Chaetogaster Limnaei Research Articles

Ecology, Morphology and Molecular Confirmation of Chaetogaster limnaei (Annelida: Naididae) retrieved from freshwater snail Physa acuta from Greater Zab River, Iraq.

The present study is concerned with the Chaetogaster limnaei retrieved from the freshwater snail Physa acuta collected from (March-October 2021) from various locations near Chama-dubz village on the Greater Zab River, Erbil province, Iraq. Some Physicochemical variables, like water temperature, pH, Dissolved Oxygen, and Calcium ion experiment on a freshwater snail. The result showed statistically significant differences among Monthly variations with variables (number of snails, water temperature, pH and DO, and Calcium ion). In addition, isolated the Chaetogaster limnaei from Physa acuta with a prevalence was 5.75% (33/574), which has no dorsal and ventral chaeta approximately 14 to 20 per bundle, lack in segments 3 to 5, and chaetae and a vestige of a prostomium with sharply bent teeth. The identified morphologically and molecularly confirmed by using a COI sequence marker confirmed a 100% match to species with accession number (KF952336.1). As a result, the current study is the first report of Chaetogaster limnaei in Iraq, supported by phylogenetic analysis using Maximum Likelihood and Maximum Parsimony Methods.

New records of <i>Physa acuta</i> (Gastropoda: Physidae) and the ectoparasite <i>Chaetogaster limnaei</i> (Oligochaeta: Naididae) in central Chile

The sewage snail Physa acuta has invaded several countries worldwide. Its presence in Chile was first reported in 2014. Recently, this species was recorded for the first time in the Bullileo Reservoir, central Chile, in association with the oligochaete Chaetogaster limnaei, which was found within the mantle cavity of the snail. The presence of juvenile and adults of P. acuta greater than 10 mm suggests that the species is well adapted to the ecosystem. A prevalence of 39.1% of C. limnaei was recorded for P. acuta, with a range of infestation of 1–4 parasites per host.

Cryptic carnivores: Intercontinental sampling reveals extensive novel diversity in a genus of freshwater annelids

Freshwater annelids are globally widespread in aquatic ecosystems, but their diversity is severely underestimated. Obvious morphological features to define taxa are sparse, and molecular phylogenetic analyses regularly discover cryptic diversity within taxa. Despite considerable phylogenetic work on certain clades, many groups of freshwater annelids remain poorly understood. Included among these are water nymph worms of the genus Chaetogaster (Clitellata: Tubificida: Naididae: Naidinae). These worms have diverged from the detritivorous diet of most oligochaetes to become more predatory and exist as omnivores, generalist predators, parasites, or symbionts on other invertebrates. Despite their unusual trophic ecology, the true diversity of Chaetogaster and the phylogenetic relationships within the genus are uncertain. Only three species are commonly referenced in the literature (Chaetogaster diaphanus, Chaetogaster limnaei, and Chaetogaster diastrophus), but additional species have been described and prior molecular data suggests that there is cryptic diversity within named species. To clarify the phylogenetic diversity of Chaetogaster, we generated the first molecular phylogeny of the genus using mitochondrial and nuclear sequence data from 128 worms collected primarily across North America and Europe. Our phylogenetic analyses suggest that the three commonly referenced species are a complex of 24 mostly cryptic species. In our dataset, Chaetogaster “diaphanus” is represented by two species, C. “limnaei” is represented by three species, and C. “diastrophus” is represented by 19 species. North American and European sequences are largely interspersed across the phylogeny, with four pairs of clades involving distinct North American and European sister groupings. Overall, our study demonstrates that the species diversity of Chaetogaster has been underestimated and that carnivory has evolved at least twice in the genus. Chaetogaster is being used as a model for symbiotic evolution and the loss of regenerative ability, and our study indicates that researchers must be careful to identify which species of Chaetogaster they are working with in future studies.

