Wednesday 12 August 2020

Manayunkia occidentalis: A new species of Sabellid Polychaete from the Pacific Northwest of the United States, and an alternate host of two Myxosporean parasites of Salmonid Fish.

Annelids are a diverse and speciose invertebrate group, particularly in marine systems. Apart from Clitellate Annelids ('Oligochaetes' and 'Leaches'), there are relatively few known freshwater species, and several of these belong to the Sabellid genus Manayunkia. Manayunkia currently contains 11 accepted nominal species, though this may need further assessment. The most recent taxa described are the marine Manayunkia mizu, described in 1996 from Papua New Guinea, and the freshwater Manayunkia zenkewitschii, described in 1997 from Lake Baikal. Currently, there are freshwater Manayunkia described from Europe and North America, and brackish/marine species known from Australia, Europe, Papua New Guinea and Brazil. Two species of Manayunkia are recorded from North America: Manayunkia aestuarina, from brackish coastal environments (though the type locality is in the UK), and Manayunkia speciosa, which was first briefly described by Joseph Leidy in 1859, from the Schuylkill River in Pennsylvania, and in much greater detail from specimens from New Jersey in 1883. The species was later reported from the Great Lakes in 1829, the Klamath and Sacramento river basins of Oregon and California in 1966, lakes in Alsaka in 1967, and lakes in North Carolina in 1971. Manayunkia speciosa has been identified as the invertebrate alternate host of two Myxosporean parasites of Salmonid Fish: Ceratonova shasta (formerly Ceratomyxa shasta) and Parvicapsula minibicornis. Myxosporeans are common Myxozoan Cnidarian parasites with complex life cycles that require two hosts: a vertebrate (usually a Fish) in which parasite Myxospores develop, and an invertebrate (usually an Annelid) in which actinospores develop. Both Ceratonova shasta and Parvicapsula minibicornis are widespread in the Pacific Northwest but have not been recorded from the Great Lakes, or east coast of North America, despite presence of both Manayunkia speciosa and susceptible Salmon hosts in these regions.

In a paper published in the journal Zootaxa on 17 March 2020, Stephen Atkinson and Jerri Bartholomew of the Department of Microbiology at Oregon State University, and Greg Rouse of the Scripps Institution of Oceanography at the University of California, San Diego, present the results of a survey based upon the hypothesis that that these two Myxozoans actually require a heretofore unrecognized Annelid host, which is present only in western North American river basins, and which has been consistently mis-identified as Manayunkia speciosa.

Atkinson et al. sampled both infected and uninfected Annelids from the two localities where the parasites were recorded originally from their annelid hosts: the Klamath River, California, and the Willamette River, near Corvallis, Oregon. Using morphology and mitochondrial Cytochrome oxidase subunit I DNA sequencing, they compared these specimens with Manayunkia speciosa samples from New Jersey and the Great Lakes. Atkinson et al. discovered that all Klamath and Willamette Manayunkia, both infected and uninfected, were a novel species, they further sequenced Annelid samples from collections made between 2006 and 2018 and identified only the new species. They did not detect any Manayunkia speciosa from either river basin.

Annelids were collected by hand at depths of 10–50 cm from rocks and periphyton from the Klamath River, California, from below Iron Gate Dam. Additional specimens were collected from the Willamette River, Oregon. Under a dissection microscope, living Annelids were separated from substrate, then examined by light microscopy either alive or fixed in 10% neutral buffered formalin, frozen for DNA analysis, or fixed in 2% glutaraldehyde in cacodylate buffer for electron microscopy. Type and voucher specimens were deposited in the Benthic Invertebrate Collection at Scripps institution of Oceanography, La Jolla, California. To confirm identity and infection status, Atkinson et al. examined additional archived Annelid samples collected opportunistically 2006–2018 by Oregon State University as part of their long term, on-going ecological and disease studies of parasites Ceratonova shasta and Parvicapsula minibicornis. These samples were collected from localities in the Klamath and Willamette Rivers. Atkinson et al. also obtained Manayunkia speciosa from Lake Superior (St. Marys River, Ontario, Canada) and South River, New Jersey, in 2009. A marine Fabriciid, Echinofabricia goodhartzorum, was used as the outgroup, since Echinofabricia has been shown to be the sister group to Manayunkia.

