. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 0 Log n+1 [Ca] (mM) Figure 10. Motility response of strain IIlu (pre-incubated at Bv = 0, Bh = 20 ^T for at least 3 months) to external [Ca] in EMF experi- ments at ion cyclotron resonance conditions (By = 0, Bh = ^T, B„„,. = /iT peak-peak at 16 Hz). Unfilled circles = EMF-exposed; filled circles = sham-exposed; » = 3 in each case. and Smith et al. (1987a) observed a maximum motility of ~45% within any diatom population, ascribing this to the presence of the raphe system on one diatom valve only. We (an
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 0 Log n+1 [Ca] (mM) Figure 10. Motility response of strain IIlu (pre-incubated at Bv = 0, Bh = 20 ^T for at least 3 months) to external [Ca] in EMF experi- ments at ion cyclotron resonance conditions (By = 0, Bh = ^T, B„„,. = /iT peak-peak at 16 Hz). Unfilled circles = EMF-exposed; filled circles = sham-exposed; » = 3 in each case. and Smith et al. (1987a) observed a maximum motility of ~45% within any diatom population, ascribing this to the presence of the raphe system on one diatom valve only. We (and Reese et al., 1991, and SaaJman et al., 1992) noted that population motility can exceed 50%, perhaps as a result of our plating technique, which allows time for the diatoms to orient themselves in liquid culture before they contact the surface of the agar. In our motility assays, in common with Parkinson and Sulik (1992) and Saalman et al. (1992), we counted only diatoms that were not in contact with any others. This condition was set because motility in one diatom may trigger motility in an adjoining diatom, thus producing non-independence of measurements (Saalman et al., 1992). McLeod et al. (1987a) and Smith et al. (1987a, b) counted some diatoms that were in clumps and some counts may have included (immotile) diatoms whose lateral surfaces were in contact with the agar (Smith, pers. comm.). Thus, it is not surpris- ing that our Ca curves (Fig. 6) do not agree with those of McLeod et al. (1987a) and Smith et al. (1987a, b). Nevertheless, although diatoms of strains 111b and lllp showed greater motility than those in the original experi- ments, the shape of the Ca response curves is similar. supporting the contention that these strains are descen- dants of diatoins used in the original experiments. Cook- sey and Cooksey (1980), Parkinson and Sulik (1992), and McLeod (pers. comm.) observed a reduction or abolition of diatom population motility in the dark. We (Table I),
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