Interactions between Anisus spirorbis (Planorbidae) and Galba truncatula (Lymnaeidae) in snail communities on sedimentary soils

Experimental infections of Omphiscola glabra (preadult snails), originating from central France, to a Czech isolate of Fascioloides magna miracidia were carried out to determine if the local populations of O. glabra may ensure the larval development of this parasite and to compare these results with those noted for a natural snail host, Galba truncatula. The presence of experimentally infected snails was noted in the six populations of snails studied. However, only a few snails shed their cercariae (O. glabra 5.3 to 17.1%, G. truncatula 15.1% in the first population, and no shedding in the other). The shell heights of cercariae-shedding (CS) snails were significantly greater than those of other infected snails, for O. glabra as well as for G. truncatula. The number of metacercariae noted in each snail group was low and showed insignificant variations. When experimental infections of O. glabra were performed in relation to the shell height of snails (from 1 to 14 mm) at miracidial exposure, the prevalence of infected snails significantly decreased with increasing shell heights at exposure. However, the presence of CS snails was only noted from the 5-6 to the 9-10 mm groups, and the mean number of metacercariae per group ranged from 27 to 44.2. Despite the high infectivity of the Czech isolate of F. magna miracidia, there was an incomplete adaptation with the French G. truncatula and O. glabra used in this study, as the metacercarial production was low, and cercarial shedding only occurred for snails which showed a strong increase of their shell height during F. magna infections.

I investigated the interactions of intra— and interspecific competition with parasitism for populations of two terrestrial isopods, Porcellio scaber and Porcellio laevis, infected with a lethal virus. In field experiments, I varied densities of one or both isopod species in enclosures in which food and virus presence were also manipulated. I estimated the effects of intra— and interspecific competition, additional food, and virus infection on both the survival of P. scaber and the prevalence of the virus. In uninfected populations, intraspecific and interspecific competition negatively affected isopod survival, although food resources had no effect. In infected treatments, interspecific competition produced higher levels of virus prevalence than did intraspecific competition. Virus infection and reduced food interacted to produce higher overall mortality in interspecific competition treatments than in intraspecific competition treatments. The lack of significant effect of food on competition suggests that interference interactions rather than resource competition predominated. This mechanism is supported by a laboratory study in which total food availability was controlled. These results indicate that competition and parasitism interacted to produce the observed mortality patterns, and that ignoring mortality due to the virus would produce apparent interspecific competition. The data suggest that the impact of P. laevis on P. scaber involves both direct and indirect effects.

Field investigations on the habitats colonized by Galba truncatula or Omphiscola glabra were carried out on 162 farms of the Limousin region, Central France, to determine whether there is currently a decline in the number and size of snail populations. Seven types of snail habitats were considered here. Compared to the numbers of snail populations recorded from 1976 to 1992, the values noted from 2013 to 2016 were significantly lower, with a decline rate of 34% for G. truncatula and 23% for O. glabra. Variations in this decline rate with the type of snail habitat were also noted. The greatest decreases in the numbers of snail populations were noted for spring heads located in meadows and for road ditches, while the lowest were noted for open drainage furrows present in meadows. The distribution of these habitats according to their area did not show any significant change over time. In contrast, overwintering snails were significantly less numerous in 2013–2016 in five types of habitats for G. truncatula and in three types only for O. glabra. Several causes underlie this population decline. Among them, the current development of mechanical cleaning in open drainage systems and road ditches, that of subsurface drainage in meadows, and regular gyro-crushing of vegetation around temporary spring heads were the most important.

