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Title: Characterization of sex-specific transcripts in the mantle of the common mussel, Mytilus edulis
Author: Anantharaman, Sandhya
ISNI:       0000 0004 2734 8883
Awarding Body: Glasgow Caledonian University
Current Institution: Glasgow Caledonian University
Date of Award: 2012
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Mussels are important to the aquaculture industries and in providing environmental services, as environmental sentinels. Blue mussels (Mytilus sp) have been used for many years as an environmental sentinel species to study stress responses and the biological/chemical analysis made on them act as a diagnostic tool of the presence of environmental contaminants. Such responses are distinct in different sexes of mussels and thus it is very important to know the sex of the mussels while using them as a sentinel organism. The problem is that while mussels are gonochoristic, sex cannot be established by anatomy and instead requires resource-demanding histology. To circumvent this difficulty molecular techniques for sex identification have been developed and also used to study the reproductive cycle. The analysis of reproductive cycle is important for the aquaculture industries so that ropes can be placed during the spawning stages to increase the settlement of spat. The Scottish government has challenged the aquaculture industry to double their production by 2020 and it is very , important to more accurately identify the mussel spawning season at different locations. This study focuses on the molecular characterisation of the reproductive , genes, identifying new sex-specific genes and also analysing the reproductive cycle. Since the cycle may be subject to environmental factors, the effects of heavy metals on the levels of sex-specific transcripts were also studied. A temporal study using a qPCR assay was performed to analyse the level of male- specific VCL (vitelline coat lysin) and female-specific VERL (vitelline envelope \, receptor for lysin) transcripts thereby analysing the gametogenesis and spawning stages of the cycle. This study of mussels from Lunderston Bay, Firth of Clyde, UK showed that gametogenesis was initiated during September, gametes were mature by February and spawning occurred between then and June. Mussels were quiescent between July and August. Parallel histology anchored the observation in variation of the transcripts to specific gametogenic stages. It was observed that water temperature is correlated with the reproductive cycle and initiation of gametogenesis occurred as temperature declined from their maxima whiles the start of spawning coincided with temperatures rising from' their winter minima. Using gametes collected by artificial spawning it was shown that the VCL and VERL transcripts were present in the gametes and thus their decline through the spring is a proxy for spawning. This study set out to discover new sex -specific transcripts, and focussed on female specific targets isolated from a previously prepared female-specific SSH library. One such transcript, termed H5, because its identity could not be established through BLAST searches, was found to follow the same temporal profile as VERL and to be present in eggs. A study on the effects of metals (copper and arsenic) on the levels of VCL/VERL and metallothionein transcripts was also conducted and it showed that exposure to metals does affect the levels of the sex-specific transcripts. The exposure to copper resulted in an increased level of expression in VCLNERL transcripts while exposure to arsenic resulted in a decrease in the mussel gonads. The level of metallothionein transcripts were also assessed in the mussels exposed to metals during a field experiment in a site putatively contaminated with 'copper and the exposure experiment. The levels of metallothioneins varied, in a sex-specific, concentration- dependent tissue-specific and metal-specific way. So as to understand local variation in the timing of the reproductive cycle a study of the levels of VCL/VERL transcription in mussels at various locations in the Hebrides, mainly Isle of Lewis, was conducted. Significant differences were found in the time at which gamete maturity and initiation of spawning were reached and in apparent fecundity even over small spatial distances in a period between January and March. ", Surprisingly at one location in Lewis, mussels matured earlier than at Lunderston Bay even though the site is at significantly higher latitude. This study demonstrates the importance of knowing the reproductive cycle for mussel growers. and for the use of mussels as environmental sentinels.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available