The small crustacean Idotea balthica facilitates the dispersal and fertilization of male gametes in the red alga Gracilaria gracilis. They use bushy and densely branched red algae as shelter and feed on the microalgae that grow 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 until now algal fertilization assisted by marine animals was thought to be non-existent. A team led by a CNRS researcher from the Franco-Chilean Algae Evolutionary Biology and Ecology research unit at the Roscoff Marine Station has discovered that small crustaceans known as idotes contribute to the algae’s reproductive cycle red Gracilaria gracilis. The scientists’ findings are published in science. They suggest that animal-mediated fertilization is much older than previously thought.
Are marine animals involved in the reproductive cycle of algae, like pollinating insects on dry land? Dispersal of the male gametes, or spermatozoa, of red algae generally depends on water movement, and until now, scientists did not recognize the role that animals played.
However, an 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 idotea act as “sea bees” for the red alga Gracilaria gracilis.
This video shows the aquarium containing male (left) and female (right) G. gracilis with I. balthica. Isopods of different sizes feed on algae. Some of them are difficult to observe as they are firmly attached to the algae and therefore the spermatia can be deposited in the pods of their pereiopods. Credit: IRL 3614, Station Biologique de Roscoff, CNRS, SU, Roscoff, France
Idotea contribute to the fertilization of G. gracilis while swimming among these algae. The surfaces of male algae are dotted with reproductive structures that produce spermatia coated in mucilage, a sticky substance. As an idotea passes, the spermatia adhere to its cuticle and are then deposited on the thalli of any female algae with which the crustacean comes into contact, thus aiding in the reproduction of G. gracilis.
But the disabled will also benefit from this provision. The kelp gives them space and food: the idotea cling to the kelp as protection against strong currents, and they eat small organisms that grow on their thallus. This is an example of a mutualistic interaction—a win-win situation for both plants and animals—and the first time such an interaction between an alga and an animal has been observed.
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The complex interactions, and their results, between algae (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 G. gracilis females with (D) I. balthica pre-incubated with male gametophytes, (E) Negative control with G. gracilis females without I balthica Credit: © E. Mardones
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Sperm (particles shown in green) stick to their cuticle. The close-up shows them clustered at the ends of their legs. Credit: © Sébastien Colin
Although these initial findings do not indicate the extent to which animal transport of gametes contributes to algal fertilization relative to the role of water movement, which was previously thought to be the only means of gamete dispersal , they do offer a surprising insight into the origin of animal mediation. fertilization of plants. Before this discovery, it was assumed that the latter arose among land plants 140 million years ago. Red algae arose more than 800 million years ago, and their fertilization by animal intermediaries may predate the origin of pollination on land. Valero’s team now aims to focus on several other questions: Do idoteas trigger the release of spermatia? Are they able to distinguish male G. gracilis algae from female individuals? And most importantly, do similar interactions exist among other marine species?
Ancient algal lineage found to include five ‘cryptic’ species 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
Citation: Crustaceans help fertilize seaweed, study finds (2022, July 28) retrieved July 28, 2022 from
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