Gyrodactylus spp. diversity in native and introduced minnow (Phoxinus phoxinus) populations: no support for "the enemy release" hypothesis

Unclear host taxonomy hinders parasite studies: An up-to-date checklist of the protozoan and metazoan parasites of Phoxinus minnows (Teleostei: Leuciscidae)

Phoxinus minnows are small freshwater fish found throughout Eurasia. The taxonomy of this genus is still under investigation, and new species are regularly described. They are frequently introduced outside their native range due to their use as live bait for angling, and such fish introductions can have diverse impacts on the recipient areas. Before the rise in interest regarding the diversity of this genus in the past 15 years, studies carried out on their biology and ecology reported their findings for the Eurasian minnow Phoxinus phoxinus Linnaeus, 1758, which was then considered ubiquitous. A parasites checklist for Phoxinus minnows has yet to be published, and the recent progress on the taxonomy of this genus has enabled us to propose a reassignment of parasite records to their proper host. The most thoroughly studied potential species were the North European species Phoxinus sp. 7 sensu Palandačić et al. 2017, Phoxinus isetensis, and P. phoxinus. We were able to highlight a gap in knowledge for numerous species that have received little-to-no attention in terms of parasitology. Systematic molecular identification of Phoxinus minnows should be conducted when studying their parasites, as a reliable identification of the host is vital in parasitology research. Future research will certainly reveal a species-specific composition of the parasitofauna occurring in Phoxinus, especially among widespread parasites such as Gyrodactylus and Diplostomum. Such specificities could even become tools for assessing the introduction routes of Phoxinus species.

Are Rattus rattus fleas invasive? Evaluation of flea communities in invasive and native rodents in Chile

Co-invasion, characterized by the simultaneous introduction of hosts and parasites with the latter establishing themselves in native hosts, is a phenomenon of ecological concern. Rattus rattus, a notorious invasive species, has driven the extinction and displacement of numerous avian and mammalian species and serves as a key vector for diseases affecting both humans and wildlife. Among the parasites hosted by R. rattus are fleas, which exhibit obligate parasitic behaviour, a generalist nature and high prevalence, increasing the likelihood of flea invasion. Simultaneously, invasive species can serve as hosts for native parasites, leading to potential amplification or dilution of parasite populations in the environment. In Chile, R. rattus has been present since the 17th century because of the arrival of the Spanish colonizers through the ports and has spread throughout urban, rural and wild Chilean territories. This study aims to evaluate whether co-invasion of native fleas of invasive rats occurs on native rodents in Chile and to determine whether black rats have acquired flea native to Chile during their invasion. For this, we captured 1132 rodents from 26 localities (20° S-53° S). Rattus rattus was found coexisting with 11 native rodent species and two species of introduced rodents. Among the native rodents, Abrothrix olivacea and Oligoryzomys longicaudatus exhibited more extensive sympatry with R. rattus. We identified 14 flea species associated with R. rattus, of which only three were native to rats: Xenopsylla cheopis, Leptopsylla segnis and Nosopsyllus fasciatus. These three species presented a higher parasite load in black rats compared to native fleas. Leptopsylla segnis and N. fasciatus were also found associated with native rodent species that cohabit with R. rattus. The remaining species associated with R. rattus were fleas of native rodents, although they were less abundant compared to those associated with native rodents, except for Neotyphloceras pardinasi and Sphinctopsylla ares. Although there has been evidence of flea transmission from rats to native species, the prevalence and abundance were relatively low. Therefore, it cannot be definitively concluded that these fleas have established themselves in native rodent populations, and hence, they cannot be classified as invasive fleas. This study underscores R. rattus' adaptability to diverse environmental and geographical conditions in Chile, including its capacity to acquire fleas from native rodents. This aspect has critical implications for public health, potentially facilitating the spread of pathogens across various habitats where these rats are found.

Seasonal Effects on Health Status and Parasitological Traits of an Invasive Minnow in Iberian Waters

