Host-parasite associations on a coral reef: pomacentrid fishes and digenean trematodes

Evidence for two morphologically cryptic species of Hysterolecitha Linton, 1910 (Trematoda: Lecithasteridae) infecting overlapping host ranges in Moreton Bay, Australia

Integration of morphological and molecular approaches to species delineation has become an essential part of digenean trematode taxonomy, particularly when delimiting cryptic species. Here, we use an integrated approach to distinguish and describe two morphologically cryptic species of Hysterolecitha Linton, 1910 (Trematoda: Lecithasteridae) from fishes of Moreton Bay, Queensland, Australia. Morphological analyses of Hysterolecitha specimens from six fish species demonstrated a complete overlap in morphometric data with no reliable differences in their gross morphological characters that suggested the presence of more than one species. Distinctions in ITS2 rDNA and cox1 mtDNA sequence data for corresponding specimens suggested the presence of two forms. A principal component analysis on an imputed dataset showed clear separation between the two forms. These two forms are partially separated on the basis of their host's identity. Therefore, we describe two morphologically cryptic species: Hysterolecitha melae n. sp. from three species of Abudefduf Forsskål and one species of Parma Günther (Pomacentridae), with the Bengal sergeant, Abudefduf bengalensis (Bloch), as the type-host; and Hysterolecitha phisoni n. sp. from species of Pomacentridae (including A. bengalensis), Pomatomidae and Siganidae, with the black rabbitfish, Siganus fuscescens (Houttuyn), as the type-host.

Variation in the parasite communities of three co-occurring herbivorous coral reef fishes

Parasites are important, diverse, and abundant components of natural ecosystems and can influence the behaviour and health of their hosts, inter- and intraspecific interactions, and ultimately community structure. Coral reefs are one of the world's most biodiverse ecosystems, yet our understanding of the abundance, diversity, and composition of parasite communities of coral reef fishes is limited. Here, the authors aimed to compare the abundance, richness and composition of parasite communities among three co-occurring herbivorous coral reef fishes (the barred rabbitfish Siganus doliatus, Ward's damsel Pomacentrus wardi and the obscure damsel Pomacentrus adelus) from an inshore reef of the Great Barrier Reef (GBR). In total, 3978 parasites (3869 endoparasites and 109 ectoparasites) from 17 families were recovered from 30 individuals of each of the three fish species (mean = 44 ± 22 s.e. parasites per fish; range = 0-1947 parasites per fish). The parasite communities of P. wardi and P. adelus were characterised by pennellid copepods, derogenid and lecithasterid digeneans and were distinct from those of S. doliatus that were characterised by a higher abundance of atractotrematid and gyliauchenid digeneans. The abundance and family richness of all parasites were greatest in S. doliatus (abundance: 22.1 ± 5.0 parasites per fish; richness: 3.2 ± 0.3 families per fish), intermediate in P. wardi (abundance: 4.8 ± 1.1 parasites per fish; richness: 2.3 ± 0.3 families per fish) and lowest in P. adelus (abundance: 1.4 ± 0.4 parasites per fish; richness: 0.9 ± 0.2 families per fish). Similarly, the abundance of endoparasites was greatest in S. doliatus (19.7 ± 5.1 endoparasites per fish), intermediate in P. wardi (2.6 ± 0.7 endoparasites per fish) and lowest in P. adelus (1.2 ± 0.4 endoparasites per fish). Ectoparasite abundances were also lowest for P. adelus (0.2 ± 0.1 ectoparasites per fish), and S. doliatus and P. wardi had comparable abundances of ectoparasites (1.3 ± 0.3 and 2.1 ± 0.5 parasites per fish, respectively). Similarities between the parasite assemblages of the two pomacentrids may be related to their similar behaviours and/or diets vs. those of the larger-bodied and more mobile rabbitfish. Investigating the causes and consequences of variation in parasite communities across a broader range of fish species will be critical to understand the potential role of parasites in coral reef ecosystems.

A new species, new host records and life cycle data for lepocreadiids (Digenea) of pomacentrid fishes from the Great Barrier Reef, Australia

