School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, 3209, South Africa.
South African Environmental Observation Network, Ndlovu Node, Phalaborwa, 1390, South Africa.
Oecologia. 2020 Nov;194(3):383-390. doi: 10.1007/s00442-020-04784-9. Epub 2020 Oct 20.
Megaherbivores have been of particular interest to scientists because of the physiological and ecological challenges associated with their extreme body size. Yet, one question that has seldom been explored is how browsing megaherbivores cope with plant secondary metabolites (PSMs), such as tannins, found in their food. It is possible that the sheer body size of these megaherbivores allows them to ingest tannins with no deleterious effects. However, it is plausible that megaherbivores must rely on other mechanisms to cope with PSMs, such as the production of salivary tannin-binding proteins. Thus, we aimed to determine whether megaherbivore browsers produce tannin-binding proteins to further reduce the consequences of ingesting a tannin-rich diet. Using a series of laboratory assays, we explored whether elephants, black rhinoceros, and giraffe had tannin-binding proteins in their saliva. We tested for the presence of proline-rich proteins in the saliva using two different approaches: (1) SDS-PAGE using Laemmli's (Laemmli, Nature 227:680-685, 1970) destaining method, and (2) comparative SDS-PAGE gels using Beeley et al.'s (Beeley et al. Electrophoresis 12:493-499, 1991) method for staining and destaining to probe for proline-rich proteins. Then, to test for the tannin-binding affinity of their saliva, we performed an inhibition assay. We did not observe proline-rich proteins in any of the megaherbivore species, but they did have other protein(s) in their saliva that have a high tannin-binding affinity. Our results highlight that, despite their large body sizes, and their abilities to tolerate low-quality food, browsing megaherbivores have likely evolved tannin-binding proteins as a way of coping with the negative effects of tannins.
巨型食草动物因其极端体型所带来的生理和生态挑战而引起了科学家的特别关注。然而，一个很少被探索的问题是，食草巨型动物如何应对其食物中发现的植物次生代谢物（PSM），如单宁。这些巨型食草动物的巨大体型可能使它们摄入单宁而不会产生有害影响。然而，巨型食草动物可能必须依赖其他机制来应对 PSM，例如产生唾液单宁结合蛋白。因此，我们旨在确定巨型食草动物浏览器是否产生单宁结合蛋白，以进一步减少摄入富含单宁的饮食的后果。我们使用一系列实验室测定来探索大象、黑犀牛和长颈鹿的唾液中是否存在单宁结合蛋白。我们使用两种不同的方法检测唾液中是否存在富含脯氨酸的蛋白质：（1）使用 Laemmli 的（Laemmli，Nature 227：680-685，1970）褪色方法的 SDS-PAGE，和（2）使用 Beeley 等人的（Beeley 等人。电泳 12：493-499，1991）方法进行染色和褪色以探测富含脯氨酸的蛋白质的比较 SDS-PAGE 凝胶。然后，为了测试它们的唾液对单宁的结合亲和力，我们进行了抑制测定。我们没有在任何巨型食草动物物种中观察到富含脯氨酸的蛋白质，但它们的唾液中确实存在其他具有高单宁结合亲和力的蛋白质。我们的结果表明，尽管巨型食草动物体型巨大，并且能够耐受低质量的食物，但它们可能已经进化出单宁结合蛋白作为应对单宁负面影响的一种方式。
