Does the landscape surrounding streams affect the occurrence of freshwater crabs? A case study of the genus Aegla (Crustacea: Decapoda: Anomura) in subtropical basins

RESUMEN Los cambios en el paisaje donde se ubican las cuencas hidrográficas pueden afectar la corriente de diferentes maneras. Con el fin de explorar esta idea, se recogieron los cangrejos de agua dulce del género Aegla Leach, 1820 en la región subtropical del sur de Brasil. También se midió una serie de características del paisaje y las variables físico-químicas en los arroyos de colección y el entorno con el fin de determinar qué factores afectan la ocurrencia de estos crustáceos. Un total de 167 individuos de Aegla fueron recolectados en 21 arroyos. La colección estaba compuesta por tres especies: A. odebrechtii, A. platensis y A. singularis. La ocurrencia de A. platensis estuvo influenciada por variables fisicoquímicas (carbono total y carbono orgánico total) y morfometría (suma de curvas de nivel). La ocurrencia de A. singularis estuvo influenciada por el uso de la tierra (pastos y suelo expuesto y agricultura) y la morfometría (suma de curvas de nivel). Sólo un pequeño número de A. odebrechtii fueron recolectados y su ocurrencia fue influenciada por el uso de la tierra (pastos y suelo expuesto y la agricultura). La topografía del área estudiada limita los tipos de uso de la tierra y las áreas menos favorables para la agricultura (zonas más montañosas) tienen más vegetación ribereña (o menos estrés antrópico). Como resultado, estas áreas están menos sujetas a cambios en la calidad del agua, lo que se refleja en la distribución de las especies de Aegla.

ABSTRACT Changes in the landscape where watersheds are located may affect the stream biota in different ways. In order to explore this idea, we collected freshwater crabs of the genus Aegla Leach, 1820 in subtropical region of southern Brazil. We also measured a number of landscape features and physico-chemical variables in the collection streams and surroundings in order to ascertain which factors affect the occurrence of these crustaceans. A total of 167 individuals of Aegla were collected in 21 streams. The collection was comprised of three species: A. odebrechtii, A. platensis, and A. singularis. The occurrence of A. platensis was influenced by physico-chemical variables (total carbon and total organic carbon) and stream morphometry factors (level curves sum). The occurrence of A. singularis was influenced by land use (pasture and exposed soil and agriculture) and the stream morphometry (level curves sum). Only a small number of A. odebrechtii were collected and their occurrence was influenced by land use (pasture and exposed soil and agriculture). The topography of the area studied limits the types of land use and areas that are less favorable for agriculture (more hilly areas) are have more riparian vegetation (or less anthropic stress). As a result, these areas are less subject to changes in water quality, which is reflected in the distribution of Aegla species.

Does the landscape surrounding streams affect the occurrence of freshwater crabs? A case study of the genus Aegla (Crustacea: Decapoda: Anomura) in subtropical basins

Los cambios en el paisaje donde se ubican las cuencas hidrográficas pueden afectar la corriente de diferentes maneras. Con el fin de explorar esta idea, se recogieron los cangrejos de agua dulce del género Aegla Leach, 1820 en la región subtropical del sur de Brasil. También se midió una serie de características del paisaje y las variables físico-químicas en los arroyos de colección y el entorno con el fin de determinar qué factores afectan la ocurrencia de estos crustáceos. Un total de 167 individuos de Aegla fueron recolectados en 21 arroyos. La colección estaba compuesta por tres especies: A. odebrechtii, A. platensis y A. singularis. La ocurrencia de A. platensis estuvo influenciada por variables fisicoquímicas (carbono total y carbono orgánico total) y morfometría (suma de curvas de nivel). La ocurrencia de A. singularis estuvo influenciada por el uso de la tierra (pastos y suelo expuesto y agricultura) y la morfometría (suma de curvas de nivel). Sólo un pequeño número de A. odebrechtii fueron recolectados y su ocurrencia fue influenciada por el uso de la tierra (pastos y suelo expuesto y la agricultura). La topografía del área estudiada limita los tipos de uso de la tierra y las áreas menos favorables para la agricultura (zonas más montañosas) tienen más vegetación ribereña (o menos estrés antrópico). Como resultado, estas áreas están menos sujetas a cambios en la calidad del agua, lo que se refleja en la distribución de las especies de Aegla.(AU)

