Taste and physiological responses to glucosinolates: seed predator versus seed disperser.

In contrast to most other plant tissues, fleshy fruits are meant to be eaten in order to facilitate seed dispersal. Although fleshy fruits attract consumers, they may also contain toxic secondary metabolites. However, studies that link the effect of fruit toxins with seed dispersal and predation are scarce. Glucosinolates (GLSs) are a family of bitter-tasting compounds. The fleshy fruit pulp of Ochradenus baccatus was previously found to harbor high concentrations of GLSs, whereas the myrosinase enzyme, which breaks down GLSs to produce foul tasting chemicals, was found only in the seeds. Here we show the differential behavioral and physiological responses of three rodent species to high dose (80%) Ochradenus' fruits diets. Acomys russatus, a predator of Ochradenus' seeds, was the least sensitive to the taste of the fruit and the only rodent to exhibit taste-related physiological adaptations to deal with the fruits' toxins. In contrast, Acomys cahirinus, an Ochradenus seed disperser, was more sensitive to a diet containing the hydrolyzed products of the GLSs. A third rodent (Mus musculus) was deterred from Ochradenus fruits consumption by the GLSs and their hydrolyzed products. We were able to alter M. musculus avoidance of whole fruit consumption by soaking Ochradenus fruits in a water solution containing 1% adenosine monophosphate, which blocks the bitter taste receptor in mice. The observed differential responses of these three rodent species may be due to evolutionary pressures that have enhanced or reduced their sensitivity to the taste of GLSs

Intraspecific Directed Deterrence by the Mustard Oil Bomb in a Desert Plant

SummaryPlant secondary metabolites (SMs) acting as defensive chemicals in reproductive organs such as fruit tissues play roles in both mutualistic and antagonistic interactions between plants and seed dispersers/predators [1–5]. The directed-deterrence hypothesis states that SMs in ripe fruits deter seed predators but have little or no effect on seed dispersers [6]. Indeed, studies have demonstrated that birds are able to cope with fruit SMs whereas rodents are deterred by them [1, 7]. However, this mechanism was only demonstrated at the class level, i.e., between birds and mammals, based on differences in the vanilloid receptors [7]. Here we present experimental and behavioral data demonstrating the use of the broad-range, class-independent “mustard oil bomb” mechanism in Ochradenus baccatus fruits to force a behavioral change at an ecological timescale, converting rodents from seed predators to seed dispersers. This is achieved by a unique compartmentalization of the mustard oil bomb, causing activation of the system only upon seed and pulp coconsumption, encouraging seed dispersal via seed spitting by rodents. Our findings demonstrate the power of SMs to shift the animal-plant relationship from predation to mutualism and provide support for the directed-deterrence hypothesis at the intraspecific level, in addition to the interspecific level.Video Abstrac

Gut retention time.

<p>Gut retention time in <i>Acomys cahirinus</i> (seed disperser) and <i>A. russatus</i> (seed predator; <i>n</i> = 6–8 for each group within each species) fed with a control diet (white bars), with <i>Ochradenus</i> pulp (light-gray bars), with <i>Ochradenus</i> seeds (dark-gray bars) or with mashed <i>Ochradenus</i> fruits (black bars). Within each species, different letters at the top of the columns indicate significant differences (Bonferroni Multiple Comparison, <i>P</i><0.05). Data are presented as means ± SE.</p

Feeding trials.

<p>Control (white bars), 80% <i>Ochradenus</i> pulp (gray bars) and 80% <i>Ochradenus</i> mash (black bars) diet of <i>A. cahirinus</i> (disperser) and <i>A. russatus</i> (predator) after two days and of <i>M. musculus</i> (mouse) after one day. <i>n</i> = 6–8 for each diet within each species. A. Body mass (% of initial). B. Dry matter intake (% body mass/day). C. Dry matter digestibility (%). Within each species, different letters at the top of the columns indicate significant differences (Bonferroni Multiple Comparison, <i>P</i><0.05). Data are presented as means ± SE.</p

Average number (± S.E.) of intact fruits (Natural) and AMP-treated fruits (AMP) fruits after 24 h by the seed predator, <i>A. russatus,</i> the seed disperser, <i>A. cahirinus</i> and a naïve rodent, <i>M. musculus</i> (<i>n</i> = 8 for each species in each of the treatments).

<p>Different letters adjacent to means indicate significant difference (Wilcoxon Signed Ranks Test, <i>P</i>>0.05) among means. N.S., not significant.</p><p>Average number (± S.E.) of intact fruits (Natural) and AMP-treated fruits (AMP) fruits after 24 h by the seed predator, <i>A. russatus,</i> the seed disperser, <i>A. cahirinus</i> and a naïve rodent, <i>M. musculus</i> (<i>n</i> = 8 for each species in each of the treatments).</p

Pyridine-type alkaloid composition affects bacterial community composition of floral nectar

Pyridine-type alkaloids are most common in Nicotiana species. To study the effect of alkaloid composition on bacterial community composition in floral nectar, we compared the nicotine-rich wild type (WT) N. attenuata, the nicotine biosynthesis-silenced N. attenuata that was rich in anatabine and the anabasine-rich WT N. glauca plants. We found that the composition of these secondary metabolites in the floral nectar drastically affected the bacterial community richness, diversity and composition. Significant differences were found between the bacterial community compositions in the nectar of the three plants with a much greater species richness and diversity in the nectar from the transgenic plant. The highest community composition similarity index was detected between the two wild type plants. The different microbiome composition and diversity, caused by the different pyridine-type alkaloid composition, could modify the nutritional content of the nectar and consequently, may contribute to the change in the nectar consumption and visitation. These may indirectly have an effect on plant fitness