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Several bloom‐forming marine algae produce concentrated intracellular dimethylsulfoniopropionate (DMSP) and display high DMSP cleavage activity in vitro and during lysis after grazing or viral attack. Here we show evidence for cleavage of DMSP in response to environmental cues among different strains of the haptophyte Emiliania huxleyi (Lohmann) Hay et Mohler and the dinoflagellate Alexandrium spp. (Halim). Sparging or shaking live cells of either taxon increased dimethyl sulfide (DMS), especially in dinoflagellates, known to be very sensitive to shear stresses. Additions of polyamines, known triggers of exocytosis in some protists, also stimulated DMSP cleavage in a dose‐responsive manner. We observed DMS production by some algae after shifts in light regime. When most exponential‐phase E. huxleyi were transferred to continuous darkness, cells decreased in volume and DMSP content within 24 h; DMSP content per unit cell volume remained relatively steady. DMS accumulated as long as cells remained in the dark, but on returning to a light:dark cycle DMS accumulation ceased within 24 h. However, E. huxleyi strain CCMP 373, containing highly active in vitro DMSP lyase, produced only transient accumulations of DMS in the dark. This was apparently due to production and concomitant oxidation or uptake of DMS, because cells of this strain rapidly removed DMS added to cultures. Three strains of the dinoflagellate Alexandrium tamarense containing high in vitro DMSP lyase activity showed no DMS production in the dark, and all appeared to remove additions of DMS. Alexandrium tamarense strain CCMP 1771 also removed dimethyl disulfide, an inhibitor of bacterial DMS consumption. These data suggest that physical or chemical cues can trigger algal DMSP cleavage, but DMS production may be masked by subsequent oxidation and/or uptake.

In this study, the hypothesis that Emiliania huxleyi, a cosmopolitan, bloom-forming coccolithophorid, produces chemical defenses against protist grazers was tested using four axenic strains of the alga. The putative chemical defense involves the cleavage of dimethylsulfoniopropionate (DMSP) by the enzyme DMSP lyase to yield dimethylsulfide (DMS) and acrylate. Out of six tested protist grazer species, five (including ciliates and heterotrophic dinoflagellates) showed lower feeding rates on E. huxleyi strains with high DMPS lyase activity than on low-lyase strains. Reductions in population growth rate were consistent with feeding reductions. These results suggest that high levels of DMSP lyase activity somehow promote reduced palatability, although covariation of E. huxleyi protein and carbohydrate content with DMSP lyase activity meant that prey ''nutritional quality'' could not be ruled out as a contributing factor. Additional experiments with the heterotrophic dinoflagellate Amphidinium longum demonstrated that (1) individuals need not ingest E. huxleyi cells to receive the ''don't eat me'' cue and (2) exposure to highlyase E. huxleyi cells confers no harmful consequences in terms of the ability to feed and grow on alternate phytoplankton prey. Thus, factors promoting reduced grazing on high-lyase E. huxleyi are hypothesized to constitute signals rather than acute toxins. Furthermore, although cell surface carbohydrates (as assayed by lectin binding) showed few differences among strains, results of feeding studies indicate that the deterrent signal resides on the cell surface or in the near-cell dissolved phase. Behavior responses to such cues might play an important role in the outcome of encounters between protist grazers and their prey, with profound consequences for planktonic community structure.Chemical defenses-chemicals used by individuals to reduce or eliminate agents of mortality-are widespread throughout the natural world. Best studied in terrestrial systems, chemical defense compounds are highly diverse (Berenbaum 1995), ranging from the tannins in oaks to the mustard oil bomb of the bombardier beetle. Similarly, marine macroalgae and invertebrates utilize chemical defenses in systems ranging from kelp forests to coral reefs (Hay 1996). Chemical defenses are employed by bacteria, fungi, plants, and animals, and can defend against attack and mortality due to herbivory, carnivory, and parasitic or microbial infections. The myriad ways in which chemical defenses can be deployed, countermined, co-opted, and mimicked provide not only a rich source of ecological insight, but appear to be fundamental in structuring terrestrial and marine benthic ecosystems.Examples of chemical defenses are known from marine planktonic ecosystems as well, although the significance of the phenomenon for ecosystem structure and function has AcknowledgmentsWe thank Kelley Bright, Marnie Zirbel, Jennifer Clough, and Brady Olson for assistance. We are grateful to Tim Bates and Bruce Frost for the loan of equipment. Juan...

The influence of parental alcoholism on the personalities of the children was studied by use of the Devereux Rating Scales to delineate problem behavior patterns. The subjects for the investigation were identified as a result of their parents being in treatment for alcoholism, and a control group matched for age, sex, race, family size, and socioeconomic status was utilized. The findings suggest that the presence of parental alcoholism acts as a serious deterrent to healthy personality development in the children, and the degree of disturbance in these individuals might be greater than previously suspected. Several implications of these observations are discussed, including the importance of considering alcohol abuse as a total family problem.

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