Mutikainen Pia, Delph Lynda F
Department of Biology, Indiana University, Bloomington, Indiana, 47405.
Experimental Ecology, ETH-Zurich, ETH-Zentrum NW, CH-8092, Zurich, Switzerland.
Evolution. 1998 Dec;52(6):1572-1582. doi: 10.1111/j.1558-5646.1998.tb02238.x.
If inbreeding depression is caused by deleterious recessive alleles, as suggested by the partial dominance hypothesis, a negative correlation between inbreeding and inbreeding depression is predicted. This hypothesis has been tested several times by comparisons of closely related species or comparisons of populations of the same species with different histories of inbreeding. However, if one is interested in whether this relationship contributes to mating-system evolution, which occurs within populations, comparisons among families within a population are needed; that is, inbreeding depression among individuals with genetically based differences in their rate of selfing should be compared. In gynodioecious species with self-compatible hermaphrodites, hermaphrodites will have a greater history of potential inbreeding via both selfing and biparental inbreeding as compared to females and may therefore express a lower level of inbreeding depression. We estimated the inbreeding depression of female and hermaphrodite lineages in gynodioecious Lobelia siphilitica in a greenhouse experiment by comparing the performance of selfed and outcrossed progeny, as well as sibling crosses and crosses among subpopulations. We did not find support for lower inbreeding depression in hermaphrodite lineages. Multiplicative inbreeding depression (based on seed germination, juvenile survival, survival to flowering, and flower production in the first growing season) was not significantly different between hermaphrodite lineages (δ = 0.30 ± 0.08) and female lineages (δ = 0.15 ± 0.18), although the trend was for higher inbreeding depression in the hermaphrodite lineages. The population-level estimate of inbreeding depression was relatively low for a gynodioecious species (δ = 0.25) and there was no significant inbreeding depression following biparental inbreeding (δ = 0.01). All measured traits showed significant variation among families, and there was a significant interaction between family and pollination treatment for four traits (germination date, date of first flowering, number of flowers, and aboveground biomass). Our results suggest that the families responded differently to selfing and outcrossing: Some families exhibited lower fitness following selfing whereas others seemed to benefit from selfing as compared to outcrossing. Our results support recent simulation results in that prior inbreeding of the lineages did not determine the level of inbreeding depression. These results also emphasize the importance of determining family-level estimates of inbreeding depression, relative to population-level estimates, for studies of mating-system evolution.
如果近亲繁殖衰退是由有害隐性等位基因引起的，如部分显性假说所暗示的那样，那么预计近亲繁殖与近亲繁殖衰退之间存在负相关。这一假说已经通过比较近缘物种或比较具有不同近亲繁殖历史的同一物种的种群进行了多次检验。然而，如果有人想知道这种关系是否有助于交配系统的进化（这发生在种群内部），则需要比较种群内不同家族；也就是说，应该比较在自交率上存在基于遗传差异的个体之间的近亲繁殖衰退情况。在具有自交亲和雌雄同体的雌全同株物种中，与雌性相比，雌雄同体通过自交和双亲近亲繁殖都有更大的潜在近亲繁殖历史，因此可能表现出较低水平的近亲繁殖衰退。在温室实验中，我们通过比较自交和异交后代以及同胞杂交和亚种群间杂交的表现，估计了雌全同株半边莲中雌性和雌雄同体谱系的近亲繁殖衰退情况。我们没有发现雌雄同体谱系中近亲繁殖衰退较低的证据。在雌雄同体谱系（δ = 0.30 ± 0.08）和雌性谱系（δ = 0.15 ± 0.18）之间，基于种子萌发、幼苗存活、存活到开花以及第一个生长季节的花产量的乘法近亲繁殖衰退没有显著差异，尽管趋势是雌雄同体谱系中的近亲繁殖衰退更高。对于一个雌全同株物种来说，种群水平的近亲繁殖衰退估计相对较低（δ = 0.25），并且双亲近亲繁殖后没有显著的近亲繁殖衰退（δ = 0.01）。所有测量的性状在不同家族间都表现出显著差异，并且对于四个性状（萌发日期、首次开花日期、花的数量和地上生物量），家族和授粉处理之间存在显著的相互作用。我们的结果表明，不同家族对自交和异交的反应不同：与异交相比，一些家族在自交后表现出较低的适合度，而另一些家族似乎从自交中受益。我们的结果支持了最近的模拟结果，即谱系的先前近亲繁殖并没有决定近亲繁殖衰退的水平。这些结果还强调了相对于种群水平估计，确定家族水平的近亲繁殖衰退估计对于交配系统进化研究的重要性。
