I have collated data on the number of ganglia and the fusion patterns of neuromeres from over 750 species. This data set, when mapped onto an insect phylogeny, allows the patterns of nerve cords from across the whole of the insects to be seen. For the first time trends through evolution can be identified in the insects. There are independent evolutionary trends towards neuromere fusion in several insect lineages. Most fusion of neuromeres occurs either with the metathoracic neuromere or with the terminal ganglion. There is also evidence for some neuromeres having separated from ganglia to which they had been fused. There are many convergent fusion patterns across the insects particularly in the holometabolous orders. To investigate possible mechanisms that drive the diversity of neuromere position and fusion patterns the position of the fifth abdominal neuromere of the locust <i>Schistocerca gregaria </i>and the cricket<i> Acheta domesicta</i> was modelled. Cost minimization and physical tension models, using data on the size and number of axons in the connectives and main peripheral nerves, were used to study whether the observed position of the neuromere in either species matched predicted positions. The results show that the predictions from some tension-based models match the observed neuromere position for both the locust and the cricket, whereas, the cost minimisation models do not match the observed position of the neuromere in either species. To investigate whether there are any correlations between the fusion patterns and positions of neuromeres, and ganglion size, anatomy and, body size and shape a comparative study of neuromere fusion pattern in ground beetles and neuromere position in hoverflies was used. Neuromere position varies as the sizes of adjacent ganglia vary. Body size but not body shape varies with degree of fusion and neuromere position. Eye size and antenna length vary with ganglion size, and eye size varies with the degree of fusion, when controlling for body size.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:599593 |
| Date | January 2003 |
| Creators | Graham, C. M. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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