Johnson Steven D, Midgley Jeremy J, Illing Nicola
Centre for Functional Biodiversity, University of KwaZulu-Natal, 3209 Pietermaritzburg, South Africa.
Department of Biological Sciences, University of Cape Town, 7701 Cape Town, South Africa.
Ann Bot. 2025 Aug 23. doi: 10.1093/aob/mcaf189.
Evolutionary floral modifications that enable plants to exploit particular body parts of animals for pollen transfer are considered a key contributor to the angiosperm radiation. Species of Dilatris (Haemodoraceae) have an unusual combination of floral traits including a centrally-positioned stamen with a large anther flanked by two stamens with smaller anthers (heteranthery), and styles that are deflected either to the right or left on flowers of the same plant (monomorphic enantiostyly). We investigated the pollination functions of these traits in D. ixioides to better understand their evolution.
We quantified floral traits including morphology, pollen production by different anthers and spectral reflectance of various organs. We also assessed the identity and pollen loads of flower visitors and their behavioural responses to anther removal, as well as the levels of self-compatibility and pollinator dependence of D. ixioides.
Left- and right-styled flowers of D. ixiodes alternate consistently along inflorescence branches (pendulum symmetry). They do not produce nectar and were found to be pollinated primarily by female carpenter bees that collect pollen from the large central anther. The central anther is yellow, has spectral properties that are similar to those of pollen, and produces more than twice as many pollen grains as do each of the smaller lateral anthers which are red. Flowers with the central anther experimentally removed were ignored by bees. Pollen is transferred via the bee's wings as they beat against the deflected lateral anthers and stigma while the bees grasp the central anther. Plants are self-compatible but reliant on pollinator visits for seed production.
The absence of nectar production and development of a large central pollen-rewarding anther in combination with laterally deflected anthers and styles in D. ixioides are functional components of an effective and novel system of wing pollination by female bees.
进化过程中的花部变异使植物能够利用动物身体的特定部位来进行花粉传播，这被认为是被子植物辐射演化的关键因素。Dilatris属（血草科）植物具有一系列独特的花部特征组合，包括位于中央的具有大花药的雄蕊，两侧各有一个具有较小花药的雄蕊（异型花药），以及在同一植株花朵上花柱向右或向左弯曲的现象（单态对花柱性）。我们研究了这些特征在D. ixioides中的授粉功能，以更好地理解其进化过程。
我们对花部特征进行了量化，包括形态、不同花药的花粉产量以及各器官的光谱反射率。我们还评估了访花者的身份和花粉负载量、它们对花药去除的行为反应，以及D. ixioides的自交亲和性和对传粉者的依赖程度。
D. ixioides的左花柱花和右花柱花在花序分支上交替排列（钟摆对称性）。它们不产生花蜜，主要由雌性木蜂授粉，这些木蜂从中央的大花药上采集花粉。中央花药呈黄色，其光谱特性与花粉相似，产生的花粉粒数量是两侧较小的红色花药的两倍多。实验去除中央花药的花朵被蜜蜂忽视。当蜜蜂抓住中央花药时，花粉通过蜜蜂翅膀拍打弯曲的侧花药和柱头而传播。植株具有自交亲和性，但种子生产依赖传粉者的访花。
D. ixioides中不产生花蜜以及具有一个大的能提供花粉回报的中央花药，再加上侧生弯曲的花药和花柱，是一种由雌性蜜蜂进行有效且新颖的翅膀授粉系统的功能组成部分。
