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

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

Energetic costs and implications of the intake of plant secondary metabolites on digestive and renal morphology in two austral passerines

Seed-eating birds have a diet of high nutritional value; however, they must cope with plant secondary metabolites (PSM). We postulated that the detoxification capacity of birds is associated with a metabolic cost, given that the organs responsible for detoxification significantly contribute to energetic metabolism. We used an experimental approach to assess the effects of phenol-enriched diets on two passerines with different feeding habits: the omnivorous rufous-collared sparrow (Zonotrichia capensis) and the granivorous common diuca-finch (Diuca diuca). The birds were fed with one of three diets: control diet, supplemented with tannic acid, or supplemented with Opuntia ficus-indica phenolic extract (a common food of the sparrow but not the finch). After 5 weeks of exposure to the diets, we measured basal metabolic rates (BMR), energy intake, glucuronic acid output and digestive and kidney structure. In both species, detoxification capacity expressed as glucuronic acid output was higher in individuals consuming phenol-enriched diets compared to the control diet. However, whereas sparrows increase energy intake and intestinal mass when feeding on phenol-enriched diets, finches had lower intestinal mass and energy intake remains stable. Furthermore, sparrows had higher BMR on phenol-enriched diets compared to the control group, whereas in the finches BMR remains unchanged. Interspecific differences in response to phenols intake may be determined by the dietary habits of these species. While both species can feed on moderate phenolic diets for 5 weeks, energy costs may differ due to different responses in food intake and organ structure to counteract the effects of PSM intake.Fil: Barceló, Gonzalo. Universidad de Chile; ChileFil: Rios, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Maldonado, Karin. Universidad de Chile; ChileFil: Sabatino, Pablo. Universidad de Chile; Chile. Pontificia Universidad Católica de Chile; Chil