On the relationship between sugar digestion and diet preference in two Chilean avian species belonging to the Muscicapoidea superfamily

Abstract

It has been hypothesized that species belonging to the Sturnidae-Muscicapidae lineage, despite having generalist diets comprising fruits with sugars of diverse kinds, do not express intestinal sucrase. In order to increase the taxonomical range of species for which sucrase intestinal activity has been investigated, we analyzed the relationship between enzymatic activity (sugar digestion) and feeding preference for native fruits containing sucrose, in two South American members of the superfamily Muscicapoidea, the Austral thrush (Turdus falcklandii) and the Chilean mockingbird (Mimus thenca). We hypothesized that these birds would lack intestinal sucrase activity and that in preference tests they would reject sucrose solutions. Both thrushes and mockingbirds lacked significant intestinal sucrase activity. Considering the phylogenetic constraint hypothesis for sucrose digestion in the Muscicapoidea superfamily, our results support the notion that lack of sucrase activity is a shared derived-character only for the Cinclidae-Sturnidae-Turdinae lineage, and suggests that the selective pressure that these birds can exert on the plants whose seeds they disperse and whose flowers they visit are consistent across world hemispheres. Food preference by thrushes was significantly biased toward glucose and fructose, showing scant to nil consumption of sucrose, thus corroborating a positive relationship between digestion capabilities and food preference for different sugar types.