Immunolocalization of the 38.3 kDa calponin-like protein in stratified muscles of the tail of Schistosoma japonicum cercariae

Calponins are proteins present in vertebrate smooth musculature where they occur in association with thin myofilaments. Calponins are not present in vertebrate or invertebrate striated muscles. The blood fluke Schistosoma japonicum expresses a 38.3-kDa protein that bears substantial homology with vertebrate calponin and occurs entirely within smooth musculature of adults. Calponin-like immunoreactivity has been demonstrated in smooth muscles of many invertebrate phyla. The Schistosoma japonicum calponin has been localised in smooth myofibrils of adults where it is associated with myofilaments and sarcoplasmic reticulum. In this study, the ultrastructural localisation of the protein in muscles of S. japonicum cercariae is described. The protein is present in smooth muscles of the forebody and the stratified muscle of the tail. Within the stratified layer, the protein occurs predominantly in transverse arrays of sarcoplasmic reticulum. The localisation data suggest that the calponin-like protein of S. japonicum is involved in contraction of the stratified tail muscle. Furthermore, the presence of a calponin system in the stratified muscle suggests that this muscle is simply a superior form of muscle, closely related to smooth muscles that use a caldesmin-calponin system in contraction. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.

Platyhelminth phylogenetics - a key to understanding parasitism?

The comparative method, the inference of biological processes from phylogenetic patterns, is founded on the reliability of the phylogenetic tree. In attempting to apply the comparative method to the understanding of the evolution of parasitism in the phylum Platyhelminthes, we have highlighted several points we consider to be of value along with many problems. We discuss four of these topics. Firstly, we view the group at a phylum level, in particular discussing the importance of establishing the sister taxon to the obligate parasite group, the Neodermata, for addressing such questions as the monophyly, parasitism or the endo or ectoparasitic nature of the early parasites. The variety of non-congruent phylogenetic trees presented so far, utilising either or both morphological and molecular data, gives rise to the suggestion that any evolutionary scenarios presented at this stage be treated as interesting hypotheses rather than well-supported theories. Our second point of discussion is the conflict between morphological and molecular estimates of monogenean evolution. The Monogenea presents several well-established morphological autapomorphies, such that morphology consistently estimates the group as monophyletic, whereas molecular sequence analyses indicate paraphyly, with different genes giving different topologies. We discuss the problem of reconciling gene and species trees. Thirdly, we use recent phylogenetic results on the tapeworms to interpret the evolution of strobilation, proglottization, segmentation and scolex structure. In relation to the latter, the results presented indicate that the higher cestodes are diphyletic, with one branch difossate and the other tetrafossate. Finally, we use a SSU rDNA phylogenetic tree of the Trematoda as a basis for the discussion of an aspect of the digenean life-cycle, namely the nature of the first intermediate host. Frequent episodes of host-switching, between gastropod and bivalve hosts or even into annelids, are indicated.

Identical digeneans in coral reef fishes from French Polynesia and the Great Barrier Reef (Australia) demonstrated by morphology and molecules

Three coral reef fish species, Zanclus cornutus, Chaetodon vagabundus and Naso lituratus, were collected in French Polynesia and on the Great Barrier Reef, Queensland. These fish species were each infected by one morphologically similar digenean species in both localities; Schistorchis Zancli Hanson, 1953 was found in Zanclus cornutus. Preptetos laguncula Bray and Cribb, 1996 in Naso lituratus and Neohypocreadium dorsoporum Machida and Uchida, 1987 in Chaetodon vagabundus. In addition, on the Great Barrier Reef P. laguncula was also found in Naso unicornis and N. dorsoporum in Chaetodon ephippium and Chaetodon flavirostris. Morphometric differences between the species from the two sites were only slight. Sequences from the second internal transcribed spacer of the ribosomal DNA of each worm revealed total homology or negligible divergence between samples from hosts caught in French Polynesia and on the Great Barrier Reef. These results show that across more than 6000 km these digeneans are similar in morphology and genotype. Some species of fishes and molluscs a-re considered to have distributions that encompass the entire tropical Indo-West Pacific. These findings suggest that at least some of their parasites have similarly broad distributions. (C) 2001 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.

