Matthew Gilbert: Flowers of a South African succulent plant predict tomorrow’s weather, synchronizing flower opening with pollinator activity

In this new post Matthew Gilbert—Associate Professor at University of California, Davis, CA, USA—presents his recently published paper “Flowers of a South African succulent plant predict tomorrow’s weather, synchronizing flower opening with pollinator activity“. He discusses the connection between phenology and weather, shows how inspiration can come from anywhere, and highlights the importance of observing nature to find interesting research questions.

About the paper

It’s March 2020, I’m at home under COVID lockdown and frustrated that I can’t do field work. So, each morning, I stare out my kitchen window looking at a large population of bulbine—a succulent plant with orange flowers that bees love. Being at home all day meant that I could watch these plants for a few minutes each day, and I started to see a pattern—some days there were a thousand flowers open, but the next day none! Initially, it seemed that cool, cloudy days led to flowers staying closed, but a simple experiment with DIY shades indicated that the amount of sunlight didn’t play a role (the flowers will open in very dark conditions). What’s more, the flowers would close the day after the cool, cloudy conditions! It was almost as if the flowers were using today’s weather to predict whether to open tomorrow.

Bulbine flowers start as tiny buds (top of inflorescence) and progress through developmental stages until they are ready to open. Each growth stage is temperature responsive, allowing buds to open the day after favorable weather (good weather tends follow good weather) (credit: Matthew Gilbert)

Flowers predicting the weather isn’t as absurd as it sounds. Firstly, many plants require a pollinator to cross-pollinate between flowers on different plants in order to set seed; however, insect pollinators are mostly active when temperatures are warm. Secondly, in California and other winter rainfall locations (e.g. Western Cape of South Africa), weather is actually pretty regular; if today is good for pollinators, then the chances are good that tomorrow will be good too. Therefore, not only is weather predictable, but it is important that flowers open under weather conditions when pollinators are active. Therefore, I asked myself if bulbine had evolved to predict the weather so that it could match its flower opening with pollinator activity.

Over the next two years of lockdowns and remote work, I was able to observe flowering and pollinator activity on 448 days (I didn’t have to go far, as this was outside my kitchen window). The data clearly showed that flowers will open tomorrow based upon favorable weather today. After the lockdown, I found that I could observe many populations of bulbine as I rode my bike home from work. These data confirmed patterns I found in the garden. Finally, my family lives in South Africa—where bulbine is from—and they were able to make measurements there, also confirming this pattern (thanks Mom!).

About the research

But how do the flowers predict the weather? I made a series of measurements in the garden, and a few in the lab, and it seems that bulbine flowers take at least 16 hours to complete their final development. Thus, favorable weather today can trigger the final development, but it would only be at sunrise or later the following day that the flowers would be ready to open. While predicting tomorrows weather may sound like a poor strategy (what if flowers get the prediction wrong?), simulations suggest that it is at least as good a strategy as opening on a day with favorable weather. Predicting the weather and preparing to open has the added bonus of flowers being ready to open at sunrise, maximizing the time when they are open to insect pollinators.

A selection of bulbine pollinators in California: a small solitary bee (top left), a syrphid fly (top right), a carpenter bee (bottom left) and a honey bee (bottom right). The pollinators are attracted to the pollen and the tufts of pollen-mimicking hairs (credit: Matthew Gilbert)

Plants predicting the weather has not had much research focus. Maybe we’ll find more species that predict the weather, particularly in winter-rainfall regions of the world like California or parts of South Africa. Bulbine is a unique species in that it flowers year-round, which enables us to study flower development over an extreme 45 oC range in temperature. Thus, experimental procedures developed on such an easy-to-study species can be applied to more important, but difficult-to-study, species such as crops. A key implication is that plant development is complicated and responses are not linear; this means that predicting how climate change will affect flower pollination won’t be easy.

About the author

Matthew Gilbert

I’m an associate professor of Plant Sciences at UC Davis, so plant environmental responses are what I normally study. But I was surprised that I could do interesting research in my garden, with relatively few scienc-y tools and no dedicated funding. Students often perceive science as something that happens formally, in an expensive lab or exotic location, with lots of jargon; these appear to be large hurdles for many young people joining STEM fields. But science can also be cheap, personal, local and inquisitive—it is really about asking critical questions regarding what you see in the world. Anyone can be observant and inquisitive, and we need to promote this philosophy in schools and universities. I was inspired by reading the natural history books of Bernd Heinrich. These led to me making time each day to observe the nature around me and ask questions, even if it was from my kitchen window. I’d encourage anyone to do the same. Maybe walk to work once a week. Observe what is flowering. What pollinates that flower? What is making that loud dramatic squeak in my front yard? It turns out that it is a tiny male Anna’s hummingbird! There is a world of wonder just outside one’s kitchen window.

Enjoyed the blogpost? Read the research here!

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