Generalized food-deceptive orchid species flower earlier and occur at lower altitudes than rewarding ones

Aims Food-deceptive pollination,in which plants do not offer any food reward to their pollinators,is common within the Orchidaceae.As food-deceptive orchids are poorer competitors for pollinator visitation than rewarding orchids,their occurrence in a given habitat may be more constrained than that of rewarding orchids.In particular,the success of deceptive orchids strongly relies on several biotic factors such as interactions with co-flowering rewarding species and pollinators,which may vary with altitude and over time.Our study compares generalized food-deceptive(i.e.excluding sexually deceptive)and rewarding orchids to test whether(i)deceptive orchids flower earlier compared to their rewarding counterparts and whether(ii)the relative occurrence of deceptive orchids decreases with increasing altitude.Methods To compare the flowering phenology of rewarding and deceptive orchids,we analysed data compiled from the literature at the species level over the occidental Palaearctic area.Since flowering phenology can be constrained by the latitudinal distribution of the species and by their phylogenetic relationships,we accounted for these factors in our analysis.To compare the altitudinal distribution of rewarding and deceptive orchids,we used field observations made over the entire Swiss territory and over two Swiss mountain ranges.Important Findings We found that deceptive orchid species start flowering earlier than rewarding orchids do,which is in accordance with the hypotheses of exploitation of naive pollinators and/or avoidance of competition with rewarding co-occurring species.Also,the relative frequency of deceptive orchids decreases with altitude,suggesting that deception may be less profitable at high compared to low altitude.

In nomen omen:the effect of flower distance on female reproductive success of the lax-flowered orchid Anacamptis laxiflora(Orchidaceae)

Aims In multiflowered species,the architecture of inflorescences is of primary importance in shaping plant attractiveness.The aim of this study was to disentangle the role of inflorescence traits in plant female reproductive success and pollination patterns along the inflorescence in the lax-flowered orchid Anacamptis laxiflora,a terrestrial species exploiting a deceptive pollination strategy.We also evaluated whether the relationship between inflorescence traits and female reproductive success was modified by the height of surrounding vegetation and/or by population density.Methods We delimited experimental plots in a natural population of A.laxiflora.We tallied the individuals within each plot and categorized low-density plots and high-density plots;then,in part of the plots we manually removed surrounding grass thus producing an equal number of plots with high grass and low grass.Within these plots,we recorded inflorescence traits and female reproductive success(i.e.the number of fruit and their position along the inflorescence).We analyzed these data using generalized linear mixed-effects models(GLMMs)and calculated selection gradients.Important Findings We found that all the investigated inflorescence traits influenced female reproductive success.In particular,our GLMMs showed that'average flower distance'was the best predictor for shaping reproductive success patterns.We detected significant positive selection on the investigated inflorescence traits,but these selective trends were strictly linked to both the height of the surrounding vegetation and the population density,suggesting a significant influence of local environmental context in shaping selective patterns.Female reproductive success was not linked to the position of flowers along the inflorescence,suggesting that pollinators visit flowers randomly along the inflorescence without a detectable preference for a specific part.This study highlights the importance of inflorescence traits in shaping female reproductive success of multiflowered deceptive orchids,and confirms a primary role for the environmental context in modifying pollinator-mediated selection patterns.