FOLIA PARASITOLOGICA 55: 122–126, 2008

Euparyphium albuferensis and friedi (: Echinostomatidae): experimental cercarial transmission success in sympatric snail communities

Carla Muñoz-Antoli, Antoni Marin, Amparo Vidal, Rafael Toledo and José Guillermo Esteban

Departamento de Parasitología, Facultad de Farmacia, Universidad de Valencia, Av. Vicente Andrés Estellés s/n, 46100 Burjassot – Valencia, Spain

Key words: Euparyphium albuferensis, Echinostoma friedi, cercarial transmission success, compatibility, sympatry, Radix peregra, Lymnaea fuscus, Physella acuta, Gyraulus chinensis

Abstract. Euparyphium albuferensis and Echinostoma friedi cercarial infectivity to four species of sympatric snails was exam- ined under single- or multiple-choice laboratory conditions to show the level of parasite-snail host compatibility. Radix peregra, Lymnaea fuscus, Physella acuta and Gyraulus chinensis act as second intermediate hosts of both parasite species although differ- ent cercarial transmission success (CTS) was observed. In single-host experiments, R. peregra and P. acuta showed a high de- gree of compatibility with E. albuferensis, while only P. acuta in the case of E. friedi. In two-choice snail communities, a snail with high CTS increased the values of another with low compatibility, in both parasite species. In multiple-choice snail commu- nities, high CTS of some hosts decreased, while low CTS of other hosts increased. The degree of parasite-host compatibility of each snail species could be determined by the presence of other snails in the community.

Euparyphium albuferensis Esteban, Toledo, Sanchez and occurrence of the metacercarial cysts might reflect et Muñoz-Antoli, 1997 and Echinostoma friedi Toledo, the contribution of each host species to the flow of Muñoz-Antoli et Esteban, 2000 (Trematoda: Echino- parasites through that community (Evans et al. 1981). stomatidae) are sympatric parasites of rats in the Albuf- The experimental results of second intermediate host era Natural Park of Valencia (Spain) (Esteban et al. utilisation have shown close parallels with that sug- 1997, Toledo et al. 2000). These two parasite species gested by occasional field studies (McCarthy and Kanev present an aquatic three-host life cycle, using Gyraulus 1990, Morley et al. 2004). Thus, experiments of cer- chinensis (Dunker) (Planorbidae) and Radix peregra carial infections have been considered appropriate for (Müller) (), respectively, as natural first defining the order of host utilisation as an indirect way intermediate hosts. The general low specificity towards to measure the parasite-snail host compatibility. How- the second intermediate host is well known in digenetic ever, variations in parasite-host compatibility could be trematodes, and these two parasites are able to use these related to the composition of the snail community, and and other different snail species. In fact, echinostomatid to protection effects (decoy effects) between snail spe- metacercarial stages have been recorded in a variety of cies with different levels of compatibility (Evans and molluscs, planarians, fish and amphibian larvae (Huff- Gordon 1983). man and Fried 1990). However, in general for all the In the present work, cercarial infectivity of E. albuf- echinostomatids, Fried (2001) observed different de- erensis and E. friedi, under laboratory conditions, in grees of compatibility/susceptibility not only towards four species of gastropods from the Albufera Natural the second intermediate host, but also towards the first Park, has been studied as a model to provide some in- intermediate host snail. In that sense, recently Muñoz- formation on the pattern of second intermediate host Antoli et al. (2006) found six snail species susceptible utilisation in natural systems where different parasite to be infected with E. friedi miracidia, with rates of and snail species coexist. Moreover, we combined dif- infection up to 36%. ferent snail communities with the purpose of identifying The broad specificity towards second intermediate any possible modification in the parasite-snail host hosts increases the density of potential host individuals compatibility. in a particular habitat, helps to maintain a degree of genetic variability in the parasite population, and pro- MATERIALS AND METHODS tects the parasite from the deleterious effects of a local population decline in any single mollusc host species Cercariae of E. albuferensis and E. friedi were obtained (Evans et al. 1981). from experimentally infected G. chinensis and R. peregra Cercarial infection might be particularly important in snails, respectively. Four species of freshwater snails were the pattern of host utilisation in the natural habitat. exposed to infection with cercariae: R. peregra and Lymnaea Within a community of mollusc hosts, the distribution fuscus (Müller) (Lymnaeidae), Physella acuta (Draparnaud)

