Dissertation Defense: Shadaesha Green

Host: Dr. Sook Chung

Speaker: Shadaesha Green (PhD Candidate, UMCES-IMET)

Title: Understanding the Reproductive Biology and Endocrinology of the Female Red Deep-Sea Crab, Chaceon quinquedens.

Abstract: The red deep-sea crab, Chaceon quinquedens, a cold-water decapod found along the continental shelf and slope of the eastern United States has a limited amount of literature available describing their physiological processes. The present research aimed to advance the current knowledge of the reproductive physiology of C. quinquedens females by investigating essential hormones regulating vitellogenesis and ovarian development. In decapod crustaceans, members of the crustacean hyperglycemic hormone (CHH) superfamily control molting, growth, and reproduction, while reproduction and somatic growth are antagonistic. The red deep-sea crab with an extended intermolt period may adopt a similar approach to the blue crab, Callinectes sapidus, which utilizes the molt-inhibiting hormone (MIH) as a gonad-stimulating factor. Hence, a relationship between MIH and CHH levels and vitellogenin is examined, together with the potential role of other eyestalk neuropeptides in vitellogenesis using a transcriptomic analysis. Ten of the 28 eyestalk-neuropeptides found in the de novo assembly are differentially expressed between ovarian stages 1 and 3, suggesting their role in vitellogenesis. The onset of vitellogenesis (synthesis of vitellogenin, the precursor of vitellin) initiates the ovarian development of all oviparous animals. Decapod crustaceans mainly utilize two tissues for vitellogenesis: hepatopancreas and ovary. The hepatopancreas of most crab species is the primary site for vitellogenesis, producing >99.9% of vitellogenin for the ovarian development, while the ovary takes up vitellogenin subunits from the hemolymph. It is found using qPCR assay that the hepatopancreas of C. quinquedens also is the main site and provides >99.9% of vitellogenin. The following is then investigated on how the vitellogenin is cleaved into two subunits using a transcriptomic analysis. First, two transcripts are pieced together to obtain the putative 2,570 amino acid vitellogenin protein. Following three subtilisin-like endopeptidases are found in the de novo assembly, potentially cleaving vitellogenin into subunits: trypsin-like serine protease, furin, and proprotein convertase subtilisin/Kexin7. Since the 1970s, the red deep-sea crab has been supporting a small fishing industry in the Atlantic Ocean, mainly harvesting adult males with >94 mm carapace width. However, a recent study reports that there is a reduction in the size of the males. To address population structure of this species in the future, microsatellite markers are developed using MiSeq data combined with a bioinformatic pipeline. Over 37,000 microsatellites are identified, from which 122 markers are considered for initial PCR testing with a limited number of crabs. Overall, 14 novel, polymorphic microsatellite markers are developed. In conclusion, the reproduction of female C. quinquedens is regulated by eyestalk neuropeptides. With this study, the reproductive role of MIH needs investigating in the decapod crustaceans experiencing an extended intermolt stage. Novel microsatellite markers developed here will assist to study population structure and connectivity that will help towards the conservation of this species facing increasing fishing pressure.