Taxonomic and geographic bias in the genetic study of helminth parasites

Integrative taxonomy of metazoan parasites of the bluntnose sixgill shark Hexanchus griseus (Bonnaterre, 1788) in the Mediterranean Sea, with the resurrection of Grillotia acanthoscolex Rees, 1944 (Cestoda: Trypanorhyncha)

Appropriate diagnoses of parasites of apex marine predators are crucial to understand their biodiversity, host specificity, biogeography, and life cycles. Such diagnoses are also informative of ecological and biological characteristics of both host and environment in which the hosts and their parasites live. We here (i) investigate the parasite fauna of a bluntnose sixgill shark Hexanchus griseus (Bonnaterre, 1788) obtained from the Gulf of Naples (Tyrrhenian Sea), (ii) characterize molecularly all its metazoan parasites, and (iii) resurrect and report the main morphological features and phylogenetic position of Grillotia acanthoscolex, a cestode species previously synonymized with Grillotia adenoplusia. A rich parasite fauna represented by eight different taxa was found, including two monogeneans (Protocotyle grisea and Protocotyle taschenbergi), one digenean (Otodistomum veliporum), four cestodes (Crossobothrium dohrnii, Clistobothrium sp., G. acanthoscolex, and G. adenoplusia), and one copepod (Protodactylina pamelae). Sequencing of these samples accounts for an important molecular baseline to widen the knowledge on the parasitic fauna of bluntnose sixgill sharks worldwide and to reconstruct their correct food chains. The bluntnose sixgill shark was found to be a definitive host for all endoparasites found here, confirming that it occupies an apex trophic level in the Mediterranean Sea. The taxa composition of the trophic parasite fauna confirms that the bluntnose sixgill shark mostly feeds on teleost fish species. However, the occurrence of two phillobothrid cestodes (C. dohrnii and Clistobothrium sp.) suggests that it also feeds on squids. Finally, we emphasize the importance of using integrative taxonomic approaches in the study of parasites from definitive and intermediate hosts to elucidate biology and ecology of taxa generally understudied in the Mediterranean Sea.

NEW RECORDS OF HELMINTHS OF THE JAGUAR IN MEXICO, WITH AN UPDATED LIST OF SPECIES IN THE AMERICAS

An inventory of parasites infecting the jaguar (Panthera onca) across its distribution range is relevant for the conservation of this threatened big cat. In this study, we report the occurrence of helminths in a jaguar from Mexico using morphological techniques (cleared and stained mounts and scanning electron microscopy) and partial sequences of the 28S ribosomal RNA (28S rRNA) gene and the cytochrome c oxidase 1 mitochondrial (COI) gene. We also provide an updated list of helminth species reported in jaguars in the Americas. Three helminth taxa are identified in the jaguar examined from Mexico: Toxocara cati, Physaloptera sp., and Taenia sp. The new 28S rRNA sequences of To. cati, Physaloptera sp., and Taenia sp. and the COI sequence of Taenia sp. corroborate the identity of the helminths isolated from this host. One hundred and twenty-nine records of helminths parasitizing jaguars from 49 studies up to May 2023 were identified in the Americas. In most of these studies (73.6%), helminths were identified using coproparasitological techniques. Sixteen helminths (7 nematodes, 5 cestodes, 3 acanthocephalans, and 1 trematode) were identified at the species level in free-ranging and captive jaguars. The study demonstrates the value of an integrative taxonomy approach to increase the accuracy of parasite identification in wildlife, especially when helminth specimens are scarce or poorly fixed.

Phylogenetic Relationships of Avian Cestodes from Brine Shrimp and Congruence with Larval Morphology

