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Week 15/2010: Sloth and algae co-exist

It is very evident that sloths lives in a symbiosis with a green algae called Trichophilus welckeri. The assumption was reinforced by observations made by an algae systematics research team at the Department of Environmental Sciences of the University of Helsinki.

The team analyses hair samples taken from sloths in Panama, Costa Rica, Brazil and the French Guyana. The goal was to find out whether sloths are so slow that any algae grows in its fur, or whether sloth cubs receive a specific algae from their mothers.

Both hypotheses turned out to be correct. A total of 426 eukaryotic organisms - from microbes to spiders - were found in the hair samples. The majority of the organisms were microscopic ciliates and algae.

“The fur of sloths absorbs water, whereas the fur of other mammals rejects it. Moreover, sloth fur has grooves which provides a good growth base for algae,” says Jaanika Blomster, the head of the research team.

Algae gives the fur of sloths a greenish tint. The protective colour functions so well that it slows down the research on sloths. “Even though a sloth would have a transmitter on its collar, it may take an entire day to find it in the tree.”
Algae obtain nutrients from sloth excretion. It is suspected that sloths get additional nutrition by licking their fur.

However, proving the actual symbiosis is more complex.
The research led by Blomster showed that in one sloth species the Trichophilus welckeri stocks are closer to each other than in another sloth species. This means that sloth and algae have evolutionarily diverged together.

The same algae was found in all sloth hair research objects, even though they are geographically distant from each other. Trichophilus is not even known to occur elsewhere than sloth fur.

“Baby sloth hair did not yet have any algae. It probably moves there from the mother's fur later on, perhaps during the rainy season,” says Blomster.

Text: Antti Kivimäki
Translation: AAC Global
Photo: Milla Suutari

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