Address for correspondence: J.G. Esteban Sanchis, Departamento de Parasitología, Facultad de Farmacia, Universidad de Valencia, Av. Vicente Andrés Estellés s/n, 46100 Burjassot – Valencia, Spain. Phone: ++34 963 544 492; Fax: ++34 963 544 769; E-mail: [email protected]

122 Muñoz-Antoli et al.: Compatibility of cercariae with snail hosts

(Physidae) and G. chinensis (Planorbidae). All the snails were hosts considered (P(F = 37.94) <0.01; D.F. = 4 and laboratory-reared under aquarium conditions and fed with 145). Physella acuta and R. peregra had the highest lettuce ad libitum. They were free of larval trematode infec- number of metacercariae recovered, without significant tions. The size range of all snails employed was 0.3–0.5 cm differences between them, and approximately 40 times (length for lymnaeids and the physid and diameter for the higher CTS values than the other two snail species con- planorbid). sidered. The lowest number of cysts recovered (lowest Snails were exposed, using Petri dishes of 8.5 cm of di- CTS values) was found in L. fuscus and G. chinensis, ameter, to a constant ratio of 20 cercariae/snail in 10 ml of without significant differences between them. spring water for 24 hours at 20°C, under constant fluorescent In contrast, in the case of E. friedi, analysis of vari- light, and were examined for metacercarial cysts 14 days post- ance revealed no significant differences between the exposure. Twenty replicate exposures were conducted for number of cysts recovered in any of the snail hosts con- each experiment. sidered (P(F = 1.06) >0.01; D.F = 4 and 145). However, Single-host experiments: 20 specimens of each snail spe- nearly 10 times variations of CTS values were detected cies considered were individually exposed to E. albuferensis between snail species: P. acuta had the highest CTS, or E. friedi cercariae. Two-choice experiments: a couple of two different snail followed by G. chinensis and R. peregra with interme- species were exposed simultaneously to E. albuferensis or E. diate CTS, and finally L. fuscus with the lowest CTS. friedi cercariae. A total of four two-choice communities were In the case of E. albuferensis two-choice experi- designed mixing lymnaeids with planorbids or physids follow- ments, when a physid and a lymnaeid snail species of ing the high, low or intermediate degree of compatibility after previous high CTS (P. acuta and R. peregra) were single-host experiments results. In the case of E. albuferensis exposed simultaneously, both values were significantly the material only reached 3 possible combinations. lower than in single-host experiments (P(t = 16.36 and Four-choice experiments: four different snail species with 4.28) <0.001; D.F. = 38). When a physid snail of high different degrees of compatibility were simultaneously ex- CTS (P. acuta) was exposed together with a lymnaeid posed to E. albuferensis or E. friedi cercariae. of low CTS (L. fuscus), P. acuta showed a statistically For all the experiments, cercarial transmission success significant reduction of their CTS (P(t = 4.77) <0.001; (CTS) was calculated as the total number of metacercarial D.F. = 38). However, when a lymnaeid and a planorbid cysts established/total number of cercariae exposed × 100 snail species of former low CTS (L. fuscus and G. (McCarthy and Kanev 1990). Cyst counts transformed by log chinensis) were exposed simultaneously, the number of (x+1) were used in analysis of variance and the Bonferroni t- cysts recovered in L. fuscus was significantly higher test, as a post-hoc analysis, was performed to establish the than that of single-host experiments (P(t = 3.00) <0.001; level of parasite-host compatibility. P<0.001 was considered D.F. = 38). as significant. In the case of E. friedi, when a physid snail of former high CTS (P. acuta) and a lymnaeid of former interme- RESULTS diate level of CTS (R. peregra) were exposed together, The results obtained are shown in Table 1. In the the total number of cysts recovered and the CTS values case of E. albuferensis, single-host experiments analysis were significantly reduced compared to those of single- of variance revealed significant differences between the host experiments (P(t = 3.19 and 6.10) <0.001; D.F. = numbers of cercariae established in the different snail 38), respectively. When a physid snail of former high

