The taxonomic history of members of the 37-collar-spine group within the genus Echinostoma has been very confused. We obtained DNA sequence data from the nuclear rDNA ITS1, 5.8S and ITS2 of 7 nominal species belonging to this group, Echinostoma trivolvis (Cert, 1914), E. revolutum (Frolich, 1802), E. caproni Richard, 1964, E. acaproni arasasingam et nl. 1952, E. paraelzsei Lie & Basch, 1967, two African isolates, E. sp.I and E. sp.II, and of one 28-collar-spined echinostome, E. holtense (,4sada, 1926). Five of the eight species n;ere clearly distinguishable using ITS data. Sequences from the remaining three tasa, E. cnpl olzi, E. sp.ll and E. liel mere identical to one another and the group containing these laxa was distant from other 3'7-collar-spine species on a phylogenetic tree. E. tvizrolzris and E. pavaensei form a second, but less distinct group within the 35-collar-spine group. The resolution obtained using DNA sequencing will assist in the current reclassification of the group. It also provides a model for future work on sibling species.

Nuclear rDNA ITS sequence variation in the trematode genus Echinostoma : an aid to establishing relationships within the 37-collar-spine group

In order to investigate the relationships within the Echinostomatidae two data sets of gene sequences were analysed. The first consisted of all previously published ND1 sequences (20) together with 17 new sequences. The latter represented six species from the cosmopolitan genera Echinostoma, Echinoparyphium, Hypoderaeum and Isthmiophora. The second data-set of ITS sequences again included all previously published sequences (12) and three new sequences from species of Echinostoma, Echinoparyphium and Isthmiophora. All new isolates, as well as voucher material from five previously sequenced isolates, were identified on the basis of morphological characters. The phylogenetic trees inferred from the ND1 data set helped to clarify the generic affiliation of all isolates and confirmed the morphological identifications. The only exception was Echinoparyphium aconiatum, whose current position in the genus Echinoparyphium was not supported by the sequence data. Although the ITS data provided insufficient resolution for an unequivocal solution to the relationships within the genus Echinostoma, it supported the identification of Echinoparyphium ellisi and the distinct species status of three isolates of Echinostoma revolutum as predicted from the ND1 data.

Phylogenetic relationships of Echinostoma Rudolphi, 1809 (Digenea: Echinostomatidae) and related genera re-assessed via DNA and morphological analyses.

The life-cycle of Echinostoma revolutum (Froelich, 1802) Dietz, 1909 has been completed experimentally beginning with infected snails collected at the type-locality, near Erlangen, Germany. Based on the specimens obtained, each stage of the life-cycle has been redescribed. Important taxonomic features are discussed and hitherto unknown characteristics are described. Synonyms for E. revolutum are: Fasciola revoluta Froelich, 1802; Echinostoma paraulum Dietz, 1909; E. audyi Lie & Umathevy, 1965; and E. ivaniosi Mohandas, 1973. Adults and larvae described as E. revolutum in other works are found to be identical with Echinostoma echinatum (Zeder, 1803), E. trivolvis (Cort, 1914), E. jurini (Skvortsov, 1924), E. caproni Richard, 1964, Moliniella anceps (Molin, 1859), Echinochasmus beleocephalus (Linstow, 1873) and other echinostome species. For nearly a century, incorrect morphological, biological, life-cycle and host information has been attributed to E. revolutum, and at times these data have contributed to the diagnoses of the species. Occasionally, authors actually working with E. revolutum have ascribed their results to other species. Based on extensive experimental life-cycle studies beginning with infected snails from type-localities, it is shown that (1) the first intermediate host is a lymnaeid snail; (2) the second intermediate hosts are various pulmonate and prosobranch snails, mussels, frogs and freshwater turtles; (3) the final hosts are birds; (4) E. revolutum cercariae and adults have 37 collar spines; (5) the species occurs only in Europe and Asia; (6) Cercaria echinata Siebold, 1937, Echinostoma echinatum (Zeder, 1803) and E. jurini (Skvortsov, 1924) are the closely related 37-spined allies in Europe; and (7) species specific characteristics are expressed only in the larvae and the host-parasite relationships. The adults of E. revolutum cannot be identified using morphological criteria and it is proposed that worms with 37 collar spines belonging to the genus Echinostoma and occurring in naturally infected birds in Europe and Asia be referred to an “E. revolutum group.”

Life-cycle, delimitation and redescription of Echinostoma revolutum (Froelich, 1802) (Trematoda: Echinostomatidae)

Echinostomes are simultaneous hermaphrodite trematodes, parasitizing the intestine of vertebrates. They are able to self- and cross-inseminate. Using electrophoretic markers specific for three geographical isolates (strains) of Echinostoma caproni, we studied the outcrossing rate from a ‘progeny-array analysis’ by comparing the mother genotype with those of its progeny. In a simultaneous infection of a single mouse with two individuals of two different strains, each individual exhibits an unrestricted mating pattern involving both self- and cross-fertilization. The association in mice of two adults of the same strain and one adult of another strain shows a marked mate preference between individuals of the same isolate. From mice coinfected with one parent of the three isolates, each parent was shown to be capable of giving and receiving sperm to and from at least two different partners. Mating system polymorphism in our parasitic model is thus discussed in the context of the theories usually advanced.

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Selfing and outcrossing in a parasitic hermaphrodite helminth (Trematoda, Echinostomatidae)

Metacercarial excystment of trematodes.

With reference to a recent taxonomic revision the species of the echinostomes used in key studies on the population regulation in infections with 37-collar-spined Echinostoma species in experimental rodent hosts were reconsidered. This was considered essential to prevent taxonomic problems blocking further fruitful progress within this field of experimental parasitology.

B. Fried

Papers

Taxonomy of 37-collar spined Echinostoma (Trematoda: Echinostomatidae) in studies on the population regulation in experimental rodent hosts.