Changes in the landscape where watersheds are located may affect the stream biota in different ways. In order to explore this idea, we collected freshwater crabs of the genus Aegla Leach, 1820 in subtropical region of southern Brazil. We also measured a number of landscape features and physico-chemical variables in the collection streams and surroundings in order to ascertain which factors affect the occurrence of these crustaceans. A total of 167 individuals of Aegla were collected in 21 streams. The collection was comprised of three species: A. odebrechtii, A. platensis, and A. singularis. The occurrence of A. platensis was influenced by physico-chemical variables (total carbon and total organic carbon) and stream morphometry factors (level curves sum). The occurrence of A. singularis was influenced by land use (pasture and exposed soil and agriculture) and the stream morphometry (level curves sum). Only a small number of A. odebrechtii were collected and their occurrence was influenced by land use (pasture and exposed soil and agriculture). The topography of the area studied limits the types of land use and areas that are less favorable for agriculture (more hilly areas) are have more riparian vegetation (or less anthropic stress). As a result, these areas are less subject to changes in water quality, which is reflected in the distribution of Aegla species.(AU)

Does the landscape surrounding streams affect the occurrence of freshwater crabs? A case study of the genus Aegla (Crustacea: Decapoda: Anomura) in subtropical basins

Los cambios en el paisaje donde se ubican las cuencas hidrográficas pueden afectar la corriente de diferentes maneras. Con el fin de explorar esta idea, se recogieron los cangrejos de agua dulce del género Aegla Leach, 1820 en la región subtropical del sur de Brasil. También se midió una serie de características del paisaje y las variables físico-químicas en los arroyos de colección y el entorno con el fin de determinar qué factores afectan la ocurrencia de estos crustáceos. Un total de 167 individuos de Aegla fueron recolectados en 21 arroyos. La colección estaba compuesta por tres especies: A. odebrechtii, A. platensis y A. singularis. La ocurrencia de A. platensis estuvo influenciada por variables fisicoquímicas (carbono total y carbono orgánico total) y morfometría (suma de curvas de nivel). La ocurrencia de A. singularis estuvo influenciada por el uso de la tierra (pastos y suelo expuesto y agricultura) y la morfometría (suma de curvas de nivel). Sólo un pequeño número de A. odebrechtii fueron recolectados y su ocurrencia fue influenciada por el uso de la tierra (pastos y suelo expuesto y la agricultura). La topografía del área estudiada limita los tipos de uso de la tierra y las áreas menos favorables para la agricultura (zonas más montañosas) tienen más vegetación ribereña (o menos estrés antrópico). Como resultado, estas áreas están menos sujetas a cambios en la calidad del agua, lo que se refleja en la distribución de las especies de Aegla.

Changes in the landscape where watersheds are located may affect the stream biota in different ways. In order to explore this idea, we collected freshwater crabs of the genus Aegla Leach, 1820 in subtropical region of southern Brazil. We also measured a number of landscape features and physico-chemical variables in the collection streams and surroundings in order to ascertain which factors affect the occurrence of these crustaceans. A total of 167 individuals of Aegla were collected in 21 streams. The collection was comprised of three species: A. odebrechtii, A. platensis, and A. singularis. The occurrence of A. platensis was influenced by physico-chemical variables (total carbon and total organic carbon) and stream morphometry factors (level curves sum). The occurrence of A. singularis was influenced by land use (pasture and exposed soil and agriculture) and the stream morphometry (level curves sum). Only a small number of A. odebrechtii were collected and their occurrence was influenced by land use (pasture and exposed soil and agriculture). The topography of the area studied limits the types of land use and areas that are less favorable for agriculture (more hilly areas) are have more riparian vegetation (or less anthropic stress). As a result, these areas are less subject to changes in water quality, which is reflected in the distribution of Aegla species.

Population biology of Aegla platensis (Decapoda: Anomura: Aeglidae) in a tributary of the Uruguay River, state of Rio Grande do Sul, Brazil

Aeglids are freshwater anomurans that are endemic from southern South America. While their population biology at the species-level is relatively well understood, intraspecific variation within populations has been poorly investigated. Our goal was to investigate the population biology of Aegla platensis Schmitt, 1942 from the Uruguay River Basin, and compare our data with data from other populations. We estimated biometric data, sex ratio, population density and size-class frequencies, and frequencies of ovigerous females and juveniles, from the austral spring of 2007 until autumn 2008. Sexual dimorphism was present in adults, with males being larger than females. Furthermore, males and females were significantly larger than previously recorded for the species. The overall sex ratio was 1.33:1 (male:female), and population density ranged from 1.8 (spring) to 3.83 ind.m-² (winter). Data from this population differ from published information about A. platensis in almost all parameters quantified except for the reproductive period, which happens in the coldest months, and a population structure with two distinct cohorts. Difference among studies, however, may be in part due to methodological differences and should be further investigated in order to determine their cause. In addition to different methodologies, they may result from ecological plasticity or from the fact that the different populations actually correspond to more than one species.

