Trematode prevalence-occupancy relationships on regional and continental spatial scales in marine gastropod hosts

The positive inter-specific relationship between local abundance and large-scale spatial occupancy is one of the most universal patterns in the distribution of species. However, evidence for the validity of this relationship in the marine realm is still scarce, especially for parasites. Using data from published studies, we investigated this relationship in trematode parasites infecting several marine gastropod species. On a regional spatial scale (<100 km between any pair of sites), we found a positive relationship between mean local prevalence (percentage of infected individuals in a population) and large-scale site occupancy among trematode species in all 4 gastropod host species investigated (Littorina obtusata, L. saxatilis, Hydrobia ventrosa, Ilyanassa obsoleta), although this was not significant in the case of L. saxatilis. Similar positive relationships were observed on a continental scale (> 1000 km between the most distant sites) in 2 host species (L. littorea, H. ulvae). Further analyses pointed to the role of dispersal by the definitive hosts in shaping these prevalence-occupancy relationships as we found a significant interaction between definitive host type and mean local prevalence affecting the spatial occupancy of the trematodes infecting H. ulvae. While trematode species that use highly dispersive birds as definitive hosts exhibited a significant positive relationship, the ones that use less dispersive fish did not. Our results indicate that a positive relationship between local abundance and large-scale distribution also holds true for marine parasites, and they suggest a strong role of definitive host dispersal in linking local epidemiological infection patterns of parasites with their large-scale biogeographic distributions

Impacts of agriculture on the parasite communities of northern leopard frogs (Rana pipiens) in southern Quebec, Canada

Given that numerous amphibians are suffering population declines, it is becoming increasingly important to examine the relationship between disease and environmental disturbance. Indeed, while many studies relate anthropogenic activity to changes in the parasitism of snails and fishes, little is known of the impact on the parasites of amphibians, particularly from agriculture. For 2 years, the parasite communities of metamorphic northern leopard frogs from 7 agricultural wetlands were compared with those from 2 reference wetlands to study differences in parasite community diversity and abundance of various species under pristine conditions and 3 categories of disturbance: only agricultural landscape, only pesticides, and agricultural landscape with pesticides. Agricultural (and urban) area was negatively related to species richness, and associated with the near absence of adult parasites and species that infect birds or mammals. We suggest that agriculture and urbanization may hinder parasite transmission to frogs by limiting access of other vertebrate hosts of their parasites to wetlands. The only parasite found at all localities was an unidentified echinostome infecting the kidneys. This parasite dominated communities in localities surrounded by the most agricultural land, suggesting generalist parasites may persist in disrupted habitats. Community composition was associated with dissolved organic carbon and conductivity, but few links were found with pesticides. Pollution effects may be masked by a strong impact of land use on parasite transmission

A large-scale molecular survey of Clinostomum (Digenea, Clinostomidae)

Members of the genus Clinostomum Leidy, 1856 are parasites that mature in birds, with occasional reports in humans. Because morphological characters for reliable discrimination of species are lacking, the number of species considered valid has varied by an order of magnitude. In this study, sequences from the DNA barcode region of cytochrome c oxidase I (CO1) and/or internal transcribed spacer (ITS) from specimens from Mexico, Bolivia, Peru, Brazil, Kenya, China and Thailand were analysed together with published sequences from Europe, Africa, Indonesia and North America. Although ITS and CO1 distances among specimens were strongly correlated, distance-based analysis of each marker yielded different groups. Putative species indicated by CO1 distances were consistent with available morphological identifications, while those indicated by ITS conflicted with morphological identifications in three cases. There was little overlap in sequence variation within and between species, particularly for CO1. Although ITS and CO1 distances tended to increase in specimens that were further apart geographically, this did not impair distance-based species delineation. Phylogenetic analysis suggests a deep division between clades of Clinostomum inhabiting the New World and Old World, which parallels the distribution of their principal definitive hosts, the Ardeidae

Population biology of eyeflukes in fish from a large fluvial ecosystem: the importance of gulls and habitat characteristics