Table 1. Infectivity of Euparyphium albuferensis and Echinostoma friedi cercariae in single-host, two-choice and four-choice experiments (Abundance – No. metacercariae/examined snail; SE – standard error; CTS – cercarial transmission success). Euparyphium albuferensis Echinostoma friedi Snail species No. % snails Abundance CTS % snails Abundance CTS cercariae infected mean ± SE infected mean ± SE Single-host Physella acuta 20 100 11.43 ± 0.77 57.2 85 9.72 ± 6.41 32.5 Radix peregra 20 100 11.57 ± 0.80 57.9 90 7.06 ± 5.46 23.5 Lymnaea fuscus 20 67 2.30 ± 0.48 11.5 85 5.76 ± 5.63 19.3 Gyraulus chinensis 20 57 3.47 ± 0.70 17.4 95 7.13 ± 5.09 23.8 Two-choice 1 P. acuta + 40 65 5.55 ± 1.49 13.8 55 4.30 ± 1.44 10.7 1 R. peregra 35 0.60 ± 0.20 1.5 45 1.25 ± 0.42 3.1 1 P. acuta + 40 70 4.70 ± 1.06 11.7 95 4.25 ± 0.81 10.6 1 L. fuscus 70 3.55 ± 0.67 8.9 85 3.95 ± 0.62 9.9 1 L. fuscus + 40 90 6.75 ± 1.22 16.9 65 2.00 ± 0.45 5.0 1 G. chinensis 35 0.80 ± 0.35 2.0 75 2.50 ± 0.43 6.3 1 R. peregra + 40 – – – 80 2.20 ± 0.37 5.5 1 G. chinensis 45 1.55 ± 0.48 3.9 Four-choice 1 P. acuta + 80 80 12.85 ± 3.03 16.1 65 2.35 ± 0.59 2.9 1 R. peregra + 35 1.60 ± 0.77 2.0 50 1.15 ± 0.39 1.4 1 L. fuscus + 85 7.25 ± 1.50 9.1 70 3.55 ± 0.67 4.4 1 G. chinensis 60 1.50 ± 0.38 1.9 70 3.30 ± 1.06 4.1

