Evolutionary Ecology Group, Institute for Zoology, University of Regensburg, Regensburg, Germany.
PLoS One. 2013 Dec 6;8(12):e82780. doi: 10.1371/journal.pone.0082780. eCollection 2013.
Microbes pose severe threats to animals as competitors or pathogens and strongly affect the evolution of life history traits like parental care. Females of the European beewolf Philanthus triangulum, a solitary digger wasp, provision their offspring with paralyzed honeybees and embalm them with the secretion from large postpharyngeal glands (PPG) that contain mainly unsaturated hydrocarbons. This coating changes the physico-chemical properties of the prey surface, causes a reduction of water condensation and retards growth of mold fungi. Here we examined the closely related South American genus Trachypus, which shows a life-history similar to Philanthus. We investigated whether Trachypus spp. also possess PPGs and embalm larval provisions. Using histological methods and 3D reconstructions we show that Trachypus boharti and T. elongatus possess PPGs that are similar to P. triangulum but somewhat smaller. The ultrastructure of the gland epithelium suggests that the gland content is at least partly sequestered from the hemolymph. Chemical analyses using gas chromatography / mass spectrometry revealed that both the cuticle and PPGs of Trachypus contain mainly unsaturated long-chain hydrocarbons. The gland of T. boharti additionally contains long-chain ketones. The hydrocarbons from the PPG of T. elongatus occurred on prey bees excavated from nests in the field but not on conspecific control bees. While the embalming only slightly elevated the amount of hydrocarbons on prey bees, the proportion of unsaturated hydrocarbons, which is crucial for the antifungal effect, was significantly increased. The Trachypus species under study possess PPGs that are very similar to the PPG of P. triangulum with regard to morphology, ultrastructure and chemistry. Moreover, we provide clear evidence that T. elongatus females embalm their prey, presumably as a means of prey preservation. The observed differences among Trachypus and Philanthus in gland size and prey embalming may have evolved in response to divergent ecological conditions.
微生物对动物构成严重威胁，既是竞争者又是病原体，强烈影响着亲代照顾等生命史特征的进化。欧洲大黄蜂的独居挖掘蜂 Philanthus triangulum 会为其后代提供麻痹的蜜蜂，并将其用大型后咽腺（PPG）分泌的物质包裹起来，这种分泌物主要包含不饱和碳氢化合物。这种涂层改变了猎物表面的物理化学性质，减少了水凝结，并延缓了霉菌的生长。在这里，我们研究了密切相关的南美属 Trachypus，它表现出与 Philanthus 相似的生活史。我们调查了 Trachypus spp. 是否也拥有 PPG 并包裹幼虫食物。我们使用组织学方法和 3D 重建技术表明，Trachypus boharti 和 T. elongatus 拥有与 P. triangulum 相似但略小的 PPG。腺上皮的超微结构表明，腺体分泌物至少部分与血淋巴隔离。使用气相色谱/质谱分析化学物质表明，Trachypus 的外骨骼和 PPG 都主要包含不饱和长链碳氢化合物。T. boharti 的腺体还含有长链酮。T. elongatus 的 PPG 中的碳氢化合物出现在从野外巢穴中挖出的猎物蜜蜂上，但不出现在同种对照蜜蜂上。虽然包裹处理只是略微增加了猎物蜜蜂上碳氢化合物的含量，但对抗真菌效果至关重要的不饱和碳氢化合物的比例却显著增加。在所研究的 Trachypus 物种中，其 PPG 在形态、超微结构和化学性质上与 P. triangulum 的 PPG 非常相似。此外，我们提供了明确的证据表明，T. elongatus 雌性会包裹它们的猎物，可能是作为猎物保存的一种手段。Trachypus 和 Philanthus 之间在腺体大小和猎物包裹处理方面的观察到的差异可能是对不同生态条件的进化反应。