Helisoma duryi, a planorbid snail species, which is a potential biological control agent of the intermediate hosts of schistosomiasis, was introduced in an irrigation scheme (T.P.C.) in northern Tanzania in 1972. The species has been present at T.P.C. since, and during a snail survey in January 1981, a great variation in the shell morphology of H. duryi, ranging from typical H. duryi forms to forms resembling Biomphalaria pfeifferi, the intermediate host of Schistosoma mansoni in the area, was observed. The Biomphalaria- Wkc forms of H. duryi could constitute an entire population but also occasionally occurred in populations of typical H. duryi. This study was undertaken to determine whether simple shell measurements, or ratios between some of these could be useful in discriminating between H. duryi and B. pfeifferi. Following parameters were considered: shell height, shell diameter, diameter of the umbilicus, ratio between shell height and diameter of the umbilicus, and the number of whorls.

The geographical distributions of the Japanese eel (Anguilla japonica) and Giant-mottled eel (A. marmorata) overlap in many regions in East Asia and therefore suffer from interspecific competition in the same rivers. After a long period of adaptation, the Japanese eel and Giant-mottled eel may exhibit habitat partitioning in the rivers to diminish the interspecific competition between them. In this study, we conducted a field investigation in the Fengshan River in Taiwan to survey the habitat distributions of the Japanese eel and Giant-mottled eel throughout a river. Moreover, we investigated whether their habitat distributions are related to their swimming and upstream migration. Thus, the mRNA expression levels of several candidate genes that may be associated with the swimming and upstream migration of eel were examined in the glass eels of the Japanese eel and Giant-mottled eel. Field investigation indicated that the Japanese eel mainly inhabited the lower and middle reaches of the Fengshan River, but the Giant- mottled eel was distributed over the middle to upper reaches. The mRNA expression levels of fMYH, dio2, gria3, and neurod1 were higher in the Giant-mottled eel than in the Japanese eel, implying that Giant- mottled eels might have better swimming bursts and more active upstream migration than Japanese eels. These results suggest that there is a habitat partition at which these two eel species coexist in a river, and their habitat distributions may be linked to their swimming bursts and upstream migration. Determining the habitat distributions of freshwater eels is important for developing applicable plans for eel conservation and resource management.

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A retrospective study was carried out over a 10- to 12-year period to analyse the changes in prevalences of natural fasciolosis and paramphistomosis among cattle and snails in central France, and to determine the causes which had induced these changes. The prevalences of natural fasciolosis in cattle increased from 1990 to 1993 (13.6% to 25.2%) and diminished afterwards up to 1999 (at 12.6%). Those of natural paramphistomosis showed a progressive increase between 1990 and 1999 (from 5.2 to 44.7%). The prevalences of natural infections and the numbers of free rediae counted in the snails (Lymnaea truncatula) infected with F. hepatica did not show any significant variations over time. By contrast, the prevalences of natural paramphistomosis in snails significantly increased from 1989 to 1996 and remained afterwards in the same range of values (3.7-5.3%), while the number of free rediae significantly increased up to 2000 (from a mean of 6.5 to 13.8 rediae per infected snail, respectively). Three hypotheses may explain the increase of paramphistomosis in cattle and snails: a better quality of diagnosis for the detection of P. daubneyi eggs in veterinary analysis laboratories, the use of specific molecules in the treatment of cattle fasciolosis since 1993, and the lack of an effective treatment up to now against cattle paramphistomosis. Since the objective of most farmers in central France is to obtain the highest antiparasitic efficiency with a single treatment of cattle per year, it is reasonable to assume that the prevalence of bovine paramphistomosis will continue to increase in the future.

Field investigations were carried out during three periods (from 1976 to 1997, in 2013-2014, and in 2020-2021) on 39 cattle-raising farms on acidic soils to track changes in the populations of two Lymnaeidae (Galba truncatula and Omphiscola glabra) and their infection with Fasciola hepatica and/or Calicophoron daubneyi. Compared to the survey between 1976 and 1997 on these farms, there was a significant decrease in the number of the two lymnaeid populations and the size of the G. truncatula populations in both 2013-2014 and 2020-2021. This decline was significantly faster in the last nine years than it was before 2013. The area of habitats colonized by G. truncatula showed no significant variation over the years, while that of habitats with O. glabra significantly decreased in the period covered by the three surveys. The prevalence of F. hepatica infection in snails significantly decreased over the years, while C. daubneyi infection increased over time in both lymnaeid species. These changes are due to the use of triclabendazole to treat fasciolosis in ruminants since the 1990s, and are probably a consequence of the successive heatwaves that have occurred since 2018 in the region.

