Morphological variability, spatial distribution and abundance of <em>Helicostomella</em> species (Ciliophora: Tintinnina) in relation to environmental factors (Argentine shelf; 40-55°S)

Abstract

SuMMarY: For the first time a taxonomic and ecological study of species belonging to Helicostomella was performed over a mesoscale spatial distribution by examining ca. 3000 loricae collected in argentine shelf waters during the austral autumn. Microscopic and statistical analysis revealed that the general shape and the oral diameter remained practically constant in the whole area surveyed, despite a continuous length fluctuation of ca. 300 µm, which includes the entire range present in eight previously reported species. consequently, we consider that the genus may be represented only by H. subulata, whose strong fluctuations in length (mostly attributed to an increase in the collar length), density and biomass seem to respond to temperature, food availability and front-related processes. in Buenos aires coastal waters associated with a quasi permanent estuarine front (40-40.5°S), mixed conditions would favour moderate abundances of long loricae, whereas in northern (42.5-45.5°S) and southern (46-54.5°S) Patagonian waters, high (10 3 ind. L -1 ) and low (<5 ind. L -1 ) densities of short loricae seem to be a consequence of stratification and encystment, respectively. the non-occurrence of the species at 41-42°S, together with a three-fold reduction in length-related parameters between specimens from Buenos aires and Patagonian waters, suggests a disjunct distribution.Keywords: tintinnids, genus Helicostomella, lorica polymorphism, abundance, shelf dynamics, fronts, environmental factors.reSuMen: Variabilidad morfológica, distribución espacial y abundancia de las especies de Helicostomella (Ciliophora: Tintinnina) en relación con las condiciones ambientales (Mar Argentino; 40-55ºS). -Se realizó el primer estudio taxonómico y ecológico de mesoescala sobre las especies del género Helicostomella, examinando ca. 3000 lórigas colectadas en el Mar argentino durante el otoño austral. Los análisis microscópicos y estadísticos revelaron que la forma general de la lóriga y su diámetro oral permanecen prácticamente constantes en toda el área analizada, mientras que su longitud presenta una variación de ca. 300 µm, incluyendo todo el rango correspondiente a 8 especies previamente reportadas. en consecuencia, el género estaría representado por una única especie, H. subulata, cuyas variaciones en longitud (atribuidas principalmente a la longitud del cuello), densidad y biomasa responderían a la temperatura, disponibilidad y calidad del alimento y procesos frontales. en aguas costeras de Buenos aires asociadas a un frente estuarino casi permanente (40-40.5°S), las condiciones de mezcla favorecerían el desarrollo de lórigas largas en abundancias moderadas, mientras que en aguas del norte (42.5-45.5°S) y del Sur (46-54.5°S) de la Patagonia prevalecen lórigas cortas en densidades elevadas (10 3 ind. L -1 ) o muy bajas (<5 ind. L -1 ) como consecuencia de procesos de estratificación y enquistamiento, respectivamente. La no detección de la especie entre 41-42ºS, junto con la reducción en 3 veces de los parámetros relacionados con la...

Species Boundaries in Tintinnid Ciliates: A Case Study – Morphometric Variability, Molecular Characterization, and Temporal Distribution of Helicostomella species (Ciliophora, Tintinnina)

“…All studies, including ours, support the assumption that there might be only one species in the genus Helicostomella if one considers only the overlapping lorica features (Alder ; Santoferrara and Alder ; present study). However, the fact that the morphological features in tintinnids have a considerable phenotypic plasticity makes the above conclusion doubtful.…”

“…Alder () concluded that the other members of Helicostomella should be considered as synonyms of H. subulata as the constancy of the oral diameter and the continuity of the lorica length made it impossible to establish a cutting point between previously reported Helicostomella species. The most recent study targeting Helicostomella species performed by Santoferrara and Alder () also support such an assumption. Unfortunately, these conclusions were either based on previous publications or lorica morphology from field samples, and thus could not be accepted as conclusive evidence for revising classification at the species level.…”

“…The most recent study on Helicostomella species was performed over a mesoscale spatial distribution by examining about 3,000 individuals of Helicostomella collected along the Argentine shelf, South America (Santoferrara and Alder ). After microscopic observations on about 300 individuals, their results showed that the morphological characteristics of these specimens included almost all values previously reported for Helicostomella species (Santoferrara and Alder ).Hence, the above results based on mesoscale sampling do not support keeping these species as independent entities, which seems reasonable considering the overlapping in morphological characteristics of these morphospecies.…”

“…Considering the high variability in lorica shape in tintinnids, the difference between these two genera is minute. Actually, it has been suggested that at least one species in the genus Metacylis , Metacylis annulifera is a synonym of H. subulata (Santoferrara and Alder ). Although supported by low values, our trees also indicate a potential close relationship between Helicostomella and Metacylis .…”

Loricate Ciliate Tintinnids in a Tropical Mangrove Wetland

“…This represents 5 % of the total species included in the most w-idely used classification system, which encompasses hundreds of taxa often distinguished on the basis of variations in the shape, size, and details of the lorica Campbell 1929, 1939). Therefore, lorica morphology remains the most important feature in tintinnid taxonomy (Santoferrara and Alder 2009;Kršinić 2010a). Thus, individuals, untreated other than preserved, may be identified by examination using a transmitted light microscope rather than requiring cytological staining, biochemical screening, or RNA sequencing.…”