Flowers have often been characterised as functionally integrated units, but it has been difficult to demonstrate adaptive floral integration against a background of conserved correlations among floral whorls due to their serial homology.
Using an internal control for serial homology, and an experimental design that provides separate estimates of genetic and environmental correlations, Heywood et al. demonstrate tight adaptive integration among floral traits that interact to promote the deposition and export of pollen in hawkmoth-pollinated Ruellia humilis (Acanthaceae). Genetic and environmental correlations between non-homologous components of the hawkmoth pollination syndrome were found to be weak and discordant, providing little evidence for adaptive integration of these traits.
Heywood, J. S., Michalski, J. S., McCann, B. K., Russo, A. D., Andres, K. J., Hall, A. R., & Middleton, T. C. (2017). Genetic and environmental integration of the hawkmoth pollination syndrome in Ruellia humilis (Acanthaceae). Annals of Botany, 119(7), 1143–1155. https://doi.org/10.1093/aob/mcx003