As most natural watercress beds in central France are located upstream of the permanent habitats of two lymnaeid species, Galba truncatula and Omphiscola glabra, field investigations were made from 1999 to 2004 on 67 beds to determine why the contamination of watercress with Fasciola hepatica is irregular over time in these sites, while definitive hosts, especially lagomorphs, are regularly found infected around them. Snails are able to migrate upstream in winter and spring towards the beds, and a 4-year survey demonstrated the existence of annual variation in the colonization of these sites by snails. In the 45 beds irregularly contaminated with F. hepatica over time, 37.7-62.2%, according to the year, were not populated by lymnaeids, in spite of the presence of snail populations downstream. G. truncatula was found alone in 8.8-13.3% of sites and was the first colonizing snail in 24.3-33.3% when the two lymnaeid species successively settled in these waterholes. The colonizing ability of O. glabra was more limited, as it was observed alone in 2.2% of beds and was the first colonizing snail in only 2.2-20% of them. The distances covered by these snails significantly increased with increasing migration time. After migration, a few overwintering snails (3.8% of G. truncatula and 6.8% of O. glabra) are able to colonize the beds, but their numbers decreased when the distance of migration was greater. O. glabra migrated more quickly and reached more watercress beds than G. truncatula. However, this did not influence the natural infections of snails, which were more frequent in the F1 of G. truncatula. The variability observed in the colonization of beds by snails might explain the regular or irregular contamination of wild watercress by metacercariae of F. hepatica. One of the factors which may explain this variability is the occurrence of showers in spring, so that a few snails are able to reach watercress beds after their upstream migration.

Field investigations were carried out over a two-year period in 52 natural watercress beds located in the Limousin region of central France to list the mammal and bird species that frequented these sites. This enabled detection of the definitive hosts of Fasciola hepatica and determination of the prevalence of natural infection in snails. A total of 13 mammal and five bird species were listed in these watercress beds. Adult flukes were found in Lepus capensis (39.2%), Oryctolagus cuniculus (42.0%), and Sylvilagus floridanus (25.0%). No infection with F. hepatica was noted in the five species of rodents studied. Snails infected with F. hepatica were found in 14 watercress beds. The global prevalence of natural infection was 1.1% in Lymnaea truncatula and 0.3% in L. glabra. Among the other trematode larval forms detected, the most frequent was Haplometra cylindracea (0.5%). In the Limousin region, the presence of hares and rabbits in watercress beds ensured the continuation of the F. hepatica life cycle and permitted the subsequent infection of humans when this wild watercress was eaten.

The present work includes investigation of some features of shell morphology; shell size, shell thickness, shell colour of the land snail Monacha cantiana, in addition to the correlation between height and diameter of shell and between shell aperture diameter and shell diameter at four sites within Baghdad Province, Iraq. Also, measurements of three environmental variables were made; soil temperature, soil moisture and soil calcium content in adition to population density. Shell Aperture Index (Ia) and Shell Index (SI) for individuals from size class ranged between (9-12)mm were measured. The results showed that the deference in shell size by using (Ia) within population related to temperature, moisture and population density but, the value of Shell Index decreased in AL-Kadhimiya site (0.81-0.97) due to increase in population density. The species was characterized by shell colour variation (creamy white, white ,creamy). Also, The results showed strong and positive correlation between shell height and diameter and between shell aperture diameter and shell diameter for all size classes.