A new species of lepocreadiid, Opechonoides opisthoporus n. sp., is described infecting 12 pomacentrid fish species from the Great Barrier Reef, Australia, with Abudefduf whitleyi Allen & Robertson as the type-host. This taxon differs from the only other known member of the genus, Opechonoides gure Yamaguti, 1940, in the sucker width ratio, cirrus-sac length, position of the testes, position of the pore of Laurer's canal, and relative post-testicular distance. The new species exhibits stenoxenic host-specificity, infecting pomacentrids from seven genera: Abudefduf Forsskål, Amphiprion Bloch & Schneider, Neoglyphidodon Allen, Neopomacentrus Allen, Plectroglyphidodon Fowler & Ball, Pomacentrus Lacépède and Stegastes Jenyns. Phylogenetic analyses of 28S rDNA sequence data demonstrate that O. opisthoporus n. sp. forms a strongly supported clade with Prodistomum orientale (Layman, 1930) Bray & Gibson, 1990. The life cycle of this new species is partly elucidated on the basis of ITS2 rDNA sequence data; intermediate hosts are shown to be three species of Ctenophora. New host records and molecular data are reported for Lepocreadium oyabitcha Machida, 1984 and Lepotrema amblyglyphidodonis Bray, Cutmore & Cribb, 2018, and new molecular data are provided for Lepotrema acanthochromidis Bray, Cutmore & Cribb, 2018 and Lepotrema adlardi (Bray, Cribb & Barker, 1993) Bray & Cribb, 1996. Novel cox1 mtDNA sequence data showed intraspecific geographical structuring between Heron Island and Lizard Island for L. acanthochromidis but not for L. adlardi or O. opisthoporus n. sp.

Lepotrema Ozaki, 1932 (Lepocreadiidae: Digenea) from Indo-Pacific fishes, with the description of eight new species, characterised by morphometric and molecular features

We review species of the genus Lepotrema Ozaki, 1932 from marine fishes in the Indo-West Pacific. Prior to the present study six species were recognised. Here we propose eight new species on the basis of combined morphological and molecular analysis: Lepotrema acanthochromidis n. sp. ex Acanthochromis polyacanthus from the Great Barrier Reef (GBR); Lepotrema hemitaurichthydis n. sp. ex Hemitaurichthys polylepis and H. thompsoni from Palau and French Polynesia; Lepotrema melichthydis n. sp. ex Melichthys vidua from Palau and the GBR; Lepotrema amansis n. sp. ex Amanses scopas from the GBR; Lepotrema cirripectis n. sp. ex Cirripectes filamentosus, C. chelomatus and C. stigmaticus from the GBR; Lepotrema justinei n. sp. ex Sufflamen fraenatum from New Caledonia; Lepotrema moretonense n. sp. ex Prionurus microlepidotus, P. maculatus and Selenotoca multifasciata from Moreton Bay; and Lepotrema amblyglyphidodonis n. sp. ex Amblyglyphidodon curacao and Amphipron akyndynos from the GBR. We also report new host records and provide novel molecular data for two known species: Lepotremaadlardi Bray, Cribb & Barker, 1993 and Lepotremamonile Bray & Cribb, 1998. Two new combinations are formed, Lepotrema cylindricum (Wang, 1989) n. comb. (for Preptetos cylindricus) and Lepotrema navodonis (Shen, 1986) n. comb. (for Lepocreadium navodoni). With the exception of a handful of ambiguous records, the evidence is compelling that the host-specificity of species in this genus is overwhelmingly oioxenous or stenoxenous. This renders the host distribution in three orders and ten families especially difficult to explain as many seemingly suitable hosts are not infected. Multi-loci molecular data (ITS2 rDNA, 28S rDNA and cox1 mtDNA) demonstrate that Lepotrema is a good generic concept, but limited variability in sequence data and differences in phylogenies produced for different gene regions make relationships within the genus difficult to define.

Economic costs of protistan and metazoan parasites to global mariculture

Parasites have a major impact on global finfish and shellfish aquaculture, having significant effects on farm production, sustainability and economic viability. Parasite infections and impacts can, according to pathogen and context, be considered to be either unpredictable/sporadic or predictable/regular. Although both types of infection may result in the loss of stock and incur costs associated with the control and management of infection, predictable infections can also lead to costs associated with prophylaxis and related activities. The estimation of the economic cost of a parasite event is frequently complicated by the complex interplay of numerous factors associated with a specific incident, which may range from direct production losses to downstream socio-economic impacts on livelihoods and satellite industries associated with the primary producer. In this study, we examine the world's major marine and brackish water aquaculture production industries and provide estimates of the potential economic costs attributable to a range of key parasite pathogens using 498 specific events for the purposes of illustration and estimation of costs. This study provides a baseline resource for risk assessment and the development of more robust biosecurity practices, which can in turn help mitigate against and/or minimise the potential impacts of parasite-mediated disease in aquaculture.

