Johnson N A, Wade M J
Department of Biology, University of Texas at Arlington 76019, USA.
J Theor Biol. 1995 Oct 21;176(4):493-9. doi: 10.1006/jtbi.1995.0215.
Hybrid inviability per se is not generally considered adaptive; it is believed to evolve as a pleiotropic consequence of other genetic changes, either adaptive or neutral, between diverging populations. However, given the pre-existence of hybrid sterility, there are circumstances under which hybrid inviability may be directly selected. In this report, we model the evolution of hybrid inviability in the context of within-family density-dependent selection (soft selection). This paper shows that under certain conditions, an allele causing hybrid inviability can increase when rare, despite also decreasing viability in conspecifics. These conditions depend upon the strength of density effects within families and upon the frequency of matings with heterospecifics. It is found that, under the most favorable conditions (strong soft selection and frequent hybridization), the inviability allele can invade when its deleterious effect on the hybrid viability exceeds four times its deleterious effects on conspecific heterozygotes. The conditions for fixation of the allele are also investigated and the circumstances under which this process might operate in natural populations are discussed. The conclusion is that the most restrictive condition is that for this process to evolve, there must be little opportunity for postzygotic reproductive isolation to evolve.
杂种 inviability 本身一般不被认为具有适应性；人们认为它是分化种群之间其他遗传变化（无论是适应性的还是中性的）的多效性结果而进化产生的。然而，鉴于杂种不育的预先存在，在某些情况下杂种 inviability 可能会被直接选择。在本报告中，我们在家庭内部密度依赖选择（软选择）的背景下对杂种 inviability 的进化进行建模。本文表明，在某些条件下，一个导致杂种 inviability 的等位基因在稀有时可以增加，尽管它也会降低同种个体的活力。这些条件取决于家庭内部密度效应的强度以及与异种个体交配的频率。研究发现，在最有利的条件下（强烈的软选择和频繁的杂交），当 inviability 等位基因对杂种活力的有害影响超过其对同种杂合子有害影响的四倍时，它就可以入侵。还研究了该等位基因固定的条件，并讨论了这一过程在自然种群中可能起作用的情况。结论是，最严格的条件是，为了这个过程能够进化，合子后生殖隔离几乎没有进化的机会。
