Synchaeta jollyae (Shiel & Koste) (Rotifera, Synchaetidae): an overlooked species or a newcomer in Neotropical freshwaters?

Populations of Synchaeta jollyae (Shiel & Koste, 1993) (Rotifera), a species recently recorded for the first time in Brazil and South America, were analyzed in reservoirs in Southeast Brazil. Sampling was carried out monthly from August 2006 to July 2007 at Furnas Reservoir in the Rio Grande basin, state of Minas Gerais, and in four cascade reservoirs in the Tietê River basin (Barra Bonita, Bariri, Ibitinga and Nova Avanhandava) state of São Paulo, in June and September 2008 and in January and May 2009. Synchaeta jollyae occurred in most samples and periods. From the results obtained it is evident that S. jollyae occurs in water bodies of varied trophic status but reaches larger populations in eutrophic water bodies and during lower temperature periods. The greatest densities of S. jollyae were found in the eutrophic Bariri Reservoir, on the Tietê River, during the winter. Mann-Whitney test confirmed the significant difference between the population densities in periods of high and low temperatures, with populations reaching higher densities at lower temperatures. It is not yet possible to tell whether S. jollyae is a widely distributed species that has been overlooked in previous plankton studies in South America. Wherever these populations of S. jollyae might have originated, it appears to be a species well established and adapted to a wide range of conditions in the Neotropics.

Gaps in our knowledge of deficiencies regarding the taxonomy of small invertebrates can impose great limitations on the study of freshwater biodiversity. In some groups such as Protozoa and Rotifera, species are easily overlooked or incorrectly identified. This seems to be the case of the rotifer Synchaeta jollyae (Shiel & Koste, 1993) (Rotifera, Synchaetidae), first described in Australia by Shiel & KoSte (1993). This species was recently recorded in the Neotropical region (NegreiroS et al., 2011) and, as originally suggested by Shiel & KoSte (1993), it could have a widespread distribution. Mapping the distribution of newly recorded species is also a tool for tracking the introduction of exotic invasive species, nowadays a priority regarding biodiversity conservation.
In this study, the populations of S. jollyae in some Southeast Brazilian reservoirs are analyzed regarding temporal occurrence, population abundances and relationships with environmental variables, aiming to provide information on the environments where this species has been found and some population parameters.
Sampling was carried out each month from August 2006 to July 2007, at six sites located in the Sapucaí River arm of Furnas reservoir. In the four Tietê River reservoirs samples were collected in June andSeptember 2008 andin January andMay 2009. Physical and chemical variables were determined in situ in all the water samples taken from the Furnas and Tietê reservoirs and are listed in Table I, with an indication of the technique employed.
The zooplankton were collected by plankton net of 68 mm mesh, preserved in 4% formaldehyde and stored in polyethylene flasks. Subsamples of 1 mL were transferred to a Sedgwick-Rafter cell, and Synchaeta jollyae specimens were counted under an optical microscope at up to 200x magnification. The species was identified from descriptions published by Shiel & KoSte (1993) and Nogrady & SegerS (2002).
Comparisons of Synchaeta jollyae densities between the periods of higher and lower temperatures were performed by the application of the Mann-Whitney test. This analysis was carried out with the program XLSTAT (addiNSoft, 2009) Specimens of Synchaeta jollyae were found in the samples collected in every month, except March and May 2007, and at all six sampling sites in the reservoir. The highest densities occurred at a site near a discharge of domestic wastewater, where a maximum of 3,370 ind m -3 was recorded in June 2007 ( Fig. 1) Mid-Low Tietê River Basin (São Paulo). In the reservoirs of Middle Tietê River, mean values of water temperature ranged from 20.07 ± 0.05°C in Barra Bonita to 26.52 ± 0.84°C in Bariri, with higher values in January and May 2009. The pH ranged from slightly acid to alkaline with readings between 5.44 ± 0.11 in Barra Bonita (June 2008) and 7.89 ± 0.81 in Bariri (January 2009). The concentration of dissolved oxygen in the water column ranged from 0.48 ± 1.82 µg L -1 in Barra Bonita (January 2009) to 5.70 ± 3.82 µg L -1 in Ibitinga (June 2008). There was a tendency for higher values of electrical conductivity to be seen in reservoirs during the dry season than during the rainy (100.0 to 277.0 µS cm -1 ). The mean Tab. I. Methods used to record or analyze physical and chemical properties of the water at sampling sites in the Furnas reservoir (state of Minas Gerais, Brazil) and those on the Mid-low Tietê River (state of São Paulo, Brazil).

