The important role of insects in the pollination of flowering plants is well known, but algal fertilization assisted by marine animals was until now considered non-existent. A team led by a CNRS researcher from the Franco-Chilean Evolutionary Biology and Algae Ecology research unit at the Roscoff marine station (CNRS / Sorbonne University / Pontificia Universidad Católica de Chile / Universidad Austral de Chile) discovered that small crustaceans called idoteas contribute to the replica cycle of the red alga Gracilaria gracilis. The scientists’ findings are published in Science (29 July 2022). They suggest that animal-assisted fertilization is much older than previously thought.
Are marine animals involved in the cycle reproduction of algae, like pollinating insects on land? Dispersal of the male gametes, or spermatia, of red algae generally relies on water movement, and until now scientists did not recognize the role played by animals.
However, an international team led by Myriam Valero, CNRS scientist affiliated with the Evolutionary Biology and Algae Ecology research unit (CNRS / Pontificia Universidad Católica de Chile / Sorbonne University / Universidad Austral de Chile) and Roscoff Marine Station (CNRS / Sorbonne University) 1, revealed that tiny sea creatures called idoteas act as “sea bees” for the red algae Gracilaria gracilis.
idotea contribute to the fertilization of G. gracilis by swimming in the middle of these algae. The surfaces of male algae are dotted with reproductive constructs that produce spermatia coated in mucilage, a sticky substance. As an idotea passes, the spermatia adhere to its cuticle and then settle on the thalli of any female algae with which the crustacean comes into contact, thus promoting the reproduction of G. gracilis.
But idoteas can also benefit from this arrangement. The seaweed offers them shelter and cover: the idotea cling to the seaweed to protect themselves from strong currents, and nibble the small organisms that grow on their thalli. This is an example of a mutualistic interaction – a win-win situation for plants and animals – and the first time a conversation of this form between an algae and an animal has been observed.
Although these first results do not indicate the extent to which animal transport of gametes contributes to algal fertilization compared to the role of water movement – previously thought to be the only means of dispersal of gametes – they offer surprising insight into the origin of animals. – the mediated fertilization of plants. Before this discovery, the latter was supposed to have emerged among terrestrial plants 29 tens of millions of years ago. Red algae arose over 29 million years ago and their fertilization by animal intermediaries may well predate the origin of terrestrial pollination . 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 above all, are there similar interactions between other marine species?
1 The other scientific contributors are from the Instituto de Ciencias Ambientales y Evolutivas (Facultad de Ciencias, Universidad Austral de Chile), the Laboratory of Integrative Biology of Marine Models (CNRS / Sorbonne University) and the Max Planck Institute of biology of Tübingen (set up of biooptics).