Nutrient acquisition across a dietary shift: fruit feeding butterflies crave amino acids, nectivores seek salt
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Evolutionary dietary shifts have major ecological consequences. One likely consequence is a change in nutrient limitation—some nutrients become more abundant in the diet, others become more scarce. Individuals’ behavior should change accordingly to match this new limitation regime: they should seek out nutrients that are deficient in the new diet. We investigated the relationship between diet and responses to nutrients using adult Costa Rican butterflies with contrasting feeding habits, testing the hypothesis that animals will respond more positively to nutrients that are scarcer in their diets. Via literature searches and our own data, we showed that nitrogen and sodium are both at lower concentration in nectar than in fruit. We therefore assessed butterflies’ acceptance of sodium and four nitrogenous compounds that ranged in complexity from inorganic nitrogen (ammonium chloride) to protein (albumin). We captured wild butterflies, offered them aqueous solutions of each substance, and recorded whether they accepted (drank) or rejected each substance. Support for our hypothesis was mixed. Across the sexes, frugivores were four times more likely to accept amino acids (hydrolyzed casein) than nectivores, in opposition to expectation. In males, nectivores accepted sodium almost three times more frequently than frugivores, supporting expectations. Together, these results suggest that in butterflies, becoming frugivorous is associated with an increased receptivity to amino acids and decreased receptivity to sodium. Nectivory and frugivory are widespread feeding strategies in organisms as diverse as insects, birds, and bats; our results suggest that these feeding strategies may put different pressures on how animals fulfill their nutritional requirements.
KeywordsFeeding guild Nutrient limitation Foraging Nectar Chemical composition
Sincere thanks are due to M. Berry for field assistance, R. Vannette for conducting the UPLC analyses, and T. Fukami for use of his UPLC equipment. L. O. Frishkoff, H. K. Frank, A. Bowring, members of the Boggs lab, and T. Fukami’s 2013 Ecological Statistics class provided insightful discussion. The staffs of OTS and La Selva Biological Station offered invaluable logistical assistance and support in the field. The Costa Rican Ministry of Environment, Energy and Telecommunications issued our research permit (202-2012-SINAC). This work was supported by a National Science Foundation Graduate Research Fellowship to AR and grants from the Stanford University Biology Department, the Stanford University Center for Latin American Studies, and the Stanford University Biosciences Office of Graduate Education.
Author contribution statement
AR and CLB conceived and designed the experiments. AR performed the experiments and analyzed the data. AR wrote the manuscript and CLB provided significant editorial feedback.
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