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CTS (P. acuta) and a lymnaeid snail of former low CTS sible for cercariae of this species to penetrate some (L. fuscus) were exposed together, similar cysts were planarians, while E. caproni, which lacks such glands, recovered in both snail species, increasing the L. fuscus is unable to penetrate these planarians (Fried et al. CTS values. When a lymnaeid snail of former low CTS 1995). In the case of E. albuferensis and E. friedi, spe- (L. fuscus) and a planorbid snail of intermediate CTS cies which both are able to penetrate the same snail (G. chinensis) were exposed together, an increase in the species, we could assume that similar mechanisms are L. fuscus CTS values was observed, but without signifi- used to locate and penetrate the second intermediate cant differences unlike in single-host experiments (P(t = hosts. However, different levels of compatibility appear 3.23) >0.001; D.F. = 38). However, the number of between the snail species considered, with differences metacercariae recovered in G. chinensis was signifi- observed in the cercarial transmission success (CTS). cantly smaller than in single-host experiments (P(t = In the case of recurvatum cer- 4.49) <0.001; D.F. = 38). Finally, when a lymnaeid and cariae infecting Radix peregra, the mean number of a planorbid snail species of former intermediate CTS cysts recovered per snail is positively correlated to the (R. peregra and G. chinensis) were exposed together, a number of same-species snails per cage (McCarthy significant reduction of CTS values was noted in both 1990). This could be explained by the fact that higher snail species (P(t = 4.31 and 6.17) <0.001; D.F. = 38), number of snails could produce greater conditioning respectively. intensity, and therefore would be expected to attract In the case of E. albuferensis, results of four-choice greater numbers of cercariae. However, in snail com- experiments revealed that the highest CTS values (P. munities formed by different snail species, the overall acuta and R. peregra) in single infections showed a transmission success could not be increased, probably great reduction with statistically significant differences due to the antagonistic effect of one chemical over an- only in R. peregra (P(t = 10.10) <0.001; D.F. = 38). In other. In this sense, our results with E. albuferensis and the four-snail community the lowest CTS values were in E. friedi show that CTS does not increase with the G. chinensis and R. peregra while the intermediate CTS number of different snail species per cage. Moreover, values were in L. fuscus. This situation was similar in the effect of the cercarial dilution upon the choice of the case of E. friedi. In the four-snail community, P. different snail species of the community could expect a acuta, the snail with the highest CTS in single-host reduction of the transmission levels (Christensen 1980, experiments, showed a significant reduction in the num- Combes and Mone 1987). In this sense, mention should ber of recovered metacercariae (P(t = 4.15) <0.001; be made of the results obtained with E. friedi, when a D.F. = 38). Moreover, R. peregra and G. chinensis, with snail of high CTS (Physella acuta) was exposed to an intermediate levels of CTS in single infections, cercariae together with a snail of intermediate CTS (R. showed a significant reduction (P(t = 3.33 and 3.81) peregra): the total number of metacercariae recovered <0.001; D.F. = 38), respectively, to the lowest CTS was smaller than in single infections in both snail spe- values in the case of R. peregra. In contrast, L. fuscus, cies. In four-choice combinations, P. acuta, the snail the snail with the lowest degree of CTS in single-host with the highest CTS in single infections, presented a experiments, showed an increase to the highest CTS sharp decrease in the number of recovered metacer- values in the four-snail community. cariae, exhibiting a low degree of compatibility with the parasite. DISCUSSION Evans et al. (1981) proposed several factors likely to be important in determining the probability that cer- Euparyphium albuferensis and Echinostoma friedi cariae encounter a mollusc host species, and thus capa- cercariae are able to infect several aquatic snail species ble of influencing CTS: temporal and spatial overlap that coexist in the same natural habitat. Despite this between host and parasite, mollusc habitat preferences, broad specificity, not all snail species show the same existence of cercarial chemotaxis to one or more host degree of compatibility with parasites. species, and relative target size of each host species. It is known that parasite larvae locate their target host McCarthy (1990) proposed the second intermediate host responding to chemical conditioning of the environment dispersion pattern as another host-related factor capable by intermediate host snails (Smyth and Halton 1983, of influencing the levels of cercarial transmission. In Haas and Haberl 1997). The orientation behaviour of any case, variable susceptibility to infection among echinostomatid cercariae has been studied for Echi- snails has been demonstrated: laboratory infections of nostoma caproni, E. revolutum, Pseudoechinopary- E. recurvatum cercariae (Evans et al. 1981) have indi- phium echinatum and conoideum. The cated that R. peregra is highly susceptible, while first three species respond to similar cues of snail- planorbid snail species are only moderately susceptible, conditioned water (Haberl et al. 2000), while H. con- and some prosobranch gastropods are non-susceptible; oideum cercariae show a different mechanism of high degree of compatibility of Pseudoechinopary- chemo-orientation (Haas et al. 1995). The following phium echinatum has been shown for planorbids and step after location of the host snail is to penetrate a lymnaeids, while prosobranchs are rarely infected suitable host individual. In the case of Echinostoma (McCarthy and Kanev 1990); Echinostoma caproni trivolvis, the presence of penetration glands makes pos- cercariae (refereed to as E. liei by Christensen et al.