Determining molecular markers for parasites provides a useful tool for their identification, particularly for larval stages with few distinguishable diagnostic characters. Avian cestodes play a key role in the food webs and biodiversity of hypersaline wetlands, yet they remain understudied. Using naturally infected Artemia, we identified cestode larvae (cysticercoids), assessed their genetic diversity, and explored phylogenetic relationships in relation to larval morphology and waterbird final hosts. We obtained partial 18S rDNA sequences for 60 cysticercoids of the family Hymenolepidae infecting Artemia spp. from seven localities and three countries (Spain, the USA, and Chile). We present the first DNA sequences for six taxa: Confluaria podicipina, Fimbriarioides sp., Flamingolepis liguloides, Flamingolepis sp. 1, Flamingolepis sp. 2, and Hymenolepis californicus. Intraspecific sequence variation (0.00-0.19% diversity) was lower than intergroup genetic distance (0.7-14.75%). Phylogenetic analysis revealed three main clades: 1-Flamingolepis, 2-Fimbriarioides, 3-Confluaria and Hymenolepis, all of which separated from hymenolepidids from mammals and terrestrial birds. This clear separation among taxa is congruent with previous morphological identification, validating the 18S gene as a useful marker to discriminate at generic/species level. Working with intermediate hosts allows the expansion of knowledge of taxonomic and genetic diversity of cestodes in wildlife, as well as elucidation of their life cycles.

Fish endoparasite metacommunity in environments with different degrees of conservation in the western Brazilian Amazon

Parasite communities correspond to the definition of metacommunity, as species interact and disperse within hosts. The present study evaluated parasite metacommunities in a tropical floodplain. The study was conducted in the Western Amazon around the municipalities of Cruzeiro do Sul, state of Acre, and Guajará, state of Amazonas, Brazil. Six sampling sites were selected and grouped into conserved and degraded environments. Fish were caught between periods of drought and flood, using passive and active sampling methods; in the laboratory, they were measured weighed, and necropsied. Parasites found were fixed, evaluated, and identified. Physical and chemical variables and environmental conservation characteristics were measured in all sites. Diversity index, ANOVA, Tukey, local contribution to beta diversity (LCBD), species contribution to beta diversity by individual species (SCBD), and variance partitioning were summarized. The α species diversity increased in conserved environments and varied between seasonal periods, mainly in detritivorous and omnivorous hosts. Local contributions to beta diversity showed significantly higher values in conserved environments for the endoparasite fauna of piscivorous and omnivorous hosts, indicating that these environments presented unique parasite infracommunities and revealing the conservation status of these environments. Variations in infracommunities were explained mainly by niche-based processes, including environmental conditions, degree of conservation, and host characteristics. Thus, these data will serve as a tool to understand the way parasite communities are structured, which is important information for the management and conservation of aquatic environments.

First Record of the Elusive Ant Parasitoid Horismenus floridensis (Hymenoptera: Eulophidae) in Mexico and New Association with an Ant Host

Most eulophid wasps are primary parasitoids, mainly of endophytic insect larvae (Diptera, Coleoptera, Lepidoptera, Hymenoptera, Hemiptera, and Thysanoptera), but can also attack spider eggs, gall-forming mites, or nematodes. A few species are known to parasitize ants. Here we report on the occurrence of Horismenus floridensis (Schauff and Bouček) attacking Camponotus atriceps (Smith) in southern Mexico (Campeche), expanding the distribution for this eulophid species and the range of its potential hosts. We also provide an updated list of the Horismenus Walker species found in Mexico, which currently includes 21 identified species. This is the second host ant ever recorded for H. floridensis and the first reliable record of C. atriceps as a host for this eulophid wasp. The first host ant reported from Florida 35 years ago was the closely related valid species, C. floridanus (Buckley), erroneously synonymized at that time with C. atriceps (formerly, C. abdominalis (Fabricius)).

Survey on helminths of bats in the Yucatan Peninsula: infection levels, molecular information and host-parasite networks

Helminth species of Neotropical bats are poorly known. In Mexico, few studies have been conducted on helminths of bats, especially in regions such as the Yucatan Peninsula where Chiroptera is the mammalian order with the greatest number of species. In this study, we characterized morphologically and molecularly the helminth species of bats and explored their infection levels and parasite–host interactions in the Yucatan Peninsula, Mexico. One hundred and sixty-three bats (representing 21 species) were captured between 2017 and 2022 in 15 sites throughout the Yucatan Peninsula. Conventional morphological techniques and molecular tools were used with the 28S gene to identify the collected helminths. Host–parasite network analyses were carried out to explore interactions by focusing on the level of host species. Helminths were found in 44 (26.9%) bats of 12 species. Twenty helminth taxa were recorded (7 trematodes, 3 cestodes and 10 nematodes), including 4 new host records for the Americas. Prevalence and mean intensity of infection values ranged from 7.1 to 100% and from 1 to 56, respectively. Molecular analyses confirmed the identity of some helminths at species and genus levels; however, some sequences did not correspond to any of the species available on GenBank. The parasite–host network suggests that most of the helminths recorded in bats were host-specific. The highest helminth richness was found in insectivorous bats. This study increases our knowledge of helminths parasitizing Neotropical bats, adding new records and nucleotide sequences.

