge on the biological features of these animals is extremely important for future conservation and management actions. In this study the reproductive and gametogenic cycle of Anodonta anatina were studied during 2 years in one population as well as the sex ratio and hermaphroditism in six distinct populations, using standard histology. Gametogenesis was continuous in both sexes and germinal epithelium in early stages of development. Gametes were present throughout the reproductive cycle. Oogenesis and spermatogenesis occurred mainly between January and May. Larvae brooding occurred between September and March and main glochidia discharge occurred over a short period (2-3 weeks) in March. For the sex-ratio and hermaphroditism assessments a variable number of individuals were collected from several populations from lakes and rivers. Previous studies described A. anatina as mainly dioecious with only a few populations presenting occasional hermaphroditism. However, the present study indicates that A. anatina sexual behavior is influenced by environmental conditions, being mainly dioecious in rivers with increased hermaphroditism in standing waters. Although self-fertilization was not confirmed, additional studies with molecular characterization of larvae using fast evolving markers should be used in future studies to enlighten this process. Overall, this study indicates that for more efficient conservation actions and management plans, freshwater mussel reproductive biology should be studied at the population level mainly in the subfamily Anodontinae. J. Exp. Zool. 9999A: XX-XX, 2013. © 2013 Wiley Periodicals, Inc.
Collections of stream drift and fishes were made weekly from May to November 1979 and twice monthly from December 1979 to June 1980 to define the periods when glochidia of four mussel species (subfamily Lampsilinae) were in the drift or attached to host fishes. Representatives of all families and most genera of fishes in the stream, including all naturally infected species, were artificially exposed in the laboratory to glochidia of the four species to enable positive identification of host species. The lampsiline mussels displayed a high degree of host specificity. The host fishes were as follows: Villosa nebulosa, smallmouth bass (Micropterus dolomieui), and rock bass (Ambloplites rupestris); Villosa vanuxemi, banded sculpin (Cottus carolinae); Medionidus conradicus, redline darter (Etheostoma rufilineatum), and fantail darter (E. flabellare); and Lampsilis fasciola, smallmouth bass. Periods of natural infestation on fishes corresponded with the occurrence of glochidia in the drift and were different fo...
Human-induced rapid environmental change (HIREC; e.g., climate change or exotic species) has caused global species declines. Although behavioral plasticity has buffered some species against HIREC, maladaptive behavioral scenarios called 'evolutionary traps' are increasingly common, threatening the persistence of affected species. Here, we review examples of evolutionary traps to identify their anthropogenic causes, behavioral mechanisms, and evolutionary bases, and to better forecast forms of HIREC liable to trigger traps. We summarize a conceptual framework for explaining the susceptibility of animals to traps that integrates the cost-benefit approach of standard behavioral ecology with an evolutionary approach (reaction norms) to understanding cue-response systems (signal detection). Finally, we suggest that a significant revision of conceptual thinking in wildlife conservation and management is needed to effectively eliminate and mitigate evolutionary traps.
The study of parasites and their hosts has typically focused on the physiological, morphological, and immunological adaptations to parasitism, adaptations which the parasite employs to survive and reproduce in the host and those used by the host in self-defense. This paper explores instead some of the behavioral aspects of the parasite-host relationship. The parasite can alter the behavior of the host in ways which will facilitate dispersal of parasite propagules to new hosts or increase the amount of energy available for the parasite's growth. The host in turn can employ behavioral defense mechanisms as well as the more familiar physio- logical and immunological defense mechanisms. In one of the most interesting forms of behavioral defense, a host may use its own death to increase its inclusive fitness. Since some types of parasitic infections cause death or sterility of the host they also result in the host's genetic death. Although the host may be unable to affect its individual reproductive fitness it can affect its inclusive fitness. The host can change the time and nature of its death; it can "commit suicide," or behave aberrantly and increase the probability of death by predation, thus preventing the maturation of its parasite and lowering the risk of parasitic infection for other members of the host species. If the mature parasite would have been more likely to infect the host's kin than nonkin, the host's suicidal behavior will increase its inclusive fitness and thus have a positive selective value. I will first discuss four types of parasitic life cycles and behavioral interactions between these parasites and their hosts. The phenomenon of host suicide and situations where this phenomenon might be expected to occur will be discussed in detail. Finally, I will outline the role that host suicide may have played in the evolution of complex life cycles.
