Scent chemistry is key in the evolutionary transition between insect and mammal pollination in African pineapple lilies

Abstract

Summary Volatile emissions may play a key role in structuring pollination systems of plants with morphologically unspecialised flowers. Here we test for pollination by small mammals in Eucomis regia and investigate whether its floral scent differs markedly from fly‐ and wasp‐pollinated congeners and attracts mammals. We measured floral traits of E. regia and made comparisons with insect‐pollinated congeners. We observed floral visitors and examined fur and faeces of live‐trapped mammals for pollen. We determined the contributions of different floral visitors to seed set with selective exclusion and established the breeding system with controlled pollination experiments. Using bioassays, we examined whether mammals are attracted by the floral scent and are effective agents of pollen transfer. Eucomis regia differs from closely related insect‐pollinated species mainly in floral scent, with morphology, colour and nectar properties being similar. We found that mice and elephant‐shrews pollinate E. regia, which is self‐incompatible and reliant on vertebrates for seed production. Mammals are strongly attracted to the overall floral scent, which contains unusual sulphur compounds, including methional (which imparts the distinctive potato‐like scent and which was shown to be attractive to small mammals). The results highlight the important role of scent chemistry in shifts between insect and mammal pollination systems.

The pollination system of the widely distributed mammal‐pollinated Mucuna macrocarpa (Fabaceae) in the tropics

“…When the pollinator shift is observed within a plant species, some plants adapt their floral traits to pollinators in each region (Boberg et al, 2014;Johnson & Steiner, 1997;Nagano et al, 2014;Wester et al, 2019). In M. macrocarpa, flowers were smaller in Thailand than in other regions (Table 5).…”

“…However, sugar composition is not different, and M. macrocarpa secrets sucrose-dominant nectar in all regions (Table 5). In addition to flower shape and nectar characteristics, floral color and odor are also important for attracting mammalian pollinators (Faegri & van der Pijl, 1979;Johnson et al, 2011;Knudsen & Tollsten, 1995;Wester et al, 2019). The flowers of M. macrocarpa have pale green and purple petals in all regions.…”

“…Moreover, flower shape and flowering timing might also differ among regions. There are also examples of changes in the attractive traits of nectar and volatile components associated with pollinator differences (Breitkopf et al, 2013;Perret, Chautems, Spichiger, Peixoto, & Savolainen, 2001;Wester, Johnson, & Pauw, 2019). Such differences in pollination systems among different region are important to understand the speciation process.…”

Good heavens what animal can pollinate it? A fungus‐like holoparasitic plant potentially pollinated by opossums

“…In summary, our discovery points out to future exciting research: (1) assess the efficiency of opossums as pollinators based on experiments of pollen load and fruit set; (2) set up exclusion experiments to quantitatively assess the relative importance of mammals, hummingbirds, and hymenopterans as pollinators; (3) uncover another important key trait related to non‐flying mammal pollination, which is the analyses of the chemical compounds of the floral scent and nectar. Since most Balanophoraceae species so far studied are regarded as pollinated by invertebrates and chemical traits of flower volatiles play a fundamental role in pollinator shifts from insects to mammals (see Wester et al ), S. fungiforme may be an important model to help broaden our understanding on the evolution of pollination systems in flowering plants. We also expect that future observations may indicate a greater importance of non‐flying mammals as pollinators of other Balanophoraceae species.…”

Mark D. Rausher

“…In another intriguing study on the evolution of mammal pollination – an uncommon event in plant evolution – Wester et al . () demonstrated that it was primarily changes in floral scent, and not floral morphological changes, that have altered to attract mammalian pollinators.…”