Nectar Chemistry or Flower Morphology—What Is More Important for the Reproductive Success of Generalist Orchid Epipactis palustris in Natural and Anthropogenic Populations?

Abstract

The aim of this study was to determine the level of reproductive success (RS) in natural and anthropogenic populations of generalist orchid Epipactis palustris and its dependence on flower structure and nectar composition, i.e., amino acids and sugars. We found that both pollinaria removal and female reproductive success were high and similar in all populations, despite differences in flower traits and nectar chemistry. Flower structures were weakly correlated with parameters of RS. Nectar traits were more important in shaping RS; although, we noted differentiated selection on nectar components in distinct populations. Individuals in natural populations produced nectar with a larger amount of sugars and amino acids. The sucrose to (fructose and glucose) ratio in natural populations was close to 1, while in anthropogenic ones, a clear domination of fructose and glucose was noted. Our results indicate that the flower traits and nectar composition of E. palustris reflect its generalist character and meet the requirements of a wide range of pollinators, differing according to body sizes, mouth apparatus, and dietary needs. Simultaneously, differentiation of nectar chemistry suggests a variation of pollinator assemblages in particular populations or domination of their some groups. To our knowledge, a comparison of nectar chemistry between natural and anthropogenic populations of orchids is reported for the first time in this paper.

In Which Way Do the Flower Properties of the Specialist Orchid Goodyera repens Meet the Requirements of Its Generalist Pollinators?

“…This may indicate that G. repens pollinators need a large amount of AAs, which contrasts with the results of Stabler et al [99]. The most abundant AA in G. repens nectar was Asp, one of the most abundant AAs in the nectar of other orchids [59][60][61][62]. Asp influences pollinator behavior, and is known as a general repellent [101].…”

“…The most simple explanation could be the suggestion of Nicolson and Thornburg [38] that nectar sugar composition is determined more by phylogeny than by pollinator preferences. This explanation may explain the low nectar concentration in other orchids [59][60][61][62]. Another possible explanation could be that bumblebees mainly rely on other plants as their main food, with this orchid being a minor component of their diet, especially when its populations are small.…”

“…The two other AAs with relatively high participation were Gln and Gly. Gln is one of the most common AAs in E. palustris nectar [60]. Gln is needed for energetically exhaustive flights [101], and Gly provokes a feeding response in honeybees [102].…”

“…Studies have reported variation in flower traits in the geographic range of species, which is the consequence of adaptation to local pollinators, mainly the most effective [20,[56][57][58][59][60][61][62]. Pollinator-mediated selection of flower traits is one of the main evolutionary mechanisms shaping plant-pollinator interactions [13,16,63,64].…”

Orchid Biochemistry 2.0

“…The authors found that carbon and the ratio of carbon to nitrogen might be the most important factor affecting flower structure and nectar composition. Furthermore, Brzosko et al investigated the impact of the flower structure and nectar chemistry in Epipactis palustris (L.) Crantz, another generalist orchid that is pollinated by over 100 species of pollinators, on reproductive success [ 3 ]. The authors concluded that there are significant differences in nectar chemical properties between natural and anthropogenic populations of E. palustris and pointed out that future study is needed to clarify the most critical factor between pollinator differentiation and soil characteristics.…”