Yannis Michalakis and Isabelle Olivieri are at INRA, Station de Genetique et d'Amélioration des Plantes, Centre de Montpellier, Domaine de Melgueil, 34130 Mauguio, France.
Trends Ecol Evol. 1992 Feb;7(2):59-62. doi: 10.1016/0169-5347(92)90108-N.
Parasites reduce the reproductive output of their hosts, limit their growth, and sometimes even castrate or hill them. Under certain conditions however, a parasitized host may be better off than an uninfected one. Such 'nice' parasites have a 'pleiotropic' action on their hosts. Parasites can be pleiotropic either in space (in which case they have a beneficial effect on the host in one environment while being detrimental in another) or in time (the parasite is beneficial at one stage of the host's development and 'costly' at another stage). Such pleiotropic parasites may constitute the intermediate stage between parasitism and mutualism.
寄生虫会降低宿主的繁殖能力，限制其生长，有时甚至会使其绝育或夭折。然而，在某些情况下，寄生虫感染的宿主可能比未感染的宿主状况更好。这种“友好”的寄生虫对宿主有“多效性”作用。寄生虫在空间上（在这种情况下，它们在一种环境中对宿主有有益的影响，而在另一种环境中则有害）或时间上（寄生虫在宿主发育的一个阶段有益，而在另一个阶段则“昂贵”）都可以具有多效性。这种多效性寄生虫可能是寄生虫和共生关系之间的中间阶段。