This study demonstrates passage of age-0+ year individuals of pikeperch Sander lucioperca, common bream Abramis brama and non-native tubenose goby Proterorhinus semilunaris from the Nové Mlýny Reservoir into the River Dyje (Danube River basin, Czech Republic) through the turbine of a hydropower facility. Most fishes had standard length (L ) in the range 12-33 mm. Seasonal patterns corresponded with spawning activity, i.e. an early single spawning event for S. lucioperca, multiple spawning events for A. brama and continuous spawning with a later start and prolonged duration for P. semilunaris. Sander lucioperca, P. semilunaris and larger A. brama (>22 mm) drifted almost exclusively during the dark; smaller A. brama displayed no preference for light or dark. Proterorhinus semilunaris displayed significantly lower mortality than other species when passing through the turbine (3% compared to 18%). The passage of high numbers of P. semilunaris from the reservoir (estimated at 473 000 individuals per year), and their subsequent mass downstream drift, may have contributed to rapid population establishment along the River Dyje and the quick downstream expansion.
A tubenose goby Proterorhinus marmoratus, a European endangered species native to the Black and Caspian seas, was recovered on 11 April 1990 from the travelling screens of the Belle River Power Plant located on the St Clair River, Michigan. Subsequently, anglers caught three round gobies Neogobius melanostomus in the St Clair River near Sarnia, Ontario. Thirty-one tubenose gobies and 11 round gobies were impinged or trawled at or near the Power Plant in the fall and winter of 1990-91. Nine round gobies (29-61 mm total length) are believed to be young-of-the-year. These species were probably transported to the Great Lakes in ballast water, may have successfully colonized the St Clair River, and will probably spread throughout the Great Lakes. They are expected to impact directly other benthic fishes. -from Authors
Parasite fauna of round goby Neogobius melanostomus (Pallas, 1814) in the Danube River was investigated in both its native range (two sites in the Bulgarian stretch of the Danube) and non-native range of distribution (Croatian, Slovak and Austrian stretches) during 2005 and 2006. The aim was to identify possible changes in parasite communities associated with the introduction of a host into the new environment. A total of 29 metazoan parasite species were found to parasitize round goby in the Danube River; twelve of these parasite species were found in both the native and non-native range of distribution. Introduction of a novel parasite species to the non-native range via the round goby was not found. Eight parasite species occurred only in the native range and nine species only in the non-native range of the round goby distribution. Losses of native parasite species in non-native round goby populations and/or acquiring of novel parasite species in a new environment were not significant. Thirteen parasite taxa were recorded for the first time in round gobies. Three parasite taxa (Diplostomum spp., Pomphorhynchus laevis and Raphidascaris acus) were found in high prevalence and abundance at each sampling site in both the native and non-native range. Parasite species diversity was assessed for each sampling site and season using three diversity indices (the Shannon, Simpson and Equitability indices), with the highest same-season values found in a non-native site in Slovakia (1.38, 0.69 and 0.60, respectively) and the lowest in a native site in Bulgaria (0.28, 0.12 and 0.14, respectively). Species diversity was higher in both non-native round goby populations (Slovak and Austrian) compared to native Bulgarian populations. However, diversity indices values varied among almost all sampling sites.
This study considers the effects of sample size on estimates of three parasitological indices (prevalence, mean abundance and mean intensity) in four different host–parasite systems, each showing a different pattern of infection. Monte Carlo simulation procedures were used in order to obtain an estimation of the parasitological indices, as well as their variance and bias, based on samples of different size. Although results showed that mean values of all indices were similar irrespective of sample size, estimates of prevalence were not significantly affected by sample size whereas mean abundance and mean intensity were affected in at least one sample. Underestimation of values was more perceptible in small (<40) sample sizes. Distribution of the estimated values revealed a different arrangement according to the host–parasite system and to the parasitological parameter. Monte Carlo simulation procedures are, therefore, suggested to be included in studies concerning estimation of parasitological parameters.
