Abstract
Foraging animals regulate their intake of macronutrients such as carbohydrates and proteins. However, regulating the intake of these two macronutrients can be constrained by the nutrient content of available food sources. Compensatory foraging is a method to adjust nutrient intake under restricted nutrient availability by preferentially exploiting food sources that contain limiting nutrients. Here we studied the potential for compensatory foraging in the dolichoderine ant Iridomyrmex mayri, which is commonly found in associations with caterpillars of the obligatorily ant-associated lycaenid butterfly Jalmenus evagoras. The caterpillars receive protection against predators and parasites, and reward the ants with nutritional secretions from specialized exocrine glands. These secretions contain a mixture of sugars and free amino acids, particularly serine. We tested the influence of nutrient-deficient diets on foraging patterns in I. mayri by recording the intake of test solutions containing single types of macronutrients during food preference tests. We also investigated the level of ant attendance on fifth instar J. evagoras caterpillars to evaluate how changes in diet influenced ant tending of caterpillars and foraging on their secretions. Foragers on a protein diet compensated for the nutritional deficit by increasing the intake of test solutions that contained sucrose, compared to their counterparts on a non-restricted diet. Ants on a sugar diet, however, did not show a corresponding increased consumption of test solutions containing the amino acid serine. Additionally, compared with their counterparts on a mixed diet, ants on limited nutrient diets showed an increase in the number of caterpillar-tending workers, suggesting that the caterpillars’ secretions are suitable to compensate for the ants’ nutritional deficit.
Highlights
The “Geometric Framework” (Simpson and Raubenheimer, 2012) provides a compelling theoretical approach to understanding foraging strategies, by assuming that animals have intake targets for all relevant nutrients, and predicting the simultaneous regulation of nutrient intake to meet particular target ratiosAnt Foraging and Caterpillar Attendance for individual organisms (Simpson and Raubenheimer, 1993; Raubenheimer and Simpson, 1999; Simpson et al, 2004; Raubenheimer et al, 2009)
One way to compensate for nutritional deficits is compensatory foraging, in which workers adjust their preferences in favor of food sources containing limiting nutrients
Pairwise contrasts showed that for colony fragments on a protein diet, consumption of sucrose and sucrose + serine solutions was higher than consumption of serine solution and water, but there was no difference in consumption between sucrose and sucrose + serine solutions (p > 0.999) or between serine solution and water (p > 0.999)
Summary
Ant Foraging and Caterpillar Attendance for individual organisms (Simpson and Raubenheimer, 1993; Raubenheimer and Simpson, 1999; Simpson et al, 2004; Raubenheimer et al, 2009) This approach has been successfully applied to a range of species, from slime molds, through insects to humans (Raubenheimer and Simpson, 1993; Simpson et al, 2003; Behmer, 2009; Dussutour et al, 2010), and furthered the understanding of nutritional dynamics and trophic interactions (Simpson et al, 2015). While solitary animals must satisfy their own nutritional needs, food acquisition in social insects requires a more complex evaluation of specific target ratios, due to their colonial lifestyle as well as accommodating the varying nutritional needs of different colony members. Evidence of nutrient compensatory foraging is provided by both field and laboratory studies of honey bees (Hendriksma and Shafir, 2016) and several species of ants, including Solenopsis invicta (Sorensen et al, 1985; Cook et al, 2010; Wilder and Eubanks, 2010), Rhytidoponera metallica (Dussutour and Simpson, 2008), Ectatomma ruidum (Cook and Behmer, 2010), and Iridomyrmex suchieri (Christensen et al, 2010)
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