Animal role in algae fertilization identified

Recently, Emma Lavaut and her colleagues from the Sorbonne University and the Austral University of Chile discovered that a species of red algae, Gracilaria gracilis, uses the isopod crustacean Idotea balthica to transfer its male gametes for fertilization . This discovery presents a whole new class of “pollination” interactions.

In a Perspective article published in Science, Professor Jeff Ollerton and Dr. REN Zongxin from the Kunming Institute of Botany of the Chinese Academy of Sciences (CAS) concluded that this new study greatly expands the phylogenetic and temporal scope of gametes. animal-mediated males. movement, bringing the concept of “pollination” from plants to algae and potentially pushing it back to the earliest evolution of marine invertebrates.

Pollination is the transfer of pollen (containing the male gametes of a plant) to a receptive stigma of a flower, which then fertilizes the ovules (containing the female gametes or eggs of a plant) for seed production. It is estimated that around 90% of angiosperms (flowering plants) are pollinated by animals. Strictly speaking, pollination is limited to seed plants, including angiosperms and gymnosperms (eg conifers and cycads, etc.).

In addition to occurring on land, animal pollination has been found in the oceans, particularly in the seagrass Thalassia testudinum, a marine angiosperm.

More broadly, the process of transferring male gametes to female gametes also occurs in other green plants and in eukaryotes such as mosses, fungi, and algae.

Red algae (a type of algae) includes over 7,000 species in the ocean. Unlike other algae, their male gametes do not have flagella and therefore are not motile, which makes them similar to pollen grains. Fertilization takes place on a distant female organ, indicating that these red algae need either water currents or animals to transfer male gametes for sexual reproduction.

Red algae are thought to have evolved around 1.2 billion years ago, long before land plants appeared. Isopods only appeared about 300 million years ago. While isopods and red algae have had a long time to evolve their “pollination” relationship, it is not known how red algae were fertilized before isopods. Extinct marine invertebrates may have done the job, but the first arthropods didn’t appear until 600 million years ago.

Isopod crustaceans may be attracted to these algae as they provide shelter from predators. In the midst of the algae, the isopod crustaceans feed on small algae (diatoms) which colonize the surface of the algae. Since diatom algae can foul algal fronds, removal of these diatoms by isopods can consequently increase the rate of algal growth.

Isopod crustaceans pollinate algae as they feed and move between the fronds. Isopods are therefore engaged in a “double mutualism” with algae, according to Lavaut.

The use of an animal vector for reproduction is very risky in a world of rapid anthropogenic change. Most of the reproduction of red algae occurs in relatively calm waters found in coastal rock pools at low tide. These habitats are threatened by pollution, invasive species, physical alteration of coastlines, and climate and sea level changes.

Additionally, crustaceans in general may be sensitive to increased ocean acidification related to increased CO2 because the acid decalcifies their exoskeletons. However, at the same time, red algae such as Gracilaria are ecologically important to their ecosystems and are promoted as a globally sustainable food source.

Unfortunately, an entirely new class of ecological interactions, as this discovery shows, may already be under threat before scientists even fully understand them.

This work was funded by the CAS Strategic Priority Research Program and the CAS President’s International Fellowship Initiative.

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