Description and Phylogenetic Relationships of Anhingatrema n. gen. (Digenea: Diplostomidae) with Two New Species from New World Anhingas (Aves: Anhingidae)

Phylogenetic Analysis of Pseudapatemon spp. (Digenea: Diplostomoidea) Reveals a Lineage Specific to Scolopacid Shorebirds

PURPOSE

Pseudapatemon Dubois, 1936 is a small genus of diplostomoidean digeneans parasitic as adults in the intestines of scolopacid birds in the Holarctic and Indomalaya. Until now, no DNA sequences of any member of the genus were available and its phylogenetic affinities remained unknown. Herein, we sequenced 2 Pseudapatemon spp. from American woodcock in the United States and conducted molecular phylogenetic analysis to examine their relationships with other diplostomoideans.

METHODS

Two species of diplostomids belonging to Pseudapatemon were collected from American woodcock in Wisconsin (USA). Partial nuclear 28S ribosomal rDNA and mitochondrial CO1 genes were sequenced. Phylogenetic analysis based on 28S ribosomal data was used for phylogenetic inference.

RESULTS

In the phylogenetic tree, both species of Pseudapatemon spp. formed a strongly supported cluster in a 100% supported clade with another diplostomoidean parasitic in scolopacid birds, Pulvinifer macrostomum (Jägerskiöld, 1900). Very low intergeneric difference in 28S sequences (2.5%) was detected between Pulvinifer and Pseudapatemon spp. The 2 Pseudapatemon spp. in our analysis differed by 1.2% in partial 28S sequences and 13.5-13.7% in CO1 sequences.

CONCLUSION

Representatives of the 2 currently sequenced genera of diplostomoideans from scolopacids proved to form a monophyletic clade. This provides evidence of an evolutionary host switch to scolopacid birds with subsequent radiation. Sequencing of other diplostomoideans from the Scolopacidae is needed to learn more about their phylogenetic relationships and address the question of the potential synonymy of Pseudapatemon and Pulvinifer Yamaguti, 1933.

Challenges in the recognition of trematode species: Consideration of hypotheses in an inexact science

The description and delineation of trematode species is a major ongoing task. Across the field there has been, and currently still is, great variation in the standard of this work and in the sophistication of the proposal of taxonomic hypotheses. Although most species are relatively unambiguously distinct from their congeners, many are either morphologically very similar, including the major and rapidly growing component of cryptic species, or are highly variable morphologically despite little to no molecular variation for standard DNA markers. Here we review challenges in species delineation in the context provided to us by the historical literature, and the use of morphological, geographical, host, and molecular data. We observe that there are potential challenges associated with all these information sources. As a result, we encourage careful proposal of taxonomic hypotheses with consideration for underlying species concepts and frank acknowledgement of weaknesses or conflict in the data. It seems clear that there is no single source of data that provides a wholly reliable answer to our taxonomic challenges but that nuanced consideration of information from multiple sources (the 'integrated approach') provides the best possibility of developing hypotheses that will stand the test of time.

PHYLOGENY AND SYSTEMATICS OF CYATHOCOTYLID DIGENEANS (DIGENEA: DIPLOSTOMOIDEA) PARASITIZING SNAKES WITH DESCRIPTION OF THREE NEW SPECIES OF GOGATEA FROM AUSTRALIA AND VIETNAM

The Cyathocotylidae Mühling, 1896 is a small but broadly distributed family of digeneans parasitic in a wide range of vertebrate definitive hosts, from fish to mammals. Despite existing taxonomic questions, only a few studies have generated DNA sequence data from cyathocotylids, and only a single publication included sequence data from a cyathocotylid parasitic in snakes. Four genera are known to infect snakes: GogateaLutz, 1935, Szidatia Dubois, 1938, MesostephanoidesDubois, 1951, and SerpentostephanusSudarikov, 1961. Members of these genera were known from only Asia and Africa. In the present study, we describe 2 new species of Gogatea from snakes in Australia and 1 from Vietnam. The new species from Vietnam described herein is the first member of the genus that lacks a ventral sucker. We used partial sequences of the nuclear large ribosomal subunit (28S) and mitochondrial cytochrome c oxidase subunit I (COI) genes to explore phylogenetic relationships among cyathocotylids and species differentiation. In addition, this is the first report of a cyathocotylid from snakes in Australia, thus posing interesting questions regarding the dispersal and historical biogeography of these parasites. Cyathocotylid genera from snakes have a long, convoluted taxonomic history. The genera Gogatea, Mesostephanoides, and Szidatia were distinguished from each other based on very small morphological differences. Therefore, the validity of Szidatia and Mesostephanoides was often questioned in the literature. Based on the detailed morphological analysis of our freshly collected high-quality specimens and comparison with published information, we synonymize Mesostephanoides and Szidatia with Gogatea.

