|Figure 3 from the paper. Schematic diagrams
illustrating the known or hypothesized pathways
for glucose and fructose uptake and
oxidation by hummingbird (top) and
nectar bat (bottom) flight muscles.
A review paper by Ken Welch and former MSc student Chris Chen (now studying for his PhD in the Hood Lab at York University) was just published in the Journal of Comparative Physiology B. The paper reviews recent findings regarding the ability of hovering vertebrate nectarivores to fuel energetically expensive flight with newly ingested sugar. The rapid flux of sugar (both glucose AND, surprisingly, fructose) from the digestive tract, through circulation, into the muscle fibers, and finally into the glycolytic pathways, is enabled by upregulation in functional capacity at every step. Comparisons are drawn between the “O2 transport cascade”, as described by Weibel, Taylor et al. in the 1980’s. Many questions about how these animals achieve equally rapid flux of glucose and fructose, and the similarities and differences among birds and mammals in how this flux is regulated, remain. Read the paper here.