Crustaceans help fertilize seaweed, research finds

The small crustacean Idotea balthica facilitates the dispersal of male gametes and fertilization in the red alga Gracilaria gracilis. They use dense, branching red algae for cover and feed on microalgae that grow on their surface. Credit: © Wilfried Thomas @Station Biologique de Roscoff, CNRS, SU, Roscoff, France

The important role of insects in pollinating flowering plants is well known, but marine animal-assisted algae fertilization has hitherto been considered non-existent. A team led by a CNRS researcher from the French-Chilean Evolutionary Biology and Ecology research unit at Roscoff Marine Station has discovered that tiny crustaceans known as idoteas contribute to the reproductive cycle of the red alga Gracilaria gracilis. The scientists’ findings were published in Science. They suggest that animal-mediated fertilization is much older than previously thought.

Are marine animals involved in the reproduction cycle of algae, such as pollinating insects on dry land? The distribution of male gametes, or spermatia, of red algae generally depends on the movement of water, and until now, scientists did not recognize the role played by the animals.

But the international team led by Myriam Valero, a CNRS scientist affiliated with the Evolutionary Biology and Ecology of Algae research unit (CNRS / Pontificia Universidad Católica de Chile / Sorbonne University / Universidad Austral de Chile) and Roscoff Marine Station (CNRS / Sorbonne University) , has revealed that tiny sea creatures called idoteas act as “sea bees” for the red algae Gracilaria gracilis.

This video shows an aquarium containing a male (on the left) and a female (on the right) of G. gracilis with I. balthica. Isopods of different sizes forage on seaweed. Some of them are difficult to observe because they grip the algae tightly, and spermatia can thus settle in their pereiopod setae. Credit: IRL 3614, Station Biologique de Roscoff, CNRS, SU, Roscoff, France

Idoteas contribute to the fertilization of G. gracilis as they swim among these algae. The surface of the male algae is decorated with reproductive structures that produce spermatia that are coated in a mucus, a sticky substance. As the idotea passes, the spermatia attach to its cuticle and are then deposited on the thalli of any female algae that come into contact with the crustaceans, thereby aiding the reproduction of G. gracilis.

But idoteas also has an advantage in this arrangement. Seaweed provides them with space and board: idotea clings to algae for protection from strong currents, and they chew on the tiny organisms that grow on their thalli. This is an example of a mutualistic interaction—a mutually beneficial situation for plants and animals—and the first time this kind of interaction between seaweed and animals has been observed.

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  Complex interactions, and outcomes, between seaweeds (Gracilaria gracilis), isopods (Idotea balthica) and diatoms. A plus sign (+) indicates a positive effect of one species on another, while a minus sign (-) indicates a negative impact. Credit: Lavaut et al.
  

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  Aquarium containing male and female Gracilaria gracilis with (A) and without (B) Idotea balthica Aquarium containing female G. gracilis with (D) I. balthica preincubated with male gametophyte, (E) Negative control with female G. gracilis without I. balthica Credit: © E. Mardones
  

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  Spermatia (green colored particles) stick to the cuticle. Close-up shows them clustered on their toes. Credit: © Sébastien Colin
  

While these preliminary findings do not indicate the extent to which animal gamete transport contributes to algal fertilization relative to the role of water movement—previously thought to be the only mode of gamete dispersal—they offer surprising insights into animal-mediated origins. plant fertilization. Prior to this discovery, the latter was assumed to have appeared among terrestrial plants 140 million years ago. Red algae appeared more than 800 million years ago and their fertilization through animals probably existed long before pollination on land. Valero’s team now aims to focus on a few other questions: Do idoteas trigger the release of spermatia? Are they able to distinguish male G. gracilis algae from female individuals? And most importantly, are there similar interactions among other marine species?

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Ancient algae lineage found including five ‘sketchy’ species

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Further information:
E. Lavaut et al, Marine pollinators: A discovery of animal-mediated fertilization in seaweed, Science (2022). DOI: 10.1126/science.abo6661. www.science.org/doi/10.1126/science.abo6661

Jeff Ollerton et al, Did pollination come before plants?, Science (2022). DOI: 10.1126/science.add3198. www.science.org/doi/10.1126/science.add3198

Quote: Crustaceans help fertilize seaweed, study findings (2022, 28 July) retrieved 28 July 2022 from https://phys.org/news/2022-07-crustaceans-fertilize-seaweeds.html

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