Most flowering plants on Earth are pollinated by insects. But this type of reproduction is clearly not limited to land plants: researchers have now discovered that small sea crabs help fertilize red algae. Similar to bees, sperms are transferred from the male plant to the female. While scientists have long assumed that animal-mediated pollination first evolved in land plants about 140 million years ago, the new findings suggest that a similar evolution occurred in water millions of years ago.
Pollination by animals is a typical feature of flowering plants on Earth: insects or small birds fly from flower to flower in search of food, spreading pollen that they capture. But it is clear that animals can also play a role in the reproduction of marine plants. In 2012, researchers discovered that small marine animals that live in seaweed pollinate them. However, it was not yet clear whether this was a rare exception or whether animal-mediated pollination also plays a role for other aquatic plants.
Teamwork of red algae and crabs
A team led by Emma Laffaut of the French Academy of Sciences found another example where animals play a critical role in the reproduction of marine plants: “In experiments with the red algae Gracilaria gracilis and the crabs Idotea balthica, we showed that the organisms interactions significantly increase the reproductive success of the algae.” Red algae, similar to spaghetti, are found in all warm seas and play an important role in Asia as food and as a source of agar.Similar to pollen in flowering plants, the germ cells of Gracilaria gracilis cannot move on their own. Until now, it is assumed that they spread passively through water currents.
To see how small crustaceans that typically live on algae also play a role, Laffot and her colleagues placed male and female algal plants 15 cm apart in an aquarium—one with and one without Idoteen. The result: “In the presence of Idotea balthica, fertilization success was about 20 times higher,” according to the researchers. Fertilization was also successful in other experiments, in which they placed Idoteen, which had previously been attached to a male alga, in an aquarium containing only female algae. Under the microscope, Laffot and her colleagues showed that the sperm from the red algae was actually stuck in the body of the authentic person, attached to sticky mucus.
Researchers believe the relationship between red algae and crabs has advantages for both parties involved: Idotea crabs can hide from predators in the algae and also feed on small diatoms that settle on the surface of the red algae. Red algae, in turn, benefit from “pollination” by crustaceans and could probably grow better because the similar identifier frees them from diatom deposits.
The invention of early