Sandro Santos

Population biology of the freshwater anomuran Aegla longirostri (Aeglidae) from South Brazilian streams

Abstract This paper describes a population of Aegla longirostri from Ibicuí-Mirim River, Itaára, Rio Grande do Sul State, Brazil, evaluating the size at onset of sexual maturity, relative growth, mean size, size-frequency distribution, sex ratio, ovigerous-rate, and recruitment. Samples were collected monthly from September 1996 to August 1997. Sex, carapace length (CL), cheliped length (ChL), abdomen width (AW), and front width (FW) were recorded for each crab. A total of 586 specimens were collected (277 males, 244 females, and 65 unsexed juveniles). The smallest specimen was 1.5 mm CL and the largest male was 23.8 mm CL. The relative growth analysis and the Mature software showed that the size at onset of sexual maturity was 13.7 mm CL in males and 10.7 mm CL in females. Females were smaller than males and were more abundant in adult classes, whereas males were more representative in juvenile classes. The sex ratio did not differ from 1:1 throughout the collecting period. Recruitment was observed throughout the entire sampling period, but it was higher in the winter months (from June to August). However, ovigerous females were present in spring and summer (from January to April). This population seemed to be at equilibrium during the study period. Recently, this area has been changed because of the construction of a reservoir, and a new study is required to evaluate the present condition of this population of A. longirostri.

Benthic communities of streams related to different land uses in a hydrographic basin in southern Brazil.

Different land uses affect the characteristics of a hydrographic basin, reflected in the river water quality, and consequently affecting the aquatic biota. The benthic community closely reflects the alterations caused by different human activities. In this study, the effects of different land uses were evaluated by analysis of the benthic community structure in streams with urban, agricultural and pasturage influences, as well as areas in better-conserved regions. The abiotic parameters showed distinct seasonal variability, which did not occur with the benthic organisms. A degradation gradient was observed among the study sites, in the headwaters–agriculture–pasture–urban direction. By the CCA its possible to observe that the density of organisms tended to increase along this gradient, whereas richness, diversity, evenness, and EPT families decreased. The most intense effects of land use on the benthic community composition, richness, and diversity were observed in urban areas (F1,4 = 16.0, p = 0.01; F1,4 = 8.97, p = 0.04; respectively). In conclusion a trend in the benthic community is observed in to predict alterations caused for the different land uses, mainly, when the source point pollution, as the case of urban area.

Differences in oxygen consumption and diel activity as adaptations related to microhabitat in Neotropical freshwater decapods (Crustacea).

This study evaluated oxygen consumption (MO(2)) and diel activity in Aegla longirostri, Trichodactylus panoplus and Parastacus brasiliensis (three species of freshwater decapods that occur in sympatry), under two different conditions of O(2) availability, limited and constant; and searched for the existence of a relationship between these two variables. The Kruskal-Wallis test showed that in all the species, MO(2) was higher under constant O(2) availability; T. panoplus and P. brasiliensis showed an oxygen-dependent pattern, while A. longirostri showed higher MO(2) values and less variation in the values between the treatments, indicating a higher and more oxygen-independent metabolism. P. brasiliensis was more active in constant O(2). A. longirostri was more active in limited O(2) and did not show a clear diel activity in any case, showing behavioral changes when in unfavorable conditions. The Spearmans rank correlation analysis did not indicate any relationship between MO(2) and activity. These results indicate a higher metabolism in A. longirostri. The less demanding metabolisms of P. brasiliensis and T. panoplus allow these species to occupy environments that are unavailable to A. longirostri due to differences in dissolved-oxygen concentrations.

Composition and Abundance of Shrimp Species (Penaeidea and Caridea) in Fortaleza Bay, Ubatuba, São Paulo, Brazil

The abundance and spatio-temporal distribution of the caridean and penaeid fauna from Fortaleza Bay, Ubatuba, Sao Paulo, Brazil, were analyzed. Seven transects were sampled over a one year period from November 1988 to October 1989. A total of 17047 shrimps were captured, representing 13 species belonging to 5 families. The interaction of temperature and type of sediment was fundamental in determining the presence and abundance of shrimp species in the area.

The Role of Aeglids in Shredding Organic Matter in Neotropical Streams

We studied the input of allochthonous plant material in Crab Creek, a first-order Neotropical stream and its processing by Aegla longirostri Bond-Buckup and Buckup, 1994, a crustacean shredder. Three experiments were performed: (1) to evaluate the input of allochthonous organic material, five suspended and ten lateral collectors were installed. The yearly input of litter was 1254 g m−2 year−1, with no difference among the seasons of the year. (2) To evaluate the importance of A. longirostri for litter shredding, two types of experimental channels were placed in the stream, both containing litter bags with leaves of Ficus luschnathiana; open channels which allowed individuals of A. longirostri to access the leaves, and channels that were closed with a 5-mm mesh to exclude the crustaceans. The leaves decomposed more rapidly in the presence of aeglids (one-way ANOVA; F = 10 . 1795 ; P = 0 . 0005 ), indicating their potential role as shredders. In addition to accelerating the decomposition rate, the presence of A. longirostri altered the community composition and density of the other macroinvertebrates associated with the litter bags. (3) To evaluate the proportion of leaf input that A. longirostri was able to process, a laboratory experiment was performed. Leaves of Cabralea canjerana, F. luschnathiana, and Nectandra megapotamica, which are common species in the vicinity of the study site, were placed in litter bags and incubated in the stream for 20 days. These leaves were offered to the aeglids, and their consumption was recorded. Leaf consumption did not differ between adult (males and females), but did differ between adults and the juveniles (one-way ANOVA; F = 4 . 1633 ; P = 0 . 0279 ). These data indicated that the adult population of A. longirostri is able to process approximately 5% of the leaves that fall in the creek. These results indicate that Crab Creek receives different types of plant material that will be accessed by the aquatic community. These locations may show a scarcity of insect shredders, with crustaceans, especially aeglids, assuming this role in the community.

