Environmental morphing enables informed dispersal of the dandelion diaspore
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eLife assessment
This boundary-crossing work on dandelion diaspore flight is an excellent demonstration of how to address fundamental questions about wind dispersal of plant seeds from biophysical and ecological perspectives. Both wind-tunnel experiments and models provide compelling evidence that the aerodynamics of dandelion diaspores change with the environment. Addition of local climate data enables the authors to make a convincing case about how the biophysical properties can scale up to affect dispersal across the landscape under different environmental conditions. In addition to the strong data, this is a clear, accessible, and very enjoyable read.
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- Evaluated articles (eLife)
- Plant Biology (eLife)
Abstract
Animal migration is highly sensitised to environmental cues, but plant dispersal is considered largely passive. The common dandelion, Taraxacum officinale , bears an intricate haired pappus facilitating flight. The pappus enables the formation of a separated vortex ring during flight; however, the pappus structure is not static but reversibly changes shape by closing in response to moisture. We hypothesised that this leads to changed dispersal properties in response to environmental conditions. Using wind tunnel experiments for flow visualisation, particle image velocimetry, and flight tests, we characterised the fluid mechanics effects of the pappus morphing. We also modelled dispersal to understand the impact of pappus morphing on diaspore distribution. Pappus morphing dramatically alters the fluid mechanics of diaspore flight. We found that when the pappus closes in moist conditions, the drag coefficient decreases and thus the falling velocity is greatly increased. Detachment of diaspores from the parent plant also substantially decreases. The change in detachment when the pappus closes increases dispersal distances by reducing diaspore release when wind speeds are low. We propose that moisture-dependent pappus-morphing is a form of informed dispersal allowing rapid responses to changing conditions.
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Author Response
Reviewer #1 (Public Review):
The idea that a passive living being can improve the wind dispersal of its seeds by passively changing their drag is enticing. The manuscript shows that high wind events in Scotland are inversely correlated with the ambient humidity. The dandelion pappus morphs with the ambient humidity, being more open in dry conditions, which is associated with stronger wind events. This passive morphing of the shape of the pappi thus leads to a dispersal of the seeds further away from their origin.
The analysis and discussion in the paper is focused on "distance", i.e., how far the pappus will fly. Could the notion of time be relevant too? In wet conditions, perhaps it's better for a seed to hit the ground quickly and start germinating, whereas if its dry, staying up in the air for longer to travel …
Author Response
Reviewer #1 (Public Review):
The idea that a passive living being can improve the wind dispersal of its seeds by passively changing their drag is enticing. The manuscript shows that high wind events in Scotland are inversely correlated with the ambient humidity. The dandelion pappus morphs with the ambient humidity, being more open in dry conditions, which is associated with stronger wind events. This passive morphing of the shape of the pappi thus leads to a dispersal of the seeds further away from their origin.
The analysis and discussion in the paper is focused on "distance", i.e., how far the pappus will fly. Could the notion of time be relevant too? In wet conditions, perhaps it's better for a seed to hit the ground quickly and start germinating, whereas if its dry, staying up in the air for longer to travel farther might be a better strategy.
This is an interesting point; however, we think that flight time is likely to be less relevant to the dispersal outcomes. This is because seeds mostly remain attached to the parent plant in wet conditions so will not fly at all and therefore will not begin germination. When they do disperse, flight time will generally be only a few seconds for the majority of seeds whether they are wet or dry, and the timescale of wet weather is generally much longer (typically hours).
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eLife assessment
This boundary-crossing work on dandelion diaspore flight is an excellent demonstration of how to address fundamental questions about wind dispersal of plant seeds from biophysical and ecological perspectives. Both wind-tunnel experiments and models provide compelling evidence that the aerodynamics of dandelion diaspores change with the environment. Addition of local climate data enables the authors to make a convincing case about how the biophysical properties can scale up to affect dispersal across the landscape under different environmental conditions. In addition to the strong data, this is a clear, accessible, and very enjoyable read.
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Reviewer #1 (Public Review):
The idea that a passive living being can improve the wind dispersal of its seeds by passively changing their drag is enticing. The manuscript shows that high wind events in Scotland are inversely correlated with the ambient humidity. The dandelion pappus morphs with the ambient humidity, being more open in dry conditions, which is associated with stronger wind events. This passive morphing of the shape of the pappi thus leads to a dispersal of the seeds further away from their origin.
The analysis and discussion in the paper is focused on "distance", i.e., how far the pappus will fly. Could the notion of time be relevant too? In wet conditions, perhaps it's better for a seed to hit the ground quickly and start germinating, whereas if its dry, staying up in the air for longer to travel farther might be a …
Reviewer #1 (Public Review):
The idea that a passive living being can improve the wind dispersal of its seeds by passively changing their drag is enticing. The manuscript shows that high wind events in Scotland are inversely correlated with the ambient humidity. The dandelion pappus morphs with the ambient humidity, being more open in dry conditions, which is associated with stronger wind events. This passive morphing of the shape of the pappi thus leads to a dispersal of the seeds further away from their origin.
The analysis and discussion in the paper is focused on "distance", i.e., how far the pappus will fly. Could the notion of time be relevant too? In wet conditions, perhaps it's better for a seed to hit the ground quickly and start germinating, whereas if its dry, staying up in the air for longer to travel farther might be a better strategy.
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Reviewer #2 (Public Review):
I will first state that I am an ecologist that studies wind dispersal, and so my expertise lies in evaluating the determination of their results, the dispersal model, and the ecological significance - I cannot evaluate the PIV methods, although their results seem very reasonable based on other work! I believe this is a very strong paper that will have a lot of interest. In my opinion, it is the perfect demonstration of how to understand wind dispersal from a fundamental and ecological perspective. They first explore the aerodynamics of dandelion diaspores and how they change with the environment. Then they use this information to scale up to how this might affect dispersal across the landscape under different environmental conditions. I think the experiments they have conducted and the models they have …
Reviewer #2 (Public Review):
I will first state that I am an ecologist that studies wind dispersal, and so my expertise lies in evaluating the determination of their results, the dispersal model, and the ecological significance - I cannot evaluate the PIV methods, although their results seem very reasonable based on other work! I believe this is a very strong paper that will have a lot of interest. In my opinion, it is the perfect demonstration of how to understand wind dispersal from a fundamental and ecological perspective. They first explore the aerodynamics of dandelion diaspores and how they change with the environment. Then they use this information to scale up to how this might affect dispersal across the landscape under different environmental conditions. I think the experiments they have conducted and the models they have included are excellent! I also really enjoyed that this work is the culmination of their body of work, where they have taken a step-by-step approach to convincing readers how dandelion diaspores disperse under different humidity conditions (see Seale et al. 2020 and 2022).
The paper is very well written. The introduction lays out a very clear case as to why the environment should (and ultimately does) influence wind dispersal, and all of the relevant references are cited. It was nice to see them all in one place and is a great summary of the literature for those who are new to the field.
The authors also claim that the environment can have an impact on dandelion dispersal by altering the shape of the diaspore (the pappus closes). This influences the terminal velocity and drag coefficient, and the authors used the appropriate PIV tests to determine that this is the case. They then go on to show that while wet conditions can decrease the terminal velocity which ultimately decreases dispersal distance, under wet/stormy conditions there are often increased wind speeds and this can actually increase dispersal because of increased wind speed. However this last point is a bit confusing to me based on the way the data is laid out.
In all, I really enjoyed this paper! There is a lot to learn from this, and I look forward to reading it in print. I would encourage the authors to make a few updates to their text to make their conclusions crystal clear for readers!
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