Biological invasions are of special conservation concern in the Iberian Peninsula and other regions with high levels of endemism. Environmental variability, such as the seasonal fluctuations of Mediterranean streams, is a key factor that affects the spread of aquatic species in novel habitats. Fish parasites have a great potential to reflect such changes in the habitat features of freshwater ecosystems. The aim of this study consisted of seasonally analysing the health status and parasitological traits of non-native fish in Iberian waters. In particular, a strongly invasive population of Languedoc minnow Phoxinus septimaniae (leuciscid species native to south-east France) was assessed in Tordera Stream (north-eastern Iberian Peninsula, Mediterranean conditions). Fish were sampled in April, July, and October 2023 by electrofishing. Health status (external/internal organs) was significantly better in autumn (HAI = 28.8) than spring (HAI = 35.6). Life-cycle complexity was higher in spring (LCI = 1.98), whereas parasite abundance and Shannon diversity were significantly lower in autumn (TA = 19.6 and H' = 2.15, respectively). In October (more 'benign' environmental conditions in Iberian streams), minnows could display elevated foraging activity, with fish increasing their health condition and level of parasite resistance/tolerance. Overall results showed a particular seasonal profile of health and parasite infra-communities that allow this minnow species to thrive under highly fluctuating habitat conditions. This information could help environmental managers to control non-native fish in Mediterranean streams.

Dactylogyrus spp. (Dactylogyridae, Monogenea) from tinfoil barb, Barbonymus schwanenfeldii imported into South Africa: morphometric and molecular characterisation

This study reports on three species of Dactylogyrus Diesing, 1850 (Dactylogyridae) collected from tinfoil barb, Barbonymus schwanenfeldii (Bleeker) which were imported into South Africa as ornamental fish from Sri Lanka and Thailand. Supplementary morphometric characterisation and molecular data (partial 18S and 28S rDNA, and ITS1 region sequences) are presented for Dactylogyrus lampam (Lim & Furtado, 1986), Dactylogyrus tapienensis Chinabut & Lim, 1993 and Dactylogyrus viticulus Chinabut & Lim, 1993. Prevalence of Dactylogyrus spp. infection was 87% and 80% for fish from Sri Lanka and Thailand, respectively. Composition of the parasites between the fish of each origin differed. All three species were found to infect fish from Thailand, but only D. lampam was present on the fish received from Sri Lanka. Phylogenetic analysis revealed the position of studied species, with D. lampam clustering within the lineages of varicorhini-type species, while D. tapienensis and D. viticulus form a sister lineage to Dactylogyrus spp. associated with Cyprinus carpio L. and Carassius spp., species parasitising central African large cyprinids (Labeo Cuvier), and species parasitising African and Middle Eastern Carasobarbus spp.

Alpine bullhead (Cottus poecilopus Heckel): a potential refuge for Gyrodactylus salaris Malmberg, 1957 (Monogenea)

The notifiable freshwater pathogen Gyrodactylus salaris Malmberg, 1957 tends to be a generalist in contrast to other monogeneans. Whilst it causes most damage to its primary host, the Atlantic salmon (Salmo salar Linnaeus), transport and reservoir hosts likely play a key role in maintaining the parasite in the environment. Here, we tested the ability of G. salaris (strain River Lierelva, southern Norway) to infect and reproduce on a population of wild caught alpine bullhead (Cottus poecilopus Heckel). Exposure of alpine bullhead yearlings (0+) to G. salaris for 24 h at low (6.5 °C) or high temperature (11.5 °C) resulted in the establishment of 1 to 104 parasites per fish. Eight to nine days post-infection at high temperature, the infection of G. salaris was eliminated, indicative of innate host immunity. In contrast, at low temperature G. salaris infections persisted for 47-48 days. The relative lengthy infection of alpine bullhead with G. salaris compared to other non-salmonids tested may be due to low temperature and high initial infection load in combination with an epibiont infection. The present results suggest that this non-salmonid may function as a temperature-dependent transport or reservoir host for G. salaris.

Contrasting morphology with molecular data: an approach to revision of species complexes based on the example of European Phoxinus (Cyprinidae)

BACKGROUND

Molecular taxonomy studies and barcoding projects can provide rapid means of detecting cryptic diversity. Nevertheless, the use of molecular data for species delimitation should be undertaken with caution. Especially the single-gene approaches are linked with certain pitfalls for taxonomical inference. In the present study, recent and historical species descriptions based upon morphology were used as primary species hypotheses, which were then evaluated with molecular data (including in type and historical museum material) to form secondary species hypotheses. As an example of cryptic diversity and taxonomic controversy, the European Phoxinus phoxinus species complex was used.

RESULTS

The results of the revision showed that of the fourteen primary species hypotheses, three were rejected, namely P. ketmaieri, P. likai, and P. apollonicus. For three species (P. strandjae, P. strymonicus, P. morella), further investigation with increased data sampling was suggested, while two primary hypotheses, P. bigerri and P. colchicus, were supported as secondary species hypotheses. Finally, six of the primary species hypotheses (P. phoxinus, P. lumaireul, P. karsticus, P. septimanae, P. marsilii and P. csikii) were well supported by mitochondrial but only limitedly corroborated by nuclear data analysis.

