A comparative study of the gastric ossicles of Trichodactylidae crabs (Brachyura: Decapoda) with comments on the role of diet and phylogeny in shaping morphological traits.

The gastric armature of decapod foregut is a feeding structure that sparks controversial debates about the role dietary and historical components have in shaping its morphological traits. Having previous information about the natural diet is an interesting way to gather evidence on this issue. For the present study, we analyzed the morphological traits of gastric ossicles involved directly in the maceration of food in nine species of freshwater crabs of the family Trichodactylidae (Brachyura: Decapoda) representing five genera, three tribes and two subfamilies. The analyzed gastric ossicles were quite consistent among closely related species, suggesting that the observed traits had a clear phylogenetic component. However, it was also noted that the morphological traits of the gastric teeth of trichodactylid crabs match well with the natural diet and presented likeness with general features of other species with a similar trophic habit. We discuss the influence of phylogeny and function on the design of morphological traits and propose to quantify the role of phylogeny and function in shaping morphological traits through the analysis of phylogenetic signals.

Functional morphology of comminuting feeding structures of Trichodactylus borellianus (Brachyura, Decapoda, Trichodactylidae), an omnivorous freshwater crab.

Crustaceans exhibit great diversity of feeding structures with morphological traits that are useful to infer the general trophic habits of species. In this study, we analyzed the functional morphology of comminuting feeding structures (mandibles, chelipeds, gastric mill) of the freshwater crab Trichodactylus borellianus directly related with the food fragmentation. The heterochely and mechanical advantage (MA) of the chelae were also studied. In both analyses, we considered the relationship between morphology and the natural diet. We expected to find a consistent relation between feeding habits and morphological traits. In general, we found simple structures armed with uniform setal systems and feeding appendages without pronounced teeth or spines. Mandibles have primarily cutting functions, helping with the food anchoring and fragmentation with mandibular palps armed with pappose setae. Chelipeds were covered with spines and simple setae. Adult males exhibited right-handedness with high MA of the major chelae. The ingested, relatively large pieces of food are finally chewed by a gastric mill equipped with sharp cusps characteristic of decapods with low ingestion of crude fiber material. The morphology of the feeding apparatus revealed that it is well adapted to an omnivorous diet, being able to cope with dietary changes.

Pesticide effects on crabs: how environmental concentrations of endosulfan and chlorpyrifos affect embryos.

The objectives of this work were to evaluate the effects of environmentally relevant chlorpyrifos and endosulfan, concentrations in the incubation period, effective hatching and survival of embryos and neonates of the freshwater burrowing crab, Zilchiopsis collastinensis (Decapoda, Trichodactylidae). Both pesticides were prepared from commercial and technical grade products. The exposure to about 100, 200, and 400 ng endosulfan L(-1), and 48, 240, and 1,200 ng chlorpyrifos L(-1) did not cause differences in the incubation period or in effective hatching but decreased survival of neonates, especially in the concentrations prepared from the technical grade product. Even if these concentrations are below the median lethal concentration (LC50) values for embryos, these caused a significant decrease in the survival of neonates, i.e. when crabs are outside the egg and not protected by chorion. The decrease in the neonate population caused by these concentrations, which could be found in the environment, might impact aquatic communities.

Morphological variation of freshwater crabs Zilchiopsiscollastinensis and Trichodactylusborellianus (Decapoda, Trichodactylidae) among localities from the middle Paraná River basin during different hydrological periods.

