Outcrossing rate and inbreeding depression in the herbaceous autotetraploid, Campanula americana
Outcrossing rate and inbreeding depression in the herbaceous autotetraploid, Campanula americana
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草本同源四倍体美洲风铃的异交率和近交衰退
DOI：
10.1038/sj.hdy.6800242
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发表时间：
2003
期刊：
影响因子：
3.8
通讯作者：
J. Hamrick
中科院分区：
文献类型：
--
作者：
Laura F. Galloway;Julie R. Etterson;J. Hamrick
被子植物的多倍体通常与自交亲和性的增加有关。自体受精可以促进多倍体的建立，理论预测多倍体相对于二倍体的近交抑制会减少。因此，我们可能期望交配系统能够促进多倍体物种的自体受精或混合交配。然而，很少有研究测量多倍体交配系统和近交衰退。我们报告了美洲风铃（一种自交亲和先熟草本植物）的异交率和近交衰退。同种异型酶基因型表明美洲美洲蝽是具有四体遗传的同源四倍体。我们发现多位点异交率 tm=0.938，与统一率没有差异。这一结果是出乎意料的，因为之前的工作表明，传粉媒介经常在同一株植物上从雄性花期转移到雌性花期，即同性受精。对三个群体进行自花授粉和异交授粉。后代在受控条件下发芽，并在自然盆中生长至成熟。对于大多数种子和发芽性状来说，近交衰退并不显着。然而，除开花日期外，所有晚年性状在近交和异交个体之间都存在差异，导致近交植物的累积适应性下降了 26%。有限的早期和中度晚年近交衰退表明，同源四倍体中发现的较高水平的杂合性可以缓冲这种衰退。美洲花似乎具有灵活的交配系统，其中当传粉媒介丰富时，花内先祖性和/或隐性自交不亲和性会导致高异交率，但当交配有限时，自交亲和性和有限的近交抑制可维持繁殖成功。
Polyploidy in angiosperms is frequently associated with an increase in self-compatibility. Self-fertilization can enhance polyploid establishment, and theory predicts reduced inbreeding depression in polyploids relative to diploids. Therefore, we may expect mating systems that promote self-fertilization or mixed-mating in polyploid species. However, few studies have measured polyploid mating systems and inbreeding depression. We report the outcrossing rate and inbreeding depression for Campanula americana, a self-compatible protandrous herb. Allozyme genotypes suggest that C. americana is an autotetraploid with tetrasomic inheritance. We found that the multilocus outcrossing rate, tm=0.938, did not differ from unity. This result was unexpected since previous work demonstrated that pollinators frequently move from male- to female-phase flowers on the same plant, that is, geitonogamy. Self and outcross pollinations were conducted for three populations. Offspring were germinated in controlled conditions and grown to maturity in pots in nature. Inbreeding depression was not significant for most seed and germination characters. However, all later life traits except flowering date differed between inbred and outcrossed individuals resulting in a 26% reduction in cumulative fitness for inbred plants. Limited early- and moderate later-life inbreeding depression suggest that it is buffered by the higher levels of heterozygosity found in an autotetraploid. C. americana appears to have a flexible mating system where within flower protandry and/or cryptic self-incompatibility result in a high outcrossing rate when pollinators are abundant, but self-compatibility and limited inbreeding depression maintain reproductive success when mates are limited.