RESULTS
Rio Grande Basin (Minas Gerais). In the period August 2006 to July 2007, during which samples were collected from the Sapucaí River arm in the Furnas reservoir, the well defined climatic seasons were reflected in wide variations in the physical and chemical properties of the water. Temperature varied between 18°C and 31°C, the pH between slightly acid and alkaline (6.35 to 8.88) and the electrical conductivity from 14.7 to 60 µS cm -1 . The water column transparency ranged from 1.08 m to 15.6 m and dissolved oxygen concentrations were high, with mean values over 8.0 mg L -1 (Tab. II).
Regarding nutrient levels, the highest nitrogen and phosphorus contents were recorded in the rainy period (from October to January); the mean total contents for the year of study were 356.62 µg L -1 ± 202.32 µg L -1 for N and 30.89 µg L -1 ± 34.57 µg L -1 for P. The chlorophyll a levels were low in all months except January, when the mean content was 79.5 µg L -1 ; there was little variation in the other months and the overall mean was 8.5 ± 13.43 µg L -1 . In general, the calculated TSI showed the Furnas reservoir to be oligotrophic (Tab. II), with a slight tendency to become mesotrophic in some compartments in certain months.
concentrations of nitrogen and phosphorus compounds were higher in September 2008 and January 2009, and the mean total content for the year of study was 2000.0 µg L -1 ± 690.0 µg L -1 for N and 94.2 µg L -1 ± 41.8 µg L -1 for P in Barra Bonita reservoir. The chlorophyll a values were high in the rainy period and the mean value varied between 0.45 ± 0.18 µg L -1 in May 2009 (Ibitinga) and 29.31 ± 28.60 µg L -1 in January 2009 (Bariri); the overall mean ranged from 10.3 ± 11.35 µg L -1 to 22.7 ± 31.3 µg L -1 (Tab. III). The calculated TSI indicated that the Barra Bonita and Bariri reservoirs were eutrophic and Ibitinga mesotrophic (Tab. III).
The water temperature in the Nova Avanhandava reservoir (Lower Tietê River), mean values varied from 21.85 ± 0.38°C to 26.73 ± 0.33°C, with higher values in January and May 2009. The pH was slightly acid to near neutral, readings ranging from 5.75 ± 0.31 in September 2008 to 7.10 ± 0.23 in July 2008. The water column of this reservoir generally was well oxygenated, though conditions close to anoxia (0.22 mg L -1 ) were observed on the bottom in January 2009. Electrical conductivity did not vary greatly, but a small rise in the readings occurred during the rainy period (152.0 to 179.0 µS cm -1 ). In contrast, the mean concentrations of nitrogen and phosphorus compounds exhibited wide variations, with higher values at most sites in September 2008 and January 2009. The mean total contents for the year of study were 681.5 µg L -1 ± 97.8 µg L -1 for N and 40.0 µg L -1 ± 18.6 µg L -1 for P. The chlorophyll a levels were highly variable during the months of study and the mean was 1.87 ± 0.93 µg L -1 in May 2009 and 24.99 ± 21.5 µg L -1 in July 2008, the overall mean being 10.2 ± 13.3 µg L -1 (Tab. III). In general, the calculated TSI showed the Nova Avanhandava reservoir to be oligotrophic (Tab. III) with a slight tendency to become mesotrophic in certain months.
In the mid Tietê basin (the first three reservoirs  Tab. IV. Changes in Synchaeta jollyae (Shiel & Koste, 1993)  Tab. V. Means and standard deviations of water temperature and densities of Synchaeta jollyae (Shiel & Koste, 1993)  Statistical analysis. Population abundances in both systems (Furnas and Tietê reservoirs) showed statistically significant differences between the summer (rainy) and winter (dry) periods (Tab. V).

DISCUSSION
Southeast Brazil is characterized by two well-defined climatic seasons, namely a cooler dry winter and a hot rainy summer, resulting in great changes in abiotic and biotic conditions of aquatic ecosystems, especially in large reservoirs. Several authors (reyNoldS, 1984;Smith, 1986;hwaNg et al., 2003) have already shown evidence of the important role environmental factors play in controlling the structure and dynamics of plankton communities. In many tropical reservoirs, the zooplankton communities undergo great changes in abundance and a noticeable seasonal species succession.
In the studied reservoirs, S. jollyae was abundant and appeared at all times around the year, although its highest population densities occurred at lower temperatures. It is likely that its distribution is correlated with mildly warm waters. According to rougier et al. (2000), Synchaeta species generally tolerate relatively cool temperatures as in the north Mediterranean. It is probable that at the mild temperatures of tropical winter outperforms this species has better performance than other rotifer and cladoceran competitors.
The occurrence of this rotifer seems to be independent of the trophic status of the freshwater habitat, as it has been found in reservoirs of contrasting trophic states.
It is not yet possible to tell whether S. jollyae is a widely distributed species that has been overlooked in previous plankton studies in South America. It is however intriguing that it has not been noticed in the reservoirs under study which have been regularly 1 Recebido em 13 de outubro de 2011. Aceito em 08 de maio de 2012. ISSN 0073-4721 Artigo disponível em: www.scielo.br/isz sampled for decades, opening the possibility that it could be a newcomer. The globalization of biodiversity, with invasive species arriving from various continents, is also a possibility.
Wherever these populations of S. jollyae might have originated, it appears to be a species well established and adapted to a wide range of conditions in the neotropics. It will be worth checking whether it has or will reach a much wider distribution in South American freshwaters.