Phylogenetic evidence for an ancestral coevolution between a major clade of coccidian parasites and elasmobranch hosts

Synopsis of the Species of Coccidians Reported in Marine Fish

Eimeriid coccidians represent one of the largest groups of parasitic unicellular organisms and comprise many species of veterinary and medical importance. The aim of this work is to provide information, as complete as possible, concerning the oocyst phase of the species of coccidians (Apicomplexa: Eimeriorina) with four sporocysts, which were reported in marine fish. For each species, the accepted scientific name and respective authorities, its synonyms, reported hosts, site of infection (organ), and geographic distribution have been assembled. Available information on morphology (oocyst, sporocyst, and sporozoite) and GenBank accession numbers were also compiled. A total of 100 species of coccidians were described and reported from 60 families of marine fishes. Most species have been described from marine teleosts, with only 14 of the species described from marine elasmobranchs. Most of the species reported in marine fish belong to the genera Eimeria and Goussia, and only a handful belong to the genera Epieimeria, Calyptospora, and Crystallospora. Although marine coccidians have began to be described for more than one century, the collection of genetic data on marine fish coccidians only started in the 2010s and remains largely disconnected from the morphological analysis of specimens, which is available for only six formally described species.

An ancient alliance: Matching evolutionary patterns of cartilaginous fishes (Elasmobranchii) and chloromyxid parasites (Myxozoa)

Myxozoa is a group of endoparasitic cnidarians covering almost 2600 species but merely 53 species, mostly from the genus Chloromyxum, have been reported from sharks, rays, and skates (Elasmobranchii). Elasmobranchs play a key role in the study of evolutionary trajectories of myxozoans as they represent ancestral vertebrate hosts. Our study provides new data on Chloromyxum spp. from 57 elasmobranchs, covering 20 species from geographical regions and host groups not previously investigated, such as Lamniformes and Hexanchiformes, the most basal phylogenetic shark lineage. In total, 28% of elasmobranchs were infected with Chloromyxum spp., indicating high diversity. Of the seven distinguished species, six are formally described based on morphological, morphometric, and genetic (18S rDNA) data. Comprehensive co-phylogenetic analyses and ancestral state reconstruction revealed that parasite and host phylogenies are clearly correlated, resulting in a distinct phylogenetic separation of chloromyxids from selachid (shark) vs. batoid (ray and skate) hosts. Species infecting the most ancient elasmobranchs formed a sublineage, branching off in the middle of the Chloromyxum sensu stricto clade. Our findings indicate that chloromyxids likely invaded an ancestral elasmobranch prior the time of divergence of shark and batoid lineages. Our analyses did not show a clear phylogeographic pattern of Chloromyxum parasites, probably due to the cosmopolitan distribution and migratory behaviour of many elasmobranch hosts, but geographical sampling must be extended to confirm or refute this observation. This study provides a complex view on species diversity, phylogeny, evolution, host-parasite co-phylogeny, and the phylogeographic origin of Chloromyxum species from elasmobranchs. Our results highlight the importance of adding missing data from previously un- or undersampled geographical regions and host species which results in a more accurate estimate of myxozoan biodiversity and a better understanding of the evolution of this parasite group in their hosts and in the different oceans of our planet.

First report of Caryospora sp. infection in free-living green turtles (Chelonia mydas) in Northeastern Brazil

Infection by Caryospora cheloniae has been reported to be responsible for green turtle strandings with high morbidity and mortality rates worldwide. Although studies have already shown the pathogenesis of these infections, many aspects of this protozoan are still poorly understood, including their life cycle and infection dynamics in free-living sea turtle populations. Due to the lack of information about the infection by this protozoan in sea turtles in Northeastern Brazil, our study aims to describe Caryospora sp. infection and its pathological findings in free-living Chelonia mydas found on the north coast of the Bahia state. Between 2018 and 2019, 64 specimens of green turtles were necropsied in partnership with Fundação Projeto Tamar; among these, 10 (1.56%) had oocysts morphologically compatible with Caryospora cheloniae in the evaluation of fecal samples and histopathological examination of intestinal samples. The infected animals were juvenile green turtles that were found stranded on the beaches of the north coast of Bahia. The pathological findings were restricted to the lower gastrointestinal tract, with different presentations and intensities. About 70% of the animals with coccidial infection exhibited erosive and ulcerative fibrinous enteritis. This is the first report of coccidiosis in green turtles on the north coast of Bahia.

