Influence of temperature and conductivity on the life-history characteristics of a pampean strain of Brachionus plicatilis.

In the present work, we provide the first approach about the life-history of Brachionus plicatilis in South America. We tested with laboratory experiments the response of the pampean strain of B. plicatilis for two of its main stressors (conductivity and temperature). We evaluated the effects of eight conductivity values from 1 to 17 mS.cm-1 and two temperatures (15 and 25 °C) to compare its abundance with those obtained in the pampean lotic and lentic environments, where this rotifer is frequent or dominant. The results demonstrated that the increase in population-growth rate and the peak of abundance occurred at the highest temperature and at medium conductivity. Minimum values were obtained at the lowest temperature and conductivities analyzed, but the final density attained was nevertheless similar to those recorded in the pampean environments at the optimum conductivity and during the spring and summer seasons. Males, mictic females, and resting eggs were observed at the minimum and maximum conductivities, revealing the strategy of this species for maintaining dominance in environments with fluctuating salinity. The experiments also indicated the possible behavior of this relevant member of the zooplankton community within a scenario of increasing temperature and salinity related to the climate changes occurring in the pampean region.

Phytoplankton chlorophyte structure as related to ENSO events in a saline lowland river (Salado River, Buenos Aires, Argentina).

We analyzed the phytoplankton present in the lower sector of the Salado River (Buenos Aires, Argentina) for 10 years (1995-2005) and detected significant changes occurring in chlorophyte abundance and species richness during La Niña event (1998-1999), which period was analyzed throughout the entire basin (main stream and tributaries). We compared the physicochemical and biologic variables between two El Niño-La Niña-Southern Oscillation (ENSO) periods - El Niño (March 1997-January 1998) and La Niña (May 1998-May 1999) - to identify possible indicators of a relationship between climatic anomalies and chlorophyte performance. Chlorophyte density increased during the La Niña. Under normal or extreme hydrologic conditions, mobile (Chlamydomonas spp.) and nonmobile (Monoraphidium spp.) chlorophytes codominated. These species belonged to Reynolds's functional groups X1 and X2, those typical of nutrient-enriched environments. Comparative analyses between El Niño and La Niña periods indicated significant differences in physicochemical (K(+), dissolved polyphenols, particulate reactive phosphorus, alkalinity, pH) and biologic (species diversity and richness, phytoplankton and chlorophyte total densities) variables between the two periods at all basin sites. During the La Niña condition, species richness was greater owing to interconnected shallow lakes and drainage-channel inputs, while the Shannon diversity index was lower because of the high abundance values of Monoraphidium minutum. A detailed analysis of the chlorophytes in the entire basin, indicated that changes in density and species dominance occurred on a regional scale although diverse chlorophyte assemblages were identified in the different sectors of the Salado River basin. After La Niña event, the entire basin had the potential to revert to the previous density values, showing the resilience to global environmental changes and the ability to reestablish the general conditions of stability.

Hypotrichous ciliates (Protozoa: Ciliophora) from a temporary pond in Argentina, with redescription of Apoamphisiella hymenophora (Stokes, 1886) Berger, 1999.

Hypotrichous ciliates collected in the plankton and soil samples from a temporary pond in Buenos Aires province, Argentina, were characterized after live observations and protargol impregnation. Apoamphisiella hymenophora (Stokes) Berger is redescribed and the neotype material deposited. Apoamphisiella hymenophora differs from its congeners in having 2 macronuclear nodules, 1 contractile vacuole with anterior and posterior collecting canals, the absence of cortical granules, 2 cirri behind the rightmost frontal cirrus, 1 postoral cirrus, 6 dorsal rows of dikinetids along with scattered dikinetids on the right body margin, and 3-9 caudal cirri arranged in groups at the ends of dorsal rows 1, 2, and 4. Rigidohymena candens, R. quadrinucleata, Histriculus histrio, Gastrostyla steinii, and Pseudouroleptus caudatus are new for the Argentine microfauna. Since especially the soil ciliates have been almost unexplored in South America, the results from the present investigation describe and contribute to the knowledge of the diversity of these microorganisms within this geographical region.

Morphology and notes on morphogenesis during cell division of Deviata polycirrata n. sp. and of Deviata bacilliformis (Gelei, 1954) Eigner, 1995 (Ciliophora: Kahliellidae) from Argentina.

Described herein are the morphology and certain morphogenetic stages of a new freshwater ciliate species, Deviata polycirrata n. sp., and of Deviata bacilliformis recorded in the soil of a dried temporary pond from Argentina. Ciliates were studied alive and after silver impregnation with Protargol. Deviata polycirrata n. sp. measures 130-180 x 45-70 microm in vivo. The species possesses 8-9 long cirral rows on the right and 9-13 on the left of the oral zone, and 3 dorsal rows of dikinetids. The adoral zone is composed of 39-48 membranelles. There are four macronuclear nodules and usually two micronuclei. A single contractile vacuole is located equatorially on the left body margin. This new species mainly differs from its congeners in having a higher number of cirral rows, the three long dorsal rows of dikinetids (vs. usually one to two dorsal rows of dikinetids), and a higher number of adoral membranelles. The other species reported here, D. bacilliformis, is recorded for the first time in Argentina. Unlike previous observations on this species, on the dorsal surface there are cirral rows that are preceded by cilia (combined cirral rows), and stomatogenesis begins with the proliferation of non-ciliferous basal bodies some distance posterior to the buccal vertex.

Description of Deviata rositae n. sp., a new ciliate species (Ciliophora, Stichotrichia) from Argentina.

Soil samples were taken from a temporary pond located in Buenos Aires province, Argentina, during the dry phase in the summer of 2005. The ciliates were studied alive and after staining with protargol. Deviata rositae n. sp. measures 112-154 microm in length and 21-28 microm in width in vivo and has a vermiform body. The contractile vacuole is located in the mid-body on the left. The macronucleus is moniliform and there are 1-3 micronuclei. The oral apparatus is composed of 14-18 adoral membranelles and straight paroral and endoral membranes that never intersect each other. The somatic ciliature is arranged in four frontal cirri, one buccal cirrus, six long and slightly spiraled rows of cirri with the first right row extending up to the equatorial or sub-equatorial region, and two dorsal rows of dikinetids. This new species of Deviata primarily differs from its congeners by the number of macronuclear nodules and the number and disposition of the dorsal rows of dikinetids.

Pelagostrobilidium wilberti n. sp. (Oligotrichea, Choreotrichida): morphology and morphogenesis.

Morphology, infraciliature, morphogenetic features, and some ecological data for Pelagostrobilidium wilberti n. sp. are described. This new species was collected from a temporary pond in Magdalena, Buenos Aires province, Argentina, which was sampled monthly from August 2003 to July 2005. The species was found in autumn and winter. Observations were made in vivo and after staining with protargol. Pelagostrobilidium wilberti n. sp. measures 63-84 x 42-49 microm in vivo and is conical in shape, with a posterior spine-like cytoplasmic process. It possesses 6 somatic kineties, with kinety 2 sinistrally curved and shorter than the others. The oral apparatus is composed of 25-32 external and two internal membranelles. The macronucleus is horseshoe-shaped and located beneath the oral apparatus; two or three spherical micronuclei lie dorsally. There is a posterior contractile vacuole. Morphogenesis is hypo-apokinetal and begins dorsally between the curved kinety 2 and kinety 3. After the discovery of this new species, the diagnosis of the genus Pelagostrobilidium was amended.