Artificial florivory decreases floral attractiveness and increases natural florivory

Background/Question/Methods

There are many insects, both mutualist and antagonist, that interact with flowers, including pollinators, nectar larcenists, flower spiders, flower galls, and florivores.  Florivory can be as common and damaging as leaf herbivory, but occurs on tissues intimately associated with plant reproduction.  However, our knowledge of how florivory affects induced floral defenses, plant-insect interactions, and plant reproduction is sorely lacking.  To mediate the effects of florivores, plants can invest in floral attractiveness traits to increase pollination or invest in floral defenses to deter antagonists.  We asked whether floral damage affects subsequent floral traits, and whether florivory affects other flower-insect interactions with mutualists or antagonists.  We hypothesized that floral damage would lead to greater investment in flower attractiveness and/or floral defenses either to attract more mutualists or deter antagonists, respectively.  We imposed three flower damage level treatments on Impatiens capensis plants, chosen based on natural levels of florivory:  a control (0% damage), 30% floral tissue removed on 1/4 of all flowers, and 60% floral tissue removed on 1/4 of all flowers.  We measured floral attractiveness traits (flower number, color, size, and nectar traits), floral defenses (anthocyanins and condensed tannins), and subsequent plant-insect interactions.

Results/Conclusions

Artificial florivory had no effect on subsequent flower production, flower size, or nectar volume, but significantly decreased the redness of subsequent I. capensis flowers, a trait that attracts many pollinators.  However, there was no effect of artificial florivory on pollinator visitation to subsequent flowers.  There was also no effect on most floral antagonisms measured (nectar robbers, nectar thieves, flower spiders, or flower galls), but artificial florivory significantly increased the frequency of and damage by naturally occurring florivores.  Future work will analyze the effects of artificial florivory on floral defenses.  The results of this study suggest that plants invest less in flower pigmentation once there has been floral damage, suggesting there may be a tradeoff between attractiveness and defenses or other shifts in resource allocation.