Pollination adaptations of group-by-group stamen movement in a meadow plant with temporal floral closure

Abstract

Floral sexual organ (stamen and pistil) movements are selective adaptations that have different functions in male-female reproduction and the evolution of flowering plants. However, the significance of stamen movements in the spatial–temporal function and separation of male and female organs has not been experimentally determined in species exhibiting floral temporal closure. The current study investigated the role of slow stamen (group-by-group) movement in male-female sexual function, and the effect of stamen movement on pollen removal, male-male and male-female interference, and mating patterns of Geranium pratense , a plant with temporal floral closure. This species uses stamen group-by-group movement and therefore anther-stigma spatial–temporal separation. Spatial separation (two whorls of stamen and pistil length) was shown to be stronger than temporal separation. We found that stamen movements to the center of the flower increase pollen removal, and the most common pollinators visited more frequently and for longer durations during the male floral stage than during the female floral stage. Petal movements increased both self-pollen deposition rate and sexual interference in G. pratense . The fruit and seed set of naturally and outcrossed pollinated flowers were more prolific than those of self-pollinated flowers. Group-by-group stamen movement, dehiscence of stamens, pistil movement, and male-female spatial–temporal functional separation of G. pratense before floral temporal closure may prevent male-female and stamen-stamen interference and pollen discounting, and may increase pollen removal and cross-pollination.

Effect of temporal changes in stamen position on reproductive success in flowers with many stamens: Manipulations of stamen position

“…In Geranium pratense, the number of self-pollen grains deposited on the stigma increased when the stamens were fixed at the top of the stigma (Abdusalam et al, 2021). Similarly, self-pollen might have been deposited on the stigma of A. flaccida when stamens were fixed in the premovement position and during early flowering with naturally moving stamens.…”

“…In hermaphroditic flowers, the positions of male and female organs strongly affect male and female reproductive success by mediating effective pollinator contacts with anthers and stigmas. The positions of these organs also affect male–male and female–male interference (Barrett, 2002; Ren and Bu, 2014; Wang et al, 2017; Abdusalam et al, 2021). Male–male interference, i.e., interference among stamens within the same flower, results in reduction of pollen delivery to other flowers (Ren and Bu, 2014; Wang et al, 2017; Abdusalam et al, 2021).…”

“…The positions of these organs also affect male–male and female–male interference (Barrett, 2002; Ren and Bu, 2014; Wang et al, 2017; Abdusalam et al, 2021). Male–male interference, i.e., interference among stamens within the same flower, results in reduction of pollen delivery to other flowers (Ren and Bu, 2014; Wang et al, 2017; Abdusalam et al, 2021). Female–male interference, i.e., interference between stigmas and stamens within the same flower, results in increased self‐fertilization in self‐compatible species and pollen loss in self‐incompatible species (Bertin and Newman, 1993; Barrett, 2002).…”

“…Stamen movement, a phenomenon where stamens of flowers change position as the flower ages (Ren, 2010), may function to reduce male–male and female–male interference, and thus enhance reproductive success. In several species, male and female reproductive success is enhanced simultaneously by stamen movement (Wang et al, 2017; Xiao et al, 2017; Abdusalam et al, 2021). In Parnassia wightiana , stamens move one by one to the floral center for anther dehiscence so that only a single stamen is close to the stigmas at one time.…”

“…The flowers in previously examined species have relatively few stamens per flower species (e.g., five stamens in Parnassia wightiana [Xiao et al, 2017]; 10 stamens in Lychnis cognata [Wang et al, 2017] and Geranium pratense [Abdusalam et al, 2021]). The effects of stamen movement on male–male and female–male interference in flowers with higher numbers of stamens, however, have not been examined.…”