Pseudobacciger cheneyae n. sp. (Digenea: Gymnophalloidea) from Weber's chromis (Chromis weberi Fowler & Bean) (Perciformes: Pomacentridae) at Lizard Island, Great Barrier Reef, Australia

A new species of digenean, Pseudobacciger cheneyae n. sp., is described from the intestines of Weber's chromis (Chromis weberi Fowler & Bean) from off Lizard Island, Great Barrier Reef, Australia. This species differs from the three described species of Pseudobacciger Nahhas & Cable, 1964 [P. cablei Madhavi, 1975, P. harengulae Yamaguti, 1938 and P. manteri Nahhas & Cable, 1964] in combinations of the size of the suckers and the length of the caeca. The host of the present species is a perciform (Family Pomacentridae) which contrasts with previous records of the genus which are almost exclusively from clupeiform fishes. The genus Pseudobacciger is presently recognised within the family Faustulidae (Poche, 1926) but phylogenetic analyses of 28S and ITS2 rDNA show that the new species bears no relationship to species of four other faustulid genera (Antorchis Linton, 1911, Bacciger Nicoll, 1924, Paradiscogaster Yamaguti, 1934 and Trigonocryptus Martin, 1958) but that instead it is nested within the Gymnophalloidea (Odhner, 1905) as sister to the Tandanicolidae (Johnston, 1927). This result suggests that the Faustulidae is polyphyletic.

Selection from parasites favours immunogenetic diversity but not divergence among locally adapted host populations

The unprecedented polymorphism in the major histocompatibility complex (MHC) genes is thought to be maintained by balancing selection from parasites. However, do parasites also drive divergence at MHC loci between host populations, or do the effects of balancing selection maintain similarities among populations? We examined MHC variation in populations of the livebearing fish Poecilia mexicana and characterized their parasite communities. Poecilia mexicana populations in the Cueva del Azufre system are locally adapted to darkness and the presence of toxic hydrogen sulphide, representing highly divergent ecotypes or incipient species. Parasite communities differed significantly across populations, and populations with higher parasite loads had higher levels of diversity at class II MHC genes. However, despite different parasite communities, marked divergence in adaptive traits and in neutral genetic markers, we found MHC alleles to be remarkably similar among host populations. Our findings indicate that balancing selection from parasites maintains immunogenetic diversity of hosts, but this process does not promote MHC divergence in this system. On the contrary, we suggest that balancing selection on immunogenetic loci may outweigh divergent selection causing divergence, thereby hindering host divergence and speciation. Our findings support the hypothesis that balancing selection maintains MHC similarities among lineages during and after speciation (trans-species evolution).

PACo: a novel procrustes application to cophylogenetic analysis

We present Procrustean Approach to Cophylogeny (PACo), a novel statistical tool to test for congruence between phylogenetic trees, or between phylogenetic distance matrices of associated taxa. Unlike previous tests, PACo evaluates the dependence of one phylogeny upon the other. This makes it especially appropriate to test the classical coevolutionary model that assumes that parasites that spend part of their life in or on their hosts track the phylogeny of their hosts. The new method does not require fully resolved phylogenies and allows for multiple host-parasite associations. PACo produces a Procrustes superimposition plot enabling a graphical assessment of the fit of the parasite phylogeny onto the host phylogeny and a goodness-of-fit statistic, whose significance is established by randomization of the host-parasite association data. The contribution of each individual host-parasite association to the global fit is measured by means of jackknife estimation of their respective squared residuals and confidence intervals associated to each host-parasite link. We carried out different simulations to evaluate the performance of PACo in terms of Type I and Type II errors with respect to two similar published tests. In most instances, PACo performed at least as well as the other tests and showed higher overall statistical power. In addition, the jackknife estimation of squared residuals enabled more elaborate validations about the nature of individual links than the ParaFitLink1 test of the program ParaFit. In order to demonstrate how it can be used in real biological situations, we applied PACo to two published studies using a script written in the public-domain statistical software R.

Taxonomic approaches to and interpretation of host specificity of trematodes of fishes: lessons from the Great Barrier Reef

The taxonomy of trematodes of Great Barrier Reef (GBR) fishes has been studied in some detail for over 20 years. Understanding of the fauna has been informed iteratively by approaches to sampling, understanding of morphology, the advent of molecular methodology and a feed-back loop from the emergent understanding of host specificity. Here we analyse 658 host-parasite combinations for 290 trematode species, 152 genera and 28 families from GBR fishes. These are reported from 8 orders, 38 families, 117 genera and 243 species of fishes. Of the 290 species, only 4 (1·4%) have been reported from more than one order of fishes and just 23 (7·9%) infect more than one family; 77·9% of species are known from only one genus, and 60% from only one species of fish. Molecular studies have revealed several complexes of cryptic species and others are suspected; we conclude that no euryxenous host distribution should be accepted on the basis of morphology only. The occurrence of individual trematode species in potential hosts is patchy and difficult to predict reliably a priori or explain convincingly a posteriori. These observations point to the need for a vigorous iterative interaction between the accretion of host specificity data and its interpretation.