Live Annelids were found in clusters of tubes, most often attached to rocks or intertwined with periphyton. Females were observed frequently with broods of larvae in their tubes. Males and females with overt parasite infections often lacked gametes. Five individuals were sequenced from the type collection locality/date, with an additional 79 from archival material from the Klamath River; 10 were sequenced from the Willamette River. The five paratype specimens were up to 1.6% divergent with each other (0–6 nucleotides differed over the total alignment of 439 nucleotides), compared with a divergence of up to 2.8% among all 84 Klamath River Annelids sequenced. The 10 Willamette River specimens were up to 0.4% divergent with each other, and pairwise distances between Willamette and Klamath River specimens were 3.1–4.1%. These west coast samples were 10.5%–12.2% divergent from the Great Lakes and East Coast Manayunkia speciosa reference sequences. The parasite Ceratonova shasta was detected in 16 Annelids from the Klamath River, whereas Parvicapsula minibicornis was detected in four annelids from the Klamath River and one from the Willamette River; these parasite abundances were typical.

The new species is named Manayunkia occidentalis, which is derived from the Latin word for 'west', to contrast with Manayunkia speciosa, which occurs in eastern and central North American drainages. The holotype (SIO-BIC A12115) is a male with eight thoracic segments and three abdominal segments. Total length (unfixed) 3.0 mm, crown 0.3 mm. Body cylindrical with tapering, dorso-ventrally flattened abdomen. Body wall translucent grey with minor brown pigmentation on peristomium and pygidium, and green pigmentation on chaetiger 6. Branchial crown about 10% of total body length. Two pairs of radioles, each with six pinnules. One ventral pinnule on radiole with 4–5 yellow-white spots in life. One pair of vascularised, unbranched ventral filamentous appendages present, extending for about two-thirds length of radiolar crown, approximately same width as pinnules. Anterior peristomial ring with membranous collar, followed by posterior peristomial ring. Collar margin smooth, higher ventrally, separated by a narrow dorsal gap that corresponds with ciliated faecal groove. Peristomial eyes, black rounded spots. Pygidial eyes absent. Superior thoracic notochaetae elongate, narrowly hooded; 5–7 per fascicle (chaetigers 1–5), 4–5 per fascicle (chaetigers 6–8). Inferior thoracic notochaetae on chaetigers 1–8 short; 3–4 per fascicle except chaetiger 2, which has 6 per fascicle. Thoracic neuropodia each with 4–7 uncini in chaetigers 2–8. Thoracic uncini with rows of evenly small teeth gradually decreasing in size away from main fang. Position of chaetae and uncini reversed in abdominal segments; number of abdominal uncini per fascicle decreasing posteriorly from 22 to 9. Abdominal uncini each with multiple rows of teeth that are uniform in size; manubrium at least five times longer than dentate region, with base about two thirds the width of the dentate region. Abdominal neuropodia are elongate, narrowly hooded, decreasing posteriorly from 4–6 to 2 per fascicle.


Gross morphological features of Manayunkia occidentalis resolved by light microscopy: (A) multiple individuals emerged and feeding from their tubes; (B) Individual annelid with prominent vascularized appendages (va) and showing refractile spots on one feeding palp on each side (arrowheads); (C) female in reflected light, showing white oocytes (o) in segments 4–6; (D) male in reflected light showing bright spermatogonic tissue (sp) in multiple posterior segments; (E) Male in transmitted light showing parallel vascularized appendages (va) and fanned-out feeding palps nteriorly with two dark eyespots in peristomium, and granular coelom posteriorly due to presence of developing sperm. Atkinson et al. (2020).

Paratypes are similar to the holotype. However, females have oocytes in thoracic chaetigers 4–5 and a pair of pigmented spermathecae in the base of the radiolar crown. Females differ from males in having thoracic neuropodia with uncini in chaetigers 2–5 followed by 3–6 elongate hooded chaetae in neuropodia of chaetigers 6–8. 


Images showing chaetal characters of Manayunkia occidentalis: (A) inferior and superior notochaete typical of thoracic segments 2–8; (B) thoracic uncini; (C) abdominal uncini; (D) dorsal view of posterior thoracic segments and abdomen of male showing typical uncini in chaetigers t7 and t8 (arrowheads) and in scanning electron micrograph shown in (F); (E) dorsal view of posterior thoracic segments and abdomen of female showing neuropodia of thoracic chaetigers 6–8 with elongate neuropodia instead of uncini, seen also in scanning electron micrograph in (G) (arrowhead). (H) anterior thoracic segment of female showing notochaetae and uncini (arrowhead), characteristic of thoracic segments 2–5 in both sexes. Atkinson et al. (2020).