Population biology of Aegla platensis (Decapoda: Anomura: Aeglidae) in a tributary of the Uruguay River, state of Rio Grande do Sul, Brazil

Aeglids are freshwater anomurans that are endemic from southern South America. While their population biology at the species-level is relatively well understood, intraspecific variation within populations has been poorly investigated. Our goal was to investigate the population biology of Aegla platensis Schmitt, 1942 from the Uruguay River Basin, and compare our data with data from other populations. We estimated biometric data, sex ratio, population density and size-class frequencies, and frequencies of ovigerous females and juveniles, from the austral spring of 2007 until autumn 2008. Sexual dimorphism was present in adults, with males being larger than females. Furthermore, males and females were significantly larger than previously recorded for the species. The overall sex ratio was 1.33:1 (male:female), and population density ranged from 1.8 (spring) to 3.83 ind.m-² (winter). Data from this population differ from published information about A. platensis in almost all parameters quantified except for the reproductive period, which happens in the coldest months, and a population structure with two distinct cohorts. Difference among studies, however, may be in part due to methodological differences and should be further investigated in order to determine their cause. In addition to different methodologies, they may result from ecological plasticity or from the fact that the different populations actually correspond to more than one species.(AU)

Maturidade sexual morfológica de Aegla platensis (Crustacea, Decapoda, Anomura) no Lajeado Bonito, norte do estado do Rio Grande do Sul, Brasil

The size at the onset of morphological sexual maturity (SOM) of the anomuran crab Aegla platensis Schmitt, 1942 was estimated through the changes in the ratios of corporal dimensions of the animals. For this, aeglids were monthly collected, from July 2007 to June 2008 in Lajeado Bonito (27º25'27''S, 53º24'39''W), a first order tributary of the rio da Várzea, in Frederico Westphalen municipality, state of Rio Grande do Sul, Brazil. Samples of 437 males and 368 females were used, with cephalothorax length (CC) ranging from 6.00 mm to 31.75 mm in males and from 6.08 mm to 27.92 mm in females. The following corporal dimensions of collected individuals were measured: cephalothoracic length, abdomen width (LA), length of the right propodus cheliped (CPD), length of the left propodus cheliped (CPE). After the register of these measures, the crabs were returned to the stream, to the same places where they were collected. Estimation of the size at the onset of morphological maturity was performed using the Mature 2 software. The most appropriated relations for this analysis in males were CPD x CC (SOM: CC=18.2 mm) and CPE x CC (SOM: CC=20.1 mm) and for females LA x CC (SOM: CC=16.5 mm).

O tamanho da primeira maturação sexual (TPM) em Aegla platensis Schmitt, 1942 foi estimado através das mudanças nas proporções de dimensões corporais dos animais. Para isso, foram realizadas coletas mensais, de julho de 2007 a junho de 2008 no Lajeado Bonito (27º25'27''S, 53º24'39''W), um tributário de primeira ordem do Rio da Várzea, município de Frederico Westphalen, Rio Grande do Sul. Foram utilizados 437 machos com comprimento de cefalotórax (CC) variando de 6,00 mm a 31,75 mm e 368 fêmeas, com tamanhos entre 6,08 mm e 27,92 mm de CC. As seguintes dimensões corporais foram mensuradas em todos os indivíduos coletados: comprimento do cefalotórax (CC), largura do abdome (LA), comprimento do própodo do quelípodo direito (CPD) e comprimento do própodo do quelípodo esquerdo (CPE). Após o registro dessas medidas, os animais foram devolvidos ao mesmo local de captura. As análises de maturidade sexual morfológica foram realizadas com auxílio do software Mature 2, nas quais foram utilizadas as medidas de CC, considerada como variável independente e relacionada com as demais dimensões. As relações que melhor se ajustaram para estas análises, em machos, foram CPD x CC (TPM: CC=18,2 mm) e CPE x CC (TPM: CC=20,1 mm) e LA x CC (TPM: CC=16,5 mm) nas fêmeas.

Maturidade sexual morfológica de Aegla platensis (Crustacea, Decapoda, Anomura) no Lajeado Bonito, norte do estado do Rio Grande do Sul, Brasil

The size at the onset of morphological sexual maturity (SOM) of the anomuran crab Aegla platensis Schmitt, 1942 was estimated through the changes in the ratios of corporal dimensions of the animals. For this, aeglids were monthly collected, from July 2007 to June 2008 in Lajeado Bonito (27º25'27''S, 53º24'39''W), a first order tributary of the rio da Várzea, in Frederico Westphalen municipality, state of Rio Grande do Sul, Brazil. Samples of 437 males and 368 females were used, with cephalothorax length (CC) ranging from 6.00 mm to 31.75 mm in males and from 6.08 mm to 27.92 mm in females. The following corporal dimensions of collected individuals were measured: cephalothoracic length, abdomen width (LA), length of the right propodus cheliped (CPD), length of the left propodus cheliped (CPE). After the register of these measures, the crabs were returned to the stream, to the same places where they were collected. Estimation of the size at the onset of morphological maturity was performed using the Mature 2 software. The most appropriated relations for this analysis in males were CPD x CC (SOM: CC=18.2 mm) and CPE x CC (SOM: CC=20.1 mm) and for females LA x CC (SOM: CC=16.5 mm).