Susceptibility of invasive Asian clams to Chaetogaster limnaei: effect of parasite density and host size on infection dynamics

Susceptibility of invasive Asian clams to Chaetogaster limnaei: effect of parasite density and host size on infection dynamics

Neglected symbionts and other metazoan invertebrates associated with molluscs from Africa's largest lake: Diversity, biotic interactions and bioindication

Abstract Freshwater molluscs are hosts for diverse metazoan symbionts. However, apart from the digenean helminths, symbionts of molluscs are underreported worldwide. Therefore, this study focused on the diversity of oligochaetes, leeches, mites, insect larvae and nematodes associated with gastropods and bivalves from Lake Victoria, East Africa. Overall, 1,633 mollusc specimens representing 14 species were sampled from the Kenyan part of the lake. Each host specimen was examined to determine co‐occurrence of symbionts (including digeneans) and other metazoan invertebrates, and their microhabitat preferences on/in the hosts. In addition, prevalence and abundance of symbionts were compared for molluscs obtained from an unpolluted site, and sites that are eutrophic and polluted with heavy metals. In total, 33 species were recovered from the molluscs: six oligochaetes, four insects, two mites, two nematodes, one leech and 18 digeneans. The nematode Daubaylia potomaca, mite Unionicola macani, leech Batracobdelloides sp., oligochaetes Chaetogaster limnaei, Dero digitata, Aulophorus africanus, Allonais paraguayensis and Ophidonais serpentina, and gorgoderid digenean larvae are new records for Lake Victoria. Moreover, the genus Bratislavia (Oligochaeta) is reported for the first time in Africa. Our results show that parasitic mites and leeches were absent from mollusc specimens that harboured chironomids. Likewise, there was no co‐occurrence of C. limnaei, D. potomaca and digeneans, suggesting that antagonistic interactions occur between the symbionts. Although co‐occurrence of mites and digeneans in individual mollusc hosts was common, the symbionts occupied different microhabitats. This study shows that prevalence and intensities of U. macani and C. limnaei, were significantly higher in hosts from the unpolluted site, compared with the polluted sites. What is more, D. potomaca and trichopteran larvae, were recorded only from the unpolluted site. The distribution of the chironomid Kiefferulus chloronatus suggests their preference for sites that are rich in organic matter and their ability to tolerate pollution. Information on antagonistic interactions between symbionts might be applicable in biocontrol, especially of digenean species that have veterinary or medical importance. Finally, this study shows a potential for the use of U. macani, C. limnaei, D. potomaca and insect larvae as discriminators of the quality of aquatic habitats.

It's a worm-eat-worm world: Consumption of parasite free-living stages protects hosts and benefits predators.

Predation on parasites is a common interaction with multiple, concurrent outcomes. Free-living stages of parasites can comprise a large portion of some predators' diets and may be important resources for population growth. Predation can also reduce the density of infectious agents in an ecosystem, with resultant decreases in infection rates. While predator-parasite interactions likely vary with parasite transmission strategy, few studies have examined how variation in transmission mode influences contact rates with predators and the associated changes in consumption risk. To understand how transmission mode mediates predator-parasite interactions, we examined associations between an oligochaete predator Chaetogaster limnaei that lives commensally on freshwater snails and nine trematode taxa that infect snails. Chaetogaster is hypothesized to consume active (i.e. mobile), free-living stages of trematodes that infect snails (miracidia), but not the passive infectious stages (eggs); it could thus differentially affect transmission and infection prevalence of parasites, including those with medical or veterinary importance. Alternatively, when infection does occur, Chaetogaster can consume and respond numerically to free-living trematode stages released from infected snails (cercariae). These two processes lead to contrasting predictions about whether Chaetogaster and trematode infection of snails correlate negatively ('protective predation') or positively ('predator augmentation'). Here, we tested how parasite transmission mode affected Chaetogaster-trematode relationships using data from 20,759 snails collected across 4years from natural ponds in California. Based on generalized linear mixed modelling, snails with more Chaetogaster were less likely to be infected by trematodes that rely on active transmission. Conversely, infections by trematodes with passive infectious stages were positively associated with per-snail Chaetogaster abundance. Our results suggest that trematode transmission mode mediates the net outcome of predation on parasites. For trematodes with active infectious stages, predatory Chaetogaster limited the risk of snail infection and its subsequent pathology (i.e. castration). For taxa with passive infectious stages, no such protective effect was observed. Rather, infected snails were associated with higher Chaetogaster abundance, likely owing to the resource subsidy provided by cercariae. These findings highlight the ecological and epidemiological importance of predation on free-living stages while underscoring the influence of parasite life history in shaping such interactions.

