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Data from: Both costs and benefits determine the removal of Datura (Solanaceae) seeds by seed-dispersing ants

Karnish, Alex12; Bronstein, Judith1

Published Oct 27, 2025 on Dryad. https://doi.org/10.5061/dryad.m0cfxppft

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Abstract

Mutualisms have both benefits and costs that organisms receive or pay when participating in the interaction. However, costs have been largely ignored when considering how mutualisms function and evolve. Plants that are dispersed by ants produce seeds with attached nutrient-rich food bodies (elaiosomes). When ants approach a diaspore (seed with attached elaiosome), they are likely to use multiple traits to decide whether or not to move it, assessing both the benefits (elaiosome mass) and costs (mass of the inedible seed) of doing so. We hypothesized that both the mass of the often-inedible seed and the elaiosome mass would affect diaspore removal rate. To test this hypothesis, we manipulated the elaiosomes of Datura wrightii and D. discolor (Solanaceae). These species produce similarly sized elaiosomes (~0.4 mg), but D. wrightii’s seeds (~16 mg) are twice the mass of D. discolor’s. To measure how variable benefits of diaspores would influence seed removal, we offered ants seed that had been subjected to one three treatments: seeds with no elaiosome, seeds with an unmanipulated elaiosome, and seeds with an experimentally enlarged elaiosome (two elaiosomes combined). We then measured the removal rates of diaspores by Novomessor cockerelli, a common seed-dispersing ant species in Datura’s native habitat. To measure how species differences in the costs of diaspores would affect seed removal by ants, another set of trials compared removal rates of diaspores when ants were presented with unmanipulated seeds of both species simultaneously. Consistent with our hypotheses, ants removed seeds with heavier elaiosomes (larger rewards) and lighter seeds (lower costs) more quickly. This study, for the first time, quantifies a cost of seed dispersal to ants. It highlights the ways in which costs, and not benefits alone, can have an impact upon when and how organisms participate in mutualisms.