124 Muñoz-Antoli et al.: Compatibility of cercariae with snail hosts

1980) found five species of the genus Bulinus and P. intermediate host population (McCarthy and Kanev acuta to be very susceptible, whereas Lymnaea natalen- 1990). sis, Helisoma duryi and three species of Biomphalaria, Differential compatibility is independent of the which act as first intermediate hosts, showed a lower phyletic position of the host. McCarthy and Kanev degree of susceptibility (Christensen et al. 1980); E. (1990) showed different degrees of compatibility trivolvis encysts more readily in Biomphalaria glabrata among the lymnaeid species R. peregra, L. fuscus and than in Helisoma trivolvis, Physa heterostropha or L. stagnalis, and among the planorbid snail species Corbicula fluminea (Anderson and Fried 1987, Fried et Planorbarius corneus and Planorbis planorbis. In our al. 1987, Huffman and Fried 1990). However, the single-infections experiments, E. albuferensis showed mechanisms underlying the differences in compatibility high CTS values in R. peregra, while L. fuscus showed among snail species remain unknown. the lowest. In the case of E. friedi, cercariae showed an We have carried out different snail host communities intermediate preference for R. peregra and a lowest infections to evaluate the level of parasite-snail com- preference for L. fuscus. patibility. In E. albuferensis single-host infections, R. Our results verified that, in constant water level ex- peregra and P. acuta snails showed the highest degree periments, high densities of hosts exhibiting only low of compatibility, while in the case of E. friedi only P. suitability may in fact reduce the level of parasite trans- acuta showed high levels of compatibility with the mission, but the presence of gastropods of high com- parasite and R. peregra seemed to reduce its compatibil- patibility contributes to increase the susceptibility of ity to an intermediate level. In contrast, Gyraulus those with low compatibility. In this sense, we have chinensis and Lymnaea fuscus showed a low degree of shown in the two-choice combinations of E. albuferen- compatibility with E. albuferensis cercariae under sin- sis and E. friedi that the snail of low compatibility (L. gle-host infections, while in the case of E. friedi, G. fuscus) is able to increase its CTS. Furthermore, in E. chinensis showed an intermediate level of compatibility. albuferensis four-choice combinations, the snails with Under multiple-choice conditions, lymnaeid snail spe- the previous highest CTS (P. acuta and R. peregra) cies are subjected to a great compatibility modification, showed a significant reduction, mainly in the case of R. while L. fuscus increased to the highest or to an inter- peregra. Again, these results are similar to those ob- mediate level of compatibility in E. friedi and E. albuf- tained in E. friedi four-choice combinations, where L. erensis infections, respectively, R. peregra snails re- fuscus reached the highest CTS values. The possible duced their level to low compatibility in both parasite explanation of L. fuscus increase in compatibility levels species. in host communities could be that as the cercariae are stimulated by the other snail species stimulus, the easy Evans et al. (1981) reported that individual snails penetrability in this snail species allows for the high acting as first intermediate host are predisposed to in- rates of metacercarial cysts recovered. fection by the cercariae which emitted by themselves. In All the results obtained demonstrated that the degree this context, Evans and Gordon (1983) showed that E. of parasite-host compatibility of each snail species con- recurvatum cercariae had a high degree of preference sidered could be determined by the presence of others. for R. peregra, its first intermediate host. However, our The total transmission pattern of two sympatric parasite results do not agree with those observations. In the case species sharing the same second intermediate host spec- of E. albuferensis it was shown that G. chinensis both, trum in a particular habitat, as is the case of E. albufer- in single- and multiple-choice combinations, yielded the ensis and E. friedi in the Albufera Natural Park, seems lowest number of metacercariae recovered. In the case to depend on the interactions between snail species of E. friedi, although R. peregra in single infections communities. seems to show an intermediate level of compatibility, when that snail specie is in multiple-choice combination Acknowledgements. The present study was supported by the Proyect CGL2005-02321/BOS from Ministerio de Educación as happens in nature, the amount of metacercariae re- y Ciencia (Spain) and FEDER (European Union) and by the covered decreases. In any case, low compatibility of Proyect GV07/006 and Ayuda Complementaria ACOMP cercariae with the snail first intermediate host may con- 07/071 from the Conselleria d’Empresa, Universitat i Ciència stitute a mechanism preventing metacercarial superin- de la Generalitat Valenciana (Valencia, Spain). The authors fection and preventing parasite pressure on the first wish to thank M. Trelis for her collaboration.

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Received 7 November 2007 Accepted 21 February 2008

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