Parasitism and fitness of invaders: oligochaete Chaetogaster limnaei produces gill damage and increased respiration rates in freshwater Asian clams

Biological interactions between invasive and resident species are perceived as a key factor mediating impacts in invaded ecosystems, although symbiotic interactions have received relatively little attention. To evaluate the association between the invasive clam Corbicula fluminea and its oligochaete symbiont Chaetogaster limnaei, we conducted laboratory assessments of prevalence and intensity of infection, external and internal macroscopic alterations, and histological analyses of the gills of uninfected and infected clams collected from the shores of the Rio de la Plata estuary in Argentina. To evaluate potential ramifications of physical alterations on physiological traits and host fitness, we conducted respiration experiments on the same clams. Worm prevalence was higher in smaller than large clams. While no macroscopical alterations were detected, several histopathological changes were observed in the gills of infected clams. Infected clams had significantly higher metabolic rates than uninfected conspecifics and smaller clams had higher metabolic rates than larger conspecifics. Increased host metabolic rates, even at very low infections intensities, were likely a compensatory response to the stress caused by gill damaged inflicted by the oligochaetes. The relationship between C. limnaei and invasive C. fluminea in Rio de la Plata best fits as parasitism.

SPECIFIC FEATURES OF HOST-PARASITE RELATIONS IN THE SYSTEM «CHAETOGASTER LIMNAEI BAER, 1887 (OLYGOCHAETA) – THE MOLLUSK OF THE LYMNAEA GENUS (GASTROPODA)» IN THE WATER RESERVOIRS OF KEMEROVO

The purpose of the research: the study of the role of Chaetogaster limnaei (Oligochaetes) in the “parasite-host” system on the example of its relationship with some mollusks of the genus Lymnaea in the aquatic biotopes in the city of Kemerovo.Materials and methods. 214 specimens of L.(Radix) auricularia and 129 specimens of L.(Lymnaea) stagnalis have been studied. The contagion of mollusks was studied using the compressor method on live temporary preparations. Species diagnostics of mollusks was carried out on the shells on the works of S.I. Andreev. Contagion of mollusks was studied by the compressor method for live temporary preparations. The definition of oligochaetes was performed using the works of V.P. Semerny and M.V. Chertoprud. Determination of trematodes in cercariae – according to the works of E.N. Frolova.Research results. The studies have shown that mollusks are infected with Chaetogaster limnaei and trematode larvae of families Strigeidae, Diplostomatidae, Plagiorchidae, Echinostomatidae. In case of joint parasitism with Ch. limnaei in R. auricularia, the intensity of invasion by trematode larvae was insignificant, and in the absence of the hetogaster, superinvasion of metacercaria strigeida and lancet cercariae plagiarchids was observed. Thus, the oligochaete Ch. limnaei, settling in R. auricularia, significantly reduces the infection of this mollusk with the other types of parasites.

First report of Chaetogaster limnaei (Annelida: Naididae) in Chile based on samples retrieved from an invasive freshwater snail

Some naidid oligochaetes establish commensal relationships with species of molluscs worldwide. In the present study, we report the finding of Chaetogaster limnaei in Illapel River, northern Chile. This worm was found inhabiting the mantle cavity of the freshwater gastropod Physa acuta, an invasive species in this country. The taxonomic status of C. limnaei was confirmed by molecular analysis based on mitochondrial 16S ribosomal RNA gene.

Effectiveness of Chaetogaster limnaei as a controller of Fasciola hepatica in experimental infections of Galba truncatula.

