Apparent Absorption Efficiencies of Nectar Sugars in the Cape Sugarbird, with a Comparison of Methods

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dc.contributor.authorJackson, Susan
dc.contributor.authorNicolson, Susan W
dc.contributor.authorvan Wyk, Ben‐Erik
dc.date.accessioned2021-10-08T07:11:53Z
dc.date.available2021-10-08T07:11:53Z
dc.date.issued1998
dc.description.abstractNectarivore sugar preferences and nectar composition in the Cape Floristic Kingdom (southern Africa) differ from trends reported for analogous systems in America and Europe in that sugarbirds and sunbirds show no aversion to sucrose, which is the dominant nectar sugar in many of their food plants. To elucidate the physiological bases (if any) of nectarivore sugar preferences, we determined apparent sugar absorption efficiencies in a passerine endemic to this region, the Cape sugarbird Promerops cafer. Apparent absorption efficiencies for the three major nectar sugars, sucrose, glucose, and fructose, were extremely high (> 99%), as in other specialized avian nectarivores. Xylose, a pentose sugar recently reported in the nectar of some Proteaceae, was absorbed and/or metabolized inefficiently, with a mean of 47.1% of ingested sugar recovered in cloacal fluid. We did not measure the proportions of xylose that were absorbed and/or metabolized. We also compared three methods of estimating absorption efficiency: (1) measurements of total sugar in cloacal fluid with refractometry, without correction for differences between volumes of ingesta and excreta; (2) the same measurements combined with correction for volume differences; and (3) HPLC analyses quantifying individual sugars in cloacal fluid, with correction for volume differences. Refractometry has been frequently used in previous studies. For all sugars except xylose, method 1 yielded results similar to those obtained with method 2, but the convergence was artifactual, and we do not recommend use of this method. Apparent absorption efficiencies calculated with method 2 underestimated true absorption efficiency, because refractometry measures nonsugar solutes, but this error is biologically significant only when efficiencies are low.
dc.identifier.apacitationJackson, S., Nicolson, S. W., & (1998). Apparent Absorption Efficiencies of Nectar Sugars in the Cape Sugarbird, with a Comparison of Methods. <i>Physiological Zoology</i>, 71(1), 106 - 115. http://hdl.handle.net/11427/34704en_ZA
dc.identifier.chicagocitationJackson, Susan, Susan W Nicolson, and "Apparent Absorption Efficiencies of Nectar Sugars in the Cape Sugarbird, with a Comparison of Methods." <i>Physiological Zoology</i> 71, 1. (1998): 106 - 115. http://hdl.handle.net/11427/34704en_ZA
dc.identifier.citationJackson, S., Nicolson, S.W. & 1998. Apparent Absorption Efficiencies of Nectar Sugars in the Cape Sugarbird, with a Comparison of Methods. <i>Physiological Zoology.</i> 71(1):106 - 115. http://hdl.handle.net/11427/34704en_ZA
dc.identifier.issn0031-935X
dc.identifier.issn1937-4267
dc.identifier.ris TY - Journal Article AU - Jackson, Susan AU - Nicolson, Susan W AU - van Wyk, Ben‐Erik AB - Nectarivore sugar preferences and nectar composition in the Cape Floristic Kingdom (southern Africa) differ from trends reported for analogous systems in America and Europe in that sugarbirds and sunbirds show no aversion to sucrose, which is the dominant nectar sugar in many of their food plants. To elucidate the physiological bases (if any) of nectarivore sugar preferences, we determined apparent sugar absorption efficiencies in a passerine endemic to this region, the Cape sugarbird Promerops cafer. Apparent absorption efficiencies for the three major nectar sugars, sucrose, glucose, and fructose, were extremely high (> 99%), as in other specialized avian nectarivores. Xylose, a pentose sugar recently reported in the nectar of some Proteaceae, was absorbed and/or metabolized inefficiently, with a mean of 47.1% of ingested sugar recovered in cloacal fluid. We did not measure the proportions of xylose that were absorbed and/or metabolized. We also compared three methods of estimating absorption efficiency: (1) measurements of total sugar in cloacal fluid with refractometry, without correction for differences between volumes of ingesta and excreta; (2) the same measurements combined with correction for volume differences; and (3) HPLC analyses quantifying individual sugars in cloacal fluid, with correction for volume differences. Refractometry has been frequently used in previous studies. For all sugars except xylose, method 1 yielded results similar to those obtained with method 2, but the convergence was artifactual, and we do not recommend use of this method. Apparent absorption efficiencies calculated with method 2 underestimated true absorption efficiency, because refractometry measures nonsugar solutes, but this error is biologically significant only when efficiencies are low. DA - 1998 DB - OpenUCT DP - University of Cape Town IS - 1 J1 - Physiological Zoology LK - https://open.uct.ac.za PY - 1998 SM - 0031-935X SM - 1937-4267 T1 - Apparent Absorption Efficiencies of Nectar Sugars in the Cape Sugarbird, with a Comparison of Methods TI - Apparent Absorption Efficiencies of Nectar Sugars in the Cape Sugarbird, with a Comparison of Methods UR - http://hdl.handle.net/11427/34704 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/34704
dc.identifier.vancouvercitationJackson S, Nicolson SW, . Apparent Absorption Efficiencies of Nectar Sugars in the Cape Sugarbird, with a Comparison of Methods. Physiological Zoology. 1998;71(1):106 - 115. http://hdl.handle.net/11427/34704.en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Biological Sciences
dc.publisher.facultyFaculty of Science
dc.sourcePhysiological Zoology
dc.source.journalissue1
dc.source.journalvolume71
dc.source.pagination106 - 115
dc.source.urihttps://dx.doi.org/10.1086/515889
dc.subject.otherAbsorption
dc.subject.otherAnalysis of Variance
dc.subject.otherAnimals
dc.subject.otherBirds
dc.subject.otherCarbohydrates
dc.subject.otherChromatography, High Pressure Liquid
dc.subject.otherDietary Carbohydrates
dc.subject.otherFemale
dc.subject.otherFructose
dc.subject.otherGlucose
dc.subject.otherOsmolar Concentration
dc.subject.otherRefractometry
dc.subject.otherSouth Africa
dc.titleApparent Absorption Efficiencies of Nectar Sugars in the Cape Sugarbird, with a Comparison of Methods
dc.typeJournal Article
uct.type.publicationResearch
uct.type.resourceJournal Article
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