Spottail shiners (Notropis hudsonius) were monitored for eyeflukes monthly at four sites in the St. Lawrence River, Quebec, from spring through autumn in 1997 and 1998. In general, mean abundance of Diplostomum spp. in the lens of spottail shiners was highest at sites near large ring-billed gull (Larus delawarensis) colonies and was higher in 1998 than in 1997. Population studies demonstrated a major period of recruitment in the late summer – early autumn. Mean abundance increased between November and May, when sampling was logistically not possible, reflecting late-fall or early-spring recruitment. Golden shiners (Notemigonus crysoleucas) and small yellow perch (Perca flavescens) were monitored at a single site (Île aux Ours) in 1997 and 1998. Mean abundance of Diplostomum spp. in the lens of golden shiners at Île aux Ours was higher in 1998 than in 1997. Recruitment occurred in the early summer and between November and May, suggesting late-fall or early-spring transmission. Mean abundance decreased between August and October in both years. Yellow perch at Île aux Ours were infected with four different parasite species in their eyes. Mean abundance of Diplostomum spp. in the vitreous humour or retina increased during the summer and fall and then decreased between the fall and following spring. Diplostomum spp. in the lens increased in abundance in the early summer, and then decreased during the fall. Both Tylodelphys scheuringi and Neascus spp. in the vitreous humour were more abundant in 0+ than in 1+ perch. Mean abundance of T. scheuringi increased over the summer in 1997 and then dropped to zero in the same cohort over winter, suggesting that the parasite lives for only 1 year. Neascus spp. only were found in 1998. Distributional data, together with seasonal information, suggest that habitat characteristics contribute significantly to the abundance of Diplostomum spp. along the St. Lawrence River. Proximity to gull colonies enhances abundance, but higher rates of predation at wetland sites depress abundance and restrict the accumulation of parasite

Estimating diet in individual pumpkinseed sunfish Lepomis gibbosus using stomach contents, stable isotopes and parasites

The diets of 99 pumpkinseed sunfish Lepomis gibbosus from a pair of small, adjacent lakes in Ontario, Canada, were estimated from their stomach contents, trophically transmitted parasites and stable isotopes of carbon and nitrogen in fish tissue. The three methods provided virtually unrelated information. There was no significant correlation in the importance of any prey item across all three methods. Fish with similar diets according to one method of estimating diet showed no tendency to be similar according to other methods. Although there was limited variation in fish size and the spatial scale of the study was small, both fish size and spatial origin showed comparatively strong associations with diet data obtained with all three methods. These results suggest that a multidisciplinary approach that accounts for fish size and spatial origins is necessary to accurately characterize diets of individual fish

Morphological and molecular differentiation of Clinostomum complanatum and Clinostomum marginatum (Digenea: Clinostomidae) metacercariae and adults.

The separation of Clinostomum complanatum Rudolphi, 1814 and Clinostomum marginatum Rudolphi, 1819 has long been unclear. Recent data confirm the validity of the junior species, C. marginatum, by ,1% differences in its 18S rDNA sequences. We collected adults and metacercariae of C. complanatum and C. marginatum and found reliable morphological differences in the genital complex at both developmental stages. In addition, we identified basic morphometrics (distance between suckers, body width) in metacercariae that may be useful for discriminating the species. The morphological differences were supported by the comparison of sequences of internal transcribed spacers of ribosomal DNA and of the mitochondrial gene cytochrome c oxidase I (COI) from 39 specimens. In 36 specimens, the average divergence between the species was 7.3% in ITS and 19.4% in COI sequences. Two specimens from North America and 1 from Europe had sequences that did not allow them to be clearly allied with either species

Spatial and temporal variation in abundance of Diplostomum spp. in walleye (Stizostedion vitreum) and white suckers (Catostomus commersoni) from the St. Lawrence River

Abundances of eye flukes (Diplostomum spp.) were compared between walleye (Stizostedion vitreum) and white suckers (Catostomus commersoni) collected in late summer 1997 from Lake St. Louis and Lake St. Pierre, two expansions of the St. Lawrence River in Quebec, Canada. The white sucker, a benthic consumer, was more heavily infected than the walleye, a pelagic piscivore, in both lakes. Infection levels increased significantly with host age and size. For both species, abundance of Diplostomum spp. within each age group and length class was higher in fish from Lake St. Louis than in those from Lake St. Pierre. Walleye of all ages and white suckers 7 years old from Lake St. Louis were also larger at age than those of corresponding age from Lake St. Pierre. Therefore, walleye and white suckers from Lake St. Louis are probably different populations from those in Lake St. Pierre. The higher infection levels in Lake St. Louis are most likely due to the larger number of ring-billed gulls (Larus delawarensis), an important definitive host of Diplostomum spp., in colonies in close proximity to that lake; there are >75 000 pairs within 40 km of Lake St. Louis and 16 000 pairs within 40 km of Lake St. Pierre. No detrimental effects of infection with Diplostomum spp. could be detected on fish fork length, body mass, condition index, or gonadosomatic index. Walleye from shallow lentic waters in Lake St. Louis were larger and possessed heavier infections of Diplostomum spp. than those from deeper lotic waters. Walleye collected from a fixed trap near Quebec City in July 1997 were smaller but more heavily infected with Diplostomum spp. than those collected in October, which implies that different populations of fish may be present seasonally at this location. A visual index developed to measure the degree of opacity of the lens of fishes does not appear to be a reliable indicator of levels of infection with eye flukes. Experimental infection of laboratory-raised juvenile ring-billed gulls with metacercariae from the lenses of various fish species collected in the St. Lawrence River demonstrated that metacercariae were primarily Diplostomum indistinctum (84–92%), the remainder being Diplostomum huronense, and this pattern is consistent across host species and localities