Shell occupation by the hermit crab Dardanus insignis (Decapoda, Diogenidae) from the north Coast of São Paulo state, Brazil / Ocupação de conchas pelo ermitão Dardanus insignis na costa norte do estado de São Paulo, Brasil

The pattern of shell occupation by the hermit crab Dardanus insignis (Saussure, 1858) from the subtropical region of southeastern coast of Brazil was investigated in the present study. The percentage of shell types that were occupied and the morphometric relationships between hermit crabs and occupied shells were analyzed from monthly collections conducted during two years (from January 1998 to December 1999). Individuals were categorized according to sex and gonadal maturation, weighed and measured with respect to their cephalothoracic shield length (CSL) and wet weight (CWW). Shells were measured regarding their aperture width (SAW), dry weight (SDW) and internal volume (SIV). A total of 1086 hermit crabs was collected, occupying shells of 11 gastropod species. Olivancillaria urceus (Roding, 1798) was most commonly used by the hermit crab D. insignis, followed by Buccinanops cochlidium (Dillwyn, 1817), and Stramonita haemastoma (Linnaeus, 1767). The highest determination coefficients (r2 > 0.50, p < 0.01) were recorded particularly in the morphometric relationships between CSL vs. CWW and SAW vs. SIV, which are important indication that in this D. insignis population the great majority the animals occupied adequate shells during the two years analysed. The high number of used shell species and relative plasticity in pattern of shell utilization by smaller individuals of D. insignis indicated that occupation is influenced by the shell availability, while larger individuals demonstrated more specialized occupation in Tonna galea (Linnaeus, 1758) shell.(AU)

O padrão de ocupação de conchas pelo ermitão D. insignis (Saussure, 1858) na região subtropical da costa sudeste do Brasil, foi investigada no presente estudo. Foram analisadas a percentual de tipos de conchas que foram ocupados e as relações morfométricas entre os ermitões e conchas ocupadas, a partir de coletas mensais realizadas durante dois anos (de janeiro de 1998 a dezembro de 1999). Os indivíduos foram classificados de acordo com o sexo e maturação, pesados ​​e medidos em relação ao comprimento escudo cefalotoracico (CEC) e peso úmido (CPU). As conchas foram medidas em relação à sua largura de abertura (LAC), peso seco (PSC) e volume interno (VIC). Um total de 1.086 ermitões foram coletados, ocupando conchas de 11 espécies de gastrópodos. Olivancillaria urceus (Roding, 1798) foi a mais utilizada pelo ermitão D. insignis, seguido por Buccinanops cochlidium (Dillwyn, 1817), e Stramonita haemastoma (Linnaeus, 1767). Os maiores coeficientes de determinação (r2 > 0,50, p < 0,01) foram registrados principalmente nas relações morfométricas entre CEC e CPU contra LAC e VIC, que é uma importante indicação de que nesta população de D. insignis a grande maioria dos animais ocupavam conchas adequadas durante os dois anos analisados. O elevado número de espécies de conchas utilizadas ​​e a relativa plasticidade no padrão de ocupação de conchas pelos menores indivíduos de D. insignis indicaram que a ocupação é influenciada pela disponibilidade de conchas, enquanto os indivíduos maiores demonstraram uma ocupação mais especializadas na concha de Tonna galea (Linnaeus, 1758).(AU)

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)