Short Note Size Variations in the Morphological Structures of Thermocyclops Decipiens (kiefer 1929) (copepoda Cyclopoida) from South-southeast Brazilian Rivers

Size variation in the morphological structures of microcrustaceans has been frequently reported for temperate environments (Einsle, 1988; Ricarddi and Mariotto, 2000). According to Dole-Olivier et al. (2005) these variations can be adaptative responses to different environmental factors, such as predation, competition, temperature and density. Most of these conclusions are based on studies of cladocerans and ostracods (DoleOlivier et al. 2005). For copepods studies have shown the influence of temperature, food availability, predatory avoidance and mainly in reproductive performance, due to the sexual reproduction strategy (Tonolli, 1971; Riera and Estrada, 1986; Einsle, 1988; Ricarddi and Mariotto, 2000; Dole-Olivier et al., 2005; Iepure, 2005). The genus Thermocyclops (Copepoda Cyclopoida) is largely distributed in Brazilian freshwater ecosystems, represented mainly by Thermocyclops decipiens (Kiefer 1929) and Thermocyclops minutus (Lowndes, 1934). Both species are frequently mentioned in studies on ecology of zooplankton communities, considering temporal and spatial fluctuation, trophy interactions and also reproductive aspects (PadovesiFonseca et al., 2002, Lansac-Tôha et al., 2004; Silva and Matsumura-Tundisi, 2005; Sartori et al., 2009). These species can also be used as efficient bioindicators of environmental conditions. Thermocyclops decipiens has successfully occupied meso and eutrophic waters, while T. minutus is more frequently registered in oligo and mesotrophic environments (Padovesi-Fonseca et al., 2002; Silva and Matsumura-Tundisi, 2005; Landa et al., 2007; Nogueira et al., 2008). The goal of this study was to investigate differences in size proportion of T. decipiens morphological structures. The analyzed animals were obtained from zooplankton samples of four Brazilian hydrographic basins (Fig. 1): Paraná River – in Patos Lagoon, adjacent to Ivinhema River (22o49’29’’S and 53 o33’40’’W); Paranapanema River Chavantes Reservoir ( 23o14’08’’S and 49o39’35’’W); Jordão River (Iguaçu River Basin) Santa Clara Reservoir (25o37’57’’S and 51o55’58’’W) and in the Uruguay River Itá Reservoir (27o17’58’’S and 52o21’36’’W). The sampling sites correspond to limnetic zones of large and deeper hydroelectric reservoirs (> 40m depth), except for Patos Lagoon (Paraná River), a shallow floodplain lake characterized by well developed littoral zone colonized by aquatic macrophytes (Lansac-Tôha et al., 2004). The hypothesis is that the different populations of these aquatic ecosystems can exhibit morphological variations. Thirty adult females from each site were dissected and 20 individual morphological structures were measured in microscope with micrometric scale (Zeiss Standard 20): body total length (BTL), caudal setae medial external length (MESL), medial internal length (MISL) and internal length (ISL), cephalothoraxes widths (CP1W, CP2W, CP3W, CP4W), genital width (GSW), basis of setae caudal medial external width (MESW), medial internal width (MISW) and internal width (ISW), coxopodit width (CoxW), inter-coxal sclerites of L4 width (ISW), and length and width measures of furca (FL and FW), L4 endopod (L4L and L4W) and apical thorn of L4 (ATL and ATW) (Fig. 2A). Several of the measured morphological structures were the same ones analyzed by Iepure (2005). The variability of individual differences was checked by multivariate analysis of variance (Manova/ Pillai’s test). Differences of all structures were significant