Yomai Viann Marie Harmony, Williams Joseph Hill
Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA.
AoB Plants. 2021 Jun 22;13(4):plab038. doi: 10.1093/aobpla/plab038. eCollection 2021 Aug.
The factors that facilitate successful colonization of islands should be especially evident where the establishment filter is strongest. Colonizers of small, remote oceanic islands should be initially rare, extremely mate-limited and often without pollinators. Hence, plant communities on such islands should reflect an establishment history in which young 'naturalized' species are most likely to display self-compatibility and autonomous selfing, whereas 'indigenous' species may exhibit more diverse reproductive strategies. To test this prediction, we characterized breeding systems of 28 species on Pohnpei, in the Federated States of Micronesia, a group of remote Pacific islands that are considered a global biodiversity hotspot. Three families with both naturalized and indigenous species were selected-Fabaceae, Malvaceae and Melastomataceae. Measurements included field observations of dichogamy/herkogamy and floral attraction traits, pollen:ovule () ratios and experimental hand-pollinations for self-compatibility and pollen limitation. Phylogenetic generalized least squares analyses tested for trait correlations between naturalized and indigenous species. Flowers of all 28 species were bisexual, and pollinator attraction features were common. Pollen:ovule ratios ranged from 9 to 557 (median = 87), and all 11 hand-pollinated species were self-compatible. All species had >5 ovules and <3500 pollen grains per flower. Indigenous species did not differ significantly from naturalized species for any trait. There is a dearth of data from remote islands bearing on the question of establishment history. In this study, we inferred all species to have some degree of autogamy and indigenous species were no more likely than naturalized species to display outcrossing mechanisms. On Pohnpei, high ovule numbers, and the inaccessibility of wind pollination and obligate outcrossing strategies, reflect the importance of retaining reproductive assurance mechanisms in the face of pollinator uncertainty.
在建立过滤最为严格的地方，那些有助于成功在岛屿上定殖的因素应该会特别明显。小型偏远海洋岛屿的定殖者最初应该很稀少，配偶极度受限，而且常常没有传粉者。因此，这类岛屿上的植物群落应该反映出一种定殖历史，即年轻的“归化”物种最有可能表现出自交亲和性和自动自花授粉，而“本土”物种可能表现出更多样化的繁殖策略。为了验证这一预测，我们对密克罗尼西亚联邦波纳佩岛上的28个物种的繁殖系统进行了特征描述，波纳佩岛是太平洋上一组偏远岛屿，被认为是全球生物多样性热点地区。我们选择了三个既有归化物种又有本土物种的科——豆科、锦葵科和野牡丹科。测量内容包括对雌雄蕊异熟/雌雄异位和花吸引特征的野外观察、花粉与胚珠比（P/O）以及用于自交亲和性和花粉限制的实验性人工授粉。系统发育广义最小二乘法分析测试了归化物种和本土物种之间的性状相关性。所有28个物种的花都是两性的，并且具有常见的传粉者吸引特征。花粉与胚珠比在9到557之间（中位数 = 87），所有11个接受人工授粉的物种都是自交亲和的。所有物种每朵花的胚珠数都大于5个，花粉粒数小于3500个。本土物种在任何性状上与归化物种没有显著差异。关于定殖历史问题，偏远岛屿的数据匮乏。在本研究中，我们推断所有物种都有一定程度的自花受精，并且本土物种并不比归化物种更有可能表现出异交机制。在波纳佩岛，高胚珠数以及风媒授粉和专性异交策略难以实现，这反映了在传粉者不确定的情况下保留繁殖保障机制的重要性。
