Spatiotemporal Variations in Seed Set and Pollen Limitation in Populations of the Rare Generalist Species Polemonium caeruleum in Poland

Abstract

A vast majority of angiosperms are pollinated by animals, and a decline in the number and diversity of insects often affects plant reproduction through pollen limitation. This phenomenon may be particularly severe in rare plant species, whose populations are shrinking. Here, we examined the variability in factors shaping reproductive success and pollen limitation in red-listed Polemonium caeruleum L. During a 5-year study in several populations of P. caeruleum (7–15, depending on year), we assessed the degree of pollen limitation based on differences in seed set between open-pollinated (control) and hand-pollinated flowers. We analysed the effects of flower visitors, population size, and meteorological data on plant reproductive success and pollen limitation. Our study showed that pollen limitation rarely affected P. caeruleum populations, and was present mainly in small populations. Pollen limitation index was negatively affected by the size of population, visitation frequency of all insects, and when considering the visitation frequency of individual groups, also by honeybee visits. Seed production in control treatment was positively influenced by the population size, average monthly precipitation in June and visits of hoverflies, while visits of honeybees, average monthly temperature in September, and average monthly precipitation in August influenced seed production negatively. As generalist plant P. caeruleum can be pollinated by diverse insect groups, however, in small populations their main visitors, the honeybees and bumblebees, may be less attracted, eventually leading to the disappearance of these populations. In pollination of P. caeruleum managed honeybees may play a dual role: while they are the most frequent and efficient flower visitors, their presence decreases seed set in open-pollinated flowers, which is most probably related to efficient pollen collection by these insects.

As prey and pollinators, insects increase reproduction and allow for outcrossing in the carnivorous plant Dionaea muscipula

“…Variation in pollen limitation within species is not unusual (Burd, 1994; Ashman et al, 2004; Burd et al, 2009), and can vary across years and populations, depending on environmental factors, presence of co‐flowering species, fluctuations in pollinator abundance, plant population size, and other factors (Knight et al, 2005). For example, significant interannual variation in pollen limitation was observed in the rare plant Polemonium caeruleum L. (Polemoniaceae), possibly in part due to variation in pollinator visitation frequency and temperature (Ryniewicz et al, 2021). Our results compared to prior studies suggest that there is also interannual or geographic variation in pollen limitation in D. muscipula .…”

Fruit set is moderately dependent on insect pollinators in strawberry and is limited by the availability of pollen under natural open conditions

“…The fertility of flowers that were exposed to supplementary insects was compared with that under natural open pollination. Pollen limitation (PL) was calculated as PL = (P s -P o )/P Max , where P s is the yield or fruit weight after supplementary pollination, P o is the yield or fruit weight from the control treatment (open pollination) and P Max is the larger of the two values (Baskin & Baskin, 2018;Ryniewicz et al, 2022). Twosided t-tests were used determine if PL was significantly (P < 0.05) lower or higher than zero.…”

“…Pollen limitation (PL) was calculated as PL = (P s -P o )/P Max , where P s is the number of seeds, etc. from the supplementary pollination treatment, P o is the number of seeds from the control treatment (open pollination) and P Max is the larger of the two values (Baskin & Baskin, 2018;Ryniewicz et al, 2022). Data are from the various authors shown in Table S5.…”

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

“…Pollinator-mediated selection of flower traits is one of the main evolutionary mechanisms shaping plant-pollinator interactions [13,16,63,64]. The spatial variation of the relationships between both groups of organisms translates into differentiation of the reproductive success of plants [5,8,19,61,65].…”