The nature and evolution of the association among digeneans, molluscs and fishes

Patterns of association of digenean families and their mollusc and vertebrate hosts are assessed by way of a new database containing information on over 1000 species of digeneans for lift-cycles and over 5000 species from fishes. Analysis of the distribution of digenean families in molluscs suggests that the group was associated primitively with gastropods and that infection of polychaetes, bivalves and scaphopods are all the results of host-switching. For the vertebrates. infections of agnathans and chondrichthyans are apparently the result of host-switching from teleosts. For digenean families the ratio of orders of fishes infected to superfamilies of molluscs infected ranges from 0.5 (Mesometridae) to 16 (Bivesiculidae) and has a mean of 5.6. Individual patterns of host association of 13 dipenean families and superfamilies are reviewed. Two, Bucephalidae and Sanguinicolidae. are exceptional in infecting a range of first intermediate hosts qualitatively as broad as their range of definitive hosts. No well-studied taxon shows narrower association with vertebrate than with mollusc clades. The range of definitive hosts of digeneans is characteristically defined by eco-physiological similarity rather than phylogenetic relationship. The range of associations of digenean families with mollusc taxa is generally much narrower. These data are considered in the light of ideas about the significance of different forms of host association. If Manter's Second Rule (the longer the association with a host group, the mure pronounced the specificity exhibited by the parasite group) is invoked, then the data may suggest that the Digenea first parasitised molluscs before adopting vertebrate hosts. This interpretation is consistent with most previous ideas about the evolution of the Digenea but contrary to current interpretations based on the monophyly of the Neodermata. The basis of Manter's Second Rule is. however, considered too flimsy for this interpretation to be robust. Problems of the inference of the evolution of patterns of parasitism in the Neodermata al-e discussed and considered so intractable that the truth may be presently unknowable. (C) 2001 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.

The trematodes of groupers (Serranidae : Epinephelinae) knowledge, nature and evolution

Groupers (Epinephelinae) are prominent marine fishes distributed in the warmer waters of the world. Review of the literature suggests that trematodes are known from only 62 of the 159 species and only 9 of 15 genera; nearly 90% of host-parasite combinations have been reported only once or twice. All 20 families and all but 7 of 76 genera of trematodes found in epinephelines also occur in non-epihephelines. Only 12 genera of trematodes are reported from both the Atlantic-Eastern Pacific and the Indo-West Pacific. Few (perhaps no) species are credibly cosmopolitan but some have wide distributions across the Indo-West Pacific. The hierarchical 'relatedness' of epinephelines as suggested by how they share trematode taxa (families, genera, species) shows little congruence with what is known of their phylogeny. The major determinant of relatedness appears to be geographical proximity. Together these attributes suggest that host-parasite coevolution has contributed little to the evolution of trematode communities of epinephelines. Instead, they appear to have arisen through localized episodes of host-switching, presumably both into and out of the epinephelines. The Epinephelinae may well be typical of most groups of marine fishes both in the extent to which their trematode parasites are known and in that, apparently, co-evolution has contributed little to the evolution of their communities of trematodes.

Trematode life cycles: short is sweet

Complex life cycles are a hallmark of parasitic trematodes. In several trematode taxa, however, the life cycle is truncated: fewer hosts are used than in a typical three-host cycle, with fewer transmission events. Eliminating one host from the life cycle can be achieved in at least three different ways. Some trematodes show even more extreme forms of life cycle abbreviations, using only a mollusc to complete their cycle, with or without sexual reproduction. The occurrence of these phenomena among trematode families are reviewed here and show that life cycle truncation has evolved independently many times in the phylogeny of trematodes. The hypotheses proposed to account for life-cycle truncation, in addition to the factors preventing the adoption of shorter cycles by all trematodes are also discussed. The study of shorter life cycles offers an opportunity to understand the forces shaping the evolution of life cycles in general.

