An extra embryonic phase in the true freshwater crab Sinopotamon yangtsekiense Bott,1967(Decapoda,Potamidae)

The true freshwater crabs(Crustacea,Decapoda,Brachyura) are highly adapted to life in freshwater and complete their life cycle entirely independently of sea water.All true freshwater crabs exhibit direct development and lack the free-living larval forms(zoea and megalopa) typical of most other brachyurans.After a prolonged embryonic period(during which they pass through the typical brachyuran larval forms embryologically) the eggs of true freshwater crabs hatch to produce juvenile(hatchling) crabs.We provide here the first report and description of the continuous record of embryonic development from egg-laying up to hatching in the Chinese true freshwater crab Sinopotamon yangtsekiense Bott,1967(Potamoidea,Potamidae).Direct development(complete secondary embryonization) in S.yangtsekiense was observed to take 77 days and to include an additional embryonic phase(termed here the egg-juvenile-crab) that occurs in the embryo between the imprisoned megalopa and the newly-emerged juvenile(hatchling) crab.This is significant because the only other freshwater crab whose embryonic development has been studied in detail is Potamon fluviatilis(Potamidae) which takes 45-47 days and involves only nine embryonic stages.

Changes during late-stage embryonic development from egg-juvenile to free-living hatchling in Chinese freshwater crab Sinopotamon yangtsekiense (Decapoda, Brachyura, Potamidae)

This study expands on recent reports that direct development in the Chinese potamid freshwater crab Sinopotamon yangtsekiense involves the completion of all brachyuran larval stages (nauplius, zoea, and megalopa) inside the egg case during embryonic development. Detailed studies of embryonic development in this species revealed the presence of an additional larval stage (the egg-juvenile) between the megalopa and the free-living hatchling crab. We described and compared the appendages of the head, thorax, and abdomen of the egg-juvenile with those of the hatchling crab in S. yangtsekiense. Significant differences were found between most of the appendages of these two stages with a soft exoskeleton in the egg-juvenile, no joint articulation, a slimmer appearance, and a lack of setae when compared with the newly emerged free-living hatchling crab. These modifications of the appendages are related to the confinement within the egg case of the egg-megalopa and egg-juvenile during direct development, and the need for the free-living hatchling freshwater crab to move, feed, and respire. In marine crabs, the megalopa gives rise to the first crab stage whereas in freshwater crabs the egg-juvenile follows the megalopa and immediately precedes the free-living first crab stage.

Rapid divergent coevolution of Sinopotamon freshwater crab genitalia facilitates a burst of species diversification

One of the most striking radiations in brachyuran evolution is the considerable morphological diversification of the external reproductive structures of primary freshwater crabs:the male first gonopod(G1)and the female vulva(FV).However,the lack of quantitative studies,especially the lack of data on female genitalia,has seriously limited our understanding of genital evolution in these lineages.Here we examined 69 species of the large Chinese potamid freshwater crab genus Sinopotamon Bott,1967(more than 80%of the described species).We used a landmark-based geometric morphometric approach to analyze variation in the shape of the G1 and FV,and to compare the relative degree of variability of the genitalia with non-reproductive structures(the third maxillipeds).We found rapid divergent evolution of the genitalia among species of Sinopotamon when compared to non-reproductive traits.In addition,the reconstruction of ancestral groundplans,together with plotting analyses,indicated that the FV show the most rapid divergence,and that changes in FV traits correlate with changes in G1 traits.Here we provide new evidence for coevolution between the male and female external genitalia of Sinopotamon that has likely contributed to rapid divergent evolution and an associated burst of speciation in this lineage.

Pesticidal Impact on the Protein Metabolism of Freshwater Field Crab, Oziotelphusa Senex Senex(Fabricius)

The total protein increased in the gills and decreased in the muscle of the freshwater field crab Oziotelphusa senex senex at days 1 and 2 on exposure to lethal concentrations and at days 1 and 10 to sublethal concentrations of furadan, endosulfan, chlorpyrifos, and a mixture of these three in a 100:10: 1 ratio. The increase in the gill protein was greater on exposure to the sublethal concentrations than to the lethal concentrations while the decrease in the muscle protein was greater on exposure to the lethal concentrations than to the sublethal concentrations. In the hepatopancreas, the protein content decreased on exposure to the lethal concentrations, but, in contrast, increased on exposure to the sublethal concentrations. These results clearly indicate that changes in the protein content are not only organ-dependent but also concentration-dependent, i.e., lethal versus sublethal. Irrespective of the changes in the total protein, the levels of free amino acids and the activities of protease, alanine and aspartate aminotransferases, and glutamate dehydrogenase increased in all the three organs of the crabs exposed to the lethal and sublethal concentrations, (more in lethal than in sublethal) and increased at a greater rate over time of exposure. Ammonia toxicity, measured by an increase in the hemolymph ammonia and a decrease in the urea, was also observed at the lethal concentrations of all the three pesticides. The ammonia and urea levels increased in the crabs exposed to the sublethal concentrations. Although the effect of each pesticide on the protein metabolism was similar, the degree of toxicity was the lowest on exposure to furadan, intermediate on exposure to endosulfan and chlorpyrifos, and cumulative on exposure to a mixture of the three pesticides