Manayunkia speciosa was described originally from Philadelphia, USA with subsequent reports from the Great Lakes and several west coast river basins. This Annelid is reported to be the obligate alternate host of two Myxozoan parasites Ceratonova shasta and Parvicapsula minibicornis. Unambiguous identification of the invertebrate hosts of Myxozoans, which produce the infectious stage to Fish, is essential for risk assessment and stock management as these parasites cause disease and death within populations of salmon and trout. Atkinson et al.'s findings support the hypothesis that the Annelid host of the parasites has likely been mis-identified as Manayunkia speciosa, and is actually a novel taxon Manayunkia occidentalis.


Morphological features of Manayunkia occidentalis resolved by scanning electron microscopy: (A) lateral view; (B) dorsal view; (C) ventral view; (D) anterior showing membranous collar (c) of the peristomal ring (pr), margin with fecal groove (fg); mucus covers the pinnules and adheres Diatoms; (E) detail of typical thoracic uncini; (F) abdominal segments and anus, showing ciliated fecal groove extending anteriorly and wrapping around to the ventral surface at boundary between abdominal and thoracic segments; (G) lateral view of thoracic segments showing contracted uncini and prominent neuropodia; (H) higher magnification view of retracted abdominal uncini. Atkinson et al. (2020).

The 94 west coast Manayunkia occidentalis specimens that Atkinson et al. characterised had cytochrome oxidase subunit I sequences at least 11% different from the reference Manayunkia speciosa sequences from Lake Superior and New Jersey. This east-west genetic divergence underpinned the rationale for describing the west coast Annelids as a distinct, novel taxon. Among the Manayunkia occidentalis specimens, the greatest genetic difference (4.1%) was between isolates from the two rivers, which are more than 500 km apart. These genetic differences are not surprising given the relative immobility of the Annelids, particularly from above- and below-dam localities, and between river basins separated by saltwater. Atkinson et al. hypothesise that similar degrees of genetic differences, with corresponding novel haplotypes, will be observed among populations in other unconnected river basins on the West Coast (Fraser, Rogue, Sacramento), and probably within large basins like the Columbia.

Atkinson et al. did not detect any Manayunkia speciosa among the 94 Annelids sampled from multiple localities in two river basins. This was surprising given historical records of that taxon in West Coast basins, particularly associated with Myxozoan parasites. The collection localities in the Klamath River included one where 'Manayunkia speciosa' was collected and sequenced previously. This published sequence is only minimally divergent (0–1%) from Manayunkia speciosa reference sequences collected from Lake Superior and the East Coast. Atkinson et al. cannot explain how these trans-continental Manayunkia speciosa sequences could be so similar, given that they observed genetic distances up to 2.8% among Manayunkia occidentalis samples from the Klamath Basin, and up to 4.1% between specimens from different West Coast river basins. Based on their survey data, Atkinson et al. postulate that Manayunkia speciosa may not be present in the Klamath or Willamette rivers, and they suspect that the earlier assignations of Klamath River Annelids as Manayunkia speciosa are incorrect. Almost all previous identifications relied on morphology, and Atkinson et al. have now shown that there are few morphological characters to distinguish the two taxa, though the markedly smaller number of pinnules in Manayunkia occidentalis is an obvious difference from Manayunkia speciosa. This and the cytochrome oxidase subunit I sequence divergence of at least 10.5% makes future discrimination between Manayunkia speciosa and Manayunkia occidentalis relatively straightforward.

Twenty-one of the 94 examined annelids were infected with either or both Ceratonova shasta and Parvicapsula minibicornis, and all were identified by sequence as Manayunkia occidentalis, and thus Atkinson et al. could not confirm that Manayunkia speciosa is a host for these Myxozoans. If Manayunkia speciosa is not a permissive host, then this would explain why Ceratonova shasta and Parvicapsula minibicornis have not become established in the Great Lakes or in East Coast river systems where Manayunkia speciosa, only, is present. It is likely, however, that Manayunkia speciosa hosts other Myxozoan species, as evidenced by detection of Ceratonova-like DNA in Annelids from the Great Lakes. Atkinson et al. predict that they will find Manayunkia occidentalis in all river basins where the parasite is found on the west coast, and none in the Great Lakes. Accordingly, they are sampling and sequencing additional Annelid populations from river basins where Ceratonova shasta and Parvicapsula minibicornis occur, to determine the phylogeography of the host, any correlation between infection and host haplotype, and if any Manayunkia speciosa sensu stricto exists on the west coast of North America.

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