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

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.

Genomic and chemical evidence for local adaptation in resistance to different herbivores in Datura stramonium

“…A number of studies have also documented geographic variation in the level of herbivory and chemical defenses (Castells et al 2005;Muola et al 2010;Agrawal et al 2012;Züst et al 2012;Castillo et al 2014;Verçosa et al 2019;Hahn et al 2019). However, there have been no previous attempts to determine how the plants' genetic background (IBD) is driven by ongoing natural selection imposed by herbivores.…”

Direct and indirect plant defenses reduce damage by a generalist but not by a specialist pod borer

“…In line with our first hypothesis, usaramine did not affect damage by the specialist U. ornatrix but greatly reduced damage by the generalist E. zinckenella. These results are the first to demonstrate that damage by E. zinckenella is negatively affected by Crotalaria PAs, since previous studies were inconclusive (Cogni et al 2011;Verçosa et al 2019). E. zinckenella must cope with a diversity of host plants, and we do not know whether it detoxifies PAs.…”

“…was included in all models as an explanatory variable for ant presence. Though this appears counterintuitive, EFNs in C. pallida are located at the base of the flower/pod pedicel (for image, see figure 1c in Verçosa et al 2019). Therefore, the number of pods is directly related to the number of active EFNs.…”

Ecological trade‐offs in development and defence in a specialist moth when feeding on four congeneric host plants

“…Pyrrolizidine alkaloid concentration in larval food has been shown to alter defence levels and male pheromone titres, so these secondary metabolites are associated with components of both larval and adult fitness (Conner et al, 1981;González et al, 1999). Crotalaria species are known to vary as a resource for U. ornatrix, both in nutritional compounds and PA concentration (Martins et al, 2015;Trigo et al, 2017;Verçosa et al, 2019).…”