Fabrizio Erra

Euplotespora binucleata n. gen., n. sp. (Protozoa: Microsporidia), a Parasite Infecting the Hypotrichous Ciliate Euplotes woodruffi, with Observations on Microsporidian Infections in Ciliophora

ABSTRACT. A new microsporidian species, Euplotespora binucleata n. gen., n. sp., from the brackish‐water ciliate Euplotes woodruffi is described and defined on the basis of life history characteristics, light and electron microscopic features, and small subunit (SSU) ribosomal DNA (rDNA) sequencing. The life cycle of E. binucleata n. sp. probably has rather short merogonic and relatively long sporogonic phases. Some uninuclear meronts and sporonts, along with diplokaryotic sporoblasts and spores, were found in experimentally infected host cells. Such a peculiar life cycle has been induced experimentally in Euplotes eurystomus and constitutively microsporidian‐free stocks of E. woodruffi. Spores of E. binucleata n. sp. are monomorphic, ovoid–cylindrical in shape, 3.44±0.17 × 1.65±0.22 μm in size, and characterized by a diplokaryotic condition and a large posterior vacuole. The polar tube is isofilar, 4.5–5.5 μm in length when ejected, and lacking a distinctive coiled region (half‐coiled). The polaroplast is divided into two regions: the anterior part has a few lamellae close to the anchoring disc; and the posterior part is a rounded body (sack), about one‐quarter of the spore length. Spores do not appear to cluster together as a group. Each spore is surrounded by a sporophorous membrane closely adjacent to the exospore layer. A phylogenetic analysis of SSU rDNA sequences by different methods placed E. binucleata n. sp. in a clade with representatives of the microsporidian genera Cystosporogenes and Vittaforma. Observations of microsporidia in several other ciliates are discussed in view of the microsporidian infection frequency in the phylum Ciliophora.

Antarctic and Arctic populations of the ciliate Euplotes nobilii show common pheromone-mediated cell-cell signaling and cross-mating.

Wild-type strains of the protozoan ciliate Euplotes collected from different locations on the coasts of Antarctica, Tierra del Fuego and the Arctic were taxonomically identified as the morpho-species Euplotes nobilii, based on morphometric and phylogenetic analyses. Subsequent studies of their sexual interactions revealed that mating combinations of Antarctic and Arctic strains form stable pairs of conjugant cells. These conjugant pairs were isolated and shown to complete mutual gene exchange and cross-fertilization. The biological significance of this finding was further substantiated by demonstrating that close homology exists among the three-dimensional structures determined by NMR of the water-borne signaling pheromones that are constitutively secreted into the extracellular space by these interbreeding strains, in which these molecules trigger the switch between the growth stage and the sexual stage of the life cycle. The fact that Antarctic and Arctic E. nobilii populations share the same gene pool and belong to the same biological species provides new support to the biogeographic model of global distribution of eukaryotic microorganisms, which had so far been based exclusively on studies of morphological and phylogenetic taxonomy.

Improved description of the bipolar ciliate, Euplotes petzi, and definition of its basal position in the Euplotes phylogenetic tree

Data improving the characterization of the marine Euplotes species, E. petzi Wilbert and Song, 2008, were obtained from morphological, ecological and genetic analyses of Antarctic and Arctic wild-type strains. This species is identified by a minute (mean size, 46 μm × 32 μm) and ellipsoidal cell body which is dorsally decorated with an argyrome of the double-patella type, five dorsal kineties (of which the median one contains 8-10 dikinetids), five sharp-edged longitudinal ridges, and a right anterior spur. Ventrally, it bears 10 fronto-ventral, five transverse, two caudal and two marginal cirri, 30-35 adoral membranelles, and three inconspicuous ridges. Euplotes petzi grows well at 4 °C on green algae, does not produce cysts, undergoes mating under the genetic control of a multiple mating-type system, constitutively secretes water-borne pheromones, and behaves as a psychrophilic microorganism unable to survive at >15 °C. While the α-tubulin gene sequence determination did not provide useful information on the E. petzi molecular phylogeny, the small subunit rRNA (SSU rRNA) gene sequence determination provided solid evidence that E. petzi clusters with E. sinicus Jiang et al., 2010a, into a clade which represents the deepest branch at the base of the Euplotes phylogentic tree.

