Negaunee Institute for Plant Conservation Science and Action, Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, Illinois, 60035, USA.
Plant Biology and Conservation, Northwestern University, 2205 Tech Drive, Evanston, Illinois, 60208, USA.
Am J Bot. 2022 May;109(5):789-805. doi: 10.1002/ajb2.1861. Epub 2022 May 21.
To avoid inbreeding depression, plants have evolved diverse breeding systems to favor outcrossing, such as self-incompatibility. However, changes in biotic and abiotic conditions can result in selective pressures that lead to a breakdown in self-incompatibility. The shift to increased selfing is commonly associated with reduced floral features, lower attractiveness to pollinators, and increased inbreeding. We tested the hypothesis that the loss of self-incompatibility, a shift to self-fertilization (autogamy), and concomitant evolution of the selfing syndrome (reduction in floral traits associated with cross-fertilization) will lead to increased inbreeding and population differentiation in Oenothera primiveris. Across its range, this species exhibits a shift in its breeding system and floral traits from a self-incompatible population with large flowers to self-compatible populations with smaller flowers.
We conducted a breeding system assessment, evaluated floral traits in the field and under controlled conditions, and measured population genetic parameters using RADseq data.
Our results reveal a bimodal transition to the selfing syndrome from the west to the east of the range of O. primiveris. This shift includes variation in the breeding system and the mating system, a reduction in floral traits (flower diameter, herkogamy, and scent production), a shift to greater autogamy, reduced genetic diversity, and increased inbreeding.
The observed variation highlights the importance of range-wide studies to understand breeding system variation and the evolution of the selfing syndrome within populations and species.
为了避免近交衰退，植物进化出了多种繁殖系统来促进异交，例如自交不亲和性。然而，生物和非生物条件的变化会导致选择压力，从而导致自交不亲和性的崩溃。向增加自交的转变通常与花部特征的减少、对传粉者吸引力的降低以及近交的增加有关。我们检验了这样一个假设，即自交不亲和性的丧失、向自交的转变（自交）以及与自交综合征（与异交相关的花部特征的减少）的伴随进化，将导致 Oenothera primiveris 中近交的增加和种群分化。在其分布范围内，该物种的繁殖系统和花部特征从具有大花朵的自交不亲和种群转变为具有小花朵的自交亲和种群。
我们进行了繁殖系统评估，在野外和受控条件下评估了花部特征，并使用 RADseq 数据测量了种群遗传参数。
我们的结果揭示了 O. primiveris 分布范围的西向东向自交综合征的双峰过渡。这种转变包括繁殖系统和交配系统的变化、花部特征（花径、雌雄蕊间距和气味产生）的减少、自交的增加、遗传多样性的减少以及近交的增加。
观察到的变异强调了进行全范围研究的重要性，以了解繁殖系统的变异以及种群和物种内自交综合征的进化。
