Abstract
There are three important finding during the study of reproductive biology of the Taiwanese freshwater crab, Candidiopotamon rathbunae (de Man). First, the immature females larger than 15 mm carapace width often find mating and possess sperm in their seminal receptacles. Immature mating is a rare event in animal kingdom. Second, mature spermatozoa are never packaged into spermatophore. This is the only exception in Brachyura. Third, most young crabs are released at the end of the rainy season. Immature mating in C. rathbunae seems to increase the reproductive potential of both sexes, and could have evolved as an adaptation for amphibious life. Releasing young crabs after rainy season, this strategy is believed to be common for freshwater crabs in areas with heavy precipitation. It can avoid hurt of the young crabs by destructive flash floods. There are also many special characters of reproductive biology in C. rathbunae. These characters are as below: The bigger mature females are more common than males, but the male is almost bigger than female in the mating pair. Only in two cases, the females had soft integument and were slightly larger than their partners. In C. rathbunae, discernible courtship behavior is absent and a forced copulation strategy is practiced by males. The male also try to mate with smaller male. Larger males are found to have more opportunity to mate than smaller ones. However, in females, it is the smaller ones mate more often. Ovigerous and brooding females also copulate. The main breeding season is from late June to October, however, mating can occur all the year round and with higher frequency from September to December. The seminal receptacles of C. rathbunae belong to the ventral-type. However, adult males of C. rathbunae frequently mate with females long before breeding season. Ovigerous females leave streams to live on the forest floor several meters away from the stream and return to the stream a few hours before hatching of the eggs. The young crabs can not recognize their mother and can even stay in the brooding female's abdomen of different species. The fecundity is highest for females of about 27.5-30.0 mm carapace width but not the bigger ones. A new mechanism of cuticle formation in Crustacea is found. According to the evidence of colloidal gold immunocytochemistry, a new group cells are supposed to be involved in cuticle formation. Some cuticle proteins are made by these cells and transported by hemolymph to cuticle tissue. These proteins enter cuticle through space of lateral boundaries of epidermis which are no longer contiguous after ecdysis. According to the evidence of WGA-gold and colloidal gold immunocytochemistry, the vesicles in epidermis before ecdysis have no relationship with the formation of cuticle chitin and extracted proteins. Pore canals also have no function for transportation of chitin and extracted proteins. A thin layer of fibrous structure cover the surface of the pre-ecdysial epicuticle. Its function is assumed to protect the pre-ecdysial cuticle from molting fluid containing enzymes for digestion of the old cuticle. Some proteins of the exocuticle deposit after ecdysis. After ecdysis, the epidermis begin to atrophy. The atrophy continues throughout the post-ecdysial period even though endocuticular synthesis continues unabated. The components of intermolt carapace in Candidiopotamon rathbunae include 80.0±0.3% calcium bicarbonate, 11.8±0.7% chitin and 8.2±0.4% proteins. The pre-ecdysial resorption of calcium bicarbonate is few in C. rathbunae, but a lot of organic matrix of the cuticle is resorbed during premolt period. The SDS-PAGE of the extracted carapace proteins is similar between populations of different areas and different sizes of the same population in Taiwan. However, the extracted carapace proteins are different in crabs with different molting stages. A major cuticle protein, 40.6 KDa protein, enters cuticle after ecdysis and distributes only in the exocuticle. This protein can be found in all species of Candidiopotamon and some species of Geothelphusa which the color of carapace is similar to C. rathbunae. The 40.6 KDa protein belongs to a carotenoprotein and also has relationship with cuticle calcification. The process of cuticle formation of hatched juvenile crab is similar to the cuticle formation of adult after ecdysis. The time need for the cuticle formation of hatched juvenile crab is about two weeks which is similar to the time of posthatching maternal care.