Effects of increased mortality on gorgonian corals (Cnidaria, Octocorallia): different demographic features may lead affected populations to unexpected recovery and new equilibrium points

Over the last years, several marine populations suffered a drastic mortality increase of different origins; assessing the changes occurring in the demographic structure of such populations will allow evaluating their future trends and their ultimate fate. The aim of our research was to assess main demographic descriptors and related dynamics in populations of the Mediterranean gorgonians Paramuricea clavata and Corallium rubrum (the “precious red coral”) both subject to increased mortality, by life-history tables and Leslie-Lewis transition matrices. Gorgonian populations have been generally been considered to have low recruitment and low dynamics. Here, we test whether these features change when mortality rises and if such populations can reach new equilibria? Our findings show large differences between the two species examined, with lower recruitment and adult colony density, shorter life-span but over-abundant reproductive output in P. clavata. Recruitment density dependence was found in crowded populations of both species, albeit with different trends. Populations of both species tend to recover even after drastic mortality increase and P. clavata reaches a new equilibrium at lower densities than at pristine values, and this in a few years time. The findings in this review could shed some light on the poorly understood dynamics occurring in deep-water dwelling, affected populations of long-lived and slow-growing gorgonian corals.

Focusing on genera to improve species identification: revised systematics of the ciliate Spirostomum.

Although many papers dealing with the description of new ciliate taxa are published each year, species taxonomy and identification in most groups of the phylum Ciliophora remain confused. This is largely due to a scarcity of surveys on the systematics of immediately higher levels (genera and families) providing data for old and new species together. Spirostomum is a common and distinctive inhabitant of fresh- and brackish water environments, including artificial and eutrophic ones, and is a good model for applied ecology and symbiosis research. Despite this, only 3 of the numerous species are commonly cited, and no studies have yet confirmed their monophyly, with the consequence that reproducibility of the results may be flawed. In this paper we present morphological and molecular data for 30 Spirostomum populations representing 6 different morphospecies, some of which were collected in previously unreported countries. We performed a detailed revision of Spirostomum systematics combining literature surveys, new data on hundreds of organisms and statistical and phylogenetic analyses; our results provide insights on the evolution, ecology and distribution of known morphospecies and a novel one: Spirostomum subtilis sp. n. We also offer tools for quick species identification.

A Quantitative Approach to Movement, Displacement, and Mobility of Protozoa

ABSTRACT Diffusion theory can completely describe the movement of a ciliate along a track of a certain length (L), travelled in a time (t), and with the extremes lying at a distance D. Three important descriptors of this behavior are: (1) the kinetic index (Ik= L/t), namely the average velocity in μm/s, which expresses the state of the “accelerator” of the ciliate; (2) the geometric index (Ig= D/L) measuring the straightness of the track by a dimensionless number. 0 ≤ Ig≤ 1, which expresses the state of the “steering wheel” and represents a sort of “directional efficiency”; and (3) the displacement rate (Rd= D/t), integrating the first two indices and expressing the combined effect of the “accelerator” and the “steering wheel” of the organism with a unique measure (in μm/s), which defines the average displacement rate or the effectiveness of the track in displacing the organism in space. A weighted estimate of general mobility is given by the mobility rate [Rmo= (R̄d.f)creeping‐ (R̄d.f)swimming], obtained by multiplying the average Rd of the creeping organisms and the average Rd of the swimming organisms by their relative frequencies of occurrence (f), and adding the two products. Values for experimental populations of Oxytricha bifaria (Ciliata, Hypotrichida) maintained at 24, 19, 14, and 9° C demonstrated both the appropriateness and the usefulness of these indices and rates to describe the tracks a posteriori, and to provide measures to reason about their possible adaptive significance.