Measures of hydrologic connectivity have been used extensively to describe spatial connections in riverine landscapes. Hydrologic fluctuations constitute an important macrofactor that regulates other environmental variables and can explain the distribution and abundance of organisms. We analysed morphological variations among individuals of two freshwater crab species, Zilchiopsiscollastinensis and Trichodactylusborellianus, from localities of the middle Paraná River basin during two phases of the local hydrological regime. Specimens were sampled at sites (localities) of Paraná River, Saladillo Stream, Salado River and Coronda River when water levels were falling and rising. The conductivity, pH, temperature and geographical coordinates were recorded at each site. The dorsal cephalothorax of each crab was represented using 16 landmarks for Zilchiopsiscollastinensis and 14 landmarks for Trichodactylusborellianus. The Canonical Variate Analyses showed differences in shape (for both species) among the crabs collected from the Paraná and Salado Rivers during the two hydrologic phases. We did not find a general distribution pattern for shape among the crab localities. During falling water, the shapes of Zilchiopsiscollastinensis were not related to latitude-longitude gradient (i.e., showing greater overlap in shape), while during rising water the shapes were ordered along a distributional gradient according to geographical location. Contrary, shapes of Trichodactylusborellianus were related to latitude-longitude during falling water and were not related to distributional gradient during rising water. The cephalothorax shape showed, in general, no statistically significant covariations with environmental variables for either species. These results show that each freshwater crab species, from different localities of the middle Paraná River, remain connected; however, these connections change throughout the hydrologic regime of the floodplain system. This study was useful for delineating how the relation among shapes of crabs of localities varies during two phases of the hydrological regime and for estimating the connections and geographical patterns in the floodplain system.

Bioaccumulation in freshwater crabs. Endosulfan accumulation in different tissues of Zilchiopsis collastinensis P. (Decapoda: Trichodactylidae).

We examined the bioaccumulation of α- and ß-endosulfan and endosulfan sulfate in tissues from the crab Zilchiopsis collastinensis. There was more endosulfan accumulated in the hepatopancreas (from <2 to 467.8 ng g(-1)) than in the gonads (from <2 to 52.1 ng g(-1)) or muscles (<2 ng g(-1)). The endosulfan concentrations in the hepatopancreas decreased over time and with the endosulfan dilution (p < 0.05). In the gonads there was little bioaccumulation, which did not vary over time (p > 0.05). The hepatopancreas is a dynamic organ that is able to depurate itself, whereas the gonads act as a sink for pesticides.

Trophic ecology of the freshwater prawn, Pseudopalaemon bouvieri (Decapoda: Palaemonidae) in Northeastern Argentina, with remarks on population structure.

Freshwater decapod crustaceans are important components of food webs in these environments, but little is known about the diet of species that live in tropical waters. We studied the feeding ecology of the prawn Pseudopalaemon bouvieri and its population structure in two different areas with six lagoons, with a different composition and abundance of aquatic macrophytes. At each site of macrophytes banks, 18 prawns sample was collected with a hand net (1mm mesh size) from 1m2. In the laboratory, prawns cephalothorax length was measured, sex determined, and a total of 208 stomachs were examined for food items. Our results showed that the population abundance varied between 10 ind/m2 and 1 411 ind/m2. The cephalothorax length ranged between 6mm and 21mm, and the male:female ratio varied between 0.3 and 1.0, with a higher proportion of ovigerous females (21%) in area one than area two. P. bouvieri is omnivorous, and its diet was principally based on algae, plant remains, Protozoa, Rotifera, Oligochaeta, Crustacea, Insecta, detritus and other items. The analysis of the stomach content did not reveal any significant difference in the diet between juveniles and adults, and males and females of both areas consumed a similar diet (Kruskal-Wallis test p=0.8273). We concluded that the dietary items consumed by prawns and the niche breadth were similar between the two areas, although the proportion of items consumed varied between lagoons of both areas. The density of P. bouvieri was different between areas, but the size of cephalothorax (CL) was similar.

Trophic ecology of the freshwater prawn, Pseudopalaemon bouvieri (Decapoda: Palaemonidae) in Northeastern Argentina: with remarks on population structure

Freshwater decapod crustaceans are important components of food webs in these environments, but little is known about the diet of species that live in tropical waters. We studied the feeding ecology of the prawn Pseudopalaemon bouvieri and its population structure in two different areas with six lagoons, with a different composition and abundance of aquatic macrophytes. At each site of macrophytes banks, 18 prawns sample was collected with a hand net (1mm mesh size) from 1m². In the laboratory, prawns cephalothorax length was measured, sex determined, and a total of 208 stomachs were examined for food items. Our results showed that the population abundance varied between 10 ind/m² and 1 411 ind/m². The cephalothorax length ranged between 6mm and 21mm, and the male:female ratio varied between 0.3 and 1.0, with a higher proportion of ovigerous females (21%) in area one than area two. P. bouvieri is omnivorous, and its diet was principally based on algae, plant remains, Protozoa, Rotifera, Oligochaeta, Crustacea, Insecta, detritus and other items. The analysis of the stomach content did not reveal any significant difference in the diet between juveniles and adults, and males and females of both areas consumed a similar diet (Kruskal-Wallis test p=0.8273). We concluded that the dietary items consumed by prawns and the niche breadth were similar between the two areas, although the proportion of items consumed varied between lagoons of both areas. The density of P. bouvieri was different between areas, but the size of cephalothorax (CL) was similar.

