Growth, survivorship and reproduction of seven species of grapsid crabs inhabiting• ntertidal cobble and boulder shores were investigated in Shirahama, Wakayama Prefecture, Japan. In general, growth rate decreased with age, was similar between the sexes for the immature crabs, and was lower in mature females than in mature males within a species. Growth rate showed considerable variations among species, which seemed to be mainly due to the interspecific differences in intermolt period. Survival rate was similar between the sexes, and tended to be lower in mature crabs than in immature crabs within a species. Survival rate varied considerably among species, and an apparent trade-off relationship to an index of reproductive activity existed. This brood index was calculated by multiplying the ratio of brood weight per body weight by the number of broods per year. Egg size and the ratio of brood weight per body weight were constant within a species regardless of body size of parent female crabs, whereas the number of eggs per brood was nearly proportional to the third power of their carapace width. Among species, mean number of eggs per brood and size at maturity were correlated with mean adult body size of the species, whereas egg size, the number of broods per year, brood index and age at maturity were not. A model which shows the relationships between the expected value of the number of eggs laid per life per female and some life history traits was made on the basis of the general rules followed by the present grapsid crabs in the intraspecific and interspecific variations in life history traits. Using this model, the factors influencing the evolution of age at maturity and brood index were analyzed. Delayed maturity and smaller brood index were predicted to be favored as survival rate in immature period increases and/or relative growth rate to maximum body size decreases.

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Poss~ble relahons between habitat and hfe history attnbutes of 4 estuarine crabs, Devatonotus tondensis Sakai, Hemigrapsus penlcdlatus (De Haan), Ptychognathus ishu S a k a and Ptychognathus capdhdgitatus Takeda were ~nveshgated Although all species Inhabited ~n t e r h d a l cobble shores in the Tonda k v e r Estuary, central Japan D tondensis dominated the upper reaches, whereas the others were prevalent in the lower reaches AU species grew rapldly after settlement, bred after thelr fust ovennntenng, and had annual breeding cycles Egg size decreased in the order D tondensis, P ~s h , H penlcdlatus, P capdhdgitatus The number of eggs per brood in same-s~zed females decreased in the order P capdhdgitatus, P ishu or H penicdlatus D tondensls Reproduchve effort per year was eshmated to be h g h e s t in D tondensis among the 4 specles The relabvely unstable e n w o n m e n t of the upper reaches, as shown by greater cobble movement, may have favored hlgher reproduchve effort

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--Male and female mate choices were investigated in the grapsid crab, Gaetice depressus (Crustacea, Decapoda) in a laboratory experiment. Males mated indiscriminately with regard to the body size of the females, and frequently copulated with the first females they encountered. In contrast, females showed mate discrimination with regard to the body size of males. The females tended to sample potential mates prior to copulation, and showed both a preference for the larger males and a tendency toward the rejection of males with body sizes smaller than their own. However, they did not discriminate between two males that were either larger or smaller than they themselves. Mate choice by the females of this species is though to be based upon threshold-criterion tactics, in which the body size of the female itself is used as a threshold value.