Research project NoSexPoorPollen: The evolutionary degeneration of pollen in asexual dandelions

The most likely explanation is that pollen production is an "evolutionary remnant", a leftover from the time when these dandelions were still sexual. As they became clonal, the pollen became obsolete, and the lack of natural selection on producing healthy pollen grains has thereby disappeared. Over time, pollen should therefore devolve (evolve to degenerate) in asexual dandelions, as it costs a lot of energy and nutrients to produce without any benefit to the plant. Indeed, some asexual dandelions have already completely lost their ability to produce pollen, at an estimated frequency of 1-5%. 

How do asexual dandelions lose their ability to produce pollen? Are the ones still producing pollen in a transitional stage? And what are the consequences for the feeding insects? Is pollen from asexual dandelions of poorer quality? These are the questions we try to answer in the project NoSexPoorPollen. By comparing asexual dandelions (from Northern Europe) with dandelions that still require sex to reproduce (from Southern Europe), we measure the drop in pollen quantity and quality when dandelions transition to asexual reproduction. Dedicated technology, such as Amphasys flow cytometry, will be used to count the exact number of pollen grains produced by plants and how many of them are viable (i.e. suitable for fertilisation). With microscopy, we investigate whether the stickiness of the pollen grains decreases: dandelion pollen has long spikes on the outside to stick to the insect pollinator like velcro.

We expose the genetic mechanism behind pollen production: which genes are expressed in sexual plants when healthy and abundant pollen is produced, and which genes are switched off to reduce the production of pollen? We also investigate the plants that have lost pollen production altogether and look at the sequence composition of the genes behind pollen and anther development. What are the mutations causing pollen production to stop?

NoSexPoorPollen investigates the evolutionary fate of sexual traits in asexual plants. Its aim is to understand the fundamental evolutionary mechanisms behind asexual reproduction and pollen production. But more than that, it is also about the ecological consequences of asexuality. Pollen is not just sperm that is important for plant reproduction, it is also essential food for insects. By understanding how pollen degrades in important pollen producers such as dandelions, we can make predictions for the biodiversity depending on it.