Cleaner fish become hosts: a novel form of parasite transmission

Adult bucephalid trematodes (Digenea) generally only occur in piscivorous fish. Within labrid fishes they are very rare, however, we have found them in labrid cleaner fish that feed on the ectoparasites of fish. We surveyed 969 labrid fishes from the tropical Pacific and found bucephalids only in cleaners (Lahroides dimidiatus, L. bicolor, and Bodianus axillaris) and none in piscivores. The prevalences of bucephalids in L. dimidiatus at Lizard Island, Heron Island, Orpheus Island (all on the Great Barrier Reef), New Caledonia, and Moorea (French Polynesia) were 51, 47, 67, 56, and 67%, respectively. All of the L. bicolor examined from Moorea were infected. Bucephalids were highly prevalent in all size classes of L. dimidiatus from Lizard Island. Bucephalids were found in a 1.6-cm long juvenile L. dimidiatus, in which, piscivory is highly unlikely. We examined the literature on the worldwide bucephalid fauna in labrids and all hosts were found to be cleaners (Symphodus tinca, S. mediterraneus, L. dimidiatus, L. bicolor, and Bodianus axillaris) except Notolabrus parilus, whose ecology is unknown. We suggest that cleaners eat bucephalid metacercariae directly from the exterior surface of client fish during cleaning interactions. This is the first evidence of digeneans in the diet of L. dimidiatus, and the first study to show this novel form of parasite transmission where infective stages are eaten as a result of cleaning behaviour. Cleaning-mediated parasite transmission may result in behavioural modification of second intermediate hosts because clients and parasites both benefit from transmission. If the infection is costly to cleaners and acquired during cheating behaviour, then this parasite might regulate mutualism. Alternatively, if infective stages are targeted, infection by these bucephalids may be a negative consequence of an honest foraging strategy.

First report of a bucephalid digenean from an apogonid teleost: Prosorhynchoides apogonis n. sp from Cheilodipterus macrodon on the southern Great Barrier Reef, Australia

Prosorhynchoides apogonis n. sp. (Digenea: Bucephalidae) is described from the intestine of the apogonid Cheilodipterus macrodon on the southern Great Barrier Reef, Australia. The new species is differentiated from other species of Prosorhynchoides Dollfus, 1929 by the configuration of its digestive system, shape and distribution of its vitelline follicles, and the shape and extent of its uterus. This is the first bucephalid to be described from the teleost family Apogonidae, and our records suggest that this species is strongly host-specific, at least to the genus Cheilodipterus. The host family is consistent with the pattern of Prosorhynchoides being reported from a very wide range of piscivorous fish families. As a result of comparisons made in the description of this species, 18 species formerly included in Bucephaloides Hopkins, 1954, Bucephalopsis Diesing, 1855 and Neobucephalopsis Dayal, 1948 are transferred to Prosorhynchoides, 16 as new combinations and two as replacement names to prevent secondary homonymy.

The use and implications of ribosomal DNA sequencing for the discrimination of digenean species