Somewhere I belong: phylogeny and morphological evolution in a species-rich lineage of ectoparasitic flatworms infecting cichlid fishes

A substantial portion of biodiversity has evolved through adaptive radiation. However, the effects of explosive speciation on species interactions remain poorly understood. Metazoan parasites infecting radiating host lineages could improve our knowledge because of their intimate host relationships. Yet limited molecular, phenotypic and ecological data discourage multivariate analyses of evolutionary patterns and encourage the use of discrete characters. Here, we assemble new molecular, morphological and host range data widely inferred from a species-rich lineage of parasites (Cichlidogyrus, Platyhelminthes: Monogenea) infecting cichlid fishes to address data scarcity. We infer a multimarker (28S/18S rDNA, ITS1, COI mtDNA) phylogeny of 58 of 137 species and characterize major lineages through synapomorphies inferred from mapping morphological characters. We predict the phylogenetic position of species without DNA data through shared character states, a morphological phylogenetic analysis, and a classification analysis with support vector machines. Based on these predictions and a cluster analysis, we assess the systematic informativeness of continuous characters, search for continuous equivalents for discrete characters, and suggest new characters for morphological traits not analysed to date. We also model the attachment/reproductive organ and host range evolution using the data for 136 of 137 described species and multivariate phylogenetic comparative methods (PCMs). We show that discrete characters not only can mask phylogenetic signals, but also are key for characterizing species groups. Regarding the attachment organ morphology, a divergent evolutionary regime for at least one lineage was detected and a limited morphological variation indicates host and environmental parameters affecting its evolution. However, moderate success in predicting phylogenetic positions, and a low systematic informativeness and high multicollinearity of morphological characters call for a revaluation of characters included in species characterizations.

Phylum Nematoda: trends in species descriptions, the documentation of diversity, systematics, and the species concept

This paper summarizes the trends in nematode species description and systematics emerging from a comparison of the latest comprehensive classification and census of Phylum Nematoda (Hodda 2022a, b) with earlier classifications (listed in Hodda 2007).   It also offers some general observations on trends in nematode systematics emerging from the review of the voluminous literature used to produce the classification.   The trends in nematodes can be compared with developments in the systematics of other organisms to shed light on many of the general issues confronting systematists now and into the future.  

Dactylogyridae 2022: a meta-analysis of phylogenetic studies and generic diagnoses of parasitic flatworms using published genetic and morphological data

Dactylogyridae is one of the most studied families of parasitic flatworms with more than 1000 species and 166 genera described to date including ecto- and endoparasites. Dactylogyrid monogeneans were suggested as model organisms for host-parasite macroevolutionary and biogeographical studies due to the scientific and economic importance of some of their host lineages. Consequently, an array of phylogenetic research into different dactylogyrid lineages has been produced over the past years but the last family-wide study was published 16 years ago. Here, we provide a meta-analysis of the phylogenetic relationships of Dactylogyridae including representatives of all genera with available molecular data (n=67). First, we investigate the systematic informativeness of morphological characters widely used to diagnose dactylogyrid genera through a parsimony analysis of the characters, character mapping, and phylogenetic comparative methods. Second, we provide an overview of the current state of the systematics of the family and its subfamilies, and summarise potentially poly- and paraphyletic genera. Third, we elaborate on the implications of taxonomic, citation, and confirmation bias in past studies. Fourth, we discuss host range, biogeographical, and freshwater-marine patterns. We found two well-supported macroclades which we assigned to the subfamilies Dactylogyrinae and Ancyrocephalinae. These subfamilies further include 16 well-supported clades with only a few synapomorphies that could be deduced from generic diagnoses in the literature. Furthermore, few morphological characters considered systematically informative at the genus level display a strong phylogenetic signal. However, the parsimony analysis suggests that these characters provide little information on the relationships between genera. We conclude that a strong taxonomic bias and low coverage of DNA sequences and regions limit knowledge on morphological and biogeographical evolutionary patterns that can be inferred from these results. We propose addressing potential citation and confirmation biases through a 'level playing field' multiple sequence alignment as provided by this study.

