Abstract

Most herbivorous insect species are restricted to a narrow taxonomic range of host plant species. Herbivore species that feed on mustard plants and their relatives in the Brassicales have evolved highly efficient detoxification mechanisms that actually prevent toxic mustard oils from forming in the bodies of the animals. However, these mechanisms likely were not present during the initial stages of specialization on mustard plants ~100 million years ago. The herbivorous fly Scaptomyza nigrita (Drosophilidae) is a specialist on a single mustard species, bittercress (Cardamine cordifolia; Brassicaceae) and is in a fly lineage that evolved to feed on mustards only in the past 10–20 million years. In contrast to many mustard specialists, S. nigrita does not prevent formation of toxic breakdown products (mustard oils) arising from glucosinolates (GLS), the primary defensive compounds in mustard plants. Therefore, it is an appealing model for dissecting the early stages of host specialization. Because mustard oils actually form in the bodies of S. nigrita, we hypothesized that in lieu of a specialized detoxification mechanism, S. nigrita may mitigate exposure to high GLS levels within plant tissues using behavioral avoidance. Here, we report that jasmonic acid (JA) treatment increased GLS biosynthesis in bittercress, repelled adult female flies, and reduced larval growth. S. nigrita larval damage also induced foliar GLS, especially in apical leaves, which correspondingly displayed the least S. nigrita damage in controlled feeding trials and field surveys. Paradoxically, flies preferred to feed and oviposit on GLS‐producing Arabidopsis thaliana despite larvae performing worse in these plants versus non‐GLS‐producing mutants. GLS may be feeding cues for S. nigrita despite their deterrent and defensive properties, which underscores the diverse relationship a mustard specialist has with its host when lacking a specialized means of mustard oil detoxification.

Highlights

  • Many herbivorous insect lineages have evolved mechanisms allowing them to avoid or neutralize toxic plant defense compounds (Wittstock et al 2004; Winde and Wittstock 2011)

  • That specialized biochemical means of subverting plant secondary compounds such as those exhibited by these classic mustard specialists are not a precondition for the evolution of extreme host plant specialization of the type exhibited by S. nigrita (Gloss et al 2014)

  • We tested whether S. nigrita females prefer host plants with or without foliar GLS, and monitored larval a 2016 The Authors

Read more

Summary

Introduction

Many herbivorous insect lineages have evolved mechanisms allowing them to avoid or neutralize toxic plant defense compounds (Wittstock et al 2004; Winde and Wittstock 2011). Specialized detoxification mechanisms are among the salient traits linked to ecological specialization on a narrow range of toxic host plants, as is typical for most herbivorous insect species (Ehrlich and Raven 1964; Mitter et al 1988; Forister et al 2015). Because such highly efficient mechanisms of resisting plant defenses evolved so long ago (on the order of hundreds of million years ago), it is difficult to establish whether they are prerequisites for, or rather a consequence of, host plant specialization (Futuyma and Moreno 1988; Forister et al 2015). We tested the hypothesis that the relatively evolutionarily young mustard specialist Scaptomyza nigrita exhibits behavioral strategies that mitigate costs of ingesting mustard oils, given that it lacks a specialized means of avoiding exposure through detoxification (Gloss et al 2014)

Methods
Results
Discussion
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call