Bivalvulidan (Myxozoa: Myxosporea) parasites of damselfishes with description of twelve novel species from Australia's Great Barrier Reef

Bivalvulidan parasites from the gall bladder of 31 species of damselfishes (family Pomacentridae) were examined for their taxonomic identity and their relatedness to other species of myxozoans. This paper describes 11 novel ceratomyxid species and a novel Myxidium sp. Each species is characterized morphologically and small subunit (SSU) rDNA sequences were used in molecular phylogenetic analyses. Five pomacentrid species were found to harbour multiple infections of bivalvulidan species. One species of Ceratomyxa and Myxidium were found to infect more than a single species of damselfish. Phylogenetic analyses revealed there has been no radiation of ceratomyxids that can be associated with the fish host taxon and that Myxidium queenslandicus n.sp. was more closely related to Zschokkella mugilis and Ellipsomyxa gobii than other members of the genus Myxidium.

Resource predictability and host specificity in fleas: the effect of host body mass

Ecological specialization is hypothesized to result from the exploitation of predictable resource bases. For parasitic organisms, one prediction is that parasites of large-bodied host species, which tend to be long-lived, should specialize on these hosts, whereas parasites of small host species, which represent more ephemeral and less predictable resources, should become generalists. We tested this prediction by quantifying the association between the level of host specificity of fleas and the mean body mass of their mammalian hosts, using published data from 2 large, distinct geographical regions (South Africa and northern North America). In general, we found supporting evidence that flea host specificity, measured either as the number of host species exploited or their taxonomic distinctness, became more pronounced with increasing host body mass. There were, however, some discrepancies among the results depending on the different measures of host specificity, the geographical region studied, or whether we used the raw values or phylogenetically independent contrasts. These are discussed with respect to other forces acting on the evolution of host specificity in parasites, as well as in the context of the regions' contrasting evolutionary histories. Overall, though, our findings indicate that the exploitation of large-bodied, and therefore long-lived, host species has promoted specialization in fleas, most likely because these hosts represent predictable resources.

Latitudinal differences in species and community richness and in community structure of metazoan endo- and ectoparasites of marine teleost fish

Relative species diversity of gastrointestinal helminths of 55 teleost fish species did not differ significantly at different latitudes, whereas relative species diversity of metazoan ectoparasites on the heads and gills of 108 teleost fish species showed a significant increase with decreasing latitude and from deep to surface waters. Abundance of endoparasites also was the same at all latitudes, whereas abundance of ectoparasites increased with decreasing latitude and from deep to shallow waters. A comparative analysis using phylogenetically independent contrasts supported these conclusions. Possible reasons for the differences between endo- and ectoparasites are discussed. A detailed analysis of the community structure of gastrointestinal helminths of five Antarctic and three tropical teleosts and of metazoan ectoparasites on the heads and gills of five Antarctic and seven tropical fish species showed the following: abundance and prevalence of infection of endoparasites are similar in Antarctic and tropical fish, but are much greater for tropical than for Antarctic ectoparasites. Relative species diversity of endoparasites is similar for Antarctic and tropical endoparasites, but much greater for tropical than Antarctic ectoparasites. In both Antarctic and tropical fish, different fish of the same species may have different dominant species of endo- and ectoparasites, although there is a greater range of dominant species of tropical ectoparasites, a consequence of the greater species pool available. The most dominant parasite (irrespective of species) represented 80-99% of all endoparasites of Antarctic, and about 50-80% of all endoparasites of tropical fish. The most dominant parasites (irrespective of species) represented about 90-100% of all ectoparasites of Antarctic, and about 20-70% of all ectoparasites of tropical fish, the difference a consequence of the greater species pool of tropical ectoparasites available. The data suggest that both endo- and ectoparasites live in assemblages not structured by interspecific competition.

The evolutionary expansion and host-parasite relationships of the Digenea

Relevant data on the Digenea extracted from a host-parasite data-base are analysed in relation to host-groups, host-specificity, speciation, radiation and geographical distribution. The classification, evolution, co-evolution, and co-speciation of the group are discussed. Principal components analyses indicated that 119 families formed 11 groups in relation to their vertebrate hosts and the 55 families with molluscan records formed 6 groups in relation to their molluscan hosts. The most prominent host-groups are the Fish and Mammals. Individual digenean families did not exhibit the host combinations Fish+Birds, Fish+Mammals, Herpetiles+Birds and Herpetiles+Mammals. Families with Fish hosts tended to use Prosobranch and, to a lesser extent Bivalve, molluscs, whereas families in Herpetiles, Birds and Mammals tended to use Pulmonates. Families using 3 or 4 mixed vertebrate groups tended to use mixed molluscan groups. Families using Herpetiles as the vertebrate host tend to be the most host-specific and the least speciose, whereas those using 3 to 4 mixed vertebrate groups are the most speciose. In a detailed examination of three zoogonid genera, few indications of co-evolution with their vertebrate hosts were detected, and geographical information from the data-base appeared to shed no light upon the geographical origins of the Digenea. Some of these findings are commented upon in relation to the evolution of the Digenea.