Barringer Brian C, Geber Monica A
Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA.
Evolution. 2008 May;62(5):1040-51. doi: 10.1111/j.1558-5646.2008.00361.x. Epub 2008 Mar 1.
Inbreeding depression is the reduction in offspring fitness associated with inbreeding and is thought to be one of the primary forces selecting against the evolution of self-fertilization. Studies suggest that most inbreeding depression is caused by the expression of recessive deleterious alleles in homozygotes whose frequency increases as a result of self-fertilization or mating among relatives. This process leads to the selective elimination of deleterious alleles such that highly selfing species may show remarkably little inbreeding depression. Genome duplication (polyploidy) has also been hypothesized to influence levels of inbreeding depression, with polyploids expected to exhibit less inbreeding depression than diploids. We studied levels of inbreeding depression in allotetraploid and diploid species of Clarkia (Onagraceae) that vary in mating system (each cytotype was represented by an outcrossing and a selfing species). The outcrossing species exhibited more inbreeding depression than the selfing species for most fitness components and for two different measures of cumulative fitness. In contrast, though inbreeding depression was generally lower for the polyploid species than for the diploid species, the difference was statistically significant only for flower number and one of the two measures of cumulative fitness. Further, we detected no significant interaction between mating system and ploidy in determining inbreeding depression. In sum, our results suggest that a taxon's current mating system is more important than ploidy in influencing levels of inbreeding depression in natural populations of these annual plants.
近亲繁殖衰退是指与近亲繁殖相关的后代适合度降低，被认为是阻止自花受精进化的主要力量之一。研究表明，大多数近亲繁殖衰退是由纯合子中隐性有害等位基因的表达引起的，这些等位基因的频率会因自花受精或近亲交配而增加。这个过程导致有害等位基因的选择性消除，因此高度自交的物种可能表现出非常少的近亲繁殖衰退。基因组加倍（多倍体）也被认为会影响近亲繁殖衰退的程度，预计多倍体比二倍体表现出更少的近亲繁殖衰退。我们研究了Clarkia（柳叶菜科）异源四倍体和二倍体物种的近亲繁殖衰退程度，这些物种在交配系统上有所不同（每种细胞型都由一个异交物种和一个自交物种代表）。对于大多数适合度成分以及两种不同的累积适合度测量方法，异交物种比自交物种表现出更多的近亲繁殖衰退。相比之下，虽然多倍体物种的近亲繁殖衰退通常比二倍体物种低，但这种差异仅在花的数量和两种累积适合度测量方法之一上具有统计学意义。此外，我们在确定近亲繁殖衰退时未检测到交配系统和倍性之间的显著相互作用。总之，我们的结果表明，在影响这些一年生植物自然种群的近亲繁殖衰退程度方面，一个分类群当前的交配系统比倍性更重要。
