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ALLOMETRY OF THE SECONDARY SEXUAL CHARACTERS OF THE SHORE CRAB PACHYGRAPSUS TRANSVERSUS (GIBBES, 1850) (BRACHYURA, GRAPSIDAE)

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The allometric growth of secondary sexual characters in Pachygrapsus transversus is investigated from the 2nd crab stage onward. Clear sexual dimorphism is restricted to abdominal morphology, but ANCOVA analyses showed that chelae become larger in males and the carapace becomes wider in females. Size at the puberty moult in both sexes was estimated using Somerton's computer techniques. Mature II analyses applied to bi-log gonopod length vs. carapace length relationships indicated a puberty moult at 5.0 mm in males. In females, Mature I analyses detected the overlapping growth phase lines in bi-log carapace length vs. abdomen width scatterplots. Fitting the logistic equation provided an estimate of 50% maturity at 5.5 mm. The regression lines separate young and resting individuals from the potentially reproductive females, but they do not separate young from adult crabs. Year-round monthly samples showed that the proportion of small adult-like females is higher during the breeding season. After breeding, females may moult to a young-like morphotype, as observed in controlled laboratory conditions. Moulting to a resting condition splits smaller mature females into different "growth phase" lines. Therefore, estimates of female size at sexual maturity by means of abdomen allometric growth analyses are inadequate in this species.

El crecimiento alometrico de los caracteres sexuales secundarios de Pachygrapsus transversus ha sido investigado desde el segundo estadio pos-larval. El dimorfismo abdominal es la unica caracterostica que permite distinguir claramente los sexos, pero los analisis de covarianza aplicados a las regresiones obtenidas demuestran que las quelas se vuelven m as grandes en machos y que el caparazon se vuelve mas ancho en hembras. La talla en que ambos sexos alcanzan la maturidad sexual ha sido estimada atraves de las tecnicas de Somerton. La aplicacion del programa Mature II a la regresion bi-log entre el largo del caparazon y el largo del gonopodo indica que la muda de la pubertad de los machos ocurre a los 5,0 mm. En las hembras, el programa Mature I detecto la sobreposicion de loneas de regresi on en los diagramas de dispersion de la regresion bi-log entre el largo del caparazon y el ancho del abdomen. Del ajuste de la ecuacion logostica se obtiene que 50% de las hembras son sexualmente adultas a los 5,5 mm. Estas rectas de regresion separan las hembras con potencial reproductivo de los indivoduos j ovenes y aquellos en reposo sexual. Sin embargo, las rectas no separan jovenes de adultos. Muestreos mensuales a lo largo de un ano indican que la proporcion de hembras de talla puberal con morfologia adulta es mas elevada durante el peroodo reproductivo. Despues de la reproduccion, estas hembras pueden obtener en la siguiente muda una condicion morfologica semejante a la joven, como fue verificado en condiciones de laboratorio controladas. La obtencion del reposo sexual divide a las hembras de talla puberal en rectas de regresion distintas, por lo que las estimativas de talla a la maturidad sexual atraves del analisis del crecimiento alometrico del abdomen son inadequadas para esta especie.

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/content/journals/10.1163/156854099504013
1999-12-01
2015-08-04

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