Data from: Analysis of inbreeding depression in mixed-mating plants provides evidence for selective interference and stable mixed mating

Hermaphroditic individuals can produce both selfed and outcrossed progeny, termed mixed mating. General theory predicts that mixed-mating populations should evolve quickly toward high rates of selfing, driven by rapid purging of genetic load and loss of inbreeding depression (ID), but the substantial number of mixed-mating species observed in nature calls this prediction into question. Greater average ID reported for selfing than for outcrossing populations is consistent with purging and suggests that mixed-mating taxa in evolutionary transition will have intermediate ID. We compared the magnitude of ID from published estimates for highly selfing (r > 0.8), mixed-mating (0.2 < r > 0.8), and highly outcrossing (r < 0.2) plant populations across 58 species. We found that mixed-mating and outcrossing taxa have equally high average lifetime ID (d = 0.58 and 0.54, respectively) and similar ID at each of four life-cycle stages. These results are not consistent with evolution toward selfing in most mixed-mating taxa. We suggest that prevention of purging by selective interference could explain stable mixed mating in many natural populations. We identify critical gaps in the empirical data on inbreeding depression and outline key approaches to filling them.

雌雄同体个体可同时产生自交与异交后代，此类交配模式被称为混合交配（mixed mating）。主流演化理论预测，受遗传负荷（genetic load）快速清除与近交衰退（inbreeding depression, ID）丧失的驱动，混合交配种群会快速向高自交率方向演化；但自然界中大量观测到的混合交配物种，对这一理论预测提出了质疑。相较于异交种群，自交种群被报道的平均近交衰退程度更高，这一结果与遗传负荷清除理论相符，并暗示处于演化过渡阶段的混合交配类群将表现出中等程度的近交衰退。我们针对涵盖58个物种的三类植物种群的已发表近交衰退估计值展开了比较：高度自交种群（自交率r > 0.8）、混合交配种群（0.2 < r < 0.8）以及高度异交种群（r < 0.2）。研究结果显示，混合交种类群与异交类群的平均终生近交衰退水平相当（分别为d=0.58和0.54），且在四个生命周期阶段的近交衰退程度相似。上述结果与“大多数混合交配类群会向自交方向演化”的理论预测并不一致。我们提出，选择性干扰引发的遗传负荷清除受阻，或可解释众多自然种群中稳定存在的混合交配模式。最后，我们明确了近交衰退相关实证研究中的关键空白，并概述了填补这些空白的核心研究路径。