In the River Great Ouse, 0+ roach, bream, chub, bleak and gudgeon were each divided into three‘ ecospecies’ on the basis of their morphology: young larvae, old larvae and juveniles. Ecologically similar species were positively associated and dissimilar species were negatively associated. All ecospecies, except juvenile bleak preferred water < 1 m deep, within 6 m of the bank with some plant cover. Habitat use was similar for all species. It is suggested that this habitat offers increased growth rate, reduced predation risk and increased food abundance to all species, and that species overlap is due to complementary habitat use rather than aggregation. During the early larval period all species fed predominantly upon rotifers and diatoms. During the late larval period there was a switch to Cladocera, primarily Chydoridae and Ceriodaphnia sp., and chironomid larvae. Species-specific dietary selection was evident during the juvenile period, with roach feeding primarily upon aufwuchs, bream upon Cladocera, chub upon Diptera, and gudgeon upon Copepoda.
1. Anthropogenic pollution and disease can cause both lethal and sub-lethal effects in aquatic species but our understanding of how these stressors interact is often not known. Contaminants can reduce host resistance to disease, but whether hosts are impacted at environmentally relevant concentrations is poorly understood.
2. We investigated the independent and combined effects of exposure to the common herbicide glyphosate and the trematode parasite Telogaster opisthorchis on survival and the development of spinal malformations in juvenile Galaxias anomalus, a New Zealand freshwater fish. We then investigated how exposure to a glyphosate concentration gradient (0·36, 3·6, 36 mg active ingredient (a.i.) L−1) affected the production and release of the infective cercarial stage of the parasite by its snail intermediate host Potamopyrgus antipodarum.
3. Survival of juvenile fish was unaffected by exposure to glyphosate alone (at an environmentally relevant concentration; 0·36 mg a.i. L−1) or by T. opisthorchis infection alone. However, simultaneous exposure to infection and glyphosate significantly reduced fish survival.
4. Juvenile fish developed spinal malformations when exposed either to infections alone or to infections and glyphosate, with a trend towards greater severity of spinal malformation after exposure to both stressors.
5. All snails exposed to the highest glyphosate concentration (36 mg a.i. L−1) died within 24 h. Snails exposed to a moderate concentration (3·6 mg a.i. L−1) produced significantly more T. opisthorchis cercariae than snails in the control group or the low concentration group (0·36 mg a.i. L−1; the same concentration as in the fish experiment).
6. Synthesis and applications. This is the first study to show that parasites and glyphosate can act synergistically on aquatic vertebrates at environmentally relevant concentrations, and that glyphosate might increase the risk of disease in fish. Our results have important implications when identifying risks to aquatic communities and suggest that threshold levels of glyphosate currently set by regulatory authorities do not adequately protect freshwater systems.
Metazoan parasites were investigated in three non-native fishes (monkey goby Neogobius fluviatilis, bighead goby Neogobius kessleri and round goby Neogobius melanostomus) collected from the former and current main channel of the River Danube and from the River Hron, Slovakia, in November 2003. Thirteen parasite species were identified: Triaenophorus crassus, Diplostomum sp., Tylodelphys clavata, Metorchis xanthosomus, Nicolla skrjabini, Gyrodactylus proterorhini, Pomphorhynchus laevis, Contracoecum sp., Raphidascaris acus, Anguillicola crassus, Unio tumidus, Anodonta anatina and Pseudoanodonta complanata. The maximum parasite diversity was found in N. fluviatilis. Total parasite abundance was significantly higher in N. kessleri, but no significant differences among sampling sites were observed. Pomphorhynchus laevis and glochidia of Anodonta anatina reached 100% prevalence in N. kessleri in the new channel of the Danube and, in general, these species were also the most prevalent parasites in all three goby species. For endoparasites, gobies served mostly as intermediate (digenean, cestodes and nematodes) or paratenic (acantocephalan and nematodes) hosts. All parasite species found are common parasites in the Middle Danube basin. No parasites specific to Neogobius, known from their native populations, were observed.
Aim Geographical variation in parasite diversity is examined among populations of fish in their original heartland and in areas where they have been introduced. The diversity in heartland and introduced populations is contrasted, and also compared with the expectations of a null model.
Location Data on the parasite communities of two salmonid fish species were obtained: the rainbow trout Oncorhynchus mykiss in its British Columbia heartland and in introduced populations in North America, Great Britain, South America and New Zealand; and the brown trout Salmo trutta in heartland populations from Great Britain, and in introduced populations in North America, South America and New Zealand.
Methods The average taxonomic distinctness and its variance were computed for each parasite community, and used as measures of the taxonomic diversity of parasite species in each fish population. Observed values of taxonomic distinctness were also compared with those expected if each community was a random selection from the world list of parasite species known for each of the two host species.
