Diatoms and ducks make a dispersal dream team

Primary source: Manning F.S. et al. 2021. Potential long distance dispersal of freshwater diatoms adhering to waterfowl plumage. Freshwater Biology 00:1-13. https://doi.org/10.1111/fwb.13706

Dispersal, or the movement of organisms from one place to another, is a key process in establishing and maintaining biodiversity across space and time. With some organisms, the process of dispersal is easy to see. Birds fly through the skies, whales swim across the sea, and dandelion seeds drift with the wind. However, in other organisms, dispersal is more difficult to observe.

Diatoms are a type of unicellular, microscopic algae. They have unique cell walls made of silica, which make them appear to live in glass houses. Diatoms inhabit all sorts of aquatic environments, provide energy and nutrients to their ecosystems, and are good indicators of water quality.

Diatom diversity patterns suggest that they undergo dispersal, but the mechanism of dispersal has been difficult to parse. Diatoms cannot move like animals, and they do not produce seeds or motile spores.

Scientists have long suspected that diatoms hitch a ride with waterfowl, which do have the capacity to easily disperse by flying. Researchers have hypothesized that diatoms ride on the surface of waterfowl in a process called ectozoochory. However, this hypothesis has proved challenging to test. In order to successfully disperse through ectozoochory, a diatom must come into close enough contact with a bird to attach, survive without drying up and remain attached as the bird flies at speeds up to 69 km/hr, detach in its new habitat, and successfully colonize its new home. To figure out if ectozoochory is a viable strategy, scientists needed to come up with an experiment to test these steps. A team of Canadian scientists were up to the task!

First, the team had to acquire diatoms and bird feathers. They chose an easy-to-culture strain of diatoms collected from a pond, and asked duck hunters to send them feathers. The feathers were frozen to remove any diatoms which may have already been present. The scientists then built several contraptions which allowed them to control internal humidity and wind speed, to mimic conditions of that ducks and diatoms would experience during flight.

To address the question of whether diatoms would adhere to ducks, the scientists dragged duck feathers through a solution containing diatoms. They found that the diatoms did successfully adhere, likely due to the barbed texture of the feathers.

To test whether the diatoms would remain attached to the feathers in simulated flight conditions, the feathers with diatoms were then added to the flight simulators at eight combinations with 4 different humidity levels, 4 different exposure times, and a constant temperature. After their “flight”, the feathers were transferred to Petri dishes filled with the nutrients that would allow the diatoms to grow if they were still alive and still attached to the feathers.

Results showed that as exposure time increased and humidity decreased, diatom viability worsened. However, the most telling results came when the team extrapolated these experimental results to the real world. By gathering data about real-world flying conditions, bird migration patterns, and diatom distribution, the researchers found that waterfowl are a potential dispersal vector for freshwater diatoms. They were also able to create maps with geographical predictions of diatom dispersal.

While this experiment was not able to address how diatoms detached from the feathers in order to colonize their new habitat, the scientists were able to make some predictions of these mechanisms. They suggested that feathers may detach, allowing diatoms to colonize a new surface in a freshwater body.

This research creatively addressed a question that has historically been difficult to study and shows links between organisms where we may not expect them. From a quacking duck flying at windbreaking speeds to a diatom that is invisible without a microscope- these hidden links require further research so that we may better understand the role they play in maintaining biodiversity patterns.

Reviewed by: Andrew Barton