RESUMO
The interpretation of isotopic data in ecology requires knowledge about two factors: turnover rate and the trophic discrimination factor, which have not been well described in freshwater shrimps. We performed a 142-day diet shift experiment on 174 individuals of the omnivorous shrimp Macrobrachium borellii, measured their growth, and temporally serially sampled muscle and hepatopancreas tissue to quantify carbon and nitrogen incorporation rates and isotope discrimination factors. Shrimps were fed with artificial diets (δ13C = -26.1, δ15N= 2.1) for 45 days in attempt to standardize the shrimps' initial δ13C and δ15N values for subsequent experiments. Shrimps were then fed with another artificial diet (δ13C = -16.1, δ15N = 15.8) and the change in δ13C and δ15N was observed for a period of 97 days. The trophic discrimination factor (∆) for δ13C was significantly higher in hepatopancreas (0.7 ± 0.36) than in muscle (-0.1 ± 0.83); however, the opposite was the case for δ15N (1.7 ± 0.43 and 3.6 ± 0.42, respectively). In the hepatopancreas the mean residence time (τ) of 13C was 26.3 ± 4.3 days compared to a residence time of 16.6 ± 5.51 days for δ15N, whereas the τ in muscle was 75.8 ± 25 days for δ13C and 40 ± 25 days for δ15N. The rate of incorporation of carbon into muscle was higher than that predicted by allometric equations relating isotopic incorporation rate to body mass that was developed previously for invertebrates. Our results support ranges of traditional trophic discrimination factor values observed in muscles samples of different taxa (∆15N around 3â3.5 and ∆13C around 0â1), but our work provides evidence that these traditionally used values may vary in other tissues, as we found that in the hepatopancreas ∆15N is around 1.7.
RESUMO
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.
RESUMO
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.
Assuntos
Decápodes/anatomia & histologia , Dieta , Animais , Comportamento Alimentar/fisiologia , Água Doce , Masculino , Sensilas/anatomia & histologiaRESUMO
The relative growth of a number of morphological dimensions of the South American freshwater crab Trichodactylusborellianus (Trichodactylidae) were compared and related to sexual dimorphism. Crabs were collected from ponds in the Middle Paraná River in Argentina. A regression model with segmented relationship was used to test for relative growth between these measurements where breakpoints infer the body size at which crabs reach sexual maturity. In both sexes the carapace width and the length, height, and thickness of the right and left chelae were measured, as well as the male pleopod length and the female abdomen width. All of these measurements were found to show positive allometry with the exception of the male pleopod length and the left chelae, which did not show a breakpoint. In females the breakpoint for the abdomen width inferred a morphological sexual maturity at carapace width 6.9 mm. In males the break point for the pleopod length was at carapace width 6.6 mm, with that for the chelae measurements was between carapace widths 6.4 and 6.9 mm. The relative growth pattern in Trichodactylusborellianus was found to be similar to that recorded for other species of the family Trichodactylidae.
RESUMO
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
Assuntos
Catálogo , Crustáceos/classificação , Disciplinas das Ciências Naturais , MuseusRESUMO
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
