Annals of Botany

The role of herbivory in the selection of floral traits

Pollinators are often given precedence as the primary drivers behind the evolution of floral traits. Yet a growing body of research is beginning to stress the importance of other significant selective agents, particularly the role of herbivores that damage flower and fruit structures.

Effect of pollination and herbivory treatments on the strength and direction of selection on several floral and inflorescence architecture traits in Lythrum salicaria
Effect of pollination and herbivory treatments on the strength and direction of selection on several floral and inflorescence architecture traits in Lythrum salicaria. (A) Plants in the population were randomly assigned to herbivory or control treatment groups. Those in the herbivory group received artificial clipping of the developing meristem before flowering commenced. This stimulated a compensatory response in most plants that led to the production of additional inflorescences. We then applied a pollen supplementation treatment to a pair of randomly selected flowers on every plant, with one flower in the pair receiving hand pollination (red outline) and the other flower receiving no additional pollen (blue outline). (B) The strength and direction of selection (x-axis) of the two treatments on a variety of floral and inflorescence architecture traits (y-axis) were measured. We present the direct linear selection coefficients in the presence (yellow bars) and absence (blue bars) of herbivory. We also show the difference in selection coefficients between pollination treatments (orange bars). Bars that overlap with zero were not significantly different from zero. The length of the bar is proportional to the standard error of measurement (2s.e.). Positive selection is represented on the right and side of zero on the x-axis, negative selection on the left hand side.

By experimentally manipulating a population of Lythrum salicaria, Thomsen and Sargent demonstrate that leaf damage alone imposes selection on floral traits and constitutes an even stronger agent of change than selection by pollinators. Herbivores can have a greater impact on floral traits than pollinators, when such floral traits are relevant to a plant’s defense or compensation mechanisms.

Reference

Thomsen, C. J. M., & Sargent, R. D. (2017). Evidence that a herbivore tolerance response affects selection on floral traits and inflorescence architecture in purple loosestrife (Lythrum salicaria). Annals of Botany, 119(8), 1295–1303. https://doi.org/10.1093/aob/mcx026

About the author

Annals of Botany Office

The Annals of Botany Office is based at the University of Oxford.