Doctoral Thesis
Genetic Population Structure and Early Development for Resources Persistence of Japanese Sea Cucumber
By
Taha Basheir Hassan Soliman
Under supervision of
Dr. Yuji Yamazaki
Department of Biological Science
Graduate School of science and engineering for education
University of Toyama, Japan
March, 2013
Abstract
Biodiversity play an important role for increasing the productivity of ecosystem. Recently, the biological diversity of our planet is rapidly decreased as a direct and indirect consequence of human activities and climatic changes. Many species now require benign intervention by human to improve their management and ensure their survival. Conservation genetics is the use of genetics to preserve species as dynamic entities capable of adapting with environmental change. Conservation research in the past two decades has produced an important body of knowledge on the effects of many types of land use on species persistence, community organization, and ecosystem fundamental for development of conservation strategies.
Sea cucumbers are important resources for coastal livelihoods and ecosystems. At least 60 species of commercial sea cucumber are fished from more than 40 countries and most of the harvest are processed and then exported to Asian markets. The present study aims to examine the genetic population structure, contemporary and historical gene flow, early larval development, spawning behavior, growth rate, and mortality rate for red and green variants of Japanese sea cucumber Apostichopus japonicus, in order to elucidate their genetic structure and give a detailed genetic description of differentiation between red and green variants, as well as introduce the breeding behavior in each variant of Japanese sea cucumber. In addition, the deep-sea cucumber Bathyplotes tizardi was selected in the present study to re-examine its ossicles from different position of its body parts using advanced techniques such as Scanning Electron Microscope (SEM).
The present study includes:
1) genetic population structure and gene floe among 11 populations of wild A. Japonicus. A total of 438 wild A. Japonicus were collected from six locations (Uozu, Noto, Shinminato, Yamaguchi, Saga, and Sasebo) across the Sea of Japan.
Individuals of sea cucumber were genotyped at 11 microsatellite Loci. The inbreeding coefficient and genetic distance calculations showed significant divergence within each variant among populations from Toyama Bay and southern area. In addition, the phylogenetic analysis, the distinctiveness range values of pairwise of FST and Nei’s genetic distance showed divergence between red and green variants. However, the hybridization pattern produced from NEWHYBRIDS software showed in 15 and 13 individuals of red and green variants, respectively. These observations were identical with individual assignment in STRUCTURE software and principle coordinates analysis (PCA) in each color variant. The contemporary gene flow among populations of red and green variants showed low estimates at wide-range, and great estimates among geographical neighboring populations using BAYESASS software. However, estimates of historical migration rates calculated using program MIGRATE-N revealed great migration from Noto to Uozu among green variant, and in red variant, and in red variant from Uozu to Shinminato in Toyama Bay. In southern area the historical great migration rates showed from Sasebo to Saga among green variants and from Saga to Yamaguchi among red variants populations. These results are partially consistent with previous studies and support the opinion that there are gene migrations among neighboring populations of Japanese sea cucumber. In addition, the differences of gene flow rates between red and green variants may be influenced by ecological desire for each variant.
2) In the second part, the spontaneous spawning, larval development, survival rate, and larval growth rate patterns were studied in the red and green variants of A. Japonicus. The green variant adapted well to the captive conditions in the Sasebo City Fisheries Center and spontaneously spawned without any induction or stimulation. One hundred individuals of green variant spawned nine times and produced approximately 155 million eggs. In contrast, fifty individuals of red variant showed poor adaptation to captivity and spawned spontaneously only three times, producing about 12 million eggs. This study demonstrated the developmental differences between those variants, and showed that the spawning season of red and green variants relatively different. This provides useful method for maintaining sustainable harvests and eventually contributing to restocking and sea ranching of the exisiting population.
3) Finally, in order to study the species diversity from different habitat of sea cucumber the pattern of morphology and taxonomy of deep-sea cucumber Bathyplotes tizardi was reported in this part. The specimens of B.tizardi in the East China Sea. According to the redecription and photos by SEM of ossicles, it makes easier distinguish of this species than before.
The highly significant population divergence and distinct phylogenetic clustering between red and green variants as well as the results derived from the early larval development indicated there is a taxonomic divergence between color variants. In addition because A. Japonicus exhibits strong habitat preference, its dispersion is expected to be restricted, thus preventhing rapid gene flows between neighboring populations. However, they do undergo a short period of free-swimming larval stage ( auricularia larval stage), thus the gene flow is accumulated over the generation. Therefore, it recommended that each color variant of Japanese sea cucumber A. japonicus be treated as a separate management unit and populations in each area as well. The casual relationships between genetic diversity and ecological conditions should be examined further to better understand factors that preserve distinct populations.
Contents:-
Chapter 1: Genetic population structure
Chapter 2: Spontaneous captive breeding and larval development
Chapter 3: Redescription of ossicles of the deep-sea cucumber
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