Phylogenetic Affinities and Infection Patterns of Goussia Infecting Sardina pilchardus from the NE Atlantic

PURPOSE

European pilchard (Sardina pilchardus) is a highly valued fish in many European countries, particularly in Portugal. Despite current stock declines and the threats coccidia pose to European pilchards (e.g. castration), little is known about coccidian parasites infecting pilchards captured off the Portuguese coast.

METHODS

In this study, we analyzed the infection patterns, the morphology of oocysts and the phylogenetic relations of coccidian parasites from European pilchard captured in Northern Portugal.

RESULTS

Only Goussia oocysts were detected in infected tissues and prevalence of infection was 64% (n = 61). Oocysts were detected primarily in the liver with fewer infections in the stomach, intestine and gonads. No differences were found in the prevalence between seasons. Phylogenetic analysis showed these parasites are closely related to Goussia clupearum, placing them within a recently described group of Goussia, the clupearum type.

CONCLUSIONS

Our study provides more data on Goussia from the clupearum type with phylogenetic analysis indicating that these parasites cluster according to fish host taxonomy, thus suggesting some degree of co-evolution.

Effects of Goussia infecting the blue whiting and phylogenetic placement of Goussia infecting marine fish off Northern Portugal

Coccidian parasites of fish have received considerably less attention than their terrestrial counterparts, and within piscine hosts, most studies have focused on freshwater fish. The present study aimed to describe oocyst morphology, phylogenetic affinities, and the impacts of coccidian parasites infecting the internal organs of a commercially valuable marine fish, the blue whiting (Micromesistius poutassou), captured off the Portuguese coast. As part of the phylogenetic analysis, sequences from coccidians infecting the pout (Trisopterus luscus) and the Atlantic chub mackerel (Scomber colias) were included, and the oocyst morphology of the coccidians infecting the former was also reported. Results showed that the prevalence of coccidiosis in the blue whiting was very high (> 82%), occurring in all analyzed organs, despite being more abundant in the liver. A significant negative correlation was found between the abundance of the parasites in the liver and host condition index (p < 0.05), which indicates a negative effect on the fitness of this host. Phylogenetic analyses of the parasites found in all three species examined identified three different species of Goussia, closely related to Goussia clupearum. Adding to previous research, we propose the existence of a fourth group of Goussia, the clupearum type, able to infect multiple organs and phylogenetic related with G. clupearum.

Morphological and molecular identification of Isospora massardi Lopes, Berto, Luz, Galvão, Ferreira & Lopes, 2014 (Chromista: Miozoa: Eimeriidae) from thrushes Turdus spp. (Passeriformes: Turdidae) in South America

In the current work, Isospora massardi Lopes, Berto, Luz, Galvão, Ferreira & Lopes, [10] is identified from white-necked thrushes Turdus albicollis Vieillot, 1818, rufous-bellied thrushes Turdus rufiventris Vieillot, 1818 and from a new host, the yellow-legged thrush Turdus flavipes (Vieillot, 1818) in a new locality, the Itatiaia National Park, in Southeastern Brazil, providing a preliminary genotypic characterization via sequencing of the mitochondrial cytochrome c oxidase subunit 1 (COI) and 18S small subunit ribosomal RNA genes. The oocysts and sporocysts of I. massardi of the current study are morphologically similar to the original description and are uniform in the proportionality of width on length, but exhibited different patterns of size associated with each host species. Furthermore, a genotypic difference of 3% was found in the COI sequences from T. flavipes and T. albicollis. Therefore, an ecological discussion is introduced aimed at associating these morphometric and genotypic differences with an ongoing speciation process.

