School of Ecosystem and Forest Sciences, The University of Melbourne, 500 Yarra Blvd, Richmond, VIC 3121, Australia.
Department of Animal, Plant and Soil Sciences, La Trobe University, Bundoora, VIC 3086, Australia.
Ann Bot. 2021 Aug 26;128(3):261-280. doi: 10.1093/aob/mcab044.
Flowers which imitate insect oviposition sites probably represent the most widespread form of floral mimicry, exhibit the most diverse floral signals and are visited by two of the most speciose and advanced taxa of insect - beetles and flies. Detailed comparative studies on brood-site mimics pollinated exclusively by each of these insect orders are lacking, limiting our understanding of floral trait adaptation to different pollinator groups in these deceptive systems.
Two closely related and apparent brood-site mimics, Typhonium angustilobum and T. wilbertii (Araceae) observed to trap these distinct beetle and fly pollinator groups were used to investigate potential divergence in floral signals and traits most likely to occur under pollinator-mediated selection. Trapped pollinators were identified and their relative abundances enumerated, and thermogenic, visual and chemical signals and morphological traits were examined using thermocouples and quantitative reverse transcription-PCR, reflectance, gas chromatography-mass spectrometry, floral measurements and microscopy.
Typhonium angustilobum and T. wilbertii were functionally specialized to trap saprophagous Coleoptera and Diptera, respectively. Both species shared similar colour and thermogenic traits, and contained two highly homologous AOX genes (AOX1a and AOX1b) most expressed in the thermogenic tissue and stage (unlike pUCP). Scent during the pistillate stage differed markedly - T. angustilobum emitted a complex blend of sesquiterpenes, and T. wilbertii, a dung mimic, emitted high relative amounts of skatole, p-cresol and irregular terpenes. The species differed significantly in floral morphology related to trapping mechanisms.
Functional specialization and pollinator divergence were not associated with differences in anthesis rhythm and floral thermogenic or visual signals between species, but with significant differences in floral scent and morphological features, suggesting that these floral traits are critical for the attraction and filtering of beetle or fly pollinators in these two brood-site mimics.
模仿昆虫产卵场所的花可能代表了最广泛的花模仿形式，展示了最多样化的花信号，并由昆虫中最具多样性和最先进的两个类群——甲虫和蝇类——访问。缺乏对仅由这些昆虫目授粉的卵生模拟物进行详细比较研究，限制了我们对这些欺骗性系统中不同传粉群体适应花朵特征的理解。
使用两种密切相关且明显的卵生模拟物，即 Typhonium angustilobum 和 T. wilbertii（天南星科），观察到它们可以捕捉到这两种截然不同的甲虫和蝇类传粉者，以研究在传粉者介导的选择下最有可能发生的花朵信号和特征的潜在差异。通过鉴定捕获的传粉者并对其相对丰度进行计数，使用热电偶和定量逆转录聚合酶链反应、反射率、气相色谱-质谱联用、花朵测量和显微镜检查热发生、视觉和化学信号以及形态特征。
Typhonium angustilobum 和 T. wilbertii 分别专门用于捕捉腐生鞘翅目和双翅目昆虫。这两个物种具有相似的颜色和热发生特征，并且包含两个高度同源的 AOX 基因（AOX1a 和 AOX1b），这些基因在热发生组织和阶段中表达最多（与 pUCP 不同）。在雌性阶段，气味差异显著——T. angustilobum 释放出复杂的倍半萜混合物，而 T. wilbertii 作为粪生模拟物，释放出相对大量的粪臭素、对甲酚和不规则萜类。物种在与捕蝇机制相关的花朵形态上存在显著差异。
功能专业化和传粉者的分化与物种之间的开花节律和花朵热发生或视觉信号没有差异相关，而是与花朵气味和形态特征的显著差异相关，这表明这些花朵特征对于吸引和过滤这些两个卵生模拟物中的甲虫或蝇类传粉者至关重要。
