Ecology, Department of Biology, University of Konstanz, Universitätsstrasse 10, D-78457, Konstanz, Germany.
Zhejiang Provincial Key Laboratory of Plant Evolutionary Ecology and Conservation, Taizhou University, 318000, Taizhou, China.
Heredity (Edinb). 2019 Dec;123(6):723-732. doi: 10.1038/s41437-019-0268-1. Epub 2019 Sep 20.
About half of all angiosperms have some form of molecular self-incompatibility to promote outcrossing. If self-incompatibility breaks down, inbreeding depression (δ) is the main barrier to the evolution of self-fertilisation (selfing). If inbreeding depression is lower than 50% (δ < 0.5), the inherent transmission advantage of selfers should theoretically drive the evolution of selfing. However, this does not always happen in practice. For example, despite frequent breakdowns of self-incompatibility in North American Arabidopsis lyrata, selfing has only evolved in few populations. This is surprising given that previous inbreeding-depression estimates were well below the 0.5 threshold. Here, we test whether this could be due to underestimation of true inbreeding depression in competition-free environments. Specifically, we tested whether direct competition between crossed and selfed siblings magnified inbreeding-depression estimates in A. lyrata. We found that this was neither the case for belowground nor for aboveground biomass. For reproductive traits, there was hardly any significant inbreeding depression regardless of competition. Combined with previous findings that drought stress and inducing defence also did not magnify inbreeding depression, our results suggest that the relatively low estimates of inbreeding depression for biomass are indeed realistic estimates of the true inbreeding depression in North American A. lyrata.
大约一半的被子植物具有某种形式的分子自交不亲和性，以促进异交。如果自交不亲和性瓦解，近交衰退（δ）是自交进化的主要障碍。如果近交衰退低于 50%（δ<0.5），那么自交者的内在传播优势理论上应该会推动自交的进化。然而，在实践中情况并不总是如此。例如，尽管北美拟南芥中自交不亲和性经常发生崩溃，但自交仅在少数几个群体中进化。鉴于先前的近交衰退估计值远低于 0.5 的阈值，这令人惊讶。在这里，我们测试这是否可能是由于在无竞争环境中低估了真正的近交衰退。具体来说，我们测试了自交和杂交的兄弟姐妹之间的直接竞争是否会放大拟南芥中的近交衰退估计值。我们发现，无论是地下还是地上生物量，这种情况都不存在。对于繁殖特征，无论是否存在竞争，近交衰退几乎没有明显的影响。结合先前的研究结果表明，干旱胁迫和诱导防御也不会放大近交衰退，我们的研究结果表明，生物量的近交衰退相对较低的估计值确实是北美拟南芥中真正近交衰退的现实估计值。
