Sexual reproduction in the marine centric diatom Ditylum brightwellii (Bacillariophyta)

Figures & data

Table 1.  Clones of Ditylum brightwellii used in two mating system experiments. The mean diameter of each clone at the beginning of each experiment (n  = 100 cells per clone) is given. Two clones, N3 and N4, were used in both experiments, and denoted as N3′ and N4′ in the second experiment.

Clone ID	Experiment	Size (µm)  ± SD	Isolation date
N1	1	12.9  ± 0.8	12 Oct 2004
N2	1	17.3  ± 0.8	12 Oct 2004
N3	1	20.5  ± 0.9	7 Aug 2004
N4′	2	21.8  ± 0.7	12 Oct 2004
D5	2	24.4  ± 0.8	12 Oct 2004
N4	1	26.2  ± 0.7	12 Oct 2004
N3′ ^a	2	26.3  ± 0.6	12 Oct 2004
D6	2	29.0  ± 0.9	7 Aug 2004
^aN3′ is larger than N3 because of vegetative enlargement in the N3 stock culture following the first experiment, from which the N3′ cell line was isolated.

Fig. 1. Sampling location within the Gulf of Maine. The inset shows Penobscot Bay and Wadsworth Cove (circle).

Figs. 2–10. Life-cycle stages in Ditylum brightwellii. Fig. 2. Live egg (arrow) and sperm (arrowhead) and auxospore (double arrow). Fig. 3. Fixed egg viewed with bright-field microscopy. Fig. 4. The same egg stained with DAPI. Fig. 5. Mass spermatogenesis in a live culture. Note swelling of spermatogonia (arrow). Fig. 6. Spermatogonangium with rudimentary thecae (arrow) in 1% glutaraldehyde and formaldehyde fixative. Fig. 7. Early stage auxospores in living preparation. Note properizonium (arrows). Fig. 16. Auxospores developed fully; formation of both valves of the initial cells is nearly complete (living preparation). Fig. 17. Resting spore of Ditylum brightwellii in a clonal culture from a natural population at Wadsworth Cove (fixed sample). Fig. 18. Vegetative cell enlargement in living Ditylum brightwellii. Scale bars: 10 µm.

Fig. 11. Life history of Ditylum brightwellii. Size reduction occurs over time via vegetative cell division. Resting spores develop from, and germinate into vegetative cells (Hargraves, 1984). Sexual reproduction takes place between haploid eggs and sperm; the auxospore (diploid) is a specialized zygotic cell.

Fig. 12. Natural logarithm of the ratio of production of oogonia to spermatogonangia (O:S) in Ditylum brightwellii. Each clone is represented by its diameter measured on day 0. The ratio is the average of the duplicated treatments over the entire experiment  ± SD (n  = 16). The clones with the open symbol (○) did not produce gametes.

Fig. 13. The frequency (%) of gamete production in three mating crosses of Ditylum brightwellii over 7 days. Shaded areas represent the area under the curve of the mean of duplicate measurements (filled circles). Trends in gamete production are highlighted with the upper solid line representing the mean multiplied by five.

Fig. 14. Frequency (%) of auxospores produced in three mating crosses of Ditylum brightwellii over 7 days. Shaded areas represent the area under the curve of the mean of duplicate measurements (filled circles). Trends in gamete production are highlighted with the upper solid line representing the mean multiplied by five.

Fig. 15. Abundance of Ditylum brightwellii at Wadsworth Cove, autumn 2004. Mean number of cells l⁻¹  ± SD (○ indicates days on which spermatogonangia were absent).

Fig. 16. Size frequency distributions of populations of Ditylum brightwellii from Wadsworth Cove by sampling date. The stars denote presence of spermatogonangia and the dotted line is the upper size limit for gametogenesis observed in lab experiments.

Fig. 17. Changes in mean, median and principal mode of Ditylum brightwellii from the Wadsworth Cove population during autumn 2004.

Fig. 18. Size distributions in Ditylum brightwellii N2  × N4 cross over time. Straight line represents day 0, dashed line represents day 5. Day 0, n  = 50 (intraclonal crosses), n  = 200 (interclonal crosses); day 5, n  = 200 (all treatments). The dotted line is the upper size limit for gametogenesis observed in lab experiments.

Table 2.  Gamete and auxospore production by Ditylum brightwellii in two, 7-day, mating experiments.

Experiment 1
Clone		N1% (day)	N2% (day)	N3% (day)	N4% (day)
N1	O	0.02 (4)	0.04 (4)	2.97 (1)	0.01 (4)
	S	1.96 (2)	29.07 (1)	4.04 (1)	2.87 (2)
	A	0.02 (4)	4.06 (2)	2.26 (2)	0.07 (3)
N2	O		0.69 (5)	3.79 (1)	0.03 (3)
	S		64.60 (4)	39.19 (1)	32.43 (1)
	A		6.71 (4)	19.21 (2)	2.05 (2)
N3	O			7.61 (2)	2.46 (1)
	S			7.33 (1)	2.43 (1)
	A			6.34 (1)	0.88 (2)
N4	O				0.03 (2)
	S				0.08 (2)
	A				0.03 (2)
Experiment 2
Clone		N4′% (day)	D5% (day)	N3′% (day)	D6% (day)
N4′	O	0.08 (5)	0.98 (5)	0.02 (3)	0.11 (3)
	S	1.02 (2)	0.83 (2)	0.69 (2)	0.87 (2)
	A	0.37 (1)	0.11 (4)	0	0.10 (1)
D5	O		0.36 (5)	0.69 (3)	0.07 (4)
	S		0.16 (3)	0.17 (2)	0.04 (2)
	A		0	0	0
N3′	O			0	0
	S			0	0
	A			0	0.07 (7)
D6	O				0
	S				0
	A				0
Maximum production (percent of total cells) of oogonia (O), spermatogonangia (S) and auxospores (A) by each clone or clone pair is presented with the day of occurrence noted in parentheses.

Table 3.  Relative abundance and mean size of spermatogonangia of Ditylum brightwellii at Wadsworth Cove, autumn 2004.

Date	Abundance (%)	Size (µm)  ± SD	No. spermatogonangia
31 Aug 2004	1.0	16.1  ± 2.2	9
7 Sep 2004	0
14 Sep 2004	1.0	18.8  ± 3.2	14
21 Sep 2004	2.4	20.2  ± 2.7	12
28 Sep 2004	0.5	14.2  ± 2.9	3
5 Oct 2004	0
12 Oct 2004	0.4	20.6	2
19 Oct 2004	0.2	26.25	1
26 Oct 2004	0
2 Nov 2004	0.2	21.25	1
9 Nov 2004	0
16 Nov 2004	0
23 Nov 2004	0
30 Nov 2004	0
07 Dec 2004	0
Abundance is the percentage of the total number of cells counted within a sample.

Hargraves , PE . 1984 . “ Resting spore formation in the marine diatom Ditylum brightwellii(West) Grun. ex V. H. ” . In Proceedings of the 7th International Diatom Symposium , Edited by: Mann , DG . 33 – 46 . Koenigstein, Germany : Otto Koeltz .

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