Results Few parasite communities departed from the expectations of the null model, i.e. few had a taxonomic diversity of parasites greater or lower than that expected from a random selection of parasite species. However, these departures were not more or less likely among heartland fish populations than among introduced ones. In both fish species, parasite communities in introduced populations tended to be a little more taxonomically diverse than in the heartland populations.
Main conclusions Overall, the results suggest that the accumulation of parasite species in introduced hosts over short (ecological) periods of time can result in parasite assemblages that are just as, or even more, taxonomically diverse than those developed over much longer (evolutionary) time frames in the host species geographical heartland. This finding highlights the importance of ecological factors in parasite biodiversity in addition to coevolutionary processes.
1. It is well recognised that non-indigenous species (NIS) can affect native communities via the ‘spillover’ of introduced parasites. However, two other potentially important processes, the ‘spillback’ of native parasites from a competent NIS host, where the latter acts as a reservoir leading to amplified infection in native hosts, and the ‘dilution’ of parasitism by a NIS host acting as a sink for native parasites, have either not been tested or largely overlooked.
2. We surveyed the helminth parasite fauna of native New Zealand fish in Otago streams that varied in the abundance of introduced brown trout Salmo trutta, to look for evidence of spillback and/or dilution. Spillover is not an issue in this system, with trout introduced as parasite-free eggs.
3. Seven native parasite species were present across 12 sites; significant inverse relationships with an index of trout abundance (i.e. dilution) were documented for three species infecting the native upland bully Gobiomorphus breviceps, and one species infecting the native roundhead galaxias Galaxias anomalus.
4. An inverse relationship between bully energy status and infection intensity of one parasite species suggests that parasite dilution could have positive effects on bully populations. Our failure to detect similar relationships for the other parasites does not preclude the possibility that dilution is beneficial to native fish, since parasites may have subtle or unmeasured impacts.
5. The parasite dilution patterns reported are compelling in that they occurred across several native host and parasite species; as such they have important implications for invasion ecology, providing an interesting contrast to the largely negative impacts reported for NIS. Mechanisms potentially responsible for the patterns observed are discussed.
Study of interactions between pairs or larger groups of nonindigenous species has been subordinated in the literature to study of interactions between nonindigenous and native species. To the extent that interactions among introduced species are depicted at all, the emphasis has been on negative interactions, primarily resource competition and interference. However, a literature search reveals that introduced species frequently interact with one another and that facilitative interactions are at least as common as detrimental ones. The population significance of these interactions has rarely been determined, but a great variety of types of direct and indirect interactions among individuals of different nonindigenous species is observed, and many are plausibly believed to have consequences at the population level. In particular, mutualisms between plants and the animals that disperse and/or pollinate them and modification of habitat by both animals and plants seem common and often important in facilitating invasions. There is little evidence that interference among introduced species at levels currently observed significantly impedes further invasions, and synergistic interactions among invaders may well lead to accelerated impacts on native ecosystems – an invasional meltdown process.
The round goby, Apollonia melanostoma, a molluscivore specialist, was introduced to the Great Lakes in the early 1990s and rapidly expanded its distribution, especially
in Lake Erie. Adult round goby morphology suggests low dispersal and migration potential due to the lack of a swim bladder
and benthic life style. Given that the larval stage occurs inside the benthic egg, and juveniles have adult morphologies,
it has been suspected that dispersal and invasion potential is low for early life stages also. However, we identified early
juvenile round gobies in the nocturnal pelagic in Lake Erie and thus we conducted a sampling study to determine the extent
to which this life stage uses the nocturnal pelagic. Replicate ichthyoplankton samples were collected at 3-h intervals (1900–0700h)
at three depths (2m, 5m, 8m) in western Lake Erie (water depth=10m) in July and August 2002 and June 2006. Early juvenile
round gobies (6–23mm TL) were present almost exclusively in the nocturnal samples (2200h, 0100h, 0400h) with peak densities
approaching 60 individuals per 100m3 of water sampled. Nocturnal density was also significantly greater at 8-m depth versus 2-m and only the smallest fish (6–8mm
TL) migrated to the surface (2-m). Analyses of diet clearly demonstrated that these fish are foraging on plankton at night
and thus may not be light limited for foraging in ship ballast tanks. In ships that take on thousands of tonnes of water for
ballast, nocturnal ballasting could easily result in transport of thousands of young round gobies at a time. Additionally,
within-lake dispersal at this lifestage is likely common and may facilitate downstream passage across barriers designed to
limit range expansion.