A new species of Rhabdias (Nematoda: Rhabdiasidae), a lung parasite of Pristimantis chiastonotus (Anura: Strabomantidae) from the Brazilian Amazon: description and phylogenetic analyses

Rhabdias Stiles and Hassal, 1905 comprises approximately 90 species of parasitic lung nematodes of amphibians and reptiles that have a wide distribution, with 21 species occurring in the Neotropics. In the present study, we describe Rhabdias waiapi n. sp. found parasitizing the lungs of the anuran species Pristimantis chiastonotus from the Amazon Biome in the Amapá State, Northern Brazil. The new species is characterized by having an elongated body, expansions of the cuticular inflation in the anterior end that become more discrete along the body, an anterior end with a slight constriction at the level of the esophageal apex with four rounded subapical elevations of the body wall, six lips, four near the edge of the oral opening and two more distant lateral ones, and a gradually tapering elongated tail. In addition, molecular analyses and phylogenetic reconstructions were made, with sequences from the coding region of the mitochondrial cytochrome c oxidase subunit I gene. Those results strongly support the status of the new taxon, which formed a poorly supported clade with Rhabdias sp. 5 from Anolis brasiliensis from Northeast Brazil. Rhabdias waiapi n. sp. is the 19th species of the genus described in the Neotropics for amphibians, the 10th in Brazil, the second described from hosts of the family Strabomantidae from the Neotropical region, and the first amphibian nematode species described in the Amapá State.

Trade-Offs with Growth Limit Host Range in Complex Life-Cycle Helminths

AbstractParasitic worms with complex life cycles have several developmental stages, with each stage creating opportunities to infect additional host species. Using a data set for 973 species of trophically transmitted acanthocephalans, cestodes, and nematodes, we confirmed that worms with longer life cycles (i.e., more successive hosts) infect a greater diversity of host species and taxa (after controlling for study effort). Generalism at the stage level was highest for middle life stages, the second and third intermediate hosts of long life cycles. By simulating life cycles in real food webs, we found that middle stages had more potential host species to infect, suggesting that opportunity constrains generalism. However, parasites usually infected fewer host species than expected from simulated cycles, suggesting that generalism has costs. There was no trade-off in generalism from one stage to the next, but worms spent less time growing and developing in stages where they infected more taxonomically diverse hosts. Our results demonstrate that life-cycle complexity favors high generalism and that host use across life stages is determined by both ecological opportunity and life-history trade-offs.

A new species of Rhabdias (Nematoda: Rhabdiasidae), a lung parasite of Pseudopaludicola pocoto (Anura: Leptodactylidae) from north-eastern Brazil: description and phylogenetic analyses

Rhabdias pocoto n. sp. is herein described from the lungs of the swamp frog Pseudopaludicola pocoto Magalhães, Loebmann, Nogueira, Kokubum, Baptista, Haddad & Garda, 2014, from the Caatinga biome in the state of Ceará, in north-eastern Brazil. The new species is characterized by a body that dilates posteriorly, six small lips (protuberances) and two rounded lateral expansions of cuticular inflation on the anterior end, each containing an amorphous gland-like structure inside and a short and conical tail. Additionally, molecular analysis and comparison of the partial mitochondrial cytochrome c oxidase I sequence of R. pocoto n. sp. revealed genetic divergence between the new species and the sequences of Rhabdias spp. previously deposited in GenBank. Phylogenetic analysis grouped the new taxon into the R. pseudosphaerocephala species complex + R. glaurungi clade. The new discovery represents the 19th species of Rhabdias spp. described in the Neotropical region, the ninth in Brazil and the first species of Rhabdias found parasitizing South American frogs of the genus Pseudopaludicola, as well as the first Caatinga biome species of Rhabdias.