The present work includes investigation of some features of shell morphology; shell size, shell thickness, shell colour of the land snail Monacha cantiana, in addition to the correlation between height and diameter of shell and between shell aperture diameter and shell diameter at four sites within Baghdad Province, Iraq. Also, measurements of three environmental variables were made; soil temperature, soil moisture and soil calcium content in adition to population density. Shell Aperture Index (Ia) and Shell Index (SI) for individuals from size class ranged between (9-12)mm were measured. The results showed that the deference in shell size by using (Ia) within population related to temperature, moisture and population density but, the value of Shell Index decreased in AL-Kadhimiya site (0.81-0.97) due to increase in population density. The species was characterized by shell colour variation (creamy white, white ,creamy). Also, The results showed strong and positive correlation between shell height and diameter and between shell aperture diameter and shell diameter for all size classes.

Chrysomy megacephala and C. rufifacies are the two dominant necrophagous species in Taiwan, Larvae of the latter can prey on other maggots including its own species as facultative foods. This habitat enhances competition strength to other maggots. In this study, we used these two species to investigate and try to understand the effect of competition on the development and growth of larvae. Intraspecific competition mostly occurred in competing for food; increasing the rearing density, larvae pupated earlier and resulted in lighter adult dry weight. The tendencies are similar in both species, but C. megacephala could develop smaller viable adults and with higher survivorship under hight density condition. Although C. rufifacies could use food resource by cannibalism, its survivorship is still lower. Under interspecific competition, first instar larvae of C. rufifacies invaded the maggot mass of C. megacephala to feed together. Third instar larvae of C. rufifacies will expel C. megacephala larvae from their foods by using their fleshy protrusion on body surface, and the C. megacephala will be forced to pupate earlier by decreasing their larval stages. Under mixed-species rearing of different ratio, the larval duration of C. rufifacies will increase as the ratio increases, but this result did not exhibit in C. megacephala . In general, under mixed-species rearing in different temperatures and densities, both species decreased the larval duration, adult dry weight and the survivorship; in a word, decreased their overall fitness. This result is opposite to the previous studies; and the different results are probably caused by different experimental designs. We allowed the maggots left from the food resource freely, won’t affect each other outside between species, as in the wild field. Interspecific competition affects the duration of third instar, feeding and postfeeding larvae of C. megacephala and the duration of second instar larvae of C. rufifacies. Duration of larval development of both species may decreased up to 54 hours when limited the food resource in single species rearing. The largest reducing amount of duration of larvae caused by interspecific competition is 11.9 hours in C. megacephala and 18.3 hours in C. rufifacies in density of 40 larvae (per 60g medium) at 23℃. At 28℃, the longest shorten larval duration of 24.8 hours in C. megacephala is happened under the density of 160 larvae; and 34.0 hours in C. rufifacies under the density of 320 larvae. Finally, larval competition decreased the larval duration of C. megacephala and C. rufifaies up to 0.5 ~ 2 days; this results could also be applied to justify the PMI estimation when competition effects existed.

