Morphometry and Sexual Maturity in the Spider Crab Maja Squinado (Decapoda: Majidae) in Galicia, Spain

Abstract

Ontogenetic changes in the relative growth of males and females of the spider crab Maja squinado were analyzed and related to their reproductive (maturity) status in order to define criteria to assign individuals to each growth phase. The sampling was carried out in two different areas of southern Galician waters, northwestern Spain, in shallow water (�10 m) with mixed rocky-sandy bottoms (juvenile and postpubertal adult areas) and deep water (�20 m) with soft bottoms (adult habitat). A Principal Component Analysis (PCA) of morphometric variables and a nonhierarchic K-means cluster of PCA scores differentiated two morphometric groups defined as juvenile and adult phases. A significant change in allometry of cheliped size was detected in juvenile males with a break point at a 109-mm carapace length (CL). This point may indicate a change in the relative growth of juveniles, separating the immature and adolescent phases. Histological analysis of a subsample of males showed that sperm were present in most adolescent crabs, but not in immature crabs. Bivariate morphometric linear discriminant functions allow for the identification of juvenile and adult males (classified previously by K-means cluster) with over 99% correct classification using CL and the length or height of the right cheliped. Carapace length at the onset of sexual maturity was estimated to be 132.7 mm (50% of adult males), although in a broad range, 112-165 mm, the size of juveniles and adults overlap. The life history of male spider crabs shows 3 phases differentiated by the relative growth rate of chelipeds separated by two 2 critical molts: prepubertal molt (immature-adolescent) determines a slight increase in allometry, and pubertal or terminal molt (adolescent-adult) determines an increase in the relative size and allometry of chelipeds and the onset of functional maturity. Females showed only 2 phases separated by the terminal molt. Growth of chelipeds in females showed no changes in allometry and was similar to juvenile males. Juvenile females presented a smaller relative width and a higher allometry of the abdomen with regard to adult females. Unlike juvenile females with a flat abdomen, adult females with a domed abdomen have well-developed pleopods, gonads, and seminal receptacles. Carapace length at the onset of sexual maturity was estimated to be 130.4 mm (50% of adult females). The range of overlap of the size of juveniles and adults (114-143 mm) was smaller than in males.

Determinação da maturidade sexual de Ucides cordatus (Crustacea, Brachyura, Ucididae) em duas áreas de manguezal do litoral sul de Pernambuco, Brasil

“…Após a classificação, foi aplicada uma análise discriminante bivariada, que permitiu a reclassificação destes grupos, com separação dos caranguejos em jovens e adultos. Este método estatístico foi baseado no trabalho de SAMPEDRO et al (1999), que utilizaram um procedimento semelhante. Após a separação dos grupos, nos casos onde ocorreu sobreposição, cada categoria etária foi dividida em classes de tamanho de 5 mm (LC), com posterior cálculo das proporções de jovens e adultos por classe e uso da proporção de adultos para ajuste pela equação logística (y=a/(1+be -cx )).…”

Comparison of body size, relative growth and size at onset sexual maturity ofUca uruguayensis(Crustacea: Decapoda: Ocypodidae) from different latitudes in the south-western Atlantic

“…The size at the onset sexual maturity (SOM) is regularly determined using allometric techniques and is useful for studies on aspects of reproduction (Vaninni & Gherardi, 1988;Sampedro et al, 1999;Corgos & Freire, 2006). For instance, the morphological sexual maturity of the fiddler crab Uca cumulanta, studied by Pralon & NegreirosFransozo (2008), showed a similar pattern to those known for other fiddler crabs, with males attaining a larger size at the SOM than females Cardoso & Negreiros-Fransozo, 2004).…”

“…The result of the classification (K-means) was refined using discriminant analysis. This statistical methodology was based on Sampedro et al (1999) and Corgos & Freire (2006).…”

Efectos de la densidad de cultivo y de elementos de refugio en el crecimiento y supervivencia de juveniles de centollo,Maja brachydactyla (Balss, 1922)

“…Contrariamente a la mayoría de los crustáceos, el centollo se caracteriza por un ciclo de vida dividido en dos etapas, separadas por la denominada muda terminal (Conan et al 1992, Sampedro et al 1999. En la primera etapa, el ciclo de vida se caracteriza por una fase de crecimiento somático, como consecuencia de varias mudas, que provocan un crecimiento escalonado del individuo (Carlisle 1957, Hartnoll 1963, mientras que tras la muda terminal, se produce la maduración del individuo y se entra en la fase adulta, cuando el individuo deja de crecer (Sampedro et al 2003).…”

“…En la primera etapa, el ciclo de vida se caracteriza por una fase de crecimiento somático, como consecuencia de varias mudas, que provocan un crecimiento escalonado del individuo (Carlisle 1957, Hartnoll 1963, mientras que tras la muda terminal, se produce la maduración del individuo y se entra en la fase adulta, cuando el individuo deja de crecer (Sampedro et al 2003). Según Sampedro et al (1999), esta muda terminal ocurre cuando los individuos, tanto machos como hembras, alcanzan un tamaño del caparazón entre 114 y 164 mm.…”