Like sea bees, these crustaceans pollinate algae

Move over birds and bees, there is another pollinator on planet Earth, and it lives in the sea.

In a study, published Thursday in the journal Science, scientists found that a tiny crustacean, Idotea balthica, acted as a pollinator for a species of algae. They do this by inadvertently collecting the algae’s sticky spermatia, its pollen equivalent, on their bodies and sprinkling it as they move from frond to frond in search of food and shelter.

This is the first time that an animal has been observed fertilizing algae. This discovery not only expands the range of species that use this reproductive strategy, but also raises questions about whether it first evolved on land or in the sea.

It was long thought that animals pollinated only terrestrial plants. However, in 2016, scientists discovered that zooplankton pollinate Thalassia testudinum, a species of seagrass found in the Caribbean. Sea grasses are the only flowering plants that grow in marine environments, but they remain closely related to land plants. On the other hand, algae, although technically plants themselves, are not closely related to land plants.

The discovery that Thalassia testudinum was pollinated by animals was made after scientists noticed an unusually high density of marine invertebrates visiting seagrass flowers. Shortly after this discovery, Myriam Valero, a population geneticist at the Sorbonne University in France, observed something similar happening among the red algae she was studying.

The species of algae she was studying, Gracilaria gracilis, always seemed popular with invertebrates, especially the isopod species Idotea balthica. Since Gracilaria gracilis produces spermatia that, like pollen grains, cannot move on their own, Dr. Valero wondered if isopods could play a role in the dispersal of spermatia. Previous studies suggested that Gracilaria gracilis spermatids were dispersed by ocean currents, but given their abundance in quiet coastal rock basins, Dr. Valero suspected that another dispersal mechanism was at play.

To test his hypothesis, Dr. Valero and Emma Lavaut, a graduate student at the Sorbonne, cultured male and female Gracilaria gracilis and placed them 15 cm apart in seawater tanks. some tanks were populated with tiny crustaceans, while others were not. At the end of their experiment, they found that fertilization occurred about 20 times more in tanks with the isopods than in tanks without them.

In a later experiment, the researchers took crustaceans that had spent time in tanks with breeding male Gracilaria gracilis and transferred them to tanks with unfertilized female algae. They found that this also resulted in high fertilization rates. They examined the isopods under a microscope and found that they had spermatia stuck to almost every part of their body.

Researchers believe that isopods have a mutualistic relationship with algae. The algae provides isopods with food in the form of a species of microalgae that grow on its surface as well as shelter. In return, the isopods help fertilize the algae.

“This is such a deeply fascinating study that really shakes up our understanding of how algae reproduce,” said Jeff Ollerton, a visiting professor at the Kunming Institute of Botany in China, who did not. participated in the study but co-authored a perspective paper that accompanied the science study on Thursday. “This type of interaction may have existed long before plants evolved and using a third party for reproduction may have much deeper roots than we ever imagined – if you will. excuse the pun.”

The group to which Gracilaria gracilis belongs is thought to have evolved about 500 million years before the first plants appeared on earth. Although isopods only appeared 300 million years ago, it is possible that before their arrival, red algae relied on other now extinct marine invertebrates to “pollinate” them. .

“It is possible that the relationship between algae and animals predates the evolution of the animal-plant relationship,” said Dr. Valero, who acknowledged that this hypothesis could not yet be proven. Another possibility, she said, was that animal-mediated fertilization strategies evolved independently and repeatedly in the terrestrial and marine environment.

Dr Valero added that it was important to know whether other species of red algae depended on marine animals for fertilization, as this could be essential for maintaining biodiversity in our oceans. While scientists document how pollution and climate change affect the relationship between plants and pollinators on earth, we have no idea how these forces impact the relationship between algae and their “pollinators” in the world. ‘ocean.

In years to come, Dr. Valero hopes to be one of the scientists to figure this out.

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