Pollination efficiency and reproductive patterns in relation to local plant density, population size, and floral display in the rewardingListera ovata(Orchidaceae)

Abstract

Pollination efficiency and reproductive success vary strongly among populations of most animal-pollinated plant species, depending on their size and local density, whereas individual plants within populations experience varying levels of reproductive output as a result of differences in floral display. Although most orchid species have been shown to be severely pollination limited, few studies have investigated the impact of the above-mentioned factors on pollination success and reproduction, especially in rewarding species. In this study, the impact of population size, local density of flowering plants, and floral display on the rates of pollinia export and fruit production was investigated in 13 natural populations of the rewarding terrestrial orchid Listera ovata. In addition, an emasculation experiment was set up to examine how floral display and local density of flowering plants affected the relative importance of cross-vs. geitonogamous pollination in determining fruit set. In the studied populations, pollination efficiency, pollen removal, and fruit set increased with increasing population size until a threshold value of 30-40 flowering plants was reached, above which pollination efficiency and reproductive output decreased again. On average, plants with large floral displays showed higher proportional pollinia removal and fruit set compared with smaller plants. Fruit production was also significantly and positively related to local plant density, whereas emasculation did not affect the relationship between local plant density and fruit set, suggesting that geitonogamous pollination did not affect the outcome of female function. The results of this study are discussed in the light of the flowering mechanism of the species and its generalized pollination system.

The Ability of Spontaneous Autogamy in Four Orchid Species: Cephalanthera Rubra, Neottia Ovata, Gymnadenia Conopsea, and Platanthera Bifolia

“…However, self-compatibility was reported by Pedersen et al (2009) in the related Cephalanthera exigua (72.7% fruiting from 11 artificially self-pollinated flowers) and by Chung et al (2004) for Cephalanthera longibracteata (without any empirical data). For N. ovata, the high fruiting level noted after induced autogamy confirms the results after experimental pollination in Sweden (100% fruiting from 27 flowers) (Nilsson, 1981) and Belgium (> 97.5% fruiting level, without information on how many flowers were handpollinated) (Brys et al, 2008). Self-compatibility in this species was also reported for populations located in Germany (Müller, 1868) and the Czech Republic (Procházka and Velísek, 1983), also without any quantitative data.…”

“…However, even though the pollinia became compressed in older flowers, Claessens and Kleynen (2011) point out the role of the median anther wall and clinandrium in late autogamy prevention. A lack of spontaneous autogamy was also reported in natural populations of N. ovata (Hildebrand, 1863;Procházka and Velísek, 1983) and after a small bagging experiment (Brys et al, 2008).…”

“…Among the approximately 1800 species of the Orchideae tribe, two relatively common taxa are Gymnadenia conopsea and Platanthera bifolia (Pridgeon et al, 2001). There is a common view that these species are allogamous (Nilsson, 1983a,b;Nazarov, 1995;Gustafsson, 2000;Brys et al, 2008), but some reports have described each of them as being capable of autogamy (Hagerup, 1952;Kugler, 1963;Nilsson, 1981;Meyer et al, 2007;Claessens et al, 2015), which has raised the question of possible spontaneous selfpollination. Furthermore, empirical data describing self-compatibility are scarce for particular species (Nilsson, 1981;Nilsson, 1983a,b;Brys et al, 2008;Boberg and Ågren, 2009).…”

Breeding system variability, pollination biology, and reproductive success of rare Polemonium caeruleum L. in NE Poland

“…Fruits and seeds recorded after induced geitonogamy in another population (ZE) indicate that in this population the self-compatible system was realized. However, the frequency of geitonogamous fruits and mean number of seeds were not very high in comparison to many other self-compatible plants, which exhibit very high levels of fruiting (up to 100%) as a result of induced selfing [33][34][35]. Both the number of geitonogamous fruits and seeds were also significantly lower than those from controlled pollination recorded in the ZE population.…”

Masting promotes individual‐ and population‐level reproduction by increasing pollination efficiency

“…Likewise, even fewer studies have tested its predictions at both the population and individual plant level (but see Brys et al 2008). It is important to analyze the predictions of the pollination efficiency hypothesis at both levels because the ecological effects of masting are best described at the population level (e.g., Kelly 1994, Kelly et al 2001, whereas the evolutionary dynamics must be documented at the level of the individual (Yang et al 2008).…”