Evolution of defense strategies

Abstract

In nature even the most efficient defense strategy is usually surmounted by some specialists that have adapted to it. In turn, attacked organisms are forced to evolve new counterdefense mechnisms in order to keep up with the adapted specialists. This coevolutive arms race between predator and prey guarantees survival, which is however at the cost of suboptimal development for both organisms.An efficient counterdefense is to avoid toxic compounds, for example, by specialised feeding behavior, by rapid excretion, or by detoxifying a poison. Other strategies are to disturb recognition and signaling systems of the prey, thus preventing the induction of defense mechanisms. For example, microbial pathogens that are recognized by the plant’s innate immune system produce proteins that interfere with this plant’s defense system. Similarly, some viruses impede the induction of the protective RNA silencing system of their hosts. Furthermore, structural analogs of signal compounds are used by the attacking pathogen to interfere with the induction of appropriate responses.Alternatively, mutations of the molecular targets of toxins render defense compounds inactive. For example, mutations of its sodium ion channel allow the garter snake to feed on newts that are defended by the sodium channel blocker tetrodotoxin. Among microorganisms, with their short generation cycles, adaptations to gain resistance against antibiotics can be observed within a few years.