Is there rapid evolutionary response in introduced populations of tansy ragwort, Jacobaea vulgaris, when exposed to biological control?

Abstract

Differences in the herbivore community between a plant's native (specialists and generalists) and introduced range (almost exclusively generalists) may lead to the evolution of reduced allocation to defences against specialist herbivores in the introduced range, allowing for increased allocation to competitive ability and to defences against generalist herbivores. Following this logic, the introduction of biological control agents should reverse this evolutionary shift and select for plants with life-history traits that are more similar to those of plants in the native range than those of plants in the introduced range that have not been exposed to biological control. In a common garden experiment, we compared performance and resistance traits of tansy ragwort, Jacobaea vulgaris, among populations from the introduced range (New Zealand and North America) that have either been exposed to or grown free from the biological control agent Longitarsus jacobaeae. For comparison, we included populations from the native European range. We found lower levels of generalist-deterrent pyrrolizidine alkaloids (PAs) and of soluble phenolics in New Zealand populations with than in populations without exposure to L. jacobaeae, while the opposite pattern was detected among North American populations. Contrary to expectation, populations with exposure to L. jacobaeae revealed more feeding damage by L. jacobaeae than populations without exposure. Introduced populations had higher levels of PAs and reproductive output than native J. vulgaris populations. Jacobaea vulgaris was introduced in different parts of the world some 100-130 years ago, while L. jacobaeae was introduced only some 20-40 years ago. Hence, the larger differences observed between native and introduced populations, as compared to introduced C. Rapo Á U.

Can plant resistance to specialist herbivores be explained by plant chemistry or resource use strategy?

“…The relationships between total PA concentration and feeding were positive for all four beetle species after phylogenetic correction (although these correlations were not significant), indicating that PAs are not deterrent. However, only adult feeding behaviour was measured in this study, and PAs may affect feeding efficiency, pupal weights, fitness, or development time of specialist herbivores, although another study showed that larval density of L. jacobaeae in the roots of J. vulgaris is significantly correlated with adult feeding (Rapo et al 2010). An absence of a strong effect of PA composition on host choice by Longitarsus spp.…”

“…Therefore, besides adult feeding, host use by herbivores is also affected by female oviposition and larval feeding behaviour. However, in the case of L. jacobaeae, the number of larvae tunnelling the roots of J. vulgaris in spring is significantly correlated with the number of shotholes recorded in the previous autumn on the same plants (Rapo et al 2010), indicating that adult feeding is a good indicator of host use by at least L. jacobaeae.…”

Enemies lost: parallel evolution in structural defense and tolerance to herbivory of invasive Jacobaea vulgaris

“…Recently, T. jacobaeae, L. jacobaeae and other specialist herbivores have been introduced into to the invasive areas as biological controls for combating the invasion of J. vulgaris for several years (McEvoy et al 1991;McEvoy and Coombs 1999). However, Rapo et al (2010) only found small differences between traits of invasive Jacobaea vulgaris populations (New Zealand and North America) with and without biological control history of L. jacobaeae but larger differences between native and invasive populations. It suggests that the recent introduction of the biological control agents did not yet cause a rapid evolutionary adaptation of J. vulgaris populations in the introduced range towards the native phenotype.…”

No improved resistance against generalist herbivores found for invasive genotypes: a case study of Senecio vulgaris (Asteraceae) and a generalist snail (Achatina fulica)

“…For instance, protection against generalist herbivores increased in invasive populations of S. jacobaea (Joshi & Vrieling, 2005), Jacobaea vulgaris (Rapo et al, 2010) and Brassica nigra (Oduor et al, 2011) compared to their native populations.…”