Feeding behavior and trophic niche partitioning between co-existing river otter species

Niche partitioning occurs among coexisting populations to reduce the effects of competitive exclusion among species of similar niche. The aim of the present study is to verify the trophic niche partitioning and feeding behavior between two mustelids, the Giant otter and the Neotropical otter, through the dry and rainy season hydrologic of the Lower Xingu River. Our results suggest that the diets of both mustelids are composed primarily of fish of the family Anostomidae (Headstanders). Despite extensive niche overlap, our results indicate partitioning is facilitated by differences in niche breadth, with potential implications for conservation of both species in the case of declines in prey abundance and diversity. Both species inhabit an area recently impacted by completion of the Belo Monte Hydropower Plant, resulting in large changes to the hydrologic regime. Thus, our results provide important information for conservation efforts regarding the feeding behavior and co-occurrence of both species, as well as providing a baseline for monitoring future health of these mustelid populations. The present study is the first to test the hypothesis of niche partitioning between these two mustelids outside a protected area in the Amazon.

     

Influence of the culture medium composition on the excreted/secreted proteases from <Emphasis Type="Italic">Streptomyces violaceoruber</Emphasis>

Streptomyces violaceoruber produces two different classes of mycelium, the substrate and the aerial mycelium. Since proteases have been associated with morphological turnover processes in other Streptomyces species, the presence of excretory/secretory proteolytic activities was investigated here in S. violaceoruber culture supernatants. Various polypeptide bands, with apparent molecular masses ranging from 40 to 180 kDa, were detected in soy trypticase broth (STB) culture media supernatants following 72 h of growth, using Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Zymograms showed the presence of five proteolytic enzymes (Spvio1–5), which migrated as bands of 167.7, 130.7, 110.7, 48.3 and 40.9 kDa, respectively. The characterization of these proteases by specific inhibitors showed that Spvio1–4 belong to the serine protease group and Spvio5 corresponds to a cysteine protease. Additionally, Spvio2 and 5 were inhibited by a mixture of EDTA and EGTA, indicating that both require divalent cations. The protease pattern obtained in STB enriched with glucose was identical to that obtained in STB. However, Spvio3 and 4 were absent when nitrogen was added to the culture medium. Cell death was fluorescently detected following 72 h of S. violaceoruber growth in STB and in STB that was enriched with glucose. On the contrary, no cell death was detected in nitrogen-enriched STB media. Additionally, the formation of the aerial mycelium was impaired in solid cultures of STB media enriched with nitrogen. These results demonstrate that the composition of the media influences the morphological turnover of the colony and the pattern of excreted/secreted proteases from S. violaceoruber, and suggest that Spvio3 and 4 are involved in the aerial mycelium formation.     

Length‐weight relationships of three freshwater fish species from the Cujubim Sustainable Development Reserve,Amazonas, Brazil

Length–weight relationships (LWR) were provided for three fish species from Cujubim Sustainable Development Reserve, drainages of the Jutaí River Basin, a tributary of the Solimões River, part of the Central Amazon Biodiversity Corridor, Amazonas, Region North of Brazil. Specimens were collected in March 2006 using gill nets with mesh sizes range between 2 and 18 cm. The LWRs for all species are provided by the first time, and two new maximum length are recorded.     

Weight-length relationships for intertidal fish fauna in a mangrove estuary in Northern Brazil

Weight‐length relationships (WLR) are presented for 40 fish species inhabiting the mangrove creeks in the Curuçá Estuary in Northern Brazil. Samples were taken bimonthly between July 2003 and 2004 with a fyke net. This study represents the first reference available on WLR for 28 fish species.     

Length–weight relationships for seven fish species from Marajó Bay,Amazon estuary,northern Brazil

Length–weight relationships (LWR) were estimated for seven fish species inhabiting the intertidal mudflats in the Marajó Bay, northern Brazil. A total of 514 specimens were collected quarterly between November 1994 and December 1995 using a beach seine (5 mm mesh size between opposite knots). Slope b of the LWR varied between 2.93 and 3.11, with a mean of 3.02. This study represents the first reference on LWRs for seven species and a new maximum length record for one of these species.     

Exploring the molecular diversity of Eleotridae (Gobiiformes) using mitochondrial DNA

Species with wide geographic distributions can consist of different lineages or even of different species. The present study evaluated the molecular diversity of the family Eleotridae by analyzing sequences of the COI gene from species collected in different locations in a Neotropical region as well as sequences from BOLD and GenBank. The analysis revealed the distinction and differentiation of a variety of species with high statistical support, including Gobiomorus dormitor (two lineages), Dormitator maculatus (three lineages) and Eleotris fusca (three lineages), and a number of different lineages of Microphilypnus. This indicates the existence of a number of unknown cryptic species that have not been reported previously, increasing the potential diversity of eleotrid species in the Neotropics.     

Trophic niche segregation among herbivorous serrasalmids from rapids of the lower Xingu River,Brazilian Amazon

In the Amazon Basin, several species of herbivorous serrasalmid fishes inhabit rapids, but it is unknown if they partition food resources during the annual low-water period when fish densities are high within greatly reduced volume of aquatic habitat. We investigated the trophic ecology of juveniles and adults of three species, Myleus setiger, Ossubtus xinguense, and Tometes kranponhah, common in rapids of the Xingu River during the low-water period. Diets, stable isotope ratios of muscle tissue, and functional traits were analyzed for 59 specimens of M. setiger, 175 of O. xinguense and 215 of T. kranponhah. The three species overlapped in dietary and isotopic space, with adult O. xinguense being most divergent. Juvenile and adult T. kranponhah and juvenile O. xinguense, two groups with broad diets, had lowest trophic positions estimated from isotopic data. Adult O. xinguense had the highest trophic position despite having large amounts of Podostemaceae in the diet. High trophic overlap during the low-water period suggests that either food resources are not limiting, or niches are partitioned by other means. Differences in functional traits of the three serrasalmids could be associated with differential efficiencies of swimming and feeding within microhabitats that vary according to water velocity and/or structural complexity.