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

Tsahar, Ella; Rio, Carlos Martı́nez del; Arad, Zeev; Joy, Jeannine P.; Izhaki, Ido

doi:10.1086/427056

Cited by 20 publications

(8 citation statements)

References 37 publications

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“…However, in other experiments in which birds have been fed nectar-like diets, we have found only traces of other nitrogen-containing compounds such as creatine, creatinine, free amino acids and bile salts in excreta (McWhorter et al, 2003). We can conclude that our method underestimates nitrogen requirements only slightly (Tsahar et al, 2005).…”

Section: Low Nitrogen Requirements In Yellow-vented Bulbuls Andmentioning

confidence: 51%

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Can birds be ammonotelic? Nitrogen balance and excretion in two frugivores

Tsahar

Rio

Izhaki

et al. 2005

Journal of Experimental Biology

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We measured minimal nitrogen requirements (MNR), total endogenous nitrogen loss (TENL) and the effect of protein and water intake on the nitrogenous waste composition in two frugivorous bird species: yellowvented bulbuls Pycnonotus xanthopygos and Tristram's grackles Onychognathus tristrami. The nitrogen requirements of both species were much lower than expected for their body mass. The two species differed in the composition of the nitrogenous waste that they produced. The grackles were uricotelic, and the chemical composition of their nitrogenous waste products was relatively independent of water and protein intake. In contrast, the bulbuls were 'apparently ammonotelic'.Their ammonotely was related to low protein intake and high water flux, and was the result of post-renal urine modification. We suggest two non-exclusive mechanisms for the post-renal modification of urine in these birds: bacterial catabolism of uric acid and reabsorption of uric acid in the hindgut. As uric acid functions both as a nitrogenous waste product and as an antioxidant, birds might benefit from its reabsorption.

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Section: Low Nitrogen Requirements In Yellow-vented Bulbuls Andmentioning

confidence: 51%

“…MNR and TENL were calculated based on the nitrogen recovered from chemical assays. In a previous study (Tsahar et al, 2005), we recovered over 80% of the elemental nitrogen in chemical assays. Thus, we assumed that using the assayed nitrogen underestimates nitrogen requirements only slightly.…”

Section: Intake Responsementioning

confidence: 96%

Can birds be ammonotelic? Nitrogen balance and excretion in two frugivores

Tsahar

Rio

Izhaki

et al. 2005

Journal of Experimental Biology

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“…sugars, are an important source of nutritional energy, but animal species display marked differences in the degree of sugar utilization and tolerance. While the diet of carnivores is typically low in sugars, nectarivores, like hummingbirds, feed primarily on sugar-rich nectar [1], [2]. Sugars from fruits and honey have been part of the ancestral human diet.…”

Section: Introductionmentioning

confidence: 99%

Mondo/ChREBP-Mlx-Regulated Transcriptional Network Is Essential for Dietary Sugar Tolerance in Drosophila

et al. 2013

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Sugars are important nutrients for many animals, but are also proposed to contribute to overnutrition-derived metabolic diseases in humans. Understanding the genetic factors governing dietary sugar tolerance therefore has profound biological and medical significance. Paralogous Mondo transcription factors ChREBP and MondoA, with their common binding partner Mlx, are key sensors of intracellular glucose flux in mammals. Here we report analysis of the in vivo function of Drosophila melanogaster Mlx and its binding partner Mondo (ChREBP) in respect to tolerance to dietary sugars. Larvae lacking mlx or having reduced mondo expression show strikingly reduced survival on a diet with moderate or high levels of sucrose, glucose, and fructose. mlx null mutants display widespread changes in lipid and phospholipid profiles, signs of amino acid catabolism, as well as strongly elevated circulating glucose levels. Systematic loss-of-function analysis of Mlx target genes reveals that circulating glucose levels and dietary sugar tolerance can be genetically uncoupled: Krüppel-like transcription factor Cabut and carbonyl detoxifying enzyme Aldehyde dehydrogenase type III are essential for dietary sugar tolerance, but display no influence on circulating glucose levels. On the other hand, Phosphofructokinase 2, a regulator of the glycolysis pathway, is needed for both dietary sugar tolerance and maintenance of circulating glucose homeostasis. Furthermore, we show evidence that fatty acid synthesis, which is a highly conserved Mondo-Mlx-regulated process, does not promote dietary sugar tolerance. In contrast, survival of larvae with reduced fatty acid synthase expression is sugar-dependent. Our data demonstrate that the transcriptional network regulated by Mondo-Mlx is a critical determinant of the healthful dietary spectrum allowing Drosophila to exploit sugar-rich nutrient sources.

