Growth alometric – Crab (crescimento alométrico – caranguejo)
In decapods three types of allometry exist:
(i) positive allometry or progressive geometric growth, in which the dependent variable grows fast with respect to body size, (ii) isometric or arithmetic growth, and (iii) negative allometry or retrogressive geometric growth, in which the dependent variable grows slower than body size. Chelipeds are the best example of crustacean allometric growth. In males of the crab Arenaeus caribrarius (Pinheiro and Fransozo 1993), crayfish Orconectes virilis, and blue clawed (BC) males of Macrobrachium rosenbergii (Kuris et al 1987), chela growth shows positive allometry (Aiken and Waddy 1992), while it is isometric in juveniles and females (Pinheiro and Fransozo,1993).
In heterochelous decapods chelipeds are further differentiated into major (crusher) and minor (cutter) based on morphologically and functionally different dentition paterns (Levinton et al 1995). The large and robust chela with molariform teeth, known as the crusher, can yield more force than the minor, which has many cutting teeth and spiniform setae (figure 1) (Mariappan and Balasundaram 1997). Major and minor chelae possess differential operating forces measured as ideal mechanical advantage 1979). In male Uca and Alpheus , the major chela is used for aggressive and courtship displays, while the other is used for capture and manipulation of prey and grooming (Hazlett 1962; Nolan and Salmon 1970; Crane 1975). Many crustaceans have spatulate chelae which are used to scrap algae from rocks (McLaughlin 1982). The atyishrimps use brush and spiny setae on chelipeds to scrap up debris (Fryer 1960). In Macrobrachium australe thminor chela endowed with abundant bristles serves as sort of net to catch prey while the major chela is used tpick up prey. Such a differential function among chelpeds is also observed in Homarus spp. (Davis 1987Chela size is also related to feeding habits. For instance detritivorous crabs have small slender claws (Seed an Hughes 1995) while carnivorous counterparts like Ocypode spp. possess enlarged chelae to facilitate predation In Macrobrachium nobilii, the robust second pair is use for prey capture and the slender first pair functions t deliver the food to the mouth (P Mariappan and Balasundaram, unpublished data).
fonte: J. Biosci. | vol. 25 | No. 3 | September 2000