The geographical and seasonal mosaic in a plant-herbivore interaction: patterns of defences and herbivory by a specialist and a non-specialist

Diomar Verçosa,Marcos Nopper Alves,Rodrigo Cogni,José Roberto Trigo

doi:10.1038/s41598-019-51528-8

Diomar Verçosa, Marcos Nopper Alves + Show 2 more

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https://doi.org/10.1038/s41598-019-51528-8

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Abstract

In order to evaluate the geographic mosaic theory of coevolution, it is crucial to investigate geographical variation on the outcome of ecological interactions and the functional traits which dictate these outcomes. Plant populations are attacked by specialist and non-specialist herbivores and may have different types of chemical and biotic defences. We investigated geographical and seasonal variation in the interaction between the plant Crotalaria pallida and its two major herbivores (the specialist Utetheisa ornatrix and the non-specialist Etiella zinckenella). We first showed that attack by the two herbivores and a chemical and a biotic defence vary greatly in time and space. Second, we performed a common garden experiment that revealed genetic variation among populations in herbivore resistance and a chemical defence, but no genetic variation in a biotic defence. Third, we sampled 20 populations on a much larger geographical scale and showed great variation in attack rates by the two herbivores and a chemical defence. Finally, we showed that herbivory is not correlated with a chemical defence in the 20 field populations. Our study shows that to understand the evolution of ecological interactions it is crucial to investigate how the outcome of the interaction and the important species traits vary geographically and seasonally.

Highlights

In order to evaluate the geographic mosaic theory of coevolution, it is crucial to investigate geographical variation on the outcome of ecological interactions and the functional traits which dictate these outcomes
Some studies showed that spatial variation in abundance of a specialist and a generalist herbivore affect the main chemical defence of a plant, in the absence of the specialist herbivore, selection favoured the increase in the concentration of the defence, while in the presence of the specialist the trait remained neutral[29,30]
Crotalaria pallida has indirect defences based on the attraction of predators such as ants and wasps to their EFNs32,33,46 (Fig. 1C), which are located at the pedicel base (Edna Scremin Dias pers. com.), as described by Díaz-Castelazo et al.[47] in C. incana

Summary

Introduction

In order to evaluate the geographic mosaic theory of coevolution, it is crucial to investigate geographical variation on the outcome of ecological interactions and the functional traits which dictate these outcomes. Our study shows that to understand the evolution of ecological interactions it is crucial to investigate how the outcome of the interaction and the important species traits vary geographically and seasonally. Pyrrolizidine alkaloids (PAs) www.nature.com/scientificreports are compounds toxic or deterrent to several generalist polyphagous herbivores[15,16,17] They are sequestered by specialist herbivores, stored in the tissues in a metabolic safe form[15,18] and utilized against predators[15,19]. Some studies showed that spatial variation in abundance of a specialist and a generalist herbivore affect the main chemical defence of a plant, in the absence of the specialist herbivore, selection favoured the increase in the concentration of the defence, while in the presence of the specialist the trait remained neutral[29,30]. Et al.[31] verified that the biggest spatial difference in the outcome of the interactions was due to the difference in the species and behaviour of the ants visiting the EFNs

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