Comparing two strategies of counter-defense against plant toxins: a modeling study on plant–herbivore interactions

Introduction Various herbivorous insects prefer toxic plants as their hosts, although this may appear paradoxical. They have evolved specific adaptations (called counter-defenses) against the toxins. For example, two-component chemical defense system of Brassicaceae family herbivores consists glucosinolates (GLSs) and activating enzyme myrosinase. GLS hydrolysis by myrosinase leads to isothiocyanates (ITCs), which are deterrent many insect herbivores. Two different types counter-defenses can be distinguished: a preemptive counter-defense that prevents GLSs from being hydrolyzed ITCs due metabolic redirection direct counter-defense, where formed but then metabolized non-toxic conjugates. In general, is only possibility if plant stores precursor toxin, activated upon attack. Preemptive believed more efficient lower exposure ITCs, has not been satisfactorily demonstrated experimentally. Methods Here, we derive on theoretical grounds conditions under reduces compared studying dynamics with two separate ordinary differential equation models. We model how herbivory transfers gut leaf material. Thereafter, describe insects’ toxins deriving in during feeding counter-defenses. Results discussion By calculating area curve (AUC) ITC concentrations, show, based empirical data, detoxification usually less exposed ITCs. addition, our models explain decline level achieved both counter-defenses, helps understand overall mechanisms benefits these techniques. Our results also apply defenses inactive toxin precursors other than well sequester such for own defense.