Dung mimicry in Typhonium (Araceae): explaining floral trait and pollinator divergence in a widespread species complex and a rare sister species

Abstract

Abstract The process of pollinator-driven evolution is best studied at the level of populations and among closely related plant species. Araceae provide a plant model for investigating plant–pollinator interactions, but few studies have investigated intraspecific variation in their pollination systems. Typhonium brownii (Araceae) is distributed widely across 2000 km from tropical to temperate latitudes in Australia, yet the existence of intraspecific variation and ecotypes has not been investigated. Typhonium brownii from five regions, potentially representing distinct taxa, and populations of the sister species, T. eliosurum, were studied to explore pollinator and floral trait divergence. We characterize significant intraspecific floral trait variation in T. brownii, indicating the existence of a species complex, despite the taxa trapping similar Coleoptera (Staphylinidae, Scarabaeidae). Although all T. brownii showed similar temperature increases in the appendix, there were significant shifts in the timing and pattern of thermogenic and anthesis rhythms between regions (taxa), and all T. brownii taxa had distinct scent compositions, with T. sp. aff. brownii being the most dissimilar to other taxa. In contrast, T. eliosurum inflorescences almost exclusively trapped Diptera (Sphaeroceridae, Psychodidae), had modest temperature increases confined to the staminate zone and had a distinct scent profile which differed from all T. brownii taxa; this scent was confirmed in field bioassays to be important for pollinator attraction. Prevalent volatile organic compounds (VOCs) emitted by T. eliosurum and T. brownii taxa included the common dung constituents skatole, indole and p-cresol. Typhonium eliosurum and T. brownii taxa further differed significantly in morphology and trapping mechanisms, particularly the fly-pollinated T. eliosurum. It is possible that a subset of ubiquitous VOCs identified in T. eliosurum and T. brownii taxa attract local communities of dung-seeking flies and beetles, and that floral morphological features are more important for trapping different insect orders in these dung mimics.