Capacity for absorption of water-soluble secondary metabolites greater in birds than in rodents

Plant secondary metabolites (SMs) are pervasive in animal foods and potentially influence feeding behavior, interspecies interactions, and the distribution and abundance of animals. Some of the major classes of naturally occurring SMs in plants include many water-soluble compounds in the molecular size range that could cross the intestinal epithelium via the paracellular space by diffusion or solvent drag. There are differences among species in paracellular permeability. Using Middle Eastern rodent and avian consumers of fruits containing SMs, we tested the hypothesis that avian species would have significantly higher paracellular permeability than rodent species. Permeability in intact animals was assessed using standard pharmacological methodology to measure absorption of two radiolabeled, inert, neutral water-soluble probes that do not interact with intestinal nutrient transporters, L-arabinose (M r = 150.1 Da) and lactulose (M r = 342.3 Da). We also measured absorption of labeled 3-O-methyl-D-glucose (3OMD-glucose; M r = 194.2 Da), which is a nonmetabolized analogue of D-glucose that is passively absorbed through the paracellular space but also transported across the enterocyte membranes. Most glucose was absorbed by all species, but arabinose fractional absorption (f) was nearly three times higher in birds (1.03±0.17, n = 15 in two species) compared to rodents (0.37±0.06, n = 10 in two species) (P<0.001). Surprisingly, the apparent rates of absorption in birds of arabinose exceeded those of 3OMD-glucose. Our findings are in agreement with previous work showing that the paracellular pathway is more prominent in birds relative to nonflying mammals, and suggests that birds may be challenged by greater absorption of water-soluble, dietary SMs. The increased expression of the paracellular pathway in birds hints at a tradeoff: the free energy birds gain by absorbing water-soluble nutrients passively may be offset by the metabolic demands placed on them to eliminate concomitantly absorbed SMs.Fil: Karasov, William. University of Wisconsin; Estados UnidosFil: Caviedes Vidal, Enrique Juan Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto Multidisciplinario de Investigaciones Biológicas de San Luis. Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto Multidisciplinario de Investigaciones Biológicas de San Luis; ArgentinaFil: Bakken, Bradley Hartman. University of Wisconsin; Estados UnidosFil: Izhaki, Ido. University Of Haifa; IsraelFil: Samuni Blank, Michal. University Of Haifa; IsraelFil: Arad, Zeev. University Of Haifa; Israe

Study sites along the climatic gradient (white arrow).

<p>1, Goral; 2, Nadiv; 3, Bashan; and 4, Golan. For more details see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099107#pone-0099107-t001" target="_blank">Table 1</a>. The map was modified from: Israel: People and place (2007), with permission from Fein et al. (Fein Z, Segev M, Lavi R 2007, Israel: People and place. Cartography, Soffer R, Center for Educational Technology, Israel).</p

Estimated species richness (calculated as average of Chao2, Jackknife1 and ICE) in floral nectar of <i>Asphodelus aestivus</i> (open and bagged flowers) and in and out the mirid bug <i>Capsodes infuscatus</i>.

<p>The curves of the expected species richness approximately reach an asymptote, demonstrating that only a few more species would have been collected had the sampling effort been further increased.</p

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

The Role of Abiotic Environmental Conditions and Herbivory in Shaping Bacterial Community Composition in Floral Nectar

<div><p>Identifying the processes that drive community assembly has long been a central theme in ecology. For microorganisms, a traditional prevailing hypothesis states that “everything is everywhere, but the environment selects”. Although the bacterial community in floral nectar may be affected by both atmosphere (air-borne bacteria) and animals as dispersal vectors, the environmental and geographic factors that shape microbial communities in floral nectar are unknown. We studied culturable bacterial communities in <i>Asphodelus aestivus</i> floral nectar and in its typical herbivorous bug <i>Capsodes infuscatus</i>, along an aridity gradient. Bacteria were sampled from floral nectar and bugs at four sites, spanning a geographical range of 200 km from Mediterranean to semi-arid conditions, under open and bagged flower treatments. In agreement with the niche assembly hypothesis, the differences in bacterial community compositions were explained by differences in abiotic environmental conditions. These results suggest that microbial model systems are useful for addressing macro-ecological questions. In addition, similar bacterial communities were found in the nectar and on the surface of the bugs that were documented visiting the flowers. These similarities imply that floral nectar bacteria dispersal is shaped not only by air borne bacteria and nectar consumers as previously reported, but also by visiting vectors like the mirid bugs.</p></div

<i>Asphodelus aestivus</i>.

<p>A, Flower and a consumer fly (<i>Eempidoidea</i>); B, Flower collection; C, Nectar collection; D, Bagged inflorescences.</p

Variation of bacterial species isolates among the four different sites (Goral, Nadiv, Bashan and Golan) as shown by the ordination diagram (CCA).

<p>The distribution of bacterial species along the ordinates was not random (Monte Carlo test; <i>F</i> = 1.41, <i>P</i><0.005) and thus can be explained by their different locations along the climatic gradient. The first two ordination axes explained 74.1% of the variance of species-environment relation. Identity of the species related to a single site is as follows: Group 1: <i>Agromyces salentinus</i>, <i>Leuconostoc holzapfelii, Pseudomonas lini, Arthrobacter chlorophenolicus, Lysinibacillus sinduriensis, Pseudomonas syringae, Bacillus endophyticus, Microbacterium foliorum, Staphylococcus cohnii subsp. cohnii, Bacillus flexus, Pseudomonas baetica, Staphylococcus epidermidis, Brevibacterium frigoritolerans, Pseudomonas cedrina subsp. fulgida, Staphylococcus hominis subsp. hominis</i>. Group 2: <i>Lonsdalea quercina, Arthrobacter humicola, Pantoea eucalypti, Brevibacillus agri, Pseudomonas azotoformans, Erwinia persicina, Pseudomonas congelans, Gluconobacter kondonii, Gluconobacter morbifer, Gluconobacter sphaericus</i>. Group 3: <i>Arthrobacter nitroguajacolicus, Bacillus anthracis, Bacillus licheniformis, Bacillus mojavensis, Bacillus niacin, Bacillus sonorensis, Erwinia toletana, Fictibacillus nanhaiensis, Flavimonas oryzihabitans, Pseudomonas graminis, Pseudomonas koreensis, Pseudomonas lutea, Pseudomonas mohnii, Scopulibacillus darangshiensis, Staphylococcus arlettae, Staphylococcus cohnii subsp. urealyticus</i>. Group 4: <i>Acinetobacter boissieri, Acinetobacter nectaris, Neokomagataea tanensis</i>.</p