Uncovering further diversity of Ochoterenatrema Caballero, 1943 (Digenea: Lecithodendriidae) in South American bats

Ochoterenatrema Caballero, 1943 is a genus of lecithodendriid digeneans that prior to this study included 8 species parasitic in bats in the Western Hemisphere. Species of Ochoterenatrema possess a unique morphological feature in form of the pseudogonotyl on the sinistral side of the ventral sucker. In this study, we describe 2 new species of Ochoterenatrema from bats in Ecuador. The new species are readily differentiated from their congeners by a combination of morphological characters, including the distribution of vitelline follicles, length of oesophagus, sucker ratio and the body shape, among other features. We have generated partial nuclear 28S rDNA and mitochondrial cox1 gene DNA sequences from both new species. The newly obtained sequences were used to differentiate among species and study the phylogenetic interrelationships among Ochoterenatrema spp. The internal topology of the clade was weakly supported, although the cox1 tree was much better resolved than the 28S tree. Comparison of sequences revealed 0-1.2% interspecific divergence in 28S and 3.3-20.5% interspecific divergence in cox1 among Ochoterenatrema spp. The new findings demonstrate that bats in South America likely harbor multiple additional undescribed species of Ochoterenatrema. More extensive sampling from broader geographic and host ranges, especially in North America, should allow for a better understanding of the evolution of host associations and morphological traits of this lineage of lecithodendriid digeneans.

The Systematics of the Trematoda

The platyhelminth class Trematoda comprises two subclasses with largely disparate species diversity, with the small Aspidogastrea with c.80 species and the speciose Digenea with c.18,000 species, which has attracted much effort towards our understanding of evolutionary relationships among suprageneric taxa. This chapter focuses on insights into the classification of the Digenea, that have become apparent from our advanced understanding of both morphological and molecular data. The field of molecular systematics of the Digenea has experienced significant advances over the past 15 years. Phylogenetic analyses of sequence data predominantly from the 18S and 28S rRNA genes have incorporated a considerable diversity of taxa, thus increasing the accuracy of phylogenetic inferences at higher taxonomic levels. As a result, the status of long-standing supraspecific taxa has been revised, new higher-level taxa have been defined, and inferences made in association with morphological and life-cycle evidence. A substantial effort has been made towards a classification reflecting a natural system of the Digenea by considering morphological evidence in conjunction with phylogenies inferred from molecular data; this has resulted in considerable congruence. However, limited taxon sampling in the phylogeny of the Digenea still remains relevant, especially in relation to some higher-level taxa, and an outline of these omissions is presented. A framework that has led to robust estimates of phylogeny is outlined, and the application of advanced morphological and molecular approaches in digenean taxonomy and systematics is illustrated using the most comprehensively studied digenean superfamilies.

TAXONOMIC REASSESSMENT AND MORPHOLOGICAL REDESCRIPTION OF NEMATOSTRIGEA SERPENS ANNULATA (DIGENEA: STRIGEIDAE) FROM OSPREY IN NORTH AMERICA

Digenean trematodes in the strigeid genus Nematostrigea are parasites of various birds, most often ospreys (Pandion haliaetus). Nematostrigea currently contains 2 species, Nematostrigea serpens and Nematostigea hepatica. Nematostrigea serpens is divided into 2 subspecies: N. serpens serpens from the Palearctic and Indomalayan realms and N. serpens annulata from the Nearctic realm. In the present work, we studied the type material of N. serpens annulata and collected new specimens from an osprey in Wisconsin close to the type locality. The original description and illustration of N. serpens annulata were incomplete. Herein we provide a detailed redescription and new illustrations of N. serpens annulata on the basis of the type material as well as newly collected and sequenced specimens. Nematostrigea serpens annulata has a distinct tegumental thickening near the mid-length of the genital cone, which is absent in its congeners. Partial sequences of the large ribosomal subunit (28S) DNA and cytochrome c oxidase subunit 1 (COI) mitochondrial DNA gene sequences were generated from our specimens of N. serpens annulata. Comparisons with previously published sequences of N. serpens serpens from the Palearctic demonstrated 2.2% difference in 28S and 3.7% in COI. On the basis of morphological and molecular comparisons, we elevate N. serpens annulata to species status and recognize it as Nematostrigea annulata Dubois and Rausch, 1948.