Investigating genetic and molecular aspects of growth of the tropical abalone Haliotis asinina

Lucas, Timothy (2007). Investigating genetic and molecular aspects of growth of the tropical abalone Haliotis asinina PhD Thesis, School of Integrative Biology, The University of Queensland.

       
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Author Lucas, Timothy
Thesis Title Investigating genetic and molecular aspects of growth of the tropical abalone Haliotis asinina
School, Centre or Institute School of Integrative Biology
Institution The University of Queensland
Publication date 2007-02
Thesis type PhD Thesis
Supervisor Degnan, Bernard M.
Knibb, Wayne
Language eng
Subjects 300000 Agricultural, Veterinary and Environmental Sciences
Abstract/Summary The tropical abalone Haliotis asinina is a wild-caught and cultured species that is found throughout the Indo-Pacific. It is also an emerging model species for the study of growth, reproduction and development of haliotids and other vetigastropods. H. asinina has the fastest recorded natural growth rate of any abalone and reaches sexual maturity within one year. As such, it is a suitable abalone species for studying genetic and molecular aspects of commercially important traits such as growth. This thesis reports the analysis of growth and other traits in a single cohort of H. asinina that consisted of 84 families that were generated via a full-factorial mating design consisting of 14 sires and six dams. Progeny were measured and then tested for parentage and RNA expression to explain the differences in size. During this study a shell disease was discovered and investigated. Estimating the amount of variation in size that is attributable to heritable genetic differences can assist the development of a selective breeding program. In Chapter 2, I estimated heritability for growth-related traits at 12 months of age in these 84 H. asinina families. Of 500 progeny sampled, 465 were successfully assigned to their parents based on shared alleles at five polymorphic microsatellite loci. Using an animal model, heritability estimates were 0.48 ± 0.15 for shell length, 0.38 ± 0.13 for shell width 0.36 ± 0.13 for weight. Genetic correlations were > 0.98 between shell parameters and weight, indicating that breeding for weight gains could be successfully achieved by selecting for shell length. A novel method for analysis of shell colour revealed that the proportion of blue in the shell was a very good indicator of shell length in this study. In Chapter 3, large and small abalone from the aforementioned experiment were compared for differences in RNA expression levels, using microarray gene expression profiling. Big and small abalone were each represented by three pools of RNA, which each contained RNA from four individuals from that size class. Comparison of these RNA pools identified 14 genes that were significantly differentially regulated between fast and slow growers (P <0.05). From this list and another list generated by the disease study (Chapter 5), seven genes were selected for further interrogation using qRT-PCR in Chapter 4. This experiment aimed to compare gene expression for these seven genes in fast and slow growing individuals. In order to accurately evaluate relative transcription, it is important to have reference genes which are expressed stably and do not vary with growth rate. The transcription factors POU-3, POU-4, Pax-258 and Pax-6 were tested and deemed to be more suitable reference genes than other genes that were derived from microarray experiments. Expression levels in different individuals revealed high levels of variation in expression levels between individuals, and that several of these genes have potential for use as markers for fast growth in aquaculture. These include the genes ferritin, metallothionein and ribosomal protein L22. A shell and mantle disease that affected a large proportion of abalone was the focus of Chapter 5. Examination of mantle tissue showed necrosis and encapsulation in areas of abnormal shell growth. Whilst the cause of the disease is unknown, spherical virus-like particles were observed in the mantle tissue of both diseased and apparently healthy individuals. Analysis of parentage revealed that dams appeared to have a substantial effect on the extent of disease in their progeny, with progeny from one dam being almost unaffected by disease. Comparison of gene expression failed to reveal any genes associated with the disease, however, the 'growth markers' from Chapter 4 were stable across diseased and unaffected abalone, indicating that the disease symptoms were not associated with changes in metabolism. This thesis demonstrates heritable genetic differences in growth rate between individuals, provides molecular tools to assist in identification of fast growers, and describes a previously unknown shell disease in H. asinina. This information will assist in the development of a profitable aquaculture industry based on this species, and some of the findings may also be applicable to other abalone species.

 
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Created: Fri, 28 Mar 2008, 14:55:07 EST by Noela Stallard on behalf of Library - Information Access Service