Visual attraction cues associated with tachinid pollination: insights from colour variation in Succisella microcephala (Caprifoliaceae)

by João Farm

inhão & Sílvia Castro

Succisella microcephala: flower & developing fruit

Plants often evolve flowers with particular shapes, colours, or scents that match the preferences of the animals that pollinate them. These recurring patterns are known as pollination syndromes. However, applying this idea to fly-pollinated plants is challenging because different groups of flies have markedly different behaviours and preferences. This study examines the plant Succisella microcephala (from the teasel family), which initially appears to be a generalist capable of attracting many kinds of insects. Yet preliminary field observations suggest it may be pollinated predominantly by tachinids, a group of parasitic flies. Some populations bear flowers with darker colours and stronger contrast between floral parts, and these darker flowers were visited mainly by tachinids—especially in high-elevation sites where these flies were most abundant. These sites also supported a grass species that hosts the moth larvae on which many tachinid species depend, helping to explain their local prevalence. The emerging pattern suggests that darker floral colours may enhance attraction for tachinids. Similar traits in other European plants visited by tachinids (e.g. the burnt-tipped orchid) support this hypothesis. Additionally, the plant’s developing fruiting structures are dark red and visually resemble the dark, globular floral elements found in other species associated with tachinid pollination. This raises the possibility that these fruiting structures may also contribute to attracting pollinators, not only the flowers. Overall, the observations indicate that dark-coloured floral or fruiting structures may characterise a previously undescribed pollination syndrome linked to tachinid flies. Succisella microcephala therefore offers a promising system for exploring how plants evolve traits shaped by the sensory ecology and preferences of specific pollinating fly groups. 

Read the scientific article in JPE. 

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