Los crustáceos decápodos de agua dulce son un componente importante de la cadena trófica, pero poco se sabe sobre la dieta de las especies que viven en aguas tropicales. Nosotros estudiamos la ecología alimentaria del camarón Pseudopalaemon bouvieri y la estructura de su población en dos áreas diferentes con seis lagunas, con una diferente composición y abundancia de macrófitas acuáticas. En cada sitio poblado con macrófitas, se tomaron 18 muestras con una red manual (1mm de tamaño de malla) de 1m². En laboratorio, se midió la longitud de cefalotórax de los camarones y se determinó el sexo. Asimismo, fueron examinados un total de 208 estómagos para determinar su alimentación. Nuestros resultados mostraron que la abundancia de la población varió entre 10 ind/m² y 1 411 ind/ m². La longitud de cefalotórax osciló entre 6 y 21mm, y la razón macho:hembra varió entre 0.3 y 1.0, con una mayor proporción de hembras ovígeras (21%) en el área 1 que en el área 2. P. bouvieri es omnívoro y su alimentación se basa principalmente en algas, restos de plantas, protozoos, rotíferos, Oligochaeta, crustáceos, Insecta, detrito y otros ítems. El análisis del contenido estomacal no reveló ninguna diferencia significativa en la dieta entre juveniles y adultos, y los machos y hembras de ambas áreas consumieron una dieta similar (Kruskal-Wallis, p=0.8273). Nosotros concluimos que los ítems alimentarios consumidos por los camarones y la amplitud de nicho fueron similares entre las dos áreas, aunque la proporción de ítems consumidos varió entre lagunas de ambas áreas. La densidad de P. bouvieri fue diferente entre áreas, pero el tamaño del cefalotórax (CL) fue similar.

Water quality and zooplankton composition in a receiving pond of the stormwater runoff from an urban catchment.

Six storm periods were monitored from November 2002 to September 2005 at two stations of a receiving pond of the stormwater runoff from a small urban catchment of the city of Santa Fe, Argentina. Weekly samples were taken before and after rain events under different conditions of temperature, pluvial precipitation, and duration of the previous dry period. A sampling station was established at the outlet of the catchment (S1) and another one near the outlet of the receiving pond (S2). Both stations differed significantly in their dissolved oxygen (DO) concentration, temperature, transparency, and zooplankton composition. The concentrations of nutrients and BOD5 values indicated permanently eutrophic condition at both stations. After rainstorms, the concentrations of lead, zinc and suspended solids showed a marked increase. The zooplankton composition at S1 was characterized by the abundance of protozoans (Dexiostoma campylum (Stokes) Didinium nasutum Muller, Plagyopila cf nasuta, and Bdelloidea rotifers (Philodina sp and Rotaria sp), while Monogononta rotifers and small cladocerans were dominant at S2. The most abundant species were the rotifers Platyias quadricornis (Ehrenberg), Mytilina ventralis (Ehrenberg) and Lepadella ovalis (Muller), and the cladoceran Chydorus pubescens Sars.

Crustáceos superiores del Museo Provincial de Ciencias Naturales Florentino Ameghino, Sante Fe, Argentina

Listado de los crustáceos superiores, superorden eucarida, que se encuentran en la colección de invertebrados del Museo; integrada por 55 especies agrupadas en 26 familias

Crustáceos superiores del Museo Provincial de Ciencias Naturales Florentino Ameghino, Sante Fe, Argentina

Listado de los crustáceos superiores, superorden eucarida, que se encuentran en la colección de invertebrados del Museo; integrada por 55 especies agrupadas en 26 familias