圖片來源：Bettaman
文獻來源: Singer MS, Mace KC, Bernays EA (2009) Self-Medication as Adaptive Plasticity: Increased Ingestion of Plant Toxins by Parasitized Caterpillars. PLoS ONE 4(3): e4796. doi:10.1371/journal.pone.0004796「自我療癒」是指動物遭遇疾病或被寄生時，所產生的一種特殊治療性質的行為改變。關於自我療癒的經驗觀察文獻主要集中在確認何種特殊行為會連結到何種治療結果的案例上。在本研究中，作者將「自我療癒」定義在廣義的適應可塑性之內，此可提供數個可測試的假說以驗證自我療癒與提升其概念上的意義。首先，「自我療癒」應該要能提高動物受到寄生物或病菌感染時的存活率；其次，在未受到感染的情形下進行「自我療癒」，應該會降低動物的適應度；第三，感染要能引發動物的「自我療癒」 行為。少數以人類以外的動物進行的嚴謹「自我療癒」研究並未採取此推理的架構，因此無法測試在未受到感染的情形下進行「自我療癒」會付出多少減低適應度的 代價。在此研究中，作者藉由人為操作實驗，測試燈蛾幼蟲(Grammia incorrupta; Lepidoptera: Arctiidae)如何因應致死性內寄生物（寄生蠅）而改變其進食行為，以驗證他們的假說。實驗顯示幼蟲攝取含有植物毒素ー植物鹼 （pyrrolizidine alkaloids）能賦予幼蟲對寄生蠅的忍受力，並提高被寄生蠅寄生之幼蟲的存活率。和預測一致的是，未被寄生的幼蟲若攝取過量的植物毒素則會降低他們的存活率。受寄生的幼蟲明顯較未被寄生的幼蟲攝取多量的植物鹼。這個實例挑戰了過去對於自行服藥療癒僅限於具有高度辨識能力的動物（如靈長類）的成見， 並推動有關自我療癒的科學進入適應可塑性的領域中。
Abstract
Self-medication is a specific therapeutic behavioral change in response to disease or parasitism. The empirical literature on selfmedication has so far focused entirely on identifying cases of self-medication in which particular behaviors are linked to therapeutic outcomes. In this study, we frame self-medication in the broader realm of adaptive plasticity, which provides several testable predictions for verifying self-medication and advancing its conceptual significance. First, self-medication behavior should improve the fitness of animals infected by parasites or pathogens. Second, self-medication behavior in the absence of infection should decrease fitness. Third, infection should induce self-medication behavior. The few rigorous studies of self-medication in non-human animals have not used this theoretical framework and thus have not tested fitness costs of self-medication in the absence of disease or parasitism. Here we use manipulative experiments to test these predictions with the foraging behavior of woolly bear caterpillars (Grammia incorrupta; Lepidoptera: Arctiidae) in response to their lethal endoparasites (tachinid flies). Our experiments show that the ingestion of plant toxins called pyrrolizidine alkaloids improves the survival of parasitized caterpillars by conferring resistance against tachinid flies. Consistent with theoretical prediction, excessive ingestion of these toxins reduces the survival of unparasitized caterpillars. Parasitized caterpillars are more likely than unparasitized caterpillars to specifically ingest large amounts of pyrrolizidine alkaloids. This case challenges the conventional view that self-medication behavior is restricted to animals with advanced cognitive abilities, such as primates, and empowers the science of self-medication by placing it in the domain of adaptive plasticity theory.
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