Diel variations in plasma glucose concentrations of Malachite Sunbirds Nectarinia famosa

Abstract

Plasma glucose concentrations in birds are much higher than those in mammals of similar body mass, and they are thought to be kept more or less constant. We investigated plasma glucose concentrations of Malachite Sunbirds (Nectarinia famosa) to determine whether there was a circadian rhythm in plasma glucose and whether plasma glucose concentrations rose at lower temperatures. We explored the possibility that glycogenolysis and gluconeogenesis might be used by birds before daylight to generate body heat during arousal from torpor or from overnight adaptive heterothermy. Plasma glucose concentration of Malachite Sunbirds were relatively high, between 13.6 and 21.4 mmol/L. Plasma glucose concentrations were higher at 5°C than at 25°C, and generally lower during the scotophase, particularly in the early hours of the morning. Therefore, it appears that Malachite Sunbirds are not increasing plasma glucose concentrations during arousal from torpor or to increase scotophase body temperature levels to photophase levels. It is apparent that these nectarivorous birds have a circadian variation in plasma glucose concentrations that is affected by ambient temperature and feeding patterns.

Fuel for the pace of life: Baseline blood glucose concentration co‐evolves with life‐history traits in songbirds

“…Despite this, we found no association between diet and G 0 . Our dataset did not contain nectar and pollen eating species, however, some of which are known to have extremely high blood glucose concentrations (Downs et al, ). Nevertheless, our results do suggest that G 0 does not differ between herbivorous, omnivorous and insectivorous songbirds.…”

“…These studies were mostly based on values from captive individuals, however, and their glucose levels often differ from their free-living counterparts (Casado, Balbontin, & Ferrer, 2002;Ferrer & Dobado-Berrios, 1998). A further limitation of these studies is that season, time of day and stress level (i.e., handling time) were not controlled for, despite substantial evidence for their effects (Downs et al, 2010;Frelin, 1974;Remage-Healey & Romero, 2000). All these factors could contribute to the contrasting results of these studies and hamper their interpretation regarding POLS evolution.…”

“…Moreover, migratory species have been reported to have lower BMR than sedentary species (Wiersma et al, 2007; but see Jetz, Freckleton, & McKechnie, 2008;McNab, 2009). Data were analysed using a Bayesian statistical comparative approach based on individual measurements in the models, allowing the inclusion of potentially confounding individual-specific variables such as sex (Fairbrother, Craig, Walker, & O'Loughlin, 1990), individual differences in body mass (Kaliński et al, 2015), time of day (Downs, Wellmann, & Brown, 2010;Remage-Healey & Romero, 2000) and capture stress (Remage-Healey & Romero, 2000), while controlling for shared phylogeny.…”

Sources of Variation in Blood Glucose Concentrations of Free-Living Birds

“…Circadiel rhythms in P Glu have been documented in several diurnal birds, including another white-eye species (Garcia-Rodriguez et al, 1987;Lobban et al, 2010;Downs et al, 2010). Commonly P Glu is maximal at mid-photophase and minimal at midscotophase in such species, but in some it peaks at the end of overnight fasting and then declines slowly throughout the photophase (Lobban et al, 2010).…”

“…More values are required for wild adults of a variety of species in order to better gauge the representativeness of the data from captive birds. A further limitation of many published P Glu values is that the season and diurnal time of sampling are not reported or considered, despite the existence of substantial evidence of such temporal variation (Frelin, 1974;Ferrer, 1990;Remage-Healey and Romero, 2000;Downs et al, 2010;Lobban et al, 2010). Another knowledge deficiency concerns the extent to which blood glucose concentration is influenced by developmental age.…”