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

Are the Low Protein Requirements of Nectarivorous Birds the Consequence of Their Sugary and Watery Diet? A Test with an Omnivore

ABSTRACT Nectar-feeding birds have remarkably low nitrogen requirements. These may be due either to adaptation to a low-protein diet or simply to feeding on a fluid diet that minimizes metabolic fecal nitrogen losses. We measured minimal nitrogen requirements (MNR) and total endogenous nitrogen loss (TENL) in the omnivorous European starling Sturnus vulgaris, fed on an artificial nectar-like fluid diet of varying concentrations of sugar and protein. The MNR and TENL of the birds were similar and even slightly higher than allometrically expected values for birds of the starlings&apos; mass (140% and 103%, respectively). This suggests that the low measured nitrogen requirements of nectar-feeding birds are not simply the result of their sugary and watery diets but a physiological adaptation to the low nitrogen input. We also measured the effect of water and protein intake on the nitrogenous waste form in the excreta and ureteral urine in European starlings. Neither high water intake nor low protein intake increased the fraction of nitrogen excreted as ammonia. Ammonia was excreted at consistently low levels by the starlings, and its concentration was significantly higher in ureteral urine than in excreta. We hypothesize that ureteral ammonia was reabsorbed in the lower intestine, indicating a postrenal modification of the urine

Is the Egyptian fruit-bat Rousettus aegyptiacus a pest in Israel? An analysis of the bat\u27s diet and implications for its conservation

The Egyptian fruit-bat Rousettus aegyptiacus is regarded as a pest for agriculture. However, no quantitative data on its diet have been collected in Israel or in other Mediterranean areas, and control measures in the past reduced populations of insectivorous bats in Israel. We therefore studied the relative importance of native versus commercially cultivated fruit plants by analysis of bat faeces. Droppings were collected during 1993–1995 in two roost-sites in the Carmel National Park. Results show that the bat feeds mainly on fruits but leaves and pollen are also eaten. Leaf eating was observed mainly during winter, when bats may face times of severe decrease in fruit availability and quality. Only four fruit species (15%) of the bat\u27s diet are commercially grown and only two of these in the research area. Therefore the definition of the fruit-bat as a major agricultural pest should be re-examined. Two effective methods for controlling damage caused by bats are discussed

Reproductive Energetics of Captive and Free‐Ranging Egyptian Fruit Bats (Rousettus Aegyptiacus)

This study explored how a flying frugivorous mammal, the Egyptian fruit bat (Rousettus aegyptiacus), meets the increased energy requirements of reproduction. This bat feeds on low‐protein fruit, and females have bimodal polyestrous cycles that are relatively long for a small mammal. We measured the energy and water balance of captive nonreproductive, pregnant, and lactating females, and of free‐ranging lactating females. Our results indicate that females use more than one strategy to cope with the high energy demands of reproduction. These strategies may change according to the availability of food and reproductive status. The primary strategy near the end of pregnancy and at peak lactation was increased food consumption. In the laboratory, mean metabolizable energy intake (MEI) of pregnant and lactating females (271 and 360 kJ/d, respectively) increased by 35% and 80%, respectively, compared to that of nonreproductive females (200 kJ/d). At peak lactation, energy intake measured by doubly labeled water averaged 350 kJ/d. During late pregnancy, water turnover rate (WTO) increased by 15–23% compared to that of nonreproductive females. In the field, WTO at peak lactation was 44% higher than in captive lactating females, and milk production was estimated to be 22 mL/d. Absolute resting metabolic rate (RMR) in late pregnancy was significantly lower than the RMR of nonreproductive females, suggesting that a metabolic depression was used as a compensatory mechanism. Fat deposition was evident during the second pregnancy, when food availability was high, presumably in preparation for a second lactation period. Fetal tissue represented ∼1.3% of the total energy assimilated during pregnancy, and the gross efficiency of lactation averaged 24%. Both values are lower than the values reported for other eutherian mammals, but similar to estimates for other bat species, and probably reflect the high energy costs associated with flight. A long lactation period may be constrained by flight and the low‐protein diet of fruits. We

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

Cumulative absorption versus time since probe ingestion.

<p>Data for 3-O-methyl-D-glucose (3OMD-glucose) are denoted by filled circles and solid lines; L-arabinose data are represented by empty circles and broken lines. Cumulative absorption data for Tristram's grackles and yellow-vented bulbuls are shown in panels A and B, respectively. By an hour or less post-ingestion, the absorption of both compounds was essentially complete, but at early time points the absorption of L-arabinose significantly exceeded that of 3OMD-glucose, as indicated by an asterisk (P<0.05; paired t-test). Values are means (± SEM) calculated from measurements on individual animals.</p