The crowding effect: an ethologic analysis

Summary The phenomenon of crowding of ciliates in rest areas has been described previously [23]: these organisms tend to collect on the bottom of an experimental apparatus under objects interfering with the water-air interface. The behaviour of Oxytricha bifarta has been analyzed as a basic element possibly accounting for the effect itself: to monitor the phenomenon properly a well-defined time (1 h 15 min) was chosen during the formation of the overcrowded population; in addition, well-defined areas were TV recorded, the populations within them studied and their behaviour analyzed and compared. The results obtained are the following: (a) the number of idle cells is significantly larger in the Shelter-Area (S) than in the Open (O); (b) there is a net inward flow of oxytrichas, constantly enhancing the cell density in S; (c) the ethogram of oxytrichas creeping into S is quite similar to that of the populations in O: only the creeping velocity in S is smaller than in O; (d) the frequency of Side Stepping Reactions performed by O. bifaria at the level of the border between S and O is 5–6 times higher for oxytrichas creeping outwards than for those entering S. The combined effect of these phenomena well accounts for the formation of the crowding conditions.

Raikovenal, a new sesquiterpenoid favouring adaptive radiation of the marine ciliate Euplotes raikovi, and its putative biogenetic precursor, preraikovenal

The new-skeleton sesquiterpenoid raikovenal 1a, isolated from the marine ciliate Euplotes raikovi and likely to originate biogenetically from co-existing preraikovenal 2a, can be seen to favour its adaptive radiation by selectively killing the predacious ciliate Litonotus Iamella.

The ethograms of Uronychia transfuga and Uronychia setigera (ciliata, hypotrichida): a comparative approach for new insights into the behaviour of protozoa

Summary The behavioural biology of Uronychia transfuga and Uronychia setigera was studied and their complete ethograms (namely the catalogues of both the qualitative elements and the relative quantitative parameters of locomotion) were drawn. Several other points of biological relevance emerged: (a) the two hypotrichs proved to have evolved only a partial substrate dependence, their adaptive strategy relies on a very weak grip on the substrate; (b) U. transfuga and U. setigera (they share the same basic body shape, while differing in body length, 118 and 64 μ, respectively), creep on the substrate following patterns quantitatively different in terms of their absolute values (e.g. velocity: U. transfuga ∼300 μm/s; U. setigera ∼150 μm/s). When the ratio between the same values and the species-specific body size is made (namely when the measurements are expressed in Relative Units, R.U.), they become quite similar to each other; this demonstrates that creeping of these two species is size-dependent; (c) the swimming of both species occurs only backwards and at incredibly high velocities (U transfuga: v → = 6,302 μm/s, ≈54 RU/s; U setigera: v → = 7,347 μm/s, ≈115 RU/s); (d) both species show clear-cut rheo-responses and photo-responses, that is, they are capable of reacting to water currents and to sudden increases of light. Double organisms of U. setigera do not creep, but swim forewards only irregularly and backwards along straight paths at high velocity (∼3,700 μm/s).

Biogeography and Character Evolution of the Ciliate Genus Euplotes (Spirotrichea, Euplotia), with Description of Euplotes curdsi sp. nov.

Ciliates comprise a diverse and ecologically important phylum of unicellular protists. One of the most specious and best-defined genera is Euplotes, which constitutes more than 70 morphospecies, many of which have never been molecularly tested. The increasing number of described Euplotes taxa emphasizes the importance for detailed characterizations of new ones, requiring standardized morphological observations, sequencing of molecular markers and careful comparison with previous literature. Here we describe Euplotes curdsi sp. nov., distinguishable by the combination of the following features: 45–65 μm length, oval or elongated shape with both ends rounded, narrow peristome with 25–34 adoral membranelles, conspicuous paroral membrane, double-eurystomus dorsal argyrome type, 6–7 dorsolateral kineties and 10 frontoventral cirri. Three populations of the novel species have been found in brackish and marine samples in the Mediterranean and the White Sea. We provide the SSU rRNA gene sequences of these populations, and an updated phylogeny of the genus Euplotes. Using the molecular phylogenetic tree, we inferred aspects of the biogeographical history of the genus and the evolution of its most important taxonomic characters in order to provide a frame for future descriptions. Ultimately, these data reveal recurrent trends of freshwater invasion and highlight the dynamic, yet convergent, morphological evolution of Euplotes.