Complex relationship between amino acids, fitness and food intake in Bombus terrestris

Abstract

The ratio of amino acids to carbohydrates (AA:C) that bumble bees consume has been reported to affect their survival. However, it is unknown how dietary AA:C ratio affects other bumble bee fitness traits (e.g., fecundity, condition) and possible trade-offs between them. Moreover, while individual AAs affect phenotype in many species, the effects of AA blend on bumble bee fitness and food intake are unclear. We test how the AA:C ratio that bumble bees (Bombus terrestris) consume affects their condition (abdomen lipid and dry mass), survival following food removal, and ovarian activation. We then compare ovarian activation and food intake in bees fed identical AA:C ratios, but where the blend of AAs in diets differ, i.e., diets contained the same 10 AAs in an equimolar ratio or in the same ratio as in bee collected pollen. We found that AA:C ratio did not significantly affect survival following food removal or ovarian activation; however, high AA intake increased body mass, which is positively correlated with multiple fitness traits in bumble bees. AA blend (i.e., equimolar versus pollen) did not significantly affect overall ovarian activation or consumption of each experimental diet. However, there was an interaction between AA mix and dietary AA:C ratio affecting survival during the feeding experiment, and signs that there may have been weak, interactive effects of AA mix and AA:C ratio on food consumption. These results suggest that the effect of total AA intake on bumble bee phenotype may depend on the blend of individual AAs in experimental diets. We suggest that research exploring how AA blend affects bumble bee performance and dietary intake is warranted, and highlight that comparing research on bee nutrition is complicated by even subtle variation in experimental diet composition.

Keywords: Bombus; Geometric framework of nutrition; Intake array; Trade-off.

Fig. 1

Rules of compromise. a Grey lines—each nutrient rail represents a single diet varying in its ratio of nutrient A to nutrient B. Aligned along the red arrow are three possible solutions to the challenge of being unable to consume the intake target (T). b If individuals are fed different diets and consistently chose strategy 1 in (a), the intake array will be as shown in the orange line. If all individuals choose strategy 2, then the intake array will be as in the green line. Both of these strategies represent the no-interaction rule of compromise. C If all individuals in an experiment choose option 3 in (a), then the intake array may take this form—the equal distance rule. d Alternatively, individuals that adopt strategy 3 in panel A, may be adopting the closest distance rule. This schematic is based on figures from Raubenheimer and Simpson

Fig. 2

Abdomen composition. Mean abdomen dry mass (± SE) excluding lipids (turquoise circles) and lipid mass (yellow triangles) in bees fed each of the AA:C ratios

Fig. 3

Survival during the 7-day experiment. Percentage of animals surviving over the 7-day feeding experiment fed the pollen AA mix (a) or the equimolar AA mix (b). Filled square—0:1 AA:C, filled circle—1:250 AA:C, filled triangle—1:100 AA:C, filled diamond—1:75 AA:C, open circle—1:50 AA:C, open square—1:25 AA:C; open diamond—1:10 AA:C

Fig. 4

Percentage of bees fed each experimental diet surviving in minutes after their food was removed. Filled square—0:1 AA:C, filled circle—1:250 AA:C, filled triangle—1:100 AA:C, filled diamond—1:75 AA:C, open circle—1:50 AA:C, open square—1:25 AA:C; open diamond1:10 AA:C. Median lifespan for each diet is shown by colour-coded arrows aligned along the x-axis

Fig. 5

Ovarian activation. Ovarian activation in bees fed pollen AA mixture (turquoise) and equimolar AA mixture (orange) and each AA:C ratio. Lines show smoothed curves for the two AA mixes individually (turquoise and orange), and for the pooled data (grey line with shaded area representing the standard error). Figure created using ggplot (Wickham 2016)

Fig. 6

Volume of each experimental diet consumed. Total volume of each experimental diet consumed on average per bee across the entire experiment in individuals fed the pollen AA mixture (turquoise circles) and an equimolar AA mixture (purple triangles) (mean ± SE)

Fig. 7

Intake arrays. Mean cumulative intake of AAs and carbohydrate (± SE) consumed per bee by individuals fed pollen AA mixture (a) and an equimolar AA mixture (b). Each of the 7-day intake values is shown