CONCLUSION

The approach has proven useful for revision of species complexes, and the study can serve as an overview of the Phoxinus genus in Europe, as well as a solid basis for further work.

Co-introduction of ancyrocephalid monogeneans on their invasive host, the largemouth bass, Micropterus salmoides (Lacepéde, 1802) in South Africa

Largemouth bass, Micropterus salmoides (Lacepéde, 1802) were sampled from three provinces (Eastern Cape EC, North West NWP and KwaZulu-Natal KZN) in South Africa to assess for parasite diversity and community composition. Morphological evaluation of the sampled parasite specimens provided evidence for the first record of five monogeneans from the family Ancyrocephalidae: Clavunculus bursatus (Mueller, 1963), Onchocleidus dispar (Mueller, 1936), Onchocleidus furcatus (Mueller, 1937), Onchocleidus principalis (Mizelle, 1936) and Syncleithrium fusiformis (Mueller, 1934) from the African continent. Community composition differed between localities. Clavunculus bursatus were only sampled from the EC and KZN, O. dispar and O. principalis were only sampled from the EC, O. furcatus was only sampled from the NWP and KZN localities and S. fusiformis only from KZN. Prevalence was 100% at all localities. Data from this study support the enemy release hypothesis as many of the parasites reported from the native range of M. salmoides were not collected.

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Report on the parasite diversity of invasive Micropterus salmoides in South Africa.

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First identification of co-introduced Ancyrocephalidae monogeneans into South Africa.

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Enemy release supported: lower parasite diversity in South African Micropterus salmoides.

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Potential for spillover to natives exists and needs to be investigated.

To each his own: no evidence of gyrodactylid parasite host switches from invasive poeciliid fishes to Goodea atripinnis Jordan (Cyprinodontiformes: Goodeidae), the most dominant endemic freshwater goodeid fish in the Mexican Highlands

Background

Goodeid topminnows are live-bearing fishes endemic to the Mexican Highlands (Mesa Central, MC). Unfortunately, in the MC, environmental degradation and introduced species have pushed several goodeid species to the brink of extinction. Invasive fishes can introduce exotic parasites, and the most abundant goodeid, blackfin goodea Goodea atripinnis Jordan, is parasitised by six exotic helminths. Poeciliids are widely dispersed invasive fishes, which exert negative ecological effects on goodeids. Poeciliids host several species of the monogenean genus Gyrodactylus von Nordmann, 1832, including pathogenic, invasive parasites. Here, we looked for evidence of Gyrodactylus species switching hosts from poeciliids to goodeids.

Methods

Fish were collected in rivers draining the MC into both sides of the continental divide. Hosts were screened for gyrodactylid parasites in localities where G. atripinnis and poeciliids occurred sympatrically. Gyrodactylus specimens were characterised morphologically (attachment apparatus) and molecularly (internal transcribed spacer region, ITS). A Bayesian phylogenetic tree using ITS sequences established relationships between gyrodactylids collected from goodeid fishes and those from parasites infecting poeciliids.

Results

Gyrodactylids were collected from G. atripinnis in six localities on both sides of the watershed where exotic poeciliids occurred sympatrically. Morphological and molecular analyses indicated the presence of four undescribed species of Gyrodactylus infecting this goodeid host. Gyrodactylus tomahuac n. sp., the most abundant and geographically widespread species, is described here. The other three Gyrodactylus spp. are not described, but their ITS sequences are used as molecular data presented here, are the only available for gyrodactylids infecting goodeid fishes. Morphological and molecular data suggest that two distinct groups of gyrodactylids infect goodeids, one of which shares a common ancestor with gyrodactylids parasitizing poeciliids.

Conclusions

No evidence was found of gyrodactylids switching hosts from invasive poeciliids to endemic goodeids, nor vice versa. Moreover, considering that G. atripinnis is known to host both Gyrodactylus lamothei Mendoza-Palmero, Sereno-Uribe & Salgado-Maldonado, 2009 and Gyrodactylus mexicanus Mendoza-Palmero, Sereno-Uribe & Salgado-Maldonado, 2009, with the addition of G. tomahuac n. sp. and the three undescribed Gyrodactylus spp. reported, at least six gyrodactylids may infect this host. This would make monogeneans the second most abundant parasite group infecting G. atripinnis, which to date is known to harbour 22 helminth species: nine digeneans, five nematodes, four cestodes, three monogeneans and one acanthocephalan.