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Crustaceans help to fertilize seaweeds, study finds

Animal role in algae fertilization identified

The small crustacean Idotea balthica facilitates the proliferation and fertilization of male gametes in the red alga Gracilaria gracilis. They use the densely branched, bushy red algae as shelter and feed on microalgae growing on their surface. Credit: © Wilfried Thomas @Station Biologique de Roscoff, CNRS, SU, Roscoff, France

The crucial role of insects in the pollination of flowering plants is well known, but algae fertilization with the help of marine animals has been considered non-existent until now. A team led by a CNRS researcher from the French-Chilean Research Unit Evolutionary Biology and Ecology of Algae at Roscoff Marine Station has found that small crustaceans known as idoteas contribute to the reproductive cycle of the red alga Gracilaria gracilis. The scientists’ findings have been published in Science. They suggest that animal-mediated fertilization is much older than once thought.

Are marine animals involved in the reproductive cycle of algae, such as pollinating insects on dry land? The distribution of the male gametes, or spermatia, of red algae generally relies on water movement, and until now scientists have failed to recognize the role animals play.

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

This video shows the aquarium with males (left) and females (right) of G. gracilis with I. balthica. The isopods of different sizes forage on the seaweed. Some of them are difficult to spot because they are firmly attached to the algae, so spermatia can deposit on the setae of their pereiopods. 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 surfaces of the male algae are dotted with reproductive structures that produce spermatia that are covered in mucus, a sticky substance. If an idotea passes by, the spermatia attach to the cuticle and are then deposited on the thalli of any female alga that the crustaceans come in contact with, aiding reproduction of G. gracilis.

But idoteas also benefit from this arrangement. The seaweed gives them space and costs: idotea clings to the algae to protect against strong currents, and they nibble on small organisms growing on their thalli. This is an example of a mutualistic interaction – a win-win situation for plant and animal – and the first time such an interaction between a seaweed and an animal has been observed.

  • Animal role in algae fertilization identified

    The complex interactions, and their results, between the seaweed (Gracilaria gracilis), isopods (Idotea balthica) and diatoms. A plus sign (+) indicates a positive effect of one kind on another, while a minus sign (-) indicates a negative effect. Credit: Lavaut et al.

  • Animal role in algae fertilization identified

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

  • Idoteas are the bees of the sea

    Spermatia (particles shown in green) are attached to the cuticle. The close-up shows them clumped together on the ends of their legs. Credit: © Sébastien Colin

While these initial findings don’t indicate the extent to which animal transport of gametes contributes to algae fertilization relative to the role of water movement — previously thought to be the only way to disperse gametes — they do provide surprising results. understanding the origin of animal-mediated plant fertilization. Before this discovery, the latter was believed to have originated among terrestrial plants 140 million years ago. Red algae originated more than 800 million years ago, and their fertilization through animal intermediaries may predate the origin of land-based pollination. Valero’s team now wants to focus on some other questions: Do idoteas trigger the release of spermatia? Are they able to distinguish male G. gracilis algae from female individuals? And more importantly, are there similar interactions between other marine species?

Ancient ancestry of algae of which five ‘cryptic’ species have been found

More information:
E. Lavaut et al, Pollinators of the sea: 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 exist before plants?, Science (2022). DOI: 10.1126/science.add3198. www.science.org/doi/10.1126/science.add3198

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

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