Natural diet of the freshwater anomuran Aegla longirostri (Crustacea, Anomura, Aeglidae)

The present study characterized the diet of Aegla longirostri from southern Brazil, in relation to seasonality, size and sex of the animals. The aeglids were sampled bimonthly, from October 1999 to August 2000. The animals were dissected and the Stomach Repletion Degree (RD) and the food items contained in each stomach were recorded. For each food item with RD⩾0.5, the Relative Importance Index (RII) was calculated. Of 399 animals collected, 305 had RD⩾0.5. The following items were found in the stomachs: plant tissue, non‐identified material, sediment, and fragments of adult insects, as well as fragments of Aegla sp., mollusc shells, fish scales and dipteran larvae. Independently of size class and sex, the animals showed a preference for plant tissue. These results demonstrate that A. longirostri has an omnivorous feeding habit, and is mainly herbivorous.

Description of the Agonistic Behavior of Aegla longirostri (Decapoda: Aeglidae)

Abstract Among animals, conflicts are resolved through agonistic behavior, an expression of which embraces a range of fleeing behaviors, displays, up to the extreme of physical combat. This study aims to establish an observation protocol and to describe the aggressive acts of Aegla longirostri. Aeglids were collected in the field and kept for one week of acclimation in individual fishbowls with no contact with other animals. A total of ten pairs of males were paired, the members of each pair differing by no more than 1 mm in cephalothorax length. The behavioral acts were described from the combats videotaped for 20 minutes with each pair, of which 16 were considered aggressive acts. The animals took an average of 198 seconds to start combat. A table of aggression intensity was established, ranging from −2 (fleeing) to 5 (intense combat). There was a significant difference between winners and losers in the time spent in the different levels of intensity and in the duration of the acts performed. Aegla longirostri showed very intense aggression with defined aggressive acts and continued to engage in agonistic behavior for the entire duration that was recorded. This is the first report of aggressive behavior in aeglids, it will be possible to carry out more profound studies on the behavior of these animals.

Sexual dimorphism in Aegla marginata (Decapoda: Anomura)

A study on sexual dimorphism in Aegla marginata was conducted using geometric morphometric methods. The carapace of 47 females and 75 males and the left and right cheliped propodus of 29 females and 40 males were analyzed. Eighteen landmarks were established in the carapace and 10 in the cheliped propodus. A Generalized Procrustes Analysis based on landmark configurations was used to separate the components of size and shape. A Student t-test was used to determine whether statistically significant sexual dimorphism was shown by the carapace and the cheliped propodus. The variation in the shape of the structures was evaluated with a discriminant analysis. Our results show that there is no sexual dimorphism in the carapace of A. marginata. However, the size of the propodus differed statistically between the sexes. The carapace shape differed between the sexes: the females showed a wider posterior area and a narrower anterior area than the males. The shape of the cheliped propodus also differed between the sexes: overall, the females had a longer and narrower cheliped propodus than the males. The variations in the carapace shape found in this study confirm the results of other studies on aeglid morphology; however, the information presented by this study regarding variation in the shape of the cheliped propodus is new to the literature. The geometric morphometric approach applied in this study provided useful tools for achieving the proposed objectives.

Three New Species of Aegla (Anomura) Freshwater Crabs from the Upper Uruguay River Hydrographic Basin in Brazil

ABSTRACT Surveys performed in streams from the sub-basins of the Canoas and Pelotas rivers, which jointly form the Uruguay River in southern Brazil, led to the discovering of three new species of Aeglidae: Aegla brevipalma, Aegla leachi, and A. oblata. Here we present their morphological descriptions coupled with phylogenetic analyses, to infer evolutionary relationships to other aeglids using DNA sequence data from the 16S rRNA and COII gene regions of the mitochondrial genome. The presence of these new species increases the importance of the Upper Uruguay ecoregion for biodiversity richness of freshwater fauna in the Neotropical South America.

New Species and New Records of Endemic Freshwater Crabs from the Atlantic Forest in Southern Brazil (Anomura: Aeglidae)

Abstract Two new species of freshwater anomurans, Aegla pomerana and Aegla muelleri (Decapoda: Anomura: Aeglidae), are described from the Itajaí River basin, the major basin of the Atlantic range, located in the northeastern part of the state of Santa Catarina, Brazil. The new taxa can be distinguished from their congeners based on both morphological and molecular evidence (the nuclear gene 28S, and the mitochondrial genes 12S, 16S, COI, and COII). Based on molecular data, A. pomerana has a phylogenetic relationship with A. leptodactyla, but morphologically these two species differ in several characters. Aegla muelleri is a member of the same clade as A. leptochela, but several morphological characters distinguish the two species. New records of occurrence of A. jarai and A. odebrechtii, which occur in the same hydrographic basin, are provided.