Frank S A
Department of Ecology and Evolutionary Biology, University of California, Irvine 92717, USA.
Proc Biol Sci. 1996 Mar 22;263(1368):339-44. doi: 10.1098/rspb.1996.0052.
Host and symbiont often conflict over patterns of symbiont transmission. Symbionts favour dispersal out of the host to avoid competition with close relatives. Migration leads to competition among different symbiotic lineages, with potentially virulent side-effects on the host. The hosts are favoured to restrict symbiont migration and reduce the virulent tendencies of the symbionts. Reduced mixing of symbionts would, in many cases, lower symbiont virulence and increase the mean fitness of the host population. But a host modifier allele that reduced symbiont mixing increases only when directly associated with reduced virulence. The association between modifiers and reduced virulence depends on the particular details of symbiont biology. The importance of this direct association between modifier and virulence was first noted by Hoekstra (1987) when studying the evolution of uniparental inheritance of cytoplasmic elements. I apply Hoekstra's insight to a wide range of host-symbiont life histories, expanding the scope beyond cytoplasmic inheritance and genomic conflict. My comparison of differing symbiont life histories leads to a careful analysis of the conditions under which hosts are favoured to control mixing of their symbionts.
宿主和共生体常常在共生体传播模式上存在冲突。共生体倾向于从宿主中扩散出去，以避免与近亲竞争。迁移会导致不同共生谱系之间的竞争，对宿主可能产生有害的副作用。宿主则倾向于限制共生体迁移，并降低共生体的有害倾向。在许多情况下，减少共生体的混合会降低共生体的毒性，并提高宿主种群的平均适应性。但是，一个降低共生体混合的宿主修饰等位基因只有在与降低毒性直接相关时才会增加。修饰基因与降低毒性之间的关联取决于共生体生物学的具体细节。修饰基因与毒性之间这种直接关联的重要性最早是由霍克斯特拉（1987年）在研究细胞质元件单亲遗传的进化时注意到的。我将霍克斯特拉的见解应用于广泛的宿主 - 共生体生活史，将范围扩展到细胞质遗传和基因组冲突之外。我对不同共生体生活史的比较导致了对宿主倾向于控制其共生体混合的条件的仔细分析。
