Abstract
The Teredinidae are a major economic pest of wooden coastal structures, causing billions of Dollars worth of damage per annum. To fully understand the threat posed by teredinids it is necessary to examine their biology at a number of different levels. These include: the anatomical adaptations which facilitate their wood-boring and wood- feeding life-style; the mechanism of cellulose digestion, which is aided by cellulolytic symbionts retained in bacteriocytes on the teredinid gill; the early life history strategies, particularly larval development; improving the means of teredinid identification for this taxonomically challenging group; and monitoring the spread of teredinids and the impacts global warming may have on their distribution. This thesis set out to address a number of these questions.The teredinid Lyrodus pedicellatus is able to complete a life-cycle feeding exclusively on wood and is one of the most destructive of the marine borers. In this study, X-ray micro-computed tomography (MicroCT) was used to produce a three-dimensional computer-rendered model of L. pedicellatus, to examine the anatomical adaptations for wood-digestion. This was complemented by a transcriptomic analysis of the major digestive organs, which set out to determine whether L. pedicellatus is capable of independently producing cellulolytic enzymes. Investigation of the early life history strategy aimed to provide new insights into the larval-parent interactions during brooding and development – the most crucial phase in the life-cycle of teredinids. Finally, integrative taxonomy was used to improve the taxonomic resolution of the Teredinidae and these methods helped to confirm the identity of an invasive Caribbean species of teredinid, Teredothyra dominicensis, which has recently invaded and established breeding populations in the Mediterranean Sea.
This research provides the first detailed evidence that brooded L. pedicellatus larvae derive extra-embryonic nutrition from their parent. This extended parental care allows larvae to settle and metamorphose immediately after release. Development to sexual maturity is then rapid and individuals become gravid with brooded larvae within six weeks.
The examination of the digestive system of L. pedicellatus using MicroCT revealed a number of adaptations towards xylotrophy. The elongated stomach, specialised digestive gland, large caecum with a well developed typhlosole and long intestine are all modifications enabling a more complete utilization of wood for nutrition. These results corresponded with the transcriptomic analysis which suggests the specialised digestive gland produces a range of cellulolytic enzymes.
A phylogenetic survey of the Teredinidae using integrative taxonomy provides a robust model for future identification of species, including cryptic species, within this taxonomically challenging group. This formed the basis for the identification of T. dominicensis, a species thought to be confined to the Caribbean and Gulf of Mexico, which has recently invaded the Mediterranean. This species was found to have established a substantial breeding population in the region, which produce large quantities of larvae which could settle and metamorphose. Thus, T. dominicensis may be considered an established species in the Mediterranean.
Providing a more accurate means of identification and increasing knowledge on the larval development and early life histories will help efforts to monitor the spread of teredinids and identify areas under threat from the destruction they cause. Furthermore, understanding the anatomical and molecular mechanisms which allow teredinids to deconstruct lignocellulose into monomeric sugars may provide new means of protection for wooden structures and provide novel enzymes for use in the biofuel industry.
| Date of Award | Sep 2013 |
|---|---|
| Original language | English |
| Supervisor | Simon Cragg (Supervisor) & Alex Ford (Supervisor) |