Defensive mixology: combining acquired chemicals towards defence

Abstract

Summary The myriad chemicals produced by plants may act in combination to enhance chemical defence against herbivores. Many animals have evolved the ability to harness plant secondary metabolites (PSMs) and other chemical resources for their own defence, but few studies have addressed the compelling notion that non‐human animals combine exogenous chemicals from different sources to defend themselves against predators, parasites and pathogens. We consider the use of ‘defensive cocktails’ from an evolutionary ecology perspective, introducing the term, ‘acquired combinatorial chemical defence’ (ACCD). We define ACCD as the adaptive use of multiple chemicals of discrete origin resulting in defence against natural enemies. First, we discuss the defining characteristics of ACCD: the ability to harness interspecific chemical variation, to independently regulate it, and to obtain defensive benefits via synergy that exceed those associated with single sources. Then, we describe three non‐mutually exclusive modes by which acquired chemicals may operate against natural enemies: different chemical resources may provide defence during different stages of development, may be effective against different enemies or may work additively or synergistically against a given enemy at a given developmental stage. Next, we describe possible avenues by which chemical combinations may be acquired by herbivores and other taxa, including the mixing of exogenous chemicals from different items in the diet and mixing chemicals of dietary origin with those from non‐food resources. We discuss possible costs of ACCD, including detoxification costs and interactions with the immune system, and discuss methods of testing for ACCD and its costs. Finally, we discuss the evolutionary prediction that herbivores may converge on the use of complementary combinations of chemical resources from the environment or chemical defence syndromes. Opportunities to combine chemical resources abound, suggesting that animal and human medication may be more closely aligned than previously recognized.

Sequestration and functional diversification of cyanogenic glucosides in the life cycle of Heliconius melpomene

“…The expression of the P450s putatively involved in the CNglc biosynthesis was measured in eggs, larvae, pupae and freshly emerged adults of H. melpomene by qPCR ( Figure 4a). Generally, lepidopteran eggs acquired their chemical defences from their parents and do not biosynthesize them (Eisner et al, 2000;Mason and Singer, 2015). In agreement with this, our qPCR results show the lowest Cts for the analysed genes at the egg stage.…”

Effect of timing and exposure of sunflower pollen on a common gut pathogen of bumble bees

“…For example, infections with human and simian immunodeficiency viruses were prevented in monkeys when a medicinal treatment was administered within 36 h of infection, but not after this 36-h window (Tsai et al, 1995;Otten et al, 2000). With insects, timing of exposure to potentially medicinal secondary compounds can have different benefits at different ontogenetic stages (Mason & Singer, 2015); for example, a compound may be more effective against larval than against adult parasites. In these examples, the timing of medicinal dosage mattered, and early intervention reduced or prevented irritation or infection better than late intervention.…”

“…In these examples, the timing of medicinal dosage mattered, and early intervention reduced or prevented irritation or infection better than late intervention. With insects, timing of exposure to potentially medicinal secondary compounds can have different benefits at different ontogenetic stages (Mason & Singer, 2015); for example, a compound may be more effective against larval than against adult parasites. However, we know little about how timing of exposure to potential medicines affects resistance to pathogens within a life stage.…”

Defence reactions of mature Norway spruce (Picea abies) before and after inoculation of the blue-stain fungus Endoconidiophora polonica in a drought stress experiment

“…In addition, conifers are equipped with an extensive arsenal of chemical, protein-based and anatomically inducible defences, activated in response to attack or wounding (Eyles et al 2010). Encapsulating invading biotic agents and sealing wounded tissue, secondary metabolites such as terpenoids and phenolic compounds show also highly toxic effects on invading organisms (Franceschi et al 2005;Mason & Singer 2015).…”