Strategies of chemical anti-predator defences in leaf beetles: is sequestration of plant toxins less costly than de novo synthesis?

Abstract

The evolution of defensive traits is driven both by benefits gained from protection against enemies and by costs of defence production. We tested the hypothesis that specialisation of herbivores on toxic host plants, accompanied by the ability to acquire plant defensive compounds for herbivore defence, is favoured by the lower costs of sequestration compared to de novo synthesis of defensive compounds. We measured physiological costs of chemical defence as a reduction in larval performance in response to repeated removal of secretions (simulating predator attack) and compared these costs between five species synthesising defences de novo and three species sequestering salicylic glucosides (SGs) from their host plants. Experiments simulating low predator pressure revealed no physiological costs in terms of survival, weight and duration of development in any of study species. However, simulation of high predation caused reduction in relative growth rate in Chrysomela lapponica larvae producing autogenous defences more frequently, than in larvae sequestering SGs. Still meta-analysis of combined data showed no overall difference in costs of autogenous and sequestered defences. However, larvae synthesising their defences de novo demonstrated secretion-conserving behaviour, produced smaller amounts of secretions, replenished them at considerably lower rates and employed other types of defences (regurgitation, evasion) more frequently when compared to sequestering larvae. These latter results provide indirect evidence for biosynthetic constraints for amounts of defensive secretions produced de novo, resulting in low defence effectiveness. Lifting these constraints by sequestration may have driven some leaf beetle lineages toward sequestration of plant allelochemicals as the main defensive strategy.

Impact of the secondary plant metabolite Cucurbitacin B on the demographical traits of the melon aphid, Aphis gossypii

“…Therefore, plant breeding should take into account this important trait as one of the criteria used for the selection of new varieties to be incorporated into IPM programs. However, further studies are needed to better understand (i) how and when the cucurbitacin content in the plants can be enhanced, and (ii) how plants with high cucurbitacin content can be integrated with other IPM tools, such as aphid natural enemies, that can be affected by this allelochemical via their prey/hosts 63 , 64 , and with insecticides. For instance, it is well known that insect metabolic enzymes (e.g., P450s and glutathione-S-transferase), that are more active in pest populations resistant to certain insecticides, can play a key role in the detoxifying plant secondary metabolites 65 .…”

Simulated predation pressure in Pelobates cultripes tadpoles modulates morphology at the metamorphic stage

“…2017), morphological (Castellanos et al. 2015), or physiological defenses against predators (Zvereva et al. 2017), as well as life-history changes (Chivers et al.…”

Assessing the Role of Developmental and Environmental Factors in Chemical Defence Variation in Heliconiini Butterflies

“…In organisms that sequester chemical defences from their diet, differences in the chemical composition or availability of these resources can result in variable defences (Jones et al 2019). In prey that biosynthesize defensive compounds, the amount of defences can be constrained as a result of trade-offs in the allocation of limiting resources (Zvereva et al 2017). Genetic or other inheritable differences (e.g.…”