Background:Chaetogaster limnaei is an annelid symbiotically associated with lymnaeid snails as Galba truncatula. This association is considered a preventive mechanism against trematode miracidia infection, including Fasciola hepatica. The objective of this study was to determine the effectiveness of Chaetogaster limnaei as a natural controller of Fasciola hepatica in laboratory conditions.Procedures:Fascsola hepatica miracidia were inoculated in parallel into snails carrying Chaetogaster limnaei and snails without the annelid. The degree of infection was measured after 40 days of exposure. Furthermore, the number of annelids per snail was quantified, as well as the ability of Chaetogaster limnaei to devour miracidia at different times of exposure.Results:An effective 70% natural control of Fasciola hepatica in Galba truncatula was observed. The carrying capacity of the snail was established to be of 10.6 ± 1 annelids. Chaetogaster limnaei is a predator of Fasciola hepatica devouring an average of 3.79 ± 0.21 miracidia. The results of these experiments have a potential value as a control measure against fascioliasis in the environment.

Effects of Chaetogaster limnaei limnaei (Oligochaeta, Tubificidae) on freshwater snail communities

From laboratory studies, the relationship between the oligochaete Chaetogaster limnaei limnaei (CL) and its freshwater snail hosts is known to be context-dependent, ranging from mutualistic to parasitic. We monitored snail communities of seven streams in Germany during three seasons of a year and investigated infestation by CL. Some snail species never were infested. In snail species that were infested, size, substratum type, oxygen concentration and species identity were the most important variables explaining the variance in CL infestation. Independent of individual snail size, Bithynia tentaculata, Ancylus fluviatilis and Acroloxus lacustris showed the highest CL abundances. Across species, CL abundances were highest in large individuals on silty substratum at well-oxygenated sites. Reproductive success of snail populations was estimated from proportion of juveniles in populations. This measure of reproductive success of snail populations was inversely related with CL infestation level. These results suggest that CL infestation affects aquatic snails at the population and community level in the field. Differential infestation levels and different impacts of CL infestation between species lead to an asymmetric distribution of positive and negative effects among all snail species present in a habitat. Thus, CL may be an overlooked agent in structuring snail communities.

Host community composition and defensive symbionts determine trematode parasite abundance in host communities

AbstractHost species vary in their propensity to become infected by and transmit parasites, and this variation in host competency can influence parasite transmission within host communities. Host competency is often attributed to morphological, physiological, and behavioral defenses of hosts, but hosts commonly have an additional, lesser studied form of protection: defensive symbionts. For instance, snails are facultatively defended by ectosymbiotic oligochaete worms (Chaetogaster limnaei) that consume free‐living trematode parasites, bacteria protect amphibians from the fungus that causes chytridiomycosis, and ants protect plants from herbivores. In addition to reducing infection on their hosts, defensive symbionts may influence parasite transmission to other hosts by redirecting parasites toward other hosts and/or removing parasites from the system. We explored these possibilities by examining the relative roles of community composition and the presence of defensive symbionts (C. limnaei) in determining trematode infection intensity among second intermediate host communities composed of snails (Helisoma trivolvis) and tadpoles (Rana catesbeiana). Parasites were dramatically more successful at infecting snails than tadpoles, which led to more total parasites in host communities where snails were present. In addition, defensive symbionts substantially reduced snail infection intensity and thus reduced the total number of parasites in communities containing symbiont‐defended snail hosts. Neither host community composition nor the presence of defensive symbionts on snails influenced individual tadpole infection in our experiments. Therefore, in our experiments, second intermediate host community structure did not influence individual host tadpole infection risk, but did influence total parasite transmission.

The invasive Chinese pond mussel Sinanodonta woodiana (Lea, 1834) as a host for native symbionts in European waters

