Ciliate species diversity and host-parasitoid codiversification in Pseudocollinia infecting krill, with description of Pseudocollinia similis sp. nov.

Abstract

All parasitoid apostome ciliates infecting krill in the northeastern Pacific are currently assigned to the genus Pseudocollinia. Each krill specimen is apparently infected by only 1 Pseudocollinia species. We describe Pseudocollinia similis sp. nov., discovered infecting the krill Thysanoessa spinifera off Oregon, USA. Its protomite-tomite stage resembles that of P. beringensis, which infects T. inermis (type host species), T. longipes, and T. raschii females in the Bering Sea. These ciliates have similar numbers of somatic kineties (18-21 vs. 16-20) and typically have 3 oral kineties. Furthermore, these 2 apostomes are sister species on gene trees based on sequences of small subunit rRNA (0.06% difference) and cytochrome c oxidase subunit 1 (cox1; 30% difference). P. brintoni and P. oregonensis are closely related as a separate group from P. similis and P. beringensis. The similar tree topologies based on the cox1 sequences of 21 host krill individuals representing 6 krill species (Euphausia pacifica, Nyctiphanes simplex, T. inermis, T. longipes, T. raschii, and T. spinifera) and the apostomes isolated from these krill suggest host-parasitoid codiversification. However, this hypothesis was statistically rejected by an approximately unbiased test in which the host tree topology was used to model parasitoid evolution (p ≤ 0.05).

The small subunit rRNA gene sequence of the chonotrich Chilodochona carcini Jankowski, 1973 confirms chonotrichs as a dysteriid-derived clade (Phyllopharyngea, Ciliophora)

“…While the species differences noted by Jankowski (1973) are significant, they remain to be tested by molecular genetic characterizations. Given our discoveries on the codiversification of apostome ciliates and their crustacean hosts (Lynn et al, 2014) and given the discoveries of cryptic species in a variety of genera of ciliates (Gentekaki & Lynn, 2012 and references therein), this species has been identified as Chilodochona carcini, in the belief that there is also significant undiscovered biodiversity within the genus Chilodochona. Further investigations into the genetic diversity of these symbionts of crustaceans to confirm or refute Jankowski's hypothesis are awaited.…”

The Sanguicolous Apostome Metacollinia luciensis Jankowski 1980 (Colliniidae, Apostomatia, Ciliophora) Is Not Closely Related to Other Sanguicolous Apostomes

“…THE apostomes are a small group of oligohymenophorean ciliates primarily adapted to a symbiotic relationship with crustaceans (Lynn 2008). There are four major life histories: (i) the exuviotrophic apostomes remain encysted on the exoskeleton of the crustacean host and excyst to feed on the exuvial fluid and reproduce when the host molts (Chatton and Lwoff 1935); (ii) the sanguicolous species somehow penetrate the cuticle of the host and feed on the cells and fluid of the hemocoel and then reproduce (Lynn et al 2014;de Puytorac and Lom 1962); (iii) the chromidinid species are found in the renal organs, and opalinopsids in the liver and intestines of cephalopods, ingesting fluids and cells in these organs (Chatton and Lwoff 1935;Hochberg 1983); and (iv) the histotrophs, such as Vampyrophrya (Chatton and Lwoff 1935).…”

Histophagous ciliate Pseudocollinia brintoni and bacterial assemblage interaction with krill Nyctiphanes simplex. II. Host responses

“…Most infected krill collected from the Bering Sea (Thysanoessa spp. ; 14−30 mm; Lynn et al 2014), the US west coast (Euphausia pacifica and T. spinifera; 15−28 mm; , and the southwestern coast of Baja California Peninsula and the Gulf of California, Mexico (N. simplex;9− 19.2 mm;Gómez-Gutiérrez et al 2012a) have been adult females (from first maturity to full maturity). Pseudocollinia does not infect exclusively female krill; Pseudocollinia-infected males have also been reported, albeit at very low prevalences (Capriulo et al 1991, Gó -mez-Gutiérrez et al 2003.…”

“…Other protists, such as apostome ciliates of the genus Pseudocollinia, can cause epizootic events of adult krill populations (Gómez-Gutiérrez et al 2003). Research on histophagous ciliates infecting krill has mostly focused on taxonomic perspectives and biology (Capriulo & Small 1986, Capriulo et al 1991, Stankovic & RakusaSuszczewski 1996, Gómez-Gutiérrez et al 2003, 2010a, 2012a, Lynn et al 2014. Considerably less is known about aspects of Pseudocollinia ecology, parasite−host interactions, and physiological and biochemical composition between healthy and Pseudocollinia-infected krill.…”