In just over a decade, the use of molecular approaches for the recognition of parasites has become commonplace. For trematodes, the internal transcribed spacer region of ribosomal DNA (ITS rDNA) has become the default region of choice. Here, we review the findings of 63 studies that report ITS rDNA sequence data for about 155 digenean species from 19 families, and then review the levels of variation that have been reported and how the variation has been interpreted. Overall, complete ITS sequences (or ITS1 or ITS2 regions alone) usually distinguish trematode species clearly, including combinations for which morphology gives ambiguous results. Closely related species may have few base differences and in at least one convincing case the ITS2 sequences of two good species are identical. In some cases, the ITS1 region gives greater resolution than the ITS2 because of the presence of variable repeat units that are generally lacking in the ITS2. Intraspecific variation is usually low and frequently apparently absent. Information on geographical variation of digeneans is limited but at least some of the reported variation probably reflects the presence of multiple species. Despite the accepted dogma that concerted evolution makes the individual representative of the entire species, a significant number of studies have reported at least some intraspecific variation. The significance of such variation is difficult to assess a posteriori, but it seems likely that identification and sequencing errors account for some of it and failure to recognise separate species may also be significant. Some reported variation clearly requires further analysis. The use of a yardstick to determine when separate species should be recognised is flawed. Instead, we argue that consistent genetic differences that are associated with consistent morphological or biological traits should be considered the marker for separate species. We propose a generalised approach to the use of rDNA to distinguish trematode species.

An exceptionally rich complex of Sanguinicolidae von Graff, 1907 (Platyhelminthes : Trematoda) from Siganidae, Labridae and Mullidae (Teleostei : Perciformes) from the Indo-West Pacific Region

We describe an unprecedented radiation of sanguinicolid blood flukes ( Digenea: Sanguinicolidae) from two species of Labridae (Choerodon venustus and C. cauteroma), seven species of Mullidae (Mulloidichthys vanicolensis, Parupeneus barberinoides, P. barberinus, P. bifasciatus, P. cyclostomus, P. indicus and P. multifasciatus) and ten species of Siganidae (Siganus argenteus, S. corallinus, S. doliatus, S. fuscescens, S. lineatus, S. margaritiferus, S. puellus, S. punctatus, S. virgatus and S. vulpinus) from sites off Australia and Palau. The flukes were morphologically similar in having the combination of a long thread-like body, tegumental spines in lateral transverse rows, a vestigial oral sucker bearing concentric rows of fine spines, an H-shaped intestine, a cirrussac, a notch level with the male genital pore, a lateral or post-ovarian uterus, a uterine chamber and separate genital pores. These species are divided into two genera on the basis of testis number. Sanguinicolids from Siganus fuscescens have a single large testis between the intestinal bifurcation and the ovary and are placed in Ankistromeces Nolan & Cribb, 2004. Species from the remaining nine species of Siganidae, Labridae and Mullidae are placed in Phthinomita n. g.; these species have two testes, the anterior testis being large and between the intestinal bifurcation and the ovary whereas the small posterior testis is at the posterior end of the body and appears rudimentary or degenerate and probably non-functional. The second internal transcribed spacer (ITS2) of ribosomal DNA ( rDNA) from 29 host/parasite/location combinations (h/p/l) was sequenced together with that of Ankistromeces mariae Nolan & Cribb, 2004 for comparison. From 135 samples we found 19 distinct genotypes which were interpreted as representing at least that many species. Replicate sequences were obtained for 25 of 30 h/p/l combinations ( including A. mariae); there was no intraspecific variation between replicates sequences for any of these. Interspecific variation ranged from 1 - 41 base differences (0.3 - 12.7% sequence divergence). The 19 putative species were difficult to recognise by morphological examination. We describe 13 new species; we do not describe (= name) six species characterised solely by molecular sequences and three putative species for which morphological data is available but for which molecular data is not. We have neither morphological nor molecular data for sanguinicolids harboured in five hosts species ( Siganus margaritiferus, S. puellus, Choerodon cauteroma, Parupeneus indicus and P. multifasciatus) in which we have seen infections. Where host species were infected in different localities they almost always harboured distinct species. Some host species ( for example, S. argenteus and S. lineatus from Lizard Island) harboured two or three species in a single geographical location. This suggests that, for parts of this system, parasite speciation has outstripped host speciation. Distance analysis of ITS2 showed species from each host family ( Siganidae, Mullidae and Labridae) did not form monophyletic clades to the exclusion of species from other host families. However, a host defined clade was formed by the sequences from sanguinicolids from S. fuscescens.