The ecology and life history of the burrowing polychaete Scoloplos magginatus meleani were studied at two stations in Borge Bay, Signy Island (South Orkneys, B.A.T.) during 1969-72. S.m. meleani females spawned once annually, probably laying a single cocoon each during a three-six week period around midwinter. Mean fecundity was lower than in a comparable temperate species, S. Arriger. Larval development took 26 weeks, 10 spent in cocoons and the remaining 16 in the substrate. Metamorphosis was thus delayed until midsummer when the food supply was best. Ovary development began at age two years. Ovum maturation was protracted, taking two years, thus females first spawned at age four years. Females probably spawned more than once, preparing for three spawnings concurrently. In comparison with S. arajger and other polychaetes S.M. mcleani had a prolonged breeding cycle. This is a common feature of Antarctic invertebrates, that has been linked to the single brief annual plant growth period. The populations at the two stations differed in density, fecundity and individual body size. At Small Rock the mean body segment number of the adults was 163.0 and the mean preserved wet weight was 403.9 mg. Density was 661.8 ova/female in 1970 and 479.8 ova/female in 1972. At Factory Cove adults had 176.5 body segments (mean) and the mean weight was 1086.3 mg. Density was 136.5 individuals/m2 early in 1971. A model is proposed to explain changes in the populations. It is suggested that the dense population at Small Rock was close to the carrying capacity of the substrate and responded rapidly to a food shortage in 1971. The response of the Factory Cove population was delayed.

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Plant parasitic cyst nematodes induce the formation of specialised feeding structures, termed syncytia, from which they feed within the host roots. The multinucleate syncytium initiates from a single host root cell and expands by the local cell wall dissolution of neighbouring cells. In this study, a set of monoclonal antibodies were applied to reveal the microstructures of syncytial cell walls induced by four economically important cyst nematode species, Globodera pallida, Heterodera glycines, Heterodera avenae and Heterodera filipjevi, in their respective potato, soybean and wheat host roots. In situ fluorescence analysis revealed that cell walls of syncytia induced by G. pallida and H. glycines share high structural similarity. Both consisted of abundant xyloglucans, methyl-esterified homogalacturonan and pectic arabinans. In contrast, the walls of syncytia induced in wheat roots by H. avenae and H. filipjevi contain much less xyloglucan but are rich in feruloylated and substituted heteroxylans and arabinans, with variable levels of mixed-linkage glucans and galactans. Further investigations were implemented using a range of cell wall related Arabidopsis xyloglucan and pectic arabinan mutants. In situ analysis was applied on those H. schachtii induced syncytia. The results indicated the strong adaptions during the induction and formation of the syncytia while the cell wall composition of the syncytium was stable. Besides, the syncytial wall pectin methyl-esterification status was shown to fluctuate along with the syncytium development in addition to coping with induced PEG-simulated drought stress. Further analysis was carried out on selected pectic homogalacturonan related mutants, and the fluorescence-based quantifications revealed the complexity of the forming and regulating pectin methyl esterification. Transgenic wheat lines with a root-cap-specific promoter were made via biolistics, in the hope of using this system to further investigate the syncytia formed in wheat, which were shown to be different from the other syncytia analysed.

Bdelloid rotifers are microscopic aquatic animals, notable for their ancient asexuality and their extreme desiccation tolerance. In the absence of sexual reproduction, bdelloids have persisted for over 40 million years, diverging into >450 morphologically distinct species. Despite the two-fold cost of sex, asexual lineages tend to be short-lived and species poor. Many theories exist to explain the success of sexual reproduction, and in the light of these, ancient asexual lineages are an evolutionary paradox. Understanding the persistence and speciation of ancient asexuals may provide clues to factors underlying the success of sexual reproduction. Bdelloid rotifers have unusual genomic features that may have provided some compensation for their long-term absence of sexual reproduction. Here I focus on two: multiple gene copies and horizontal gene transfer (HGT). Bdelloids have multiple copies of many genes, and are considered degenerate tetraploids. In genomes influenced by the opposing forces of gene conversion and divergence of former alleles, I examine the relationships between, and biochemical implications of divergence of a multi-gene family of alpha tubulin. Horizontally acquired genes were initially identified in sub-telomeric regions of two species of bdelloid rotifer. In order to understand what role foreign genes might have played in bdelloid evolution we need to examine the extent, frequency and mechanism of HGT. Here I develop a bioinformatics pipeline for identifying horizontally acquired genes in transcriptomes. By comparing HGT in a number of bdelloid species I demonstrate that the majority of transcribed foreign genes were acquired before the divergence of extant bdelloid species, but the presence of more recently acquired genes implies that HGT is ongoing. By comparing the extent of HGT in closely related species with different desiccation frequencies I provide initial support for the hypothesis that bdelloid HGT is facilitated by DNA breakage and repair during cycles of desiccation and rehydration.

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