Data from: Relatively weak inbreeding depression in selfing but also in outcrossing populations of North American (Arabidopsis lyrata)

Hermaphroditic plants can potentially self-fertilise, but most possess adaptations that promote outcrossing. However, evolutionary transitions to higher selfing rates are frequent. Selfing comes with a transmission advantage over outcrossing, but self-progeny may suffer from inbreeding depression, which forms the main barrier to the evolution of higher selfing rates. Here, we assessed inbreeding depression in the North American herb Arabidopsis lyrata, which is normally self-incompatible, with a low frequency of self-compatible plants. However, a few populations have become fixed for self-compatibility and have high selfing rates. Under greenhouse conditions, we estimated mean inbreeding depression per seed (based on cumulative vegetative performance calculated as the product of germination, survival and aboveground biomass) to be 0.34 for six outcrossing populations, and 0.26 for five selfing populations. Exposing plants to drought and inducing defenses with jasmonic acid did not magnify these estimates. For outcrossing populations, however, inbreeding depression per seed may underestimate true levels of inbreeding depression, because self-incompatible plants showed strong reductions in seed set after (enforced) selfing. Inbreeding-depression estimates incorporating seed set averaged 0.63 for outcrossing populations (compared to 0.30 for selfing populations). However, this is likely an overestimate because exposing plants to 5% CO2 to circumvent self-incompatibility to produce selfed seed might leave residual effects of self-incompatibility that contribute to reduced seed set. Nevertheless, our estimates of inbreeding depression were clearly lower than previous estimates based on the same performance traits in outcrossing European populations of A. lyrata, which may help explain why selfing could evolve in North American A. lyrata.

雌雄同株植物理论上可进行自花受精，但多数物种演化出了促进异交的适应性特征。不过，向更高自交率的演化转变却频繁发生。自交相较于异交具备传播优势，但自交后代往往会遭受近交衰退（inbreeding depression），这也是高自交率演化的主要阻碍。本研究针对北美草本植物拟南芥（Arabidopsis lyrata）开展近交衰退评估：该物种通常为自交不亲和型，仅存在少量自交亲和的植株；但已有少数种群固定了自交亲和性状，且自交率较高。在温室培养条件下，我们以发芽率、存活率与地上生物量的乘积作为累积营养生长表现指标，估算每粒种子的平均近交衰退值：6个异交种群的估算值为0.34，5个自交种群的估算值为0.26。对植株施加干旱胁迫并利用茉莉酸（jasmonic acid）诱导防御反应，并未使上述估算值升高。不过对于异交种群而言，仅基于单粒种子的近交衰退估算可能低估了真实的近交衰退水平——因为自交不亲和植株经强制自交后，结籽量会出现显著下降。若将结籽量纳入估算指标，异交种群的近交衰退平均值可达0.63（自交种群则为0.30）。但该数值大概率存在高估：因为通过将植株暴露于5%二氧化碳以绕过自交不亲和机制产生自交种子的操作，可能残留自交不亲和的影响，进而导致结籽量进一步降低。尽管如此，我们得到的近交衰退估算值仍显著低于此前针对欧洲异交拟南芥（Arabidopsis lyrata）种群、基于相同生长表现性状得出的估算结果，这或可解释为何北美拟南芥种群能够演化出自交性状。