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“…Because it has been shown that frugivorous birds have lower nitrogen requirements than insectivorous birds (Tsahar et al 2005a(Tsahar et al , b, 2006, we assume that the contribution of nondietary sources of protein when birds feed on low-protein diets such as fruits is not as significant as it is for insectivorous birds. We recognize that this assumption needs to be experimentally tested.…”

Section: Methodsmentioning

confidence: 99%

“…The apparent constraint on insect feeding imposed by their digestive system also needs to be examined. It has been demonstrated that nitrogen requirements are lower in frugivorous than in insectivorous birds (Tsahar et al 2005a(Tsahar et al , b, 2006, but there are no data on nitrogen requirements in Euphonia, in spite of its importance for understanding the physiology of highly frugivorous vertebrates. Low nitrogen requirements may not be sufficient if fruits do not provide an adequate source of amino acids (Izhaki 1998).…”

Section: Speciesmentioning

confidence: 99%

Sources of Assimilated Protein in a Specialized Tropical Frugivorous Bird, the Yellow-throated Euphonia (Euphonia hirundinacea)

Rodrı́guez

PatriciaHernández

2009

The Auk

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Most frugivorous birds must complement their diet with insects to fulfill their protein requirements; species that rely almost exclusively on fruits are rare. We used nitrogen ( 15 N: 14 N) stable-isotope analysis of whole blood to quantify and compare the use of insects and fruits as sources of assimilated nitrogen in a specialized frugivorous bird, the Yellow-throated Euphonia (Euphonia hirundinacea). Nitrogen stable-isotope analysis is particularly useful for examining the relative contribution of animal and plant products as sources of assimilated nitrogen, because there is trophic enrichment of the heavier isotope in higher trophic levels of food webs. We found that most assimilated nitrogen was derived from fruits (76-100%), with a slight increase in the contribution of fruits as their abundance increased. In comparisons of bird species, δ 15 N values of Yellow-throated Euphonia were lower than those of insectivorous and piscivorous species but similar to the values found in seed-fruit eaters. Our results suggest that the dependence on fruits as a source of assimilated nitrogen in Yellow-throated Euphonia ranged from predominant to almost exclusive during the period of our study (February-August). Total dependence on fruits as a source of assimilated nitrogen is not a common phenomenon among birds, but it may be favored in the tropics, where fruits are more abundant and diverse. Fuentes de Proteína Asimilada en Euphonia hirundinacea, un Frugívoro EspecialistaResumen.-La mayoría de las aves frugívoras deben complementar su dieta con insectos para satisfacer sus requerimientos de proteína, por lo que son pocas las especies que se alimentan solamente de frutos. En este estudio, se realizó un análisis de isótopos de nitrógeno ( 15 N: 14 N) de la sangre de Euphonia hirundinacea para cuantificar el uso de insectos y frutos como fuentes de nitrógeno asimilado. Esta especie de ave es especialista en el consumo de frutos del muérdago. El análisis de isótopos de nitrógeno es empleado para examinar la contribución de fuentes animales y vegetales de nitrógeno asimilado, gracias a que existe un enriquecimiento trófico del isótopo más pesado en niveles más altos de la red trófica. Se encontró que la mayor parte del nitrógeno asimilado provenía de los frutos (76-100%), con un pequeño incremento en la contribución de los frutos a medida que su abundancia aumentó. Cuando se comparó con otras especies de aves, los valores de δ 15 N de E. hirundinacea fueron similares a los de las especies granívoras o frugívoras, pero menores que los de las especies insectívoras y piscívoras. Nuestros resultados sugieren que los frutos fueron la fuente primordial de nitrógeno asimilado para E. hirundinacea durante el tiempo del estudio (febrero-agosto). Este fenómeno no es común en la mayoría de las aves, pero podría verse favorecido en el trópico húmedo donde las plantas con frutos son más diversas y abundantes.

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

Cited by 20 publications

References 37 publications

Can birds be ammonotelic? Nitrogen balance and excretion in two frugivores

Can birds be ammonotelic? Nitrogen balance and excretion in two frugivores

Mondo/ChREBP-Mlx-Regulated Transcriptional Network Is Essential for Dietary Sugar Tolerance in Drosophila

Sources of Assimilated Protein in a Specialized Tropical Frugivorous Bird, the Yellow-throated Euphonia (Euphonia hirundinacea)

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