Predators indirectly induce stronger prey through a trophic cascade.

Many prey species induce defences in direct response to predation cues. However, prey defences could also be enhanced by predators indirectly via mechanisms that increase resource availability to prey, e.g. trophic cascades. We evaluated the relative impacts of these direct and indirect effects on the mechanical strength of the New Zealand sea urchin Evechinus chloroticus We measured crush-resistance of sea urchin tests (skeletons) in (i) two marine reserves, where predators of sea urchins are relatively common and have initiated a trophic cascade resulting in abundant food for surviving urchins in the form of kelp, and (ii) two adjacent fished areas where predators and kelps are rare. Sea urchins inhabiting protected rocky reefs with abundant predators and food had more crush-resistant tests than individuals on nearby fished reefs where predators and food were relatively rare. A six-month long mesocosm experiment showed that while both food supply and predator cues increased crush-resistance, the positive effect of food supply on crush-resistance was greater. Our results demonstrate a novel mechanism whereby a putative morphological defence in a prey species is indirectly strengthened by predators via cascading predator effects on resource availability. This potentially represents an important mechanism that promotes prey persistence in the presence of predators.

Predation cues rather than resource availability promote cryptic behaviour in a habitat-forming sea urchin.

It is well known that predators often influence the foraging behaviour of prey through the so-called "fear effect". However, it is also possible that predators could change prey behaviour indirectly by altering the prey's food supply through a trophic cascade. The predator-sea urchin-kelp trophic cascade is widely assumed to be driven by the removal of sea urchins by predators, but changes in sea urchin behaviour in response to predators or increased food availability could also play an important role. We tested whether increased crevice occupancy by herbivorous sea urchins in the presence of abundant predatory fishes and lobsters is a response to the increased risk of predation, or an indirect response to higher kelp abundances. Inside two New Zealand marine reserves with abundant predators and kelp, individuals of the sea urchin Evechinus chloroticus were rarer and remained cryptic (i.e. found in crevices) to larger sizes than on adjacent fished coasts where predators and kelp are rare. In a mesocosm experiment, cryptic behaviour was induced by simulated predation (the addition of crushed conspecifics), but the addition of food in the form of drift kelp did not induce cryptic behaviour. These findings demonstrate that the 'fear' of predators is more important than food availability in promoting sea urchin cryptic behaviour and suggest that both density- and behaviourally mediated interactions are important in the predator-sea urchin-kelp trophic cascade.

Biologically Active Acetylenic Amino Alcohol and N-Hydroxylated 1,2,3,4-Tetrahydro-ß-carboline Constituents of the New Zealand Ascidian Pseudodistoma opacum.

The first occurrence of an acetylenic 1-amino-2-alcohol, distaminolyne A (1), isolated from the New Zealand ascidian Pseudodistoma opacum, is reported. The isolation and structure elucidation of 1 and assignment of absolute configuration using the exciton coupled circular dichroism technique are described. In addition, a new N-9 hydroxy analogue (2) of the known P. opacum metabolite 7-bromohomotrypargine is also reported. Antimicrobial screening identified modest activity of 1 toward Escherichia coli, Staphylococcus aureus, and Mycobacterim tuberculosis, while 2 exhibited a moderate antimalarial activity (IC50 3.82 µM) toward a chloroquine-resistant strain (FcB1) of Plasmodium falciparum.

Global patterns in the impact of marine herbivores on benthic primary producers.

Despite the importance of consumers in structuring communities, and the widespread assumption that consumption is strongest at low latitudes, empirical tests for global scale patterns in the magnitude of consumer impacts are limited. In marine systems, the long tradition of experimentally excluding herbivores in their natural environments allows consumer impacts to be quantified on global scales using consistent methodology. We present a quantitative synthesis of 613 marine herbivore exclusion experiments to test the influence of consumer traits, producer traits and the environment on the strength of herbivore impacts on benthic producers. Across the globe, marine herbivores profoundly reduced producer abundance (by 68% on average), with strongest effects in rocky intertidal habitats and the weakest effects on habitats dominated by vascular plants. Unexpectedly, we found little or no influence of latitude or mean annual water temperature. Instead, herbivore impacts differed most consistently among producer taxonomic and morphological groups. Our results show that grazing impacts on plant abundance are better predicted by producer traits than by large-scale variation in habitat or mean temperature, and that there is a previously unrecognised degree of phylogenetic conservatism in producer susceptibility to consumption.

Tissue-specific induction of herbivore resistance: seaweed response to amphipod grazing.

