Department of Biological Sciences, 840 West Taylor St., M/C 067, University of Illinois at Chicago, Chicago, Illinois 60607, USA.
Evolution. 2011 Jan;65(1):139-55. doi: 10.1111/j.1558-5646.2010.01099.x. Epub 2010 Sep 24.
Breakdown of self-incompatibility occurs repeatedly in flowering plants with important evolutionary consequences. In plant families in which self-incompatibility is mediated by S-RNases, previous evidence suggests that polyploidy may often directly cause self-compatibility through the formation of diploid pollen grains. We use three approaches to examine relationships between self-incompatibility and ploidy. First, we test whether evolution of self-compatibility and polyploidy is correlated in the nightshade family (Solanaceae), and find the expected close association between polyploidy and self-compatibility. Second, we compare the rate of breakdown of self-incompatibility in the absence of polyploidy against the rate of breakdown that arises as a byproduct of polyploidization, and we find the former to be greater. Third, we apply a novel extension to these methods to show that the relative magnitudes of the macroevolutionary pathways leading to self-compatible polyploids are time dependent. Over small time intervals, the direct pathway from self-incompatible diploids is dominant, whereas the pathway through self-compatible diploids prevails over longer time scales. This pathway analysis is broadly applicable to models of character evolution in which sequential combinations of rates are compared. Finally, given the strong evidence for both irreversibility of the loss of self-incompatibility in the family and the significant association between self-compatibility and polyploidy, we argue that ancient polyploidy is highly unlikely to have occurred within the Solanaceae, contrary to previous claims based on genomic analyses.
自交不亲和性的崩溃在具有重要进化意义的开花植物中反复发生。在自交不亲和性由 S-RNases 介导的植物科中，先前的证据表明，多倍体通常可能直接通过形成二倍体花粉粒导致自交亲和性。我们使用三种方法来检验自交不亲和性和倍性之间的关系。首先，我们测试自交亲和性和多倍体进化是否在茄科（茄科）中相关，发现多倍体和自交亲和性之间存在密切关联。其次，我们比较了在没有多倍体的情况下自交不亲和性崩溃的速度与多倍体化产生的自交不亲和性崩溃的速度，发现前者更大。第三，我们将这些方法应用于一个新的扩展，表明导致自交亲和多倍体的宏观进化途径的相对大小随时间而变化。在小时间间隔内，从自交不亲和的二倍体到自交亲和的二倍体的直接途径是占主导地位的，而在较长的时间尺度上，通过自交亲和的二倍体的途径则占主导地位。这种途径分析广泛适用于比较速率连续组合的特征进化模型。最后，鉴于该科中自交不亲和性丧失的不可逆性以及自交亲和性与多倍体之间的显著关联的有力证据，我们认为，与以前基于基因组分析的观点相反，古代多倍体极不可能在茄科中发生。
