Post-settlement growth and sexual dimorphism in the size and proportion of the body of the varunid crab Gaetice depressus (De Haan, 1833) (Decapoda: Brachyura: Varunidae) based on laboratory-reared material

Abstract

We investigated post-settlement growth patterns and sexual dimorphism in the carapace, pelon, and cheliped dimensions of the varunid crab Gaetice depressus (De Haan, 1833). We reared crabs in the laboratory from hatching through megalopae to the first to tenth instars, and measurements were made of exuviae or specimens of crabs that successively molted. The males were larger than the females in all instars. The molt increments of carapace width (CW) and carapace length (CL) did not differ between the sexes; the former decreased with growth, especially up to ~3–4 mm, whereas the latter did not change with growth. This may be due to the rapid growth in CW compared to CL during early ontogeny. The proportion of CW to CL was larger in the females than in the males, and the rate of increase in pleon width accelerated greatly after growth to ~4 mm CW. Cheliped dimensions were larger in males than in females, probably as a consequence of sexual selection. Cheliped propodus length and width increased with growth in both sexes, but the rates of increase tended to decelerate after ~7 mm CW in females. This indicates that females may allocate more energy to pleon growth while limiting cheliped growth.