Zoological Studies

Sexual Dimorphism and Reproduction of the Amphipod Hyale crassicornis Haswell (Gammaridea: Hyalidae)

Kwok-Ho Tsoi and Ka-Hou Chu (2005) In the present study, we explored the sexual maturation, sexual dimorphism, and fecundity of a hyalid amphipod Hyale crassicornis in the laboratory. This amphipod passed through 11 to 21 instars, and the mean lifespan of males and females was 178 and 175 d, respectively. Males and females attained sexual competency between instars 5 and 7 at an age of 34~44 d, and between instars 5 to 8 at an age of 38~53 d, respectively. Precopulatory pairing behavior was the criterion used for the onset of sexual maturity. Nine of 10 characters studied exhibited sexual dimorphism. Transitions of growth phases can be revealed from the allometric relationships of the sexually dimorphic gnathopods 1 and 2 to body length. Male gnathopods 2 grew in 3 phases, while female gnathopods 1 and 2 grew in 2 phases. Each female generated a total of 2 to 17 (mean, 6) broods. Brood size ranged from 3 to 33 (mean, 13) offspring and was positively correlated with the body length of the female. Each female produced 16 to 290 offspring throughout its lifespan.