Herbivore damage is generally detrimental to plant fitness, and the evolu- tionary response of plant populations to damage can involve either increased resistance or increased tolerance. While characters that contribute to resistance, such as secondary chem- icals and trichomes, are relatively well understood, characters that contribute to a plant's ability to tolerate damage have received much less attention. Using Helianthus annuus (wild sunflower) and simulated damage of Haplorhynchites aeneus (head-clipping weevil) as a model system, we examined morphological characters and developmental processes that contribute to compensatory ability. We performed a factorial experiment that included three levels of damage (none, the first two, or the first four inflorescences were clipped with scissors) and eight sires each mated to four dams. We found that plants compensated fully for simulated head-clipper damage and that there was no variation among plant families in compensatory ability: seed production and mean seed mass did not vary among treat- ments, and sire X treatment interactions were not significant. Plants used four mechanisms to compensate for damage: (1) Clipped plants produced significantly more inflorescences than unclipped plants. Plants produced these additional inflorescences on higher order branches at the end of the flowering season. (2) Clipped plants filled significantly more seeds in their remaining heads than did unclipped plants. (3) Clipped plants, because they effectively flowered later than unclipped plants, were less susceptible to damage by seed- feeding herbivores other than Haplorhynchites. (4) In later heads, seed size was greater on clipped plants, which allowed mean seed size to be maintained in clipped plants. Although there was genetic variation among the families used in this experiment for most of the characters associated with compensation for damage (seed number, mean seed size, mean flowering date, length of the flowering period, and branching morphology), in analyses of these characters, no sire X treatment interactions were significant indicating that all of the families relied on similar mechanisms to compensate for damage.
The round goby Neogobius melanostomus is a bottom-dwelling fish native for the Ponto-Caspian basin, which started to colonize the Baltic Sea since 1991. The parasites of this fish species in the southwestern Baltic region are studied for the first time. The round goby in the SW Baltic Sea was infected with 12 parasite species: 1 species of Microsporidia, 1 species of Monogenea, 1 of Cestoda, 3 species of Trematoda, 3 species of Nematoda, 2 of Acanthocephala, and 1 species of Bivalvia. Microsporidia genus species have the great tendency to join the infracommunity in all localities, except the Stettiner Haff, where this tendency have Diplostomum spathaceum met and Unio sp. glochidia. The round goby was colonized by seven new parasites species not found in this fish in the Baltic Sea earlier: Microsporidia gen. sp., Gyrodactylus rugiensis, Bucephalus polymorphus, Cosmocephalus obvelatus L3, Eustrongylides excisus L3, Paracuaria adunca L3, Unio sp. glochidia. Microsporidia gen. sp., G. rugiensis, and Unio sp. are new parasites for the round goby. In general, the processes of colonization have the same tendency as in the Gulf of Gdańsk.
Geographical distances between host populations are key determinants of how many parasite species they share. In principle, decay in similarity should also occur with increasing distance along any other dimension that characterizes some form of separation between communities. Here, we apply the biogeographical concept of distance decay in similarity to ontogenetic changes in the metazoan parasite communities of three species of marine fish from the Atlantic coast of South America. Using differences in body length between all possible pairs of size classes as measures of ontogenetic distances, we find that, using an index of similarity (Bray-Curtis) that takes into account the abundance of each parasite species, the similarity in parasite communities showed a very clear decay pattern; using an index (Jaccard) based on presence/absence of species only, we obtained slightly weaker but nevertheless similar patterns. As we predicted, the slope of the decay relationship was significantly steeper in the fish Cynoscion guatucupa, which goes through clear ontogenetic changes in diet and therefore in exposure to parasites, than in the other species, Engraulis anchoita and Micropogonias furnieri, which maintain a roughly similar diet throughout their lives. In addition, we found that for any given ontogenetic distance, i.e. for a given length difference between two size classes, the similarity in parasite communities was almost always higher if they were adult size classes, and almost always lower if they were juvenile size classes. This, combined with comparisons among individual fish within size classes, shows that parasite communities in juvenile fish are variable and subject to stochastic effects. We propose the distance decay approach as a rigorous and quantitative method to measure rates of community change as a function of host age, and for comparisons across host species to elucidate the role of host ecology in the development of parasite assemblages.