Biosciences, University of Exeter, Exeter, Devon, UK.
Whitley Wildlife Conservation Trust, Paignton Zoo, Paignton, UK.
Sci Rep. 2017 Mar 24;7:45122. doi: 10.1038/srep45122.
In plants, apomixis results in the production of clonal offspring via seed and can provide reproductive assurance for isolated individuals. However, many apomicts require pollination to develop functional endosperm for successful seed set (pseudogamy) and therefore risk pollination-limitation, particularly in self-incompatible species that require heterospecific pollen. We used microsatellite paternity analysis and hand pollinations to investigate pollen-limitation in Sorbus subcuneata, a threatened endemic tree that co-occurs with its congener, S. admonitor. We confirmed that S. subcuneata is an obligate pseudogamous apomict, but open-pollinated flowers rarely produced seed (flower-to-seed conversion < 1%) even though they rapidly accumulated pollen on their stigmas. Manual heterospecific pollination by S. admonitor resulted in a high flower-to-seed conversion rate (65%), however, we estimate that the ratio of self: heterospecific pollination in open-pollinated flowers was at least 22:1. Despite the efficacy of heterospecific pollination, the contribution of S. admonitor trees to paternity in seed from open-pollinated flowers of S. subcuneata decreased rapidly with the spatial separation between paternal and maternal trees. Conservation efforts aimed at maintaining species with this breeding system must therefore manage the congeners in tandem which will also maintain the potential for rare heterospecific fertilisation that typically cause rapid diversification in these lineages.
在植物中，无融合生殖导致通过种子产生克隆后代，并可为孤立个体提供生殖保障。然而，许多无融合生殖体需要授粉来发育功能性胚乳以实现成功的种子结实（假受精），因此存在授粉限制的风险，尤其是在需要异交花粉的自交不亲和物种中。我们使用微卫星亲子分析和人工授粉来研究 Sorbus subcuneata 中的授粉限制，Sorbus subcuneata 是一种受威胁的特有树，与同属种 S. admonitor 共存。我们证实 S. subcuneata 是一种强制性的假受精无融合生殖体，但即使它们的柱头迅速积累花粉，开放授粉的花朵也很少产生种子（花到种子的转化率<1%）。由 S. admonitor 进行的异交授粉导致高花到种子的转化率（65%），然而，我们估计开放授粉花朵中的自交：异交授粉的比例至少为 22:1。尽管异交授粉有效，但 S. admonitor 树对 S. subcuneata 开放授粉花朵种子的父本贡献随着父本和母本树之间的空间分离而迅速减少。因此，旨在维持具有这种繁殖系统的物种的保护工作必须同时管理同属种，这也将维持罕见的异交受精的潜力，通常会导致这些谱系的快速多样化。