Recently, there has been an expansion of submerged aquatic vegetation (SAV) in the tidal fresh and oligohaline portions of lower Chesapeake Bay tributaries. Much like the resurgence seen in the Potomac in the 1980’s, this spread of SAV in Virginia systems such as the Mattaponi, Pamunkey and Chickahominy seems to have been initiated by the introduction and spread of the invasive species Hydrilla verticillata, and appears to have been rapid. However the resurgence in the Piankatank has occurred in the absence of the introduction of this species. The factors that are influencing the growth of SAV in these tributary environments, including water quality and habitat conditions as well as the potential for interspecific competition between H. verticillata and the other SAV species in these regions are not well known. Annual aerial mapping surveys of the Chickahominy River were used alongside historical water quality data to investigate the patterns and rates of SAV bed development, and the relationships between this development and water quality conditions. Field investigations were performed in order to better understand the seasonal community dynamics relative to water quality conditions and interspecific competition. Historical analysis, field monitoring and field experimentation all showed salinity and turbidity to be the main factors controlling SAV abundance and species distribution along the Chickahominy River. Historical analysis of the Chickahominy River revealed a decline in SAV abundance in 2002, which corresponded with seasonal mean salinities of 4.1 psu. SAV abundance from 1998-2007 showed a significant correlation with vegetation emergence period secchi depth, in which secchi depths of 0.3 meters, the lowest of the time period, occurred during the 2002 SAV decline. Field data showed species zonation, in which H. verticillata was the overall dominant species, but was limited to the upper portion of the river where salinity intrusion remained below 2 psu throughout the growing season. Najas minor was dominant in the lower portion of the river where salinities reached over 4 psu in October. Salinity was the best predictor for H. verticillata’s biomass difference between the upper and lower river. SAV in the Chickahominy was able to grow in a wide range of conditions, with total suspended solids and chlorophyll a concentrations at times greater than 20 mg l and 40 μg l, respectively, and sediment organic content ranging from less than 1% to greater than 25%. Comparisons with the Mattaponi and Piankatank rivers revealed ideal habitat for H. verticillata growth in the Mattaponi, where salinities along the vegetated reach of the upper river did not extend above 1 psu. On the other hand, this species was not found growing in the Piankatank, where salinities in the very upper portion of the river reached 3.5 psu. Finally, a field species removal experiment demonstrated that environmental conditions rather than interspecific competition were most important in determining plant performance, as both H. verticillata and N. minor exhibited poor growth in the lower river site, which had higher salinity and turbidity levels than the upper river site. Influences of Habitat Conditions on Submerged Aquatic Vegetation Development in the Chickahominy River and other Virginia Tributaries of the Chesapeake Bay

The main goal of this paper was to analyze intrapopulation variation of both morphological traits and shell banding polymorphism using the example of a continuous population (a metapopulation) of the land snail Cepaea vindobonensis (Férussac, 1821). A total of 14 samples of the land snail C. vindobonensis from a population located in the “Dubki” Park (Ukraine, Mykolayiv) were collected in May-July 2007. The land snail collection sites are divided into three areas by buildings and asphalt roads, indicated by the Latin letters A, B and C. The major diameter of shell (MJD), the minor diameter of shell (MID) and the shell height (SH) were measured with a digital calliper to the nearest 0.05 mm. Two shell shape indices (SF1 and SF2) were also computed. A high level of the intrapopulation variation of the land snail C. vindobonensis was found in our study. Significant differences between sample means were found for all shell traits and indices used (except for SF1), however, maximum difference was noted for SH and SF2 (in both cases: P ≤ 0.001). About 80% of the total variation of the variance-covariance matrix was explained by the 1st and 2nd Principal Components (PC1 and PC2). The PC1 was characterized by high positive factor loadings of MJD, MID and SH and thus can be interpreted as “shell size dimension” and the PC2 had a high correlation with SF2 and thus it can be interpreted as “shell globularity”. The PC1 and PC2 determined a high level of spatial differentiation of intrapopulation morphological variation of the land snail C. vindobonensis. Samples with small (area A) and large (areas B and C) shells were separated from each other according to the PC1. Areas B and C were characterized by individuals with flatness and globularity shells, respectively. The areas A, B and C differed significantly in the total number of morphs, average number of morphs and frequency of rare morphs (Kruskal-Wallis H-test; in all cases P ≤ 0.010). At the same time, the highest value of phenetic diversity was noted for samples collected within A and C areas. In general all phenetic diversity estimators showed a positive correlation with sample size (Spearman's correlation coefficient; in all cases P ≤ 0.05). It was found that the type of biotope did not likely affect the frequency of individual morphs with respect to the shell banding polymorphism pattern. With regard to the most common morphs two patterns of the spatial arrangement of the intrapopulation variation were found – clinal pattern was for the frequency of pallescens morph and chaotic pattern was for frequency of “12345” morph.