<p><span style="font-family: Times New Roman;"> B</span><span style="font-family: Times New Roman;">iological invasions are commonly observed in both the natural habitats and those which are altered by human activities. An understanding of the mechanisms involved in the successful introduction, establishment and invasion of exotic taxa is essential in predicting of changes in biodiversity and community structure. Symbiont-mediated interactions between exotic and native hosts are of special interest due to the indirect effects on population dynamics. The aim of this study was to estimate the presence of symbionts in Chinese pond mussel </span><span style="font-family: Times New Roman;"><em>Sinanodonta woodiana</em> (Lea, 1834), an exotic species of mussel in European fresh waters. The number of 340 individuals of <em>S. woodiana</em> was collected from Polish water bodies, including thermally heated lakes and fish ponds with natural thermal regime. The examination of mussels revealed the presence of <em>Rhipidocotyle campanula </em>sporocysts and cercariae (Digenea: Bucephalidae), water mites <em>Unionicola ypsilophora</em> (Acari: Hydracarina), oligochaetes <em>Chaetogaster limnaei limnaei</em> (Oligochaeta: Naididae) and chironomids<em> Glyptotendipes</em> sp. (Diptera: Chironomidae). The global prevalence of mussels inhabited by <em>Ch. limnaei limnaei </em>was 7.6%, by water mites and chironomids 3.5%, and by <em>R. campanula</em> cercariae 2.0%. The significant difference in the number of mussels with symbionts was identified between heated lakes and fish ponds (<em>χ</em><sup>2</sup>=4.15; df=1, P=0.04), with a higher global prevalence of mussels in fish ponds (22.3%) compared to heated lakes (13.7%). <em>R. campanula</em> or <em>U. ypsilophora</em> were only found in mussels collected from thermally polluted lakes or fish ponds, respectively. Chironomid larvae and oligochaetes occurred in both types of water bodies. However, <em>Glyptotendipes</em> sp. inhabited mussels with a higher global prevalence in fish ponds than in thermally polluted lakes, while <em>Ch. limnaei limnaei</em> was observed mainly in hosts from heated lakes, and only from one fish pond that were not drained. Our findings indicate that the alien Chinese pond mussel <em>S. woodiana</em> can be inhabited by different groups of symbionts native to Europe, including digenetic trematodes. The results show that <em>S. woodiana</em> can affect directly and indirectly water habitats and the vulnerability of infection with symbionts depends on ecosystem conditions. It occurs that even considerable climate differences do not pose a barrier for exotic mussels to spread. </span></p>

Biotic interactions under climate warming: temperature-dependent and species-specific effects of the oligochaete Chaetogaster limnaei on snails

Biological invasions impose severe threats to biodiversity, and the extent of this phenomenon is predicted to intensify under climate warming. Only a few investigators have examined how temperature interacts with other environmental variables to affect competition between native and invasive species. Physa acuta, an invasive freshwater snail in Europe, often outcompetes the indigenous congener Physa fontinalis. Both species are hosts of the oligochaete Chaetogaster limnaei limnaei (CL). We examined how the growth rates of the 2 competing physid species are co-affected by CL infestation (0, 10, 20 CL/snail) and temperature regime (15, 20, 25°C). Physa acuta grew faster than P. fontinalis. Warmer temperatures strongly favored growth rates of P. acuta, whereas P. fontinalis hardly profited from increased temperatures. CL infestation reduced the growth rates of both physids, but affected P. acuta more strongly than P. fontinalis. At the highest CL infestation level, the growth rates of both species were equal at 15 and 20°C, and faster growth of P. acuta occurred only at 25°C. Thus, using only the temperature response of a species to predict its reaction to climate warming is insufficient because biotic interactions can strongly affect species’ responses to temperature change. Additional host-preference experiments showed that physids were preferentially infested compared to Radix balthica and Bithynia tentaculata, 2 species that commonly co-occur with the physids. We showed the clear competitive superiority of P. acuta over P. fontinalis, but environmental conditions exist in which their fitness-relevant growth rates do not differ. CL infestation can reduce the competitive superiority of P. acuta, so CL might facilitate the co-existence of the 2 species. In general, its density-dependent effects and different selectivity for snail species may make CL an agent that structures snail communities in the field, a role that has been underestimated.

Sharing the load: a survey of parasitism in the invasive freshwater pulmonate, Physa acuta (Hygrophila: Physidae) and sympatric native snail populations

The highly invasive freshwater snail, Physa acuta, was examined for parasites over temporal and spatial scales. All populations studied had a high prevalence of the parasitic morph of the oligochaete worm, Chaetogaster limnaei. This worm was also found to infect two native snails, Glyptophysa gibbosa and Austropeplea tomentosa, at lower prevalences. Seasonality and collection sites did not significantly influence the worm’s infection dynamics, but strong positive correlations were found between the sizes of P. acuta individuals and both the likelihood of infection and infection intensity. The ectocommensal morph of C. limnaei was found in all three pulmonate species. Physa acuta was infected with two digenean trematode species which were also found in two native snails, Posticobia brazieri and G. gibbosa. One digenean, found within the renal gland of P. acuta, did not significantly influence the presence or infection intensity of the renal gland-dwelling C. limnaei parasitic morph. All parasites infecting P. acuta were also found to be infecting sympatric native freshwater snails. The effects that such host sharing by parasites may have upon the establishment of P. acuta as a successful invader merit further study.

