Sugar assimilation underlying dietary evolution of Neotropical bats

Abstract

Specializations in animal diets drive selective demands on morphology, anatomy, and physiology. Studying adaptations linked to diet evolution benefits from examining Neotropical bats, a remarkable group with high taxonomic and trophic diversity. In this study, we performed glucose tolerance tests on wild-caught bats, which revealed distinct responses to three sugars present in different foods: trehalose (insects), sucrose, and glucose (fruits and nectar). Insect-eating bats metabolism responded most strongly to trehalose, while bats with nectar and fruit-based diets exhibited a heightened response to glucose and sucrose, reaching blood glucose levels over 600 and 750 mg/dL. To search for signatures of positive selection in sugar assimilation genes we performed genome analysis of 22 focal bat species and 2 outgroup species. We identified selection in the ancestral vespertilionid branch (insect-eaters) for the digestive enzyme trehalase, while sucrase-isomaltase exhibited selection in branches leading to omnivorous and nectar diets. Unexpectedly, the insect-eating lineage Myotis exhibited sucrase-isomaltase selection, potentially explaining their heightened sucrose assimilation. Furthermore, the genes encoding for glucose transporters, Slc2a3 and Slc2a2, showed selection in nectar and blood feeding bats, with analyses of predicted protein structures supporting modified activity. By examining cellular features of the small intestine, we discovered that dietary sugar proportion strongly impacted numerous digestive traits, providing valuable insight into the physiological implications of the identified molecular adaptations. To elucidate this further, we used HCR RNA-FISH to perform single molecule ex vivo gene expression analysis of enterocyte response to a glucose meal in three focal species. We observed unusually high activity in the glucose transporter Slc2a2 during the fasted state of nectar bats that did not change upon feeding. Comparatively, nectar bats exhibited an enhanced capacity for intestinal absorption of dietary sugar primarily through Slc2a2, while fruit bats relied on increasing levels of Slc5a1. Overall, this study highlights the intricate interplay between molecular, morphological, and physiological aspects of diet evolution and provides new insights into our understanding of dietary diversification and sugar assimilation mechanisms in mammals. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=112 SRC="FIGDIR/small/547432v2_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@744e5dorg.highwire.dtl.DTLVardef@1c4e6fcorg.highwire.dtl.DTLVardef@18baaforg.highwire.dtl.DTLVardef@18853ee_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LISugar assimilation differences emphasize metabolic adaptations to diet C_LIO_LIGlucose tolerance tests provide a quick and practical assessment of dietary ecology C_LIO_LIBat genomes exhibit positive selection on digestive enzymes and glucose transporters C_LIO_LIStructural comparisons of proteins suggest altered activity of glucose transporters C_LIO_LIGlucose absorption differences can be explained by gut anatomy C_LIO_LIIntestinal villus diversity and novel microanatomy in bats C_LIO_LIExtreme blood glucose (above 600 and 750 mg/dL) coincides with constitutive expression of apical Slc2a2 C_LIO_LIThe regulation of apical Slc2a2 highlights differences in blood glucose levels C_LI