When it pays to cheat: Examining how generalized food deception increases male and female fitness in a terrestrial orchid

<div><p>Background</p><p>Experimental manipulations of floral nectar in food deceptive species can reveal insights into the evolutionary consequences of the deceptive strategy. When coupled to pollen tracking, the effects of the deceptive pollination syndrome on both male and female reproductive success may be quantified. Attraction of pollinators in deceit-pollinated species often relies on producing a conspicuous floral display which may increase visibility to pollinators, but in-turn may increase within plant selfing.</p><p>Methodology</p><p>To understand the role of deception in Orchidaceae reproduction we studied <i>Cypripedium candidum</i>. All species of the <i>Cypripedium</i> genus employ a generalized food deceptive pollination strategy and have been suggested as a model system for the study of pollinator deception. We conducted a nectar addition experiment that randomly assigned the four plants closest to a transect point to receive one of four histochemical dyes. Two individuals selected for nectar addition in each of altogether 25 blocks received 2μl of 25% sucrose solution in the labellum of each flower, while two others received no artificial nectar. Number of fruits produced, fruit mass and fruit abortion were scored at the end of the four-month experiment.</p><p>Results</p><p>Nectar addition increased (p<0.0001) self-pollination and pollen discounting by nearly 3x, while plants not receiving nectar had greater (p<0.0001) numbers of non-self pollinia deposited and lower rates of pollen discounting. There was a non-significant (p = 0.0645) trend for deceptive plants to set more fruit, while presence of nectar did not affect pollen export.</p><p>Conclusions</p><p>This study demonstrates the adaptive advantages of food deception by showing a concurrent reduction in particular male and female functions when a food reward is restored to a deceptive flower. We found generalized food deception to not only decrease inbreeding depression in the system, but concurrently have no effect on pollinator attraction and fruit set when compared with rewarding flowers.</p></div

Comparison of the effect of treatment on average female reproductive success of study plants using standard least squares ANOVA, blocked by quadrat.

<p>Plants that received nectar had an increased rate of fruit abortion (F_1,99 = 4.58, p = 0.035) (ANOVA F_3,51 = 1.48, p = 0.23, R² = 0.42), but no difference in fruit production (F_1,99 = 2.82, p = 0.09, ANOVA F_28,99 = 1.31, p = 0.17, R² = 0.34). Error bars represent standard errors.</p

Comparison of seed mass between selfed and outcrossed fruits using a paired t test.

<p>Plants that received outcross pollinia had significantly greater seed mass than those receiving selfed pollinia, (paired t(46) = 2.87, SD = 0.032, p = 0.006; mean self = 0.016g, SE = 0.0007, mean outcross = 0.033 g, SE = 0.005). Error bars represent standard errors.</p

Comparison of pollinia receipt by treatment using standard least squares ANOVA.

<p>There was no difference in total receipt of pollinia between treatments (F_1,99 = 0.04, p = 0.83, ANOVA F_28,99 = 1.18, p = 0.27, R² = 0.31); however, plants receiving nectar had significantly more self-pollination events (F_1,99 = 15.76, p < 0.001, ANOVA F_28,99 = 1.82, p = 0.021, R² = .041) and fewer outcross events (F_1,99 = 18.12, p < 0.0001, ANOVA F_28,99 = 1.61, p = 0.05, R² = 0.38) than flowers that did not receive supplemental nectar. Error bars represent standard errors.</p