Association of Aquatic worms and infected snails with Digenean larvae

Six species of aquatic snails were sorted from three sites, the irrigation canal of Baghdad University campus (S1), River Tigris at Al-Za'afaraniah district / Baghdad(S2) , and River Euphrates at Al-Haideriah district Al-Najaf province(S2). The species included Melanopsis nodosa ;Melanoides tuberculata ; Thaiodaxsas jordani ; Lymnaea auricularia ; Physa acuta and Bellamya bengalensis. The first specis recorded the highest total number and was found in high density in the R. Euphrates site (S3), while the last species was the most widely distributed species, and found in all study sites. The last three species were found in Tigris river (S2) , while the first and last species were collected from the irrigation canal (S1).The result revealed that the species M. nodosa, M. tuberculata and L. auricularia were infected with Digenean larval stages, and the first species recorded the highest infection percentage of 60.04%, and the lowest percentage of 5.70% was recorded in L. auriculari , while M. tuberculata recorded a percentage of 38.98%.The oligochaetes Chaetogaster limnaei was sorted from the mantle cavity of L. auriculari and P. acuta, and it was noted that the first species accommodated more worms numbers than the second species. Twelve Species of family Naididae worms (subfamily Naidinae and subfamily Pristininae) , in addition to Aeolosoma leidyi of family Aeolosomatidae were sorted from the specific aquarium of each snail species. The leech Glossiphonia heteroclite was also recorded. The Nematodes worms were recorded the highest number sorted from the aquarium of L.auricularia, which are the most associate species, and 10 species of 49 individuals of worms were sorted from its aquarium, specially Dero ( Dero)digitata. In general, the infected snails, M. nodusa, M. tuberculata, and L. auricularia showed the highest association with worms, and from their aquaria 48, 37 , and 49 individuals of worms . with a number of 8,3, and 18 species respectively.

Association of Aquatic worms and infected snails with Digenean larvae

Six species of aquatic snails were sorted from three sites, the irrigation canal of Baghdad University campus (S1), River Tigris at Al-Za'afaraniah district / Baghdad(S2) , and River Euphrates at Al-Haideriah district Al-Najaf province(S2). The species included Melanopsis nodosa ;Melanoides tuberculata ; Thaiodaxsas jordani ; Lymnaea auricularia ; Physa acuta and Bellamya bengalensis. The first specis recorded the highest total number and was found in high density in the R. Euphrates site (S3), while the last species was the most widely distributed species, and found in all study sites. The last three species were found in Tigris river (S2) , while the first and last species were collected from the irrigation canal (S1).The result revealed that the species M. nodosa, M. tuberculata and L. auricularia were infected with Digenean larval stages, and the first species recorded the highest infection percentage of 60.04%, and the lowest percentage of 5.70% was recorded in L. auriculari , while M. tuberculata recorded a percentage of 38.98%.The oligochaetes Chaetogaster limnaei was sorted from the mantle cavity of L. auriculari and P. acuta, and it was noted that the first species accommodated more worms numbers than the second species. Twelve Species of family Naididae worms (subfamily Naidinae and subfamily Pristininae) , in addition to Aeolosoma leidyi of family Aeolosomatidae were sorted from the specific aquarium of each snail species. The leech Glossiphonia heteroclite was also recorded. The Nematodes worms were recorded the highest number sorted from the aquarium of L.auricularia, which are the most associate species, and 10 species of 49 individuals of worms were sorted from its aquarium, specially Dero ( Dero)digitata. In general, the infected snails, M. nodusa, M. tuberculata, and L. auricularia showed the highest association with worms, and from their aquaria 48, 37 , and 49 individuals of worms . with a number of 8,3, and 18 species respectively.

Dispersal of a defensive symbiont depends on contact between hosts, host health, and host size.

