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

Abstract

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.

The effect of inflorescence display size and flower position on pollination success in two deceptive and one rewarding orchid

“…The effects of inflorescence display on reproductive success is often found to be under pollinator‐mediated selection (Trunschke et al, 2017). In the deceptive orchids Cypripedium acaule , Dactylorhiza lapponica and Anacamptis laxiflora the strength of pollinator‐mediated selection on an inflorescence depended on the surrounding vegetation (O'Connell & Johnston, 1998; Sletvold et al, 2010; Scopece et al., 2021). Inflorescence traits and visual display size traits are known to be important for long‐distance attraction of pollinators (Boff et al, 2021).…”

“…The influence of flower position on natural capsule production has been studied in a variety of deceptive orchid species, and heterogeneity of results in these patterns have been observed. The probability of capsule formation in orchids has often been found to be related to flower position within an inflorescence, related to competition among developing fruits for resources, differential floral attraction of pollinators, quantity and/or quality of pollen received, and surrounding vegetation (Brundrett, 2019; Baguette et al, 2020; Scopece et al., 2021). In plants whose flowers open sequentially, pollen from flowers at different positions may have different opportunities to sire offspring (Brunet & Charlesworth, 1995; Vallius, 2000).…”

What are the drivers of female success in food‐deceptive orchids?

“…The studies of relationships between the morphological and/or phenological traits and female and male success in food-deceptive orchids are well-documented (Mattila & Kuitunen, 2000;Sletvold & Ågren, 2014;Sletvold et al, 2010;Trunschke et al, 2017;Vallius et al, 2007). However, these studies encompass only single-year data sets and reveal associations such as the impact of floral display on fruit set in Anacamptis longicornu (Capó et al, 2019), the density of co-flowering rewarding plants in Orchis militaris (Henneresse et al, 2017), floral display in Caladenia valida and Tolumnia variegata (Tremblay et al, 2010), inflorescence traits in the environmental context in Anacamptis laxiflora (Scopece et al, 2021), as well as flower brightness (Sletvold et al, 2016), flower color (Trunschke et al, 2021), and flowering time (Sabat & Ackerman, 1996). The long-term study showed only Scopece et al (2017), who revealed weak directional selection in nine morphological traits in Orchis mascula and O. pauciflora.…”

Response to Midgley: the costs of reproduction cannot differ between the sexes

“…Yet, we need further evidence to support the argument. Previous studies have shown that differences in primary and physiological traits between the sexes strongly depend on the plant species and their environmental conditions, and that they may arise from a number of reasons, such as differences in trait optima of each sex along a series of resource gradients, sexual selection and sex-specific responses to sexual selection (Barrett and Josh 2013;Geber et al 1999;Juvany and Munné-Bosch 2016;Kohorn et al 1994;Rabska et al 2021;Retuerto et al 2018;Scopece et al 2021;Wang et al 2021).…”