A Paradigm for the study of insect-ciliate Relationships: Tetrahymena sialidos sp. nov. (Hymenostomatida: Tetrahymenidae), Parasite of Larval Sialis Lutaria (Linn.) (Megaloptera: Sialidae)

Abstract

A new species of hymenostome ciliate, Tetrahymena sialidos sp.nov., is described and proposed as a model for studies upon insect-ciliate interactions. This ciliate occurs as a parasite in the haemocoel of larval Sialis lutaria (Megaloptera) and exhibits field and laboratory characteristics favourable for two particular areas of study, the regulation of invertebrate populations by parasites and insect immunity to parasitic infections. The prevalence of T. sialidos infection in S. lutaria from a small lake in mid-Wales has been monitored during a four-year period. Each summer, early in the first of their two-year aquatic development, 40-70% of S. lutaria larvae become infected. Death of infected larvae due to parasite proliferation is inevitable but does not occur until 11-12 months after infection, when the mean intensity has reached 55000 ciliates per infected host. Ciliates escaping from moribund or dead host larvae undergo a distinct morphological transformation followed by a period of synchronous conjugation. Death of infected host larvae and release of ciliates coincides with the appearance of a new generation of host larvae in which the prevalence of infection rises rapidly. The possible significance of this substantial and persistent regulatory influence upon host population dynamics is discussed in relation to current ideas of parasite regulation of invertebrate populations. Sialis lutaria is not able normally to mount a successful host response against T. sialidos infections. A laboratory thermalshock technique is described by means of which parasitic ciliates may be killed in situ without incurring physical damage to the host. Infected larvae subjected to thermalshock at 39 °C for 1 h subsequently encapsulate and melanize the dead ciliates. The use of this technique is discussed in relation to recognition of non-self in insects and survival strategies of parasites infecting insects.

Barcodes Reveal 48 New Species ofTetrahymena,Dexiostoma, andGlaucoma: Phylogeny, Ecology, and Biogeography of New and Established Species

“…The finding of 32 new Tetrahymena species in the FPD/KD collection is in accord with the prediction (see Introduction) that there are many more species and is consistent with the apparent ease which past investigators (e.g., Batson , ; Cho ; Elliott ; Gruchy ; Jerome et al. ; Lynn et al.…”

“…There is a long history of sampling from these sources, but relatively little study in most cases beyond initial species descriptions. For parasites, available evidence suggests that there is host species specificity in some instances (Batson , ; Jerome et al. ; Lynn et al.…”

Flatworm transcriptomes reveal widespread parasitism by histophagous ciliates

“…Histophagous Tetrahymena prey upon a broad range of invertebrates, including midges (T. chironomi) (Corliss, 1960), mosquitoes (T. empidokyrea) (Jerome et al, 1996), black flies (T. dimorpha, T. rotunda) (Batson and Beale, 1983;Lynn et al, 1981), alderflies (T. sialidos) (Batson and Rees, 1985), slugs (T. limacis, T. rostrata) (Brooks, 1968), the glochidia larvae of freshwater mussels (T. glochidiophila) (Lynn et al, 2018), and the planarian flatworms Crenobia alpina, Dendrocoelum lacteum, Dugesia gonocephala, Girardia tigrina, Phagocata vitta, and Polycelis felina (T. acanthophora, T. corlissi, T. dugesiae, T. nigricans, T. pyriformis, T. scolopax) (Armitage and Young, 1990;Rataj and Vd'ačný, 2019;Rataj and Vďačný, 2020;Wright, 1981). Vertebrate infections have been reported in fish (T. corlissi, T.…”