Meeting Abstract

98.1  Sunday, Jan. 6  Convergence in digestive capacity in nectar-feeding birds MCWHORTER, TJ*; SCHONDUBE, JE; NICOLSON, SW; PINSHOW, B; FLEMING, PA; MARTíNEZ DEL RIO, C; University of Adelaide; Universidad Nacional Autónoma de México; University of Pretoria; Ben-Gurion University of the Negev; Murdoch University; University of Wyoming todd.mcwhorter@adelaide.edu.au

Across five continents, nectarivorous birds show striking similarities in their physiological and morphological attributes and foraging strategies. We tested whether different nectar-specialist avian taxa are convergent in characteristics of their digestive physiology and gastrointestinal morphology. Specifically, we compared the digestive traits of eight nectarivorous passerine species from the families Meliphagidae (Australasian honeyeaters) and Nectariniidae (Old World sunbirds) with published data for hummingbirds (Trochilidae) and other passerine species that are considered diet-generalists. We examined the capacity to digest three food substrates: sucrose (via the activity of the enzyme sucrase-isomaltase), maltose (via maltase-glucoamylase activity; an indirect measure of capacity to digest starch) and protein (via aminopeptidase-N activity), and also compared intestinal nominal surface area. Intestinal surface area and maltase activity were similar across species. Aminopeptidase activity was lower in hummingbirds than in passerines. Nectar-specialist passerines had lower capacity to digest sucrose (a common nectar sugar) than hummingbirds, but higher sucrase activity than diet-generalist passerines. Using a chemical reactor model of digestive function we found that the ability of nectar-specialist passerines to assimilate energy from sucrose solutions falls between that of hummingbirds and diet-generalist passerines. The ability of passerines that specialize in feeding on nectar to hydrolyse sucrose therefore appears to be convergent with that of hummingbirds.