Behavioural and physiological responses of limpet prey to a seastar predator and their transmission to basal trophic levels.

Besides the well-documented behavioural changes induced by predators on prey, predator-induced stress can also include a suite of biochemical, neurological and metabolic changes that may represent important energetic costs and have long-lasting effects on individuals and on the demography of prey populations. The rapid transmission of prey behavioural changes to lower trophic levels, usually associated with alteration of feeding rates, can substantially change and even reverse direction over the long term as prey cope with the energetic costs associated with predation-induced stress. It is therefore critical to evaluate different aspects and assess the costs of non-consumptive predator effects on prey. We investigated the behavioural and physiological responses of an herbivorous limpet, Fissurella limbata, to the presence of chemical cues and direct non-lethal contact by the common seastar predator, Heliaster helianthus. We also evaluated whether the limpets feeding behaviour was modified by the predator and whether this translated into positive or negative effects on biomass of the green alga, Ulva sp. Our experimental results show the presence of Heliaster led to increased movement activity, increased distances travelled, changes in time budget over different environmental conditions and increased feeding rate in the keyhole limpets. Moreover, additional experiments showed that, beyond the increased metabolic rate associated with limpet increased activity, predator chemical cues heighten metabolic rate as part of the induced stress response. Changes in individual movement and displacement distances observed through the 9-day experiment can be interpreted as part of the escape response exhibited by limpets to reduce the risk of being captured by the predator. Increased limpet feeding rate on algae can be visualized as a way individuals compensate for the elevated energetic costs of movement and heightened metabolic rates produced by the predator-induced stress, which can lead to negative effects on abundance of the lower trophic level. We suggest that in order to understand the total non-consumptive effect of predators in natural communities, it is necessary to evaluate not only short-term behavioural responses, but also the costs associated with the multiple interdependent pathways triggered by predator-induced stress, and determine how individuals cope with these costs in the long term.

Major consequences of minor damage: impacts of small grazers on fast-growing kelps.

Damage by small herbivores can have disproportionately large effects on the fitness of individual plants if damage is concentrated on valuable tissues or on select individuals within a population. In marine systems, the impact of tissue loss on the growth rates of habitat-forming algae is poorly understood. We quantified the grazing damage by an isopod Amphoroidea typa on two species of large kelps, Lessonia spicata and Macrocystis pyrifera, in temperate Chile to test whether non-lethal grazing damage could reduce kelp growth rates and photosynthetic efficiency. For L. spicata, grazing damage was widespread in the field, unevenly distributed on several spatial scales (among individuals and among tissue types) and negatively correlated with blade growth rates. In field experiments, feeding by A. typa reduced the concentration of photosynthetic pigments and led to large reductions (~80%) in blade growth rates despite limited loss of kelp biomass (0.5% per day). For M. pyrifera, rates of damage in the field were lower and high densities of grazers were unable to reduce growth rates in field experiments. These results demonstrate that even low per capita grazing rates can result in large reductions in the growth of a kelp, due the spatial clustering of herbivores in the field and the selective removal of photosynthetically active tissues. The impacts of small herbivores on plant performance are thus not easily predicted from consumption rates or abundance in the field, and vary with plant species due to variation in their ability to compensate for damage.

Titanocene-phosphine derivatives as precursors to cytotoxic heterometallic TiAu2 and TiM (M = Pd, Pt) compounds. Studies of their interactions with DNA.

A series of tri- and bimetallic titanium-gold, titanium-palladium, and titanium-platinum derivatives of the general formulas [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)(AuCl)}(2)]·2THF [n = 0 (1); n = 2 (2); n = 3 (3)] and [TiCl(2){η(5)-C(5)H(4)κ-(CH(2))(n)PPh(2)}(2)(MCl(2))]·2THF [M = Pd, n = 0 (4); n = 2 (5); n = 3 (6) ; M = Pt, n = 0 (7); n = 2 (8); n = 3 (9)] have been synthesized and characterized by different spectroscopic techniques and mass spectrometry. The molecular structures of compounds 1-9 have been investigated by means of density functional theory calculations. The calculated IR spectra of the optimized structures fit well with the experimental IR data obtained for 1-9. The stability of the heterometallic compounds in deuterated solvents [CDCl(3), dimethyl sulfoxide (DMSO)-d(6), and mixtures 50:50 DMSO-d(6)/D(2)O and 1:99 DMSO-d(6)/D(2)O at acidic and neutral pH] has been evaluated by (31)P and (1)H NMR spectroscopy showing a higher stability for these compounds than for Cp(2)TiCl(2) or precursors [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)}(2)]. The new compounds display a lower acidity (1-2 units) than Cp(2)TiCl(2). The decomposition products have been identified over time. Complexes 1-9 have been tested as potential anticancer agents, and their cytotoxicity properties were evaluated in vitro against HeLa human cervical carcinoma and DU-145 human prostate cancer cells. TiAu(2) and TiPd compounds were highly cytotoxic for these two cell lines. The interactions of the compounds with calf thymus DNA have been evaluated by thermal denaturation (1-9) and by circular dichroism (1, 3, 4, and 7) spectroscopic methods. All of these complexes show a stronger interaction with DNA than that displayed by Cp(2)TiCl(2) at neutral pH. The data are consistent with electrostatic interactions with DNA for TiAu(2) compounds and for a covalent binding mode for TiM (M = Pd, Pt) complexes.