Data from: The evolutionary enigma of mixed mating systems in plants: occurrence, theoretical explanations, and empirical evidence

Mixed mating, in which hermaphrodite plant species reproduce by both self- and cross-fertilization, presents a challenging problem for evolutionary biologists. Theory suggests that inbreeding depression, the main selective factor opposing the evolution of selfing, can be purged with self-fertilization, a process that is expected to yield pure strategies of either outcrossing or selfing. Here we present updated evidence suggesting that mixed mating systems are frequent in seed plants. We outline the floral and pollination mechanisms that can lead to intermediate outcrossing, review the theoretical models that address the stability of intermediate outcrossing, and examine relevant empirical evidence. A comparative analysis of estimated inbreeding coefficients and outcrossing rates suggests that mixed mating often evolves despite strong inbreeding depression. The adaptive significance of mixed mating has yet to be fully explained for any species. Recent theoretical and empirical work suggests that future progress will come from a better integration of studies of floral mechanisms, genetics, and ecology, and recognition of how selective pressures vary in space and time.

雌雄同株植物物种通过自交（self-fertilization）与异交（cross-fertilization）双重途径繁殖的混合交配模式，对进化生物学家而言是一项极具挑战性的研究课题。理论研究表明，作为对抗自交演化的主要选择因子——近交衰退（inbreeding depression），可通过自交过程得以清除，这一过程本应导向异交或自交的单一纯合策略。本文呈现了最新研究证据，表明混合交配系统在种子植物中广泛存在。我们概述了可导致中间型异交率的花部与传粉机制，回顾了阐释中间型异交稳定性的理论模型，并检视了相关实证研究证据。对估算得到的近交系数与异交率的比较分析显示，即便面临强烈的近交衰退，混合交配仍时常得以演化形成。目前尚未有任一物种的混合交配适应意义得到完整阐释。近期的理论与实证研究表明，未来的研究进展将有赖于更好地整合花部机制、遗传学与生态学研究，并充分认识选择压力在时空维度上的变化规律。