Intraspecific variation in flight metabolic rate in the bumblebeeBombus impatiens: repeatability and functional determinants in workers and drones

Abstract

The evolution of flight energetics requires that phenotypes be variable, repeatable and heritable. We studied intraspecific variation in flight energetics in order to assess the repeatability of flight metabolic rate and wingbeat frequency, as well as the functional basis of phenotypic variation in workers and drones of the bumblebee species Bombus impatiens. We showed that flight metabolic rate and wingbeat frequency were highly repeatable in workers, even when controlling for body mass variation using residual analysis. We did not detect significant repeatability in drones, but a smaller range of variation might have prevented us from finding significant values in our sample. Based on our results and previous findings, we associated the high repeatability of flight phenotypes in workers to the functional links between body mass, thorax mass, wing size, wingbeat frequency and metabolic rate. Moreover, differences between workers and drones were as predicted from these functional associations, where drones had larger wings for their size, lower wingbeat frequency and lower flight metabolic rate. We also investigated thoracic muscle metabolic phenotypes by measuring the activity of carbohydrate metabolism enzymes, and we found positive correlations between mass-independent metabolic rate and the activity of all enzymes measured, but in workers only. When comparing workers and drones that differ in flight metabolic rate, only the activity of the enzymes hexokinase and trehalase showed the predicted differences. Overall, our study indicates that there should be correlated evolution among physiological phenotypes at multiple levels of organization and morphological traits associated with flight.

Solitary bee larvae prioritize carbohydrate over protein in parentally provided pollen

“…Drosophila flies (de Carvalho and Mirth, 2017) and Helio virescens caterpillars (Telang et al, 2001), (2) protein is important for somatic growth and survival (Lee, 2007; Povey et al, 2009; Roulston and Cane, 2002; Tasei and Aupinel, 2008), (3) bees primarily receive their protein (and lipid) requirements from pollen (Vaudo et al, 2016), and (4) larval bees feed primarily on pollen (Muth et al, 2016). Although adult workers of social bees have also been shown to prioritise carbohydrate over protein, their need for protein is relatively low (Paoli et al, 2014b; Stabler et al, 2015), requiring large amounts of carbohydrate to fuel flight (Darveau et al, 2014) and their high metabolism (Harrison and Roberts, 2000). Considering that growth is concentrated in the larval stage, it would seem reasonable to expect that protein acquisition would drive nutritional decisions in larval bees, even if not adults.…”

Sex differences in pollinator behavior: Patterns across species and consequences for the mutualism

“…This difference in mobility could translate into sex differences in the average distance moved between flowers, the diversity of floral resources encountered, and patch retention times, all of which could influence the quantity and quality of pollen transfer. Indeed, male bumble bees appear to be 'built' for extensive flight, as their relatively larger wings per body size and slower wing-beat frequencies allow them to fly more efficiently than workers (Darveau, Billardon, & Belanger, 2014). (Pascarella, 2010), and Bombus impatiens drones move between flower patches more frequently than females (Ostevik et al, 2010).…”

Demystifying animal ‘personality’ (or not): why individual variation matters to experimental biologists

“…Most recently, several studies in the Journal of Experimental Biology have illustrated how these methods can also be used to estimate the repeatability of physiological and performance-related traits and gain important insight into their ecological and evolutionary implications (e.g. Laming et al, 2013;Darveau et al, 2014;Auer et al, 2016;Conradsen et al, 2016).…”