O tamanho da primeira maturação sexual (TPM) em Aegla platensis Schmitt, 1942 foi estimado através das mudanças nas proporções de dimensões corporais dos animais. Para isso, foram realizadas coletas mensais, de julho de 2007 a junho de 2008 no Lajeado Bonito (27º25'27''S, 53º24'39''W), um tributário de primeira ordem do Rio da Várzea, município de Frederico Westphalen, Rio Grande do Sul. Foram utilizados 437 machos com comprimento de cefalotórax (CC) variando de 6,00 mm a 31,75 mm e 368 fêmeas, com tamanhos entre 6,08 mm e 27,92 mm de CC. As seguintes dimensões corporais foram mensuradas em todos os indivíduos coletados: comprimento do cefalotórax (CC), largura do abdome (LA), comprimento do própodo do quelípodo direito (CPD) e comprimento do própodo do quelípodo esquerdo (CPE). Após o registro dessas medidas, os animais foram devolvidos ao mesmo local de captura. As análises de maturidade sexual morfológica foram realizadas com auxílio do software Mature 2, nas quais foram utilizadas as medidas de CC, considerada como variável independente e relacionada com as demais dimensões. As relações que melhor se ajustaram para estas análises, em machos, foram CPD x CC (TPM: CC=18,2 mm) e CPE x CC (TPM: CC=20,1 mm) e LA x CC (TPM: CC=16,5 mm) nas fêmeas.

Abundância e distribuição de Aeglidae (Crustacea: Anomura) em função do uso da terra na bacia hidrográfica do Rio Jacutinga, Rio Grande do Sul, Brasil

This study investigated the influence of land use and occupation on the density and distribution of aeglids in the hydrographic basin of the Jacutinga river (northern state of Rio Grande do Sul, Brazil). Sampling was carried out during the summer and winter of 2004, at 12 sites distributed in river spring, agriculture, grazing, and urban areas. Animals were collected using a Surber sampler. An analysis of variance (ANOVA) was conducted to evaluate differences in the density of species in each land use and sampling period. Biological data were classified using cluster analysis (Euclidian distance; UPGMA). A total of 226 aeglids were captured, including 167 (78.89%) specimens of Aegla platensis Schmitt, 1942 and 59 (26.11%) specimens of A. singularis Ringuelett, 1948. The aeglid distribution was associated with land use and occupation. In river spring and grazing areas, A. platensis was predominant, whereas in urban and agricultural areas A. singularis was the most prevalent species.

Abundância e distribuição de Aeglidae (Crustacea: Anomura) em função do uso da terra na bacia hidrográfica do Rio Jacutinga, Rio Grande do Sul, Brasil

This study investigated the influence of land use and occupation on the density and distribution of aeglids in the hydrographic basin of the Jacutinga river (northern state of Rio Grande do Sul, Brazil). Sampling was carried out during the summer and winter of 2004, at 12 sites distributed in river spring, agriculture, grazing, and urban areas. Animals were collected using a Surber sampler. An analysis of variance (ANOVA) was conducted to evaluate differences in the density of species in each land use and sampling period. Biological data were classified using cluster analysis (Euclidian distance; UPGMA). A total of 226 aeglids were captured, including 167 (78.89%) specimens of Aegla platensis Schmitt, 1942 and 59 (26.11%) specimens of A. singularis Ringuelett, 1948. The aeglid distribution was associated with land use and occupation. In river spring and grazing areas, A. platensis was predominant, whereas in urban and agricultural areas A. singularis was the most prevalent species.

Abundância e distribuição de Aeglidae (Crustacea: Anomura) em função do uso da terra na bacia hidrográfica do Rio Jacutinga, Rio Grande do Sul, Brasil

This study investigated the influence of land use and occupation on the density and distribution of aeglids in the hydrographic basin of the Jacutinga river (northern state of Rio Grande do Sul, Brazil). Sampling was carried out during the summer and winter of 2004, at 12 sites distributed in river spring, agriculture, grazing, and urban areas. Animals were collected using a Surber sampler. An analysis of variance (ANOVA) was conducted to evaluate differences in the density of species in each land use and sampling period. Biological data were classified using cluster analysis (Euclidian distance; UPGMA). A total of 226 aeglids were captured, including 167 (78.89%) specimens of Aegla platensis Schmitt, 1942 and 59 (26.11%) specimens of A. singularis Ringuelett, 1948. The aeglid distribution was associated with land use and occupation. In river spring and grazing areas, A. platensis was predominant, whereas in urban and agricultural areas A. singularis was the most prevalent species.