Floral scents, cozy shelter, and edible spathes: brood-site weevil pollination in Stenospermation weberbaueri (Araceae).

Abstract

Background and objectives: Araceae family is known for its entomophilous reproductive strategies, involving olfactory-driven pollinator attraction and diverse floral rewards. In the Neotropics, genera with unisexually-flowered inflorescences, feature short anthesis and intense thermogenesis, while those with bisexual flowers typically have longer anthesis and varied strategies. However, Monsteroideae, with short anthesis, remains an exception and is underexplored. This study focuses on the floral morphology, pollination ecology, and reproductive strategies of Stenospermation weberbaueri to enhance understanding of Neotropical aroid dynamics.

Material and methods: A natural population of S. weberbaueri was investigated in the Colombian Andes. Detailed examinations of inflorescence morphology, floral development and population phenology were conducted. Over a 1-year period, flowering and fruiting phenology were recorded, the reproductive system was assessed through controlled pollination experiments, and spadix temperatures were monitored during anthesis. Floral scent samples were collected and characterized using headspace and Gas Chromatography coupled to Mass Spectrometry methods, while pollen morphology and its position on floral visitor's body were described using scanning electron microscopy. Attractiveness assays with baited traps were employed to attract scent-oriented floral visitors.

Key results: The reproductive sequence of S. weberbaueri consists of six stages over 50 days. Anthesis, lasting three days, involves thermogenesis, spathe movements, floral chamber formation, and scent emission to attract and retain visitors. Temperature increases are synchronized with flowering, peaking at 5.4-7.2 °C above ambient during the male phase of anthesis. We identified 3-pentanol as a novel floral scent component in Araceae, which attracts Cyclanthura sp., the primary pollinators of S. weberbaueri. Controlled pollination experiments confirmed that S. weberbaueri cannot self-pollinate or undergo apomixis. We make the first report of brood-site pollination mutualism in Stenospermation and in the subfamily Monsteroideae.

Conclusions: This is the first comprehensive account of the pollination biology of genera Stenospermation, indicating a mutual dependence between S. weberbaueri and Cyclanthura sp., with weevils serving as pollen vectors and laying eggs on deciduous spathes. This BSPM in aroids, involving ectophagous and detritivorous larvae, highlights the complex interplay of floral traits-centered on long-range olfactory signals combined with putative visual and thermal signals-to attract specialized pollinators.