Nutrient balancing of the adult worker bumblebee (Bombus terrestris) depends on the dietary source of essential amino acids.

Daniel Stabler,Geraldine A Wright,Susan W Nicolson,Pier P Paoli

doi:10.1242/jeb.114249

Abstract

ABSTRACTAnimals carefully regulate the amount of protein that they consume. The quantity of individual essential amino acids (EAAs) obtained from dietary protein depends on the protein source, but how the proportion of EAAs in the diet affects nutrient balancing has rarely been studied. Recent research using the Geometric Framework for Nutrition has revealed that forager honeybees who receive much of their dietary EAAs from floral nectar and not from solid protein have relatively low requirements for dietary EAAs. Here, we examined the nutritional requirements for protein and carbohydrates of foragers of the buff-tailed bumblebee Bombus terrestris. By using protein (sodium caseinate) or an equimolar mixture of the 10 EAAs, we found that the intake target (nutritional optimum) of adult workers depended on the source and proportion of dietary EAAs. When bees consumed caseinate-containing diets in a range of ratios between 1:250 and 1:25 (protein to carbohydrate), they achieved an intake target (IT) of 1:149 (w/w). In contrast to those fed protein, bees fed the EAA diets had an IT more biased towards carbohydrates (1:560 w/w) but also had a greater risk of death than those fed caseinate. We also tested how the dietary source of EAAs affected free AAs in bee haemolymph. Bees fed diets near their IT had similar haemolymph AA profiles, whereas bees fed diets high in caseinate had elevated levels of leucine, threonine, valine and alanine in the haemolymph. We found that like honeybees, bumblebee workers prioritize carbohydrate intake and have a relatively low requirement for protein. The dietary source of EAAs influenced both the ratio of protein/EAA to carbohydrate and the overall amount of carbohydrate eaten. Our data support the idea that EAAs and carbohydrates in haemolymph are important determinants of nutritional state in insects.

Highlights

Animals obtain essential amino acids (EAAs) by the consumption of plant or animal proteins
Bees fed with both 0.5 mol l−1 sucrose and sucrose containing free EAA achieved an intake target of ∼1:255 when fed with the 1:90, 1:75 and 1:50 diets (Fig. 1B), which translates into an intake target of 1:560 w/w
Bees fed with the caseinate diets consumed approximately twice as much carbohydrate as those fed with the free EAA solutions when they were feeding on diets within the range over which they could achieve their intake target (1:50, 1:75, 1:100 w/w)

Summary

Introduction

Animals obtain essential amino acids (EAAs) by the consumption of plant or animal proteins. Because the need for AAs continues throughout an animal’s lifespan, protein intake is actively regulated around a. Received 18 September 2014; Accepted 28 December 2014 nutritional optimum that is determined by age, physiological state and reproductive capacity (Simpson and Raubenheimer, 2012). Animals regulate their protein intake by altering quantities of food eaten (Simpson et al, 2004) or by consuming a mixture of foods with the correct balance of protein and other macronutrients (Raubenheimer and Simpson, 1993; Simpson and Raubenheimer, 1993, 2012; Simpson et al, 2004). How the regulation of protein intake is accomplished by the body’s ability to detect the need for essential amino acids (EAAs) is largely unknown (Morrison et al, 2012)

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Conclusion