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Sensory systems form the first point of contact between animals and their surroundings. The study of sensory systems is both a rich and diverse anatomical and behavioural field, and a potentially invaluable tool in evolutionary biology. This thesis examines four systems in three molluscan classes and ophiuroid echinoderms, addressing novel or poorly-understood systems and examining evolutionary trends by assessing the anatomy of more familiar structures in a phylogenetic context. The primary study system is a novel discovery reported herein throughout the chiton order Lepidopleurida, named the Schwabe organ. By combining detailed anatomical study, electrophysiology and behavioural experiments, 1 demonstrated that the Schwabe organ mediates light-avoidance behaviour and likely shares developmental origins with the chiton larval eye. A similar integrative approach was applied to a putative ‘visual* system in the ophiuroid Ophiocoma wendtii. Anatomical and behavioural results indicated that animals may use an extensive network of dermal photoreceptors for image formation, however this system differs substantially from the established model. The two final chapters focus on sensory and nervous systems in evolution. A re-description of scaphopod neuroanatomy in Rhabdus rectius demonstrates the potential power of a neurocladistic approach in solving deep phylogenetic questions, highlighting important similarities with cephalopod neural architecture and prompting the re-assignment of the major body axes in adult scaphopods. Finally, a study of eye reduction and eye loss in deep sea solariellid gastropods found surprising morphological diversity and differential progression between independent eye reductions, even within genera. This thesis makes several important contributions to our knowledge of four sensory systems and their evolution across two major invertebrate phyla: the Schwabe organ, extra-ocular photoreception in 0. wendtii, the Steiner organ and gastropod eyes. Overall, it also demonstrates the powerful nature of cross-disciplinary projects as well as the versatile role of sensory biology in broader evolutionary studies.

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The plant-parasitic nematode Meloid?gyne incognita stimulates the de-differentiation of plant root cells into enlarged, multinucleate giant cells which function as transfer cells. Changes in host plant gene expression occur in response to this parasitism and these were monitored in mature feeding site structures (galls) ofM incognita fo~ed in Arabidopsis thaliana. Whole genome microarrays were hybridised with cDNA obtained from galls and from sections ofuninfected root sampled at 21 days post infection. 959 Arabidopsis genes were found to be significantly differentially expressed, of which approximately two thirds were down-regulated.. Microarray data was validated by qRT-PCR analysis of 16 genes representative of a range of microarray fold changes and a Pearson correlation coefficient of 0.78 was obtained. . . Four genes determined as differentially expressed by microarray analysis were selected for promoter::GUS reporter analysis. All constructs 'had some expression in uninfected roots. Transgenic Arabidopsis plants were infected with M incognita or the cyst nematode Heterodera schachtii. The promoter of ammonium transporter gene AtAMT1;2 was consistently repressed in roots associated with both nematode species at all developmental stages observed. GUS expression driven'by the LATERAL ORGANBOUNDARYDOMAIN GENE 41 promoter was induced strongly in galls of fusiform and saccate M incognita but the response to H. schachtii parasitism was not consistent. Promoters for actin depolymerising factor gene ADF3 and a lipid transfer protein/seed storage protein/protease inhibitor gene LTP both showed induction of GUS expression in the galls of fusiform and saccateM incognita. This appeared to be associated with the vasculature for LTP. H. schachtii parasitism at saccate and mature male stages did not alter expression of GUS. Several Solanum lycopersicum (tomato) genes possessing homology to genes differentially regulated in galls induced in Arabidopsis were identified. Expression of these homologs was determined by RT-PCR in feeding sites' structures of M. incognita, Nacobbus aberrans or Globodera pallida. Distinct patterns of expression were observed for the different types of feeding site structure.. Regulation of the homologs was monitored in M incognita galls at three developmental stages and revealed temporal variations in detected expression. Comparison of sets of Arabidopsis genes identified as highly induced or repressed in mature M incognita galls with other biotic stresses revealed that many of these genes were also differentially regulated by Agrobacterium tumefaciens. This suggests that many transcriptional modifications in both systems may be secondary effects rather than primary, causative events.

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