Fritillaria – a feast for bumblebees

Fritillaria – a feast for bumblebees

A story about pollination biology

Botanist Katarzyna Roguz, researcher at the University of Warsaw Botanic Garden has studied Fritillaria meleagris since she started doing research during her Bachelor thesis and through her Masters and PhD theses at the University of Warsaw and her recent postdoc at Tel Aviv University, Israel. She has dedicated her research to the pollination biology of Fritillaria meleagris, F. persica and recently F. imperialis.

I had the pleasure to have Katarzyna as my podcast guest and we talked about

  •  Why F. meleagris is so important for bumblebees
  • How pollination biology studies are carried out
  • Why plants may adjust self-(in)compatibility depending on where they grow
  • That even birds can be important for Fritillaria pollination
  • Why planted Fritillaria imperialis in the city centre of Warsaw is an interesting study object for pollination biology

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Why studying Fritillaria meleagris and pollination biology?

Living in Poland where there is a natural population of Fritillaria meleagris gave Katarzyna the ideal conditions for her studies. Also, both the white and the purple version (colourmorph) of F. meleagris that we mentioned in last week’s podcast, exist in this population. This allowed the young botanist to explore whether the chequered pattern of the purple colourmorph was at all recognized by pollinates (which indeed she found indeed is). In Poland the population of F. meleagris is today declining due to the decrease of its habitats in meadows that are converted to farmland or a too frequent mowing. Last but not least, Fritillaria meleagris is one of the earliest plants to flower in the spring and highly rewarding in nectar to bumblebee queens, which depend on such plants. This makes this species both from a biological and from an ecological point an interesting plant to study.

One questions that Katarzyna has addressed in her research are for example what kind of food reward F. meleagris offers to its visiting pollinators. In order to find answers, she analysis using cameras what kind of pollinators arrive at the flower and how the nectar of the flower is composed (of amino acids and sugars). Other investigations she has done concern how polinators behave inside the flowers, if all visiting insects help pollination or whether there are cheaters as well as whether flowers get pollinated by their own pollen or (cross-)pollinated with pollen form other individuals. 

The shape and the angle of the flower for example determine who can visit it. Bumblebees are especially talented to fly into the flower, whereas other insects first land on the tepals on the outside of the flower and then crawl into it. Beyond bumblebees, also honey and solitary bees are pollinators of F. meleagris. Certain flies however are cheaters, they crawl into the flowers and drink the nectar but never get into contact with the reproductive organs to transfer pollen to the female reproductive organs.

Reproductive organs in the Fritillaria meleagris flower

Concerning the reproductive organs, Katarzyna gave us a tour tour through the flowers. F. meleagris is a monocotyledon plant, that typically have tepals (the chequered purple “flower leaves”). In the picture above you can distinguish green grooves at the base of each tepal. These are are the areas where the nectar is available to pollinators. Further into the centre of the flower we find six stamens (male reproductive part). At the end of each stamen there are two anthers filled with yellow pollen grains. Have you ever wondered why pollen of many plants is yellow? You may have noticed it in the spring on your window(sill)s or on your car. Yellow is a preferential colour for pollinators. So it’s a smart choice of the flower to make its pollen look yellow. In the centre of the flower we find the style with 2-4 lobes of stigmata where the pollen will land. In F. meleagris the male and female parts are closely together in space and they mature pretty much at the same time.

To self or not to self?

Self-compatibility (when the pollen of an individual flower can pollinate the stigma in that same flower) is not uncommon in F. meleagris. Yet it can vary in a population. Generally cross-pollination, so pollination with pollen from other flower individuals of the same species will lead to better germination rate of resulting seeds and overall better plant health as the plant outcrosses. Yet it depends on aids such as wind or pollinators. So in other cases, where these encounters would be too rare to have a good chance, self-compatibility may be preferred.

Katarzyna shared an example that illustrates this very well. Imagine a large Fritillaria population on a meadow. At the centre of that population, the chance for insects to transport pollen from one flower to the next will be high, whereas at the border of the population the chances are decreasing. So at the centre we are more likely to find self-incompatible flowers whereas at the border chances are that we will find self-compatible flowers. Self-(in)compatibility is an extremely smart molecular mechanisms. Pollen carry a “key” at the papilla cells on the stigma carry the “lock”. In self-incompatible plants, when the key and the lock match, the pollen will be rejected. Pollen from other plants that doesn’t carry that key will be accepted and can grow pollentubes to fertilize the ovules at the base of the style, which will eventually lead to seed formation.

Hand pollination of a F. meleagris flower using a brush. Pollen is transfered onto the stigma.

Let’s take a closer look!

While preparing for the interview with Katarzyna, I also hand-pollinated the Fritillaria meleagris plant I had on my porch and took the stigma under the microscope. I used this stain for the pollen that would indicate whether the pollen was aborted or not, meaning whether it is viable or not. In the images below you can see the result of that staining. Pollen that looks like a blue-green hollow shell was aborted, whereas pollen that stained magenta was not aborted. Isnt’ it fantastic how some chemicals that we stain the plants with can give us a closer glimpse into what is happening in biology? Katarzyna also mentioned in the interview that she has spend hours and hours counting pollen grains on the stigma of F. meleagris plants. And they are tiny! Can you imagine spending hours in front of a microscope counting thousands of pollengrains? Or maybe you have already done that yourself?

Studying other Fritillaria species

On her research journey Katarzyna Roguz has not only studied Fritillaria meleagris. During her postdoc in the Sapir lab at Tel Aviv University in Israel in 2020, she investigated pollination biology of Fritillaria persica – the plant on the podcast cover picture above. F. persica is flowering in the desert, probably triggered by temperature and rain, but that is still somewhat of a mystery. Katarzyna mentioned that from a population of about 1 million plants only 10 specimen flowered this year for yet unknown reasons. Last year, when she was doing her research in Israel, the plant set almost no seeds despite a rather wet season that should have been beneficial for reproduction. As she evoked during the interview, the more we learn about plants, the more we realize how many unexplored phenomena there are. The delight of being a researcher!

Since 2021, Katarzyna is involved in a new project. As the municipality of Warsaw decided to plant the city centre with Fritillaria imperialis, Katarzyna saw her chance to study pollination biology in a city context. The flowers grow in different quarters, shielded from each other by buildings. Will pollinators despite the barriers of buildings transport pollen between the flowers? That will her research show in the future as she labels pollen using quantum dots and looks out for their distribution at distant sites on the stigma of other F. imperialis individuals. We wish Katarzyna the best of luck with this exciting project!

Finally Katarzyna shared some resources with us. Especially the Fritillaria Icones webpage, that Laurence Hill has build up is a great resources of amazing and detailed photographs of many different Fritillaria species. Katarzyna used one of these photographs for the beautiful tattoo of a F. meleagris plant on her forearm as you can see on the picture below. If you needed another proof for her dedication to her research and her love for Fritillaria, well, I think you have just found it!

Laurence Hill will be my guest in one of the next Flora and Friends podcast episodes to talk about his photography and the Fritillaria Icones resources. Make sure to not miss it by subscribing to our newsletter or to our podcast on the our various channels such as  Youtube, Spotify, Apple Podcast, Google Podcast and Deezer.

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