Section for Ecology and Evolution, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
Terrestrial Ecology Section, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
Ecology. 2022 Jun;103(6):e3684. doi: 10.1002/ecy.3684. Epub 2022 Apr 13.
The biochemical heterogeneity of food items often yields tradeoffs as each bite of food tends to contain some nutrients in surplus and others in deficit, as well as other less palatable or even toxic compounds. These multidimensional nutritional challenges are likely to be compounded when foraged foods are used to provision others (e.g., offspring or symbionts) with different physiological needs and tolerances. We explored these challenges in free-ranging colonies of leafcutter ants that navigate a diverse tropical forest to collect plant fragments they use to provision a co-evolved fungal cultivar. We tested the prediction that leafcutter farmers face provisioning tradeoffs between the nutritional quality and concentration of toxic tannins in foraged plant fragments. Chemical analyses of plant fragments sampled from the mandibles of Panamanian Atta colombica leafcutter ants provided little support for a nutrient-tannin foraging tradeoff. First, colonies foraged for plant fragments that ranged widely in tannin concentration. Second, high tannin levels did not appear to restrict colonies from selecting plant fragments with blends of protein and carbohydrates that maximized cultivar performance when measured with in vitro experiments. We also tested whether tannins expand the realized nutritional niche selected by leafcutter ants into high-protein dimensions as: (1) tannins can bind proteins and reduce their accessibility during digestion, and (2) in vitro experiments have shown that excess protein provisioning reduces cultivar performance. Contrary to this hypothesis, the most protein-rich plant fragments did not have highest tannin levels. More generally, the approach developed here can be used to test how multidimensional interactions between nutrients and toxins shape the costs and benefits of providing care to offspring or symbionts.
食物的生化异质性常常会产生权衡，因为每一口食物往往会含有一些过剩的营养物质和其他不足的营养物质，以及其他不太可口甚至有毒的化合物。当觅食的食物被用来为具有不同生理需求和耐受能力的其他个体（例如后代或共生体）提供营养时，这些多维的营养挑战可能会更加复杂。我们在自由放养的切叶蚁群体中探索了这些挑战，这些蚂蚁在多样化的热带森林中导航，收集它们用来为共生真菌品种提供营养的植物碎片。我们测试了这样的预测，即切叶蚁农民在觅食时面临着营养质量和觅食植物碎片中毒性单宁浓度之间的权衡。从巴拿马 Atta colombica 切叶蚁的下颚中采集的植物碎片的化学分析几乎没有支持营养与单宁的觅食权衡。首先，蚁群觅食的植物碎片的单宁浓度范围很广。其次，高单宁水平似乎并没有限制蚁群选择具有蛋白质和碳水化合物混合的植物碎片，当用体外实验测量时，这种混合可以最大限度地提高品种的性能。我们还测试了单宁是否会将切叶蚁实际选择的营养生态位扩展到高蛋白维度，原因有两个：（1）单宁可以结合蛋白质并在消化过程中降低其可及性；（2）体外实验表明，过量的蛋白质供应会降低品种的性能。与这一假设相反，蛋白质含量最高的植物碎片并不具有最高的单宁水平。更一般地说，这里开发的方法可以用来测试营养物质和毒素之间的多维相互作用如何塑造为后代或共生体提供护理的成本和收益。
