Abstract
ABSTRACTEssential macronutrients are critical to the fitness and survival of animals. Many studies have shown that animals regulate the amount of protein and carbohydrate they eat for optimal performance. Regulation of dietary fat is important but less often studied. Honeybees collect and consume floral pollen to obtain protein and fat but how they achieve the optimal balance of these two macronutrients is presently unknown. Here, using chemically defined diets composed of essential amino acids and lipids (lecithin), we show that adult worker honeybees actively regulate their intake of lipids around optimal values relative to the amount of protein in their diet. We found that broodless, nurse-age worker honeybees consume foods to achieve a ratio between 1:2 and 1:3 for essential amino acids to lipid or ∼1.25:1 protein to fat. Bees fed diets relatively high in fat gained abdominal fat and had enlarged hypopharyngeal glands. In most cases, eating diets high in fat did not result in increased mortality. Importantly, we also discovered that the total quantity of food the bees ate increased when they were given a choice of two diets relatively high in fat, implying that dietary fat influences bee nutritional state in a way that, in turn, influences behaviour. We speculate that dietary fat plays a critical role in maintaining workers in the nurse-like behavioural state independently of the influence of queen pheromone.
Highlights
Protein and fat are essential macronutrients required in most animals’ diets
3.1 Adult worker honeybees compromise their intake of essential amino acids relative to lipid (EAA) when diet is too lipid-rich When bees were confined to a diet with a specific ratio of EAA:L, they regulated their intake of macronutrients in a way that suggested a ‘rule of compromise’ (Fig. 1A, Raubenheimer and Simpson, 1997)
The predicted optimal value for EAA:L was ~1:2. Because they were confined to the diets, bees fed with this range of EAA:L actively adjusted their intake of EAAs; these bees consumed ~1.9× less amino acids than the other treatments (Table 1, Fig. 1B, Šidák’s post hoc, P < 0.001) and achieved an EAA:C ratio of 1:378
Summary
Protein provides essential amino acids whereas oils or fats provide the essential fatty acids, linoleic acid and α-linolenic acid. To satisfy their nutritional needs for growth, maintenance, and reproduction, animals have evolved mechanisms for the detection and regulation of the procurement of these nutrients. The GF is designed to measure the strategies animals employ when regulating two types of essential nutrients simultaneously (Simpson and Simpson, 1990; Raubenheimer and Simpson, 1993). It employs the use of diets of specific ratios of macronutrients. If an animal is given a choice of two diets (i.e. a ‘paired diet’ design), it is possible to identify how animals selfselect a presumed optimal quantity of each macronutrient through the measurement of the consumption of both diets
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