Reproductive isolation and drift load in selfing populations of an otherwise obligately outcrossing species

两性植物理论上可以通过自花受精（自交）繁殖，但大多数是自交不亲和的，或者已经进化出其他机制来促进异花受精（异交）。从异交到自交的转变是植物进化中最常见的转变。然而，只有相对较小比例的植物物种（10-15%）主要通过自交进行繁殖。为什么会这样呢？作为一种潜在的解释，有人提出自交促进物种形成，但这种多样化效应会被更高的灭绝率所抵消。虽然有一些系统发育支持这一假设，机制，促进物种形成的自交谱系，另一方面，他们的灭绝率增加，在很大程度上仍然是一个黑匣子。在这里，我提出了三项研究来解决这个问题，使用北美物种拟南芥。本种的大多数种群是自交不亲和的，因此专性异交，但已发现6个种群完全由自交率高的自交植物组成（自交种群）。这提供了一个很好的模型来研究生态驱动力的进化的自交，其负面后果方面的漂移负荷。在第一项研究中，我们将进行一个共同的花园实验，以测试是否在物候和昆虫访问的变化繁殖隔离自交群体从其他人群。在第二项研究中，我们将测试授粉后（但仍在受精前）的机制是否有助于自交种群的生殖隔离。具体来说，我们将测试是否从自交群体的植物和其他群体的植物之间的杂交产生更少的种子比群体内的参考杂交。第三项研究将测试是否，在一个共同的花园，植物自交群体有一个降低的性能相比，那些从同种异交群体，多年的种子生产的基础上，并考虑到种子的活力。总之，前两项研究将提高我们对生态过程的概念性理解，这些生态过程在允许自交种群发展成生殖隔离的不同谱系中发挥作用。此外，第三项研究将允许测试这种多样化的过程是否被漂移负荷导致的健身恶化所抵消。

Hermaphroditic plants can theoretically reproduce through self-fertilisation (selfing), but most are self-incompatible or have evolved other mechanisms to promote cross-fertilisation (outcrossing). Transitions from outcrossing to selfing are among the most frequent transitions in plant evolution. Nevertheless, only a relatively small proportion of plant species (10-15%) reproduce mainly by selfing. So why is this? As a potential explanation, it was proposed that selfing promotes speciation, but that this diversifying effect is countered by even higher extinction rates. Although there is some phylogenetic support for this hypothesis, the mechanisms that promote speciation of selfing lineages on the one hand, and their increased extinction rates on the other hand, are still largely a black box. Here, I propose three studies to address this using the North American species Arabidopsis lyrata. Most populations of this species are self-incompatible and thus obligately outcrossing, but six populations have been discovered that exclusively consist of self-compatible plants with high selfing rates (selfing populations). This provides an excellent model to study the ecological drivers of the evolution of selfing, and its negative consequences in terms of drift load. In the first study, we will perform a common garden experiment to test whether changes in phenology and insect visitation reproductively isolate selfing populations from other populations. In the second study, we will test whether mechanisms that act after pollination (but still before fertilisation) contribute to reproductive isolation of selfing populations. Specifically, we will test whether crosses between plants from selfing populations and plants from other populations yield fewer seeds than within-population reference crosses. The third study will test whether, in a common garden, plants from selfing populations have a reduced performance compared to those from conspecific outcrossing populations, based on multi-year seed production and taking into account seed viability. Together, the first two studies will improve our conceptual understanding of the ecological processes that play a role in allowing selfing populations to develop into reproductively isolated, divergent lineages. Additionally, the third study will allow to test whether this diversifying process is counteracted by fitness deterioration due to drift load.