Figures & data
Fig. 1. Location of the sampling stations (st 1–st 7) in the North Sea.
Table 1. List of clones used. Each clone was isolated within one or two days of sampling
Table 2. Pseudo-nitzschia pungens: dimensions and stria and fibula densities* from integrated literature data (Fryxell & Hasle, Citation2003), one of our field samples (from station 5) and four clonal cultures
Figs 2–6. Pseudo-nitzschia pungens vegetative cells: LM (, ) or SEM (). . Stepped chain of cells (live) in girdle view, clone 18. Scale bar: 50 µm. . Valve, clone 29. Note the coarse striae and the absence of a central interspace (the raphe slit is not interrupted by the central nodule). Scale bar: 20 µm. . Valve ultrastructure. Note the presence of two rows of poroids per stria (, ), the single row of paired poroids on the proximal mantle (thick arrow on ), and single row of poroids (spaced like those of the valve face) on the distal mantle. The girdle of a complete theca consists of three bands (, thin arrows), each with a row of single poroids. , . Clone 2: valve face in internal () and external () views. . Clone 23: frustule in girdle view (the epitheca is marked with an arrowhead). Scale bar: 2 µm.
Figs 7–12. Live vegetative cells. . Interphase chloroplasts. , . Cells in valve view: the chloroplasts are appressed to the same () or opposite sides () of the girdle. . Cell chain in girdle view. . Chloroplast division at mitotic cytokinesis, girdle view. . Cell division is complete and the chloroplasts have moved onto the epithecae of the newly formed cells, girdle view. . Two sibling cells after rearrangement into the characteristic stepped configuration, girdle view. Note that the chloroplasts are still appressed to the epivalves. Scale bars: 20 µm.
Figs 13–22. Abrupt cell size reduction in living vegetative cells, clone 23. . Cell of abnormal shape, valve view. . Two sibling cells of abnormal shape soon after division, girdle view. Note the constriction of the cells at the centre (arrow). . The lower chloroplast has been split into two, valve view. . Two sibling cells just after cell division, each containing three chloroplasts, girdle view. . Separation of the protoplast into two parts (arrow), girdle view. . The separated protoplast fragment, which contained one product of a divided chloroplast but lacked a nucleus (arrow), has aborted; valve view. . Division of a cell with a partly aborted protoplast has resulted in the formation of short hypothecae, girdle view. . Typical cluster of abruptly reduced cells formed by three mitoses subsequent to abrupt size reduction, girdle view. , . Stepped colonies of abruptly reduced cells in valve () and girdle views (). Scale bars: 20 µm.
Table 3. Results of mating experiments
Figs 23–32. Pairing, gametogenesis, plasmogamy and early auxospore development in crosses between anomalous clone 40 (smaller) and PNp+ clone 6 (, ), and clone 40 (smaller) and PNp− clone 17 (, ). . Valve-to-valve pairing. . Pairing between cells still connected in chains. In the left pair, plastokinesis and cytokinesis have been completed, following meiosis I. , . Pairs of gametangia stained with DAPI, after meiosis I () and after meiosis II (, upper gametangium). . Triplet of gametangia. Two cells of clone 40 (smaller cells) have paired with one cell of clone 17. The topmost clone 40 gametangium and the clone 17 gametangium below it are undergoing gamete re-arrangement; the gametes in the lower clone 40 gametangium have completed re-arrangement and contracted. . Late gametogenesis, DAPI staining: the gametes of the upper gametangium are in early gamete re-arrangement, while those of the lower gametangium have re-arranged and begun to contract. Both sibling haploid nuclei are still visible and equal (those of the left gamete of the lower gametangium are not in focus). . Gametangia after re-arrangement and partial contraction of the gametes. . Fully contracted gametes. Note attachment of the right gamete of the upper gametangium to one theca of the parental cell. . Zygotes after allogamous fusion of gametes. The zygotes lie within the compartment formed by the frustule of the upper gametangium. . Early auxospore expansion. Note the cap-like structures at the tips of auxospores (arrows), which represent the ruptured primary auxospore cell wall. Scale bars: 20 µm.
Figs 33–42. Auxospore and initial cell formation, in a cross between clones 40 and 6. . Auxospore at a late stage of expansion. Note the two unfused haploid nuclei at the centre. . Initial cell formation, girdle view. Note the epivalve is uppermost. . The contents of auxospore have contracted and the epivalve has been laid down. The chloroplasts lie on the cell side opposite to the epitheca. . Shift of the chloroplasts onto the girdle of the future initial cell. . The chloroplasts have moved onto the epivalve. . Completion of initial hypovalve. . Re-arrangement of the chloroplasts: the two marginal plastids have moved onto the hypovalve and the two central plastids onto the epivalve. . Re-alignment of chloroplasts complete. . Division of initial cell within the transverse perizonium. . Initial cell escaping from the perizonium before the first cell division. . Transverse perizonium (arrowhead) and longitudinal perizonium (arrow), after the escape of the initial cell. Scale bars: 20 µm.
Table 4. Parental and initial cell lengths* for two crosses, clone 6 × clone 40 (21.12.2003) and clone 16 × clone 18 (21.01.2004)
Figs 43–47. Anomalous development during auxosporulation, clone 40 × clone 6. , Abrupt size reduction at initial cell formation. . Partial abortion of auxospore cell contents at one pole (arrow). . The initial cell is shorter than the developed auxospore and longitudinal perizonium (arrow). . Auxospore containing two chloroplasts and a single nucleus. . Auxospore containing six chloroplasts and three nuclei (at centre). . Initial cell containing six chloroplasts. Scale bars: 20 µm.
