. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 0,4 0,6 Log n+1 [Ca) (mM) Figure 14. Motility response of strain IIIr (pre-incubated at Bv = 0, Bâ = 20 /jT for at least 3 months) to external [Ca] in EMF experi- ments at an even harmonic of ion cyclotron resonance conditions (By = 0. Bh = /jT. Bâ,, = fiT peak-peak at 32 Hz). Unfilled circles = EMF-exposed; filled circles = sham-exposed; /? = 3 in each case. E 3 2 â Before addition of 5 mM Ca O After addition of 5 mM Ca No movement before addition in any case JUL 12 3 4 5 6 â Before removal of 5 mM Ca n Af
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 0,4 0,6 Log n+1 [Ca) (mM) Figure 14. Motility response of strain IIIr (pre-incubated at Bv = 0, Bâ = 20 /jT for at least 3 months) to external [Ca] in EMF experi- ments at an even harmonic of ion cyclotron resonance conditions (By = 0. Bh = /jT. Bâ,, = fiT peak-peak at 32 Hz). Unfilled circles = EMF-exposed; filled circles = sham-exposed; /? = 3 in each case. E 3 2 â Before addition of 5 mM Ca O After addition of 5 mM Ca No movement before addition in any case JUL 12 3 4 5 6 â Before removal of 5 mM Ca n After removal of 5 mM Ca LlliMlll 4 5 6 7 Observed diatoms 10 Figure 15. Mean (±SE) diatom speed recorded in real time on addition (A) and removal (B) of 5 mM Ca to the perfusion chamber. Measurements made in 10-s period prior to addition or removal and in lO-s period I min after addition or removal (see text). r When the pre-incubation step was used, three strains of A. coff'eaefonnis (#2038. IIIb. and III, ) showed a popu- lation motihty response to EMFs. Strains IIIb and III,: might be expected to respond since they are putative de- scendants of the strain used in the original experiments. That #2038 showed a response and #2036 and #2039 did not may indicate intraspecific genetic variation in suscep- tibility to EMFsâvariation that presumably involves the metabolism of Ca. Any susceptibility may already be lost, however, because of the influence of selection and genetic bottleneck effects on genetic drift (see above). Indeed, with the exception of the experiments on strain IIIb (Figs. 10-14). EMF effects were generally ephemeral and the controlling factor (be it genetic or environmental) is, as yet, unknown. Reese et al. (1991) also reported an ephem- eral response with strain #2038. All these observations further emphasize the importance of using a responsive strain of A. coffeaefonnis for these experiments, but they also highlight the limitations of A. coffeaefor
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