Figure 1.
Reduced Ulva ITS phylogenetic tree.
Reduced version of maximum likelihood tree of Ulva ITS sequences (Figure S1), showing the species used in this study (shown in bold) and Ulva species used in previous studies investigating the reproduction of this genus. Species investigated in tropical environments are shown in italic. Pictures next to species represent the morphology (flat and blade-like or tubular and filamentous thalli).
Figure 2.
Light micrographs of Ulva sp. 3.
Transformation of vegetative cells into reproductive cells of Ulva sp. 3. (a) Vegetative cells, (b) formation of swarmers after 26 h, (c) reproductive cells with fully formed swarmers after 44 h, (d) reproductive cells with fully formed and discharged swarmers after 46 h. Scale bar, 20 µm.
Figure 3.
Discharge of swarmers in experiments testing the effect of salinity, dehydration, and segmentation.
Mean (± S.E.) discharge of swarmers (%) after two and three days post collection and treatment. Samples were rinsed in dechlorinated tap water (DC) or filtered seawater (FSW) 10 min prior to dehydration for 45 min (Dehydrated). Non-dehydrated filaments (Non-dehydrated) were used as a control. Filaments were either left whole (Whole) or segmented into pieces <5 mm (Cut).
Figure 4.
Discharge of swarmers testing the effect of time of initiation of experiments and photoperiod.
Mean (± S.E.) discharge of swarmers (%) under photoperiods of (a) 12 h light:12 h dark; (b) 18 h light:6 h dark; (c) constant light; and (d) constant darkness. Experiments were initiated at 1 pm and 7 pm on the day of collection (Day 1) and at 7 am, 1 pm, and 7 pm one day after collection (Day 2). Grey shaded background indicates duration of the dark period.
Table 1.
PERMANOVA output testing the effect of photoperiod (Ph; 12 h light:12 h dark, 18 h light:6 h dark, 24 h light, and 24 h dark), time of initiation (In; 1 pm and 7 pm on collection day, 7 am, 1 pm, and 7 pm one day after collection), sampling day (Day; 3 and 4 days past collection), and time of sampling day (sTime; 7 am, 1 pm, and 7 pm) (all fixed factors) on the discharge of swarmers.
Figure 5.
Discharge of swarmers under a 12;12 h D photoperiod testing the effect of time of initiation of experiments.
Mean (± S.E.) discharge of swarmers (%) under a 12 h light:12 h dark photoperiod. Experiments were initiated at 1 pm and 7 pm on the day of collection (Day 1), and at 7 am, 1 pm, and 7 pm one day after collection (Day 2). Grey shaded background indicates the dark period.
Figure 6.
Discharge of swarmers testing the effect of temperature shock and controlled release of swarmers.
Mean (± S.E.) discharge of swarmers (%) two days after initiation of experiments at (a) 11 am and (b) 4 pm. Filaments of Ulva were exposed to 4°C and 25°C FSW and without pre-treatment as a control. After two days, the filaments were wrapped in moist paper, dried, or remained submersed from 7 am for 4 h.
Figure 7.
Number of released swarmers over time.
(a) Mean (± S.E.) number of released swarmers over time (n = 3). (b) Mean number (± S.E.) of released swarmers over time from three independently collected batches of algal biomass (n = 50). Algal batches were collected on 6 May 2013 (Batch 1), 7 May 2013 (Batch 2), and 14 May 2013 (Batch 3).
Figure 8.
Reproductive output of Ulva sp. 3.
Mean (± S.E.) reproductive output (RO) of three independently collected algal batches (n = 50). Experiments were initiated on 6 May 2013 (Batch 1), 7 May 2013 (Batch 2), and 14 May 2013 (Batch 3).
Figure 9.
Time course of induced sporulation of tropical Ulva sp 3.
(a) Collection of algal samples and subsequent transportation to the laboratory. (b) Initiation of experiments at 1 pm by washing the thalli in FSW, subsequently chill Ulva for 10 min and then place thalli into autoclaved FSW under a 12 h light:12 h dark photoeriod at 25°C. (c) Induction of sporulation with visible formation of swarmers after approximately 26 h. (d) Release of swarmers peaks between 10∶00 and 11∶30 am.