Symbiont dispersal is necessary for the maintenance of defense mutualisms in space and time, and the distribution of symbionts among hosts should be intricately tied to symbiont dispersal behaviors. However, we know surprisingly little about how most defensive symbionts find and choose advantageous hosts or what cues trigger symbionts to disperse from their current hosts. In a series of six experiments, we explored the dispersal ecology of an oligochaete worm (Chaetogaster limnaei) that protects snail hosts from infection by larval trematode parasites. Specifically, we determined the factors that affected net symbiont dispersal from a current "donor" host to a new "receiver" host. Symbionts rarely dispersed unless hosts directly came in contact with one another. However, symbionts overcame their reluctance to disperse across the open environment if the donor host died. When hosts came in direct contact, net symbiont dispersal varied with both host size and trematode infection status, whereas symbiont density did not influence the probability of symbiont dispersal. Together, these experiments show that symbiont dispersal is not a constant, random process, as is often assumed in symbiont dispersal models, but rather the probability of dispersal varies with ecological conditions and among individual hosts. The observed heterogeneity in dispersal rates among hosts may help to explain symbiont aggregation among snail hosts in nature.

Untangling the Ecology, Taxonomy, and Evolution of Chaetogaster limnaei (Oligochaeta: Naididae) Species Complex.

Within Oligochaeta, Chaetogaster limnaei is unusual in exhibiting a parasitic relationship with freshwater pulmonate snails. Taxonomic confusion has been caused by differences in what have been considered 2 subspecies of this worm: Chaetogaster limnaei limnaei is an ectosymbiont and is present inside the mantle cavity of the snail, whereas Chaetogaster limnaei vaghini is parasitic and lives in the kidney of the snail. This study explored the distribution of these annelids in central New York and used mitochondrial DNA sequence data from the COI locus to examine the relationship, evolution, and species status of the ectosymbiotic and parasitic forms of C. limnaei. Snails ( Physa gyrina ) were collected from 6 streams and lakes in central New York, with additional specimens collected from a lake in Massachusetts for comparison. One hundred and forty snails were examined, and at least 1 form of Chaetogaster was present in 88 specimens, a prevalence of 62.9%. COI sequence data from New York and Massachusetts did not reveal separate ectosymbiotic and parasitic lineages. Instead, all parasitic forms were part of a mixed clade that included both ectosymbiotic and parasitic forms. This mixed clade was nested within clades of ectosymbiotic forms only, suggesting that a plastic lineage of C. limnaei, able to be both ectosymbionts and parasites, evolved from ectoparasitic ancestors.

Study of Naidid worms community associated with two species of aquatic plants in River Tigris inside Baghdad City / Iraq

The present study is concern with the interaction between the naidid worms diversity and the species of aquatic plant within which the worms found . For this purpose, two species of aquatic plant were used, Ceratophyllum demersum and Eichhornia crassipes. 12 samples of aquatic plants were collected , as one sample monthly for a period from September 2012 to September 2013 from different site on Tigris river within Baghdad City. From C. demersum, 1428 individuals, were sorted during the study period, related to 17 species. 12 species of subfamily Naidinae which are Chaetogaster limnaei , C. diastrophus , Ophidonais serpentine , Dero ( Dero) digitata. , D.(D.) evelinae , Nais pseudobtosa , N.simplex, N.stolci , N.Paradalis , N.elingius , N. variabilis and N. communis. In addition to five species of subfamily Pristininae, two species of Pristina , which are P. longiseta and . P. aequiseta, and three species of pristinella, which are P. . Jenkinae , P. sima , and P. osborni. Dero ( Dero) digitata was recorded the higher number of 430 individuals,with a percentage of 28.11% of the total sorted worms. About the aquatic plant Eichhornia crassipes, a total of 829 worms were sorted from it, which are related to six species of Naidinae , which are diaphanous , Ophidonais serpentine, Stylaria lacustris , Slavina appendiculata , N. variabilis and finally the species Allonais inaequalis. There was no any species of Pristininae sorted from this plant. The highest number of 467 individuals was recorded by the species Slavina appendiculata, with a percentage of 52.3% of the total number and 228 individual with a percentage of 25.5% was recorded by Allonais inaequalis.