Getting hooked? Testing the function of anther spurs in Vaccinium myrtillus

Anther spurs in blueberry flowers

by Lisette van Kolfschoten & Mario Vallejo-Marín

Flowers come in an incredible variety of shapes, many of which have evolved through their close relationships with pollinators. In our study, we looked at a small flower part called an anther spur, which is a tiny extension attached to the pollen-bearing anther, found in some plants of the heath family, like the European blueberry (Vaccinium myrtillus). In this species, the pollinators can perform a special type of pollination called buzz pollination, where bees that can vibrate their bodies at the right frequency shake the pollen loose.

We wanted to find out what role the anther spur plays in this process. Does it influence how much pollen is released, or might it be involved in pollen release when bees access nectar? To test this, we compared pollen release in flowers with their spurs intact to those where the spurs were carefully removed. We performed two types of experiments, one where bumblebees were visiting the flowers, and one with a mechanical shaker, where we mimicked bee vibrations.

The results were interesting: flowers without a spur released more pollen, and this was most clear in the shaker experiment. This suggests that the spur potentially acts as a regulator, reducing the amount of pollen that is offered to each visitor. Such control can be beneficial, especially in environments where pollinators are scarce. By spreading pollen release across multiple visits, the plant increases its chances of successful reproduction.

We also noticed that bee behaviour mattered: bees that buzzed released more pollen than those that did not buzz. This shows a fascinating back-and-forth between plant structure and pollinator behaviour. In short, the anther spur could help the flower to fine-tune its relationship with pollinators, balancing the trade-off between giving away enough pollen for reproduction and keeping some in reserve for future visits.

Read the scientific publication in JPE 

 

Managed honeybees affect the foraging behaviour of bumblebees in Geranium sylvaticum

Bumble bee visiting wood cranesbill

by Soininen et al.

Plants and their insect pollinators have coevolved. Insects respond to plant cues such as flower size and colour. Pollinators compete for pollen and nectar, but behavioural and morphological differences between pollinators allow for coexistence of different pollinator species. Honeybee (Apis mellifera) is an introduced pollinator species in northern Europe. Honeybees and the native pollinators visit the same flowers and may compete for resources instead of sharing. Therefore, honeybees may affect native pollinator species negatively.

Diverse plant communities support many pollinator species. Diversity of a plant community consists of differences between species and within species. Within plant species genetic diversity could promote more diverse pollinator community.

In this study we investigated the role of genetic diversity within a single plant species, wood cranesbill (Geranium sylvaticum), on pollinator behaviour. We did this by measuring pollinator visitation rates on wood cranesbill in an experimental field. In the field we had planted different genotypes of wood cranesbills. We tested the effect of honeybees on native bumblebee visitation rates. We compared visitation rates in the presence of a honeybee hive to when the beehive was removed from the field. We show that competition with honeybees reduced visitation rates by bumblebees, but not by other native pollinator groups. Bumblebees preferred some wood cranesbills genotypes over others in the absence of honeybees, which they did not prefer in their presence. Honeybees visited the wood cranesbills flowers readily and did not prefer any particular genotype. Our study shows that within plant species genetic diversity affects bumblebee behaviour. Furthermore, honeybees affected bumblebee behaviour, raising concern of the effects of beekeeping on native pollinators.

Read the scientific paper in JPE. 

 

Greater number of pollen donors improves female reproductive success but not progeny vigour in Allium stellatum

By Yu & Muchhala

Animal pollinators are critical for the reproduction of most flowering plants. Because different animals may deposit more or less pollen on a flower based on their body size and how often they visit flowers, it is important to understand how these differences can affect plant reproduction. One important aspect of pollination is whether a pollinator deposits pollen from one or more fathers, because having more fathers to choose from can increase the likelihood of having more fit offspring. 

In our study, we test how the number of fathers donating pollen affects offspring growth rates by pollinating prairie onion flowers with pollen mixtures with either one, two, or three fathers. We found that pollen mixtures with a greater number of fathers led to a greater number of seeds that germinated into seedlings but also led to seedlings that grew more slowly. This is potentially explained with a trade-off between quality of seedling vs. number of seedlings. 

These effects indicate that the composition of pollen mixtures deposited by pollinators can have significant effects on plant populations and that understanding differences in animal pollination will help understand plant population patterns.

Read the scientific publication in JPE.