Coccidia of Columbiformes: a taxonomic review of its Eimeriidae species and Eimeria columbinae n. sp. from Columbina talpacoti (Temminck, 1809) from Brazil

Coccidia (Chromista: Miozoa: Eimeriidae) of columbiform birds (Aves: Columbiformes) have been described since the end of the nineteenth century; however, some of these descriptions were poorly detailed or inconclusive. In this sense, the current work makes a detailed taxonomic revision reconsidering and organizing 18 Eimeria spp. and two Isospora spp. previously described or reported of Columbiformes. Along with this, a new species of Eimeria is morphologically and molecularly identified by the mitochondrial cytochrome c oxidase subunit 1 (COI) gene and by the 18S small subunit ribosomal RNA (18S) gene from the ruddy ground-dove Columbina talpacoti (Temminck, 1809) in the Médio Paraíba region of the State of Rio de Janeiro, southeastern Brazil. Eimeria columbinae n. sp. has subspheroidal oocysts, 14.7 × 13.2 μm, with smooth, bi-layered wall, ~ 1.1 μm and length/width ratio of 1.1. Micropyle and oocyst residuum are present, but polar granule is absent. Sporocysts are ellipsoidal to slightly asymmetrical, 9.0 × 5.1 μm, with both Stieda and sub-Stieda bodies. Sporocyst residuum present and sporozoites with refractile body and nucleus. This is the 19th description of an eimerian from Columbiformes in the World, and the second to have a molecular identification of the COI and 18S genes.

Genetic Diversity and Gene Family Expansions in Members of the Genus Entamoeba

Amoebiasis is the third-most common cause of mortality worldwide from a parasitic disease. Although the primary etiological agent of amoebiasis is the obligate human parasite Entamoeba histolytica, other members of the genus Entamoeba can infect humans and may be pathogenic. Here, we present the first annotated reference genome for Entamoeba moshkovskii, a species that has been associated with human infections, and compare the genomes of E. moshkovskii, E. histolytica, the human commensal Entamoeba dispar, and the nonhuman pathogen Entamoeba invadens. Gene clustering and phylogenetic analyses show differences in expansion and contraction of families of proteins associated with host or bacterial interactions. They intimate the importance to parasitic Entamoeba species of surface-bound proteins involved in adhesion to extracellular membranes, such as the Gal/GalNAc lectin and members of the BspA and Ariel1 families. Furthermore, E. dispar is the only one of the four species to lack a functional copy of the key virulence factor cysteine protease CP-A5, whereas the gene's presence in E. moshkovskii is consistent with the species' potentially pathogenic nature. Entamoeba moshkovskii was found to be more diverse than E. histolytica across all sequence classes. The former is ∼200 times more diverse than latter, with the four E. moshkovskii strains tested having a most recent common ancestor nearly 500 times more ancient than the tested E. histolytica strains. A four-haplotype test indicates that these E. moshkovskii strains are not the same species and should be regarded as a species complex.

Parasites of cartilaginous fishes (Chondrichthyes) in South Africa - a neglected field of marine science

Southern Africa is considered one of the world's 'hotspots' for the diversity of cartilaginous fishes (Chondrichthyes), with currently 204 reported species. Although numerous literature records and treatises on chondrichthyan fishes are available, a paucity of information exists on the biodiversity of their parasites. Chondrichthyan fishes are parasitised by several groups of protozoan and metazoan organisms that live either permanently or temporarily on and within their hosts. Reports of parasites infecting elasmobranchs and holocephalans in South Africa are sparse and information on most parasitic groups is fragmentary or entirely lacking. Parasitic copepods constitute the best-studied group with currently 70 described species (excluding undescribed species or nomina nuda) from chondrichthyans. Given the large number of chondrichthyan species present in southern Africa, it is expected that only a mere fraction of the parasite diversity has been discovered to date and numerous species await discovery and description. This review summarises information on all groups of parasites of chondrichthyan hosts and demonstrates the current knowledge of chondrichthyan parasites in South Africa. Checklists are provided displaying the host-parasite and parasite-host data known to date.