Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.536550
Title: The functional anatomy of the digestive system of the marine wood-boring isopod Limnoria quadripunctata, with evidence of endogenous cellulase production
Author: Dymond, Jo
Awarding Body: University of Portsmouth
Current Institution: University of Portsmouth
Date of Award: 2005
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Abstract:
Wood-boring species of the isopod family Limnoriidae cause damage to timber in the marine environment. Limnoria quadripunctata is a wood-borer with a widespread distribution in temperate waters. Key points of relevant literature are reviewed. Histological techniques, coupled with scanning electron microscopy, were used to examine the structure of the oesophagus, proventriculus and hindgut, which together comprise the alimentary canal. The midgut diverticula, which are believed to be the site of both secretion and absorption, were examined using the same techniques. The proventriculus of L. quadripunctata is described in detail for the first time. The most prominent features of this anteriorly positioned chamber are lateral ampullae, anterior ventral lamellae, and primary and secondary filters. This filtration system is probably responsible for preventing the influx of ingested particulate matter into the diverticula. Also of interest is the hindgut, in which a previously undescribed structure, the posterior ventral lamellae, was identified. Former workers have stated that no microorganisms are present in the hindgut of the wood-boring limnoriids; however, microorganisms associated with the cuticular lining of the hindgut were observed in some of the specimens during this study. A molecular approach was used to determine whether Limnoria produce an endogenous endoglucanase -a question that has been the source of much previous controversy. Reverse transcription was used to produce cDNA from mRNA, isolated from the microorganism-free midgut diverticula. Subsequent cloning and sequencing of this cDNA, along with 5' and 3' RACE, produced a contiguous cDNA sequence that was 1538 base pairs in length. The theoretical translation of this sequence indicates that it encodes for a 461 amino acid endobeta- l, 4-glucanase (cellulase). Sequence comparisons, which included phylogenetic analysis, coupled with in situ hybridisation clearly indicate the endogenous origin of this transcript. This evidence fits the hypothesis that Limnoria secrete an enzyme involved in the degradation of cellulose. Finally, this study examined the early life history of L. quadripunctata. The peak of the breeding season occurred during the warmer, summer months; throughout this period, the mean brood sizes were between 5.6 and 7.0. The development was found to resemble that of the close relatives, L. lignorum and L. tripunctata. However, mean brood sizes were consistently lower than those previously reported for L. lignorum. These data have implications for the understanding of wood degradation by marine wood-borers, which is important in the recycling of carbon. It is also hoped that a greater understanding of digestion in these animals may help in the development of novel wood preservatives that have a low environmental impact.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.536550  DOI: Not available
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