The co-optimization of fl oral display and nectar reward.

ABSTRACT

In most insect-pollinated fl owers, pollinators cannot detect the presence of nectar without entering the fl ower. Therefore, fl owers may cheat by not producing nectar and may still get pollinated. Earlier studies supported this ‘cheater fl ower’ hypothesis and suggested that the cost saving by cheater fl owers could be the most predominant selective force in the evolution of nectarless fl owers. Previous models as well as empirical studies have addressed the problem of optimizing the proportion of nectarless and nectarful fl owers. However, there has been no attempt to optimize the investment in nectar production along with that in fl oral display. One of the key questions that arises is whether the fl oral display will evolve to be an honest indicator of nectar reward. We use a mathematical model to cooptimize the investments in nectar and fl oral display in order to achieve maximum reproductive success. The model assumes that pollinators rely on a relative rather than an absolute judgement of reward. A conspicuous fl oral display attracts naïve pollinators on the one hand and enhances pollinator learning on the other. We show that under these assumptions, plant–pollinator co-evolution leads to honest signalling, i.e. a positive correlation between display and reward.