Tissues within individual plants can vary greatly in the strength of their constitutive (i.e., permanent) and induced resistance to herbivores. Optimal defense theory predicts that defenses should be allocated among tissues in proportion to the value of the tissues to the plant and the tissue-specific risk of attack by grazers. We examined the relationship between tissue value and defense in the highly-differentiated brown seaweed Sargassum filipendula. Tissues within S. filipendula varied widely in palatability to the herbivorous amphipod Ampithoe longimana, with younger tissues preferred over older tissues and blades preferred over stipes. Old stipes (at the base of the plant), which linked the other tissues to the seafloor and were thus the most valuable tissue to the plant, were defended constitutively and resisted amphipod grazing by virtue of their toughness rather than via deterrent chemistry. Induction of resistance as a result of amphipod grazing occurred only in the top stipes, which contain the meristematic tissue responsible for future growth. Induction in the top stipes was not due to toughness or other structural properties, as the unpalatability persisted when top stipes were dried, ground to a fine powder, and reconstituted into an agar matrix. This suggests that the induced resistance to grazing resulted from an increase in chemical defenses. The demonstration of constitutive or induced defenses in only the more valuable tissues of the seaweed is consistent with predictions of optimal defense theory. Our finding of induction due to mesograzer (amphipod) feeding is also consistent with the notion that it is these small, more sedentary, herbivores that are most likely to induce defenses in seaweeds.

The first alkene-platinum-silyl complexes: lifting the hydrosilation mechanism shroud with long-lived precatalytic intermediates and true pt catalysts.

The synthesis, characterization, and exploratory chemistry of two classes of alkene-platinum-silyl complexes, which have been postulated as hydrosilation intermediates, are described in this report. The unique dimeric complexes 1, [R(3)Si(mu-Cl)(eta(2)-COD)Pt](2) [R(3)Si = Et(3)Si, MeCl(2)Si, Me(2)ClSi, "(EtO)(3)Si", PhMe(2)Si, and (Me(3)SiO)Me(2)Si; COD = cycloocta-1,5-diene], and the bis-silyl complexes 2, (eta(4)-COD)Pt(SiR(3))(2) (R(3)Si = Cl(3)Si, MeCl(2)Si, Me(2)ClSi, and PhMe(2)Si), are formed from the sequential reaction of 2 and 4 equiv of the corresponding hydrosilanes, respectively, with Pt(COD)Cl(2) in the presence of a small excess of COD. Complexes 1 are stable for many days in solution at room temperature but decompose via slow elimination of chlorosilane. Some of the bis-silyl compounds 2 are stable for extended periods under inert atmosphere and especially below 0 degrees C, either in the solid state or in solution (in the presence of a small excess of free COD). Complexes 2 display catalytic activity as discrete, molecular, and mononuclear species for hydrosilation and isomerization reactions. Compound 2c (R(3)Si = MeCl(2)Si) was fully characterized via multinuclear NMR spectroscopy and X-ray crystal structure analysis. The facile H-transfer rather than Si-transfer to bound COD provides experimental support for the sequence of insertive steps in the Chalk-Harrod catalytic cycle, at least for Pt-catalyzed hydrosilation.

Intraspecific variation in palatability and defensive chemistry of brown seaweeds: effects on herbivore fitness.

When offered a choice between brown seaweeds (Phaeophyta) from shallow inshore populations versus deeper offshore populations along the mid-Atlantic coast of the United States of America, the herbivorous amphipod Ampithoe longimana consistently preferred plants from the inshore populations. This was the case for three species (Dictyota menstrualis, Spatoglossum schroederi, and Sargassum filipendula) collected from each of a single inshore and offshore site, and for one species (D. menstrualis) collected from each of three inshore and three offshore sites. Bioassay-guided fractionation of chemical crude extracts from D. menstrualis suggested that the relative unpalatability of the offshore plants was due to the lipid-soluble secondary metabolites 4beta-hydroxydictyodial A and 18, O-dihydro-4beta-hydroxydictyodial A 18-acetate, along with minor compounds that were not fully identified. The inshore-offshore pattern did not appear to result from induction of defenses due to herbivory by mesograzers, as mesograzer densities were higher on the more palatable inshore plants. Herbivore feeding preferences for inshore versus offshore seaweeds matched the effects of those seaweeds on their fitness. When juvenile amphipods were raised on inshore versus offshore tissues of D. menstrualis, amphipod survivorship, growth, and ovulation were significantly suppressed on the offshore compared to the inshore tissues. Few previous investigations have studied intraspecific variance in seaweed palatability. We extend these by showing that between-population differences in palatability can persist for several years and by demonstrating that this variance is chemically based and has dramatic effects on herbivore fitness.