Floral colour structure in two Australian herbaceous communities

Pollinator-mediated interactions between plant species may affect the composition of angiosperm communities. Floral colour signals should play a role in these interactions, but the role will arise from the visual perceptions and behavioural responses of multiple pollinators. Recent advances in the visual sciences can be used to inform our understanding of these perceptions and responses. Shrestha and colleagues outline the application of appropriate visual principles to the analysis of the annual cycle of floral colour structure in two Australian herbaceous communities.

Examples of habitat and representative herbaceous species at the study sites.
Examples of habitat and representative herbaceous species at the study sites. (A–C) Ground-layer vegetation with herbaceous species in flower, (D) Gompholobium huegelii, (E) Goodenia blackiana, (F) Burchardia umbellata, (G) Wahlenbergia gloriosa and (H) Glossodia major.

The authors used spectrographic measurements of petal reflectance to determine the location of flowers in a model of hymenopteran colour vision. These representations of colour perception were then translated to a behaviourally relevant metric of colour differences using empirically calibrated colour discrimination functions for four hymenopteran species.

They then analysed the pattern of colour similarity in terms of this metric in samples of co-flowering plants over the course of a year. The team used the same method to analyse the annual pattern of phylogenetic relatedness of co-flowering plants in order to compare colour structure and phylogenetic structure.

They found that perceived floral colour structure varied with the sensory capabilities of the observer. The lack of colour structure at most sample dates, particularly the rarity of strong dispersion, suggests that plants do not use chromatic signals primarily to enable bees to discriminate between co-flowering species. It is more likely that colours make plants detectable in a complex landscape.

Further reading

Shrestha, M., Dyer, A. G., Garcia, J. E., & Burd, M. (2019). Floral colour structure in two Australian herbaceous communities: it depends on who is looking. Annals of Botany. https://doi.org/10.1093/aob/mcz043