Macroevolutionary dynamics of parasite diversification: A reality check

Parasitism is often invoked as a factor explaining the variation in diversification rates across the tree of life, while also representing up to half of Earth's diversity. Yet, patterns and processes of parasite diversification remain mostly unknown. In this study, we assess the patterns of parasite diversification and specifically determine the role of life-history traits (i.e. life cycle complexity and host range) and major coevolutionary events in driving diversification across eight phylogenetic datasets spanning taxonomically different parasite groups. Aware of the degree of incomplete sampling among all parasite phylogenies, we also tested the impact of sampling bias on estimates of diversification. We show that the patterns and rates of parasite diversification differ among taxa according to life cycle complexity and to some extent major host transitions. Only directly transmitted parasites were found to be influenced by an effect of major host transitions on diversification rates. Although parasitism may be a main factor responsible for heterogeneity in diversification among the tree of life, the high degree of incomplete parasite phylogenies remains an obstacle when modelling diversification dynamics. Nevertheless, we provide the first comparative test of parasite diversification, revealing some consistent patterns and insight into the processes that shape it.

The state of fish parasite discovery and taxonomy: a critical assessment and a look forward

Efforts to find and characterise new parasite species in fish hosts are crucial not just to complete our inventory of Earth's biodiversity, but also to monitor and mitigate disease threats in fisheries and aquaculture in the face of global climate change. Here, we review recent quantitative assessments of research efforts into fish parasite discovery and taxonomy. We address broad questions including: Are efforts aimed at finding new parasite species targeted at geographical hotspots of fish biodiversity, where there should be more parasite species to be found? Is the application of molecular tools to study parasite genetic diversity deployed strategically across regions of the world, or focused disproportionately on certain areas? How well coordinated is the search for new parasite species of fish among workers specialising on different higher helminth taxa? Are parasite discovery efforts in any geographical area consistent over time, or subject to idiosyncrasies due to the waxing and waning of highly prolific research careers? Is the quality of taxonomic descriptions of new species improving over time, with the incorporation of new tools to characterise species? Are taxonomic descriptions moving away from a focus on the adult stage only toward attempts to characterise the full life cycle of newly-discovered helminth species? By using empirical evidence to answer these questions, we assess the current state of research into fish parasite discovery and taxonomy. We also explore the far-reaching implications of recent research on parasite microbiomes for parasite taxonomy. We end with recommendations aimed at maximising the knowledge gained per fish sacrificed, and per dollar and time invested into research on fish parasite biodiversity.

Morphological comparison of genetically differentiated Polymorphus cf. minutus types

In the present study, we analyzed the morphology of three genetic types of the bird-infecting acanthocephalan Polymorphus cf. minutus (PspT1, PspT2, PspT3), mainly based on the cystacanth-stage obtained from amphipods (Gammarus fossarum, Gammarus pulex, Gammarus roeselii, Echinogammarus spp.). Males and females were pooled as there was no considerable difference between the sexes concerning the hook measurements. Additionally, we conducted a laboratory infection of one domestic duck for each Polymorphus type, to compare their performance and localization in this host species, and to obtain adult specimens for morphological comparison. The recovery rate from the ducks 4 weeks after infection was 16% for PspT1, 23.8% for PspT2, and 25% for PspT3. The adult worms were gravid, and the females contained mature eggs. Hook size did not differ considerably between cystacanths and adults of the respective type. The three Polymorphus types could be distinguished based on the cystacanth stage by a linear discriminant analysis that included hook measurements, proboscis length, proboscis width, and number of longitudinal hook rows and hooks per row. Furthermore, PspT3 was more different from PspT1 and PspT2 than the latter types from each other. Mainly the number of longitudinal hook rows differed in PspT3 from the existing descriptions of P. minutus (mainly 14 vs. mainly 16 rows). Potentially, PspT3 could be a non-indigenous parasite that was introduced with G. roeselii and that adapted to use the indigenous G. pulex as a host, while PspT2 might have been introduced to central Europe together with Echinogammarus spp.