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

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

Nectar bacterial community composition clustered by site (Goral, Nadiv, Bashan and Golan) and treatments (open and bagged).

<p>Sites varied significantly in OTUs composition (Adonis test; <i>F</i>₃ = 1.36, R² = 0.5, <i>P</i><0.05; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099107#pone-0099107-t001" target="_blank">Table 1</a>).</p

List of bacterial isolates from <i>Capsodes infuscatus</i> at the four sites (Goral, Nadiv, Bashan and Golan) and within each treatment (in or out).

<p>The numbers indicated in the table are the number of isolates and the numbers in parentheses are the percentage of 16S rRNA gene similarities to the closest known species. The sequences coverage of most isolates was 700–850 bp. For more details see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099107#pone.0099107.s002" target="_blank">Table S2</a>.</p

<i>Asphodelus aestivus</i>.

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

Adult mirid bugs (<i>Capsodes infuscatus</i>) on bagged flowers inserting their piercing-sucking mouthparts through the bag and into the flower.

<p>The orange marks on the covering bags are the bugs' waste.</p

Environmental factors at each of the four sites (Goral, Nadiv, Bashan and Golan).

<p>For temperature we used average data of the month sampled.</p

Comparison of fractional absorption of three probe molecules among four species.

<p>Means and SEM are shown, and sample sizes are the numbers within each of the bars. For each probe type, where bars are accompanied by common letters, the means did not differ significantly based on statistical analyses described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032417#s3" target="_blank">Results</a>. Thus, all species absorbed 3OMD-glucose to the same high extent, arabinose absorption was significantly higher in the bird species than in the rodent species, and lactulose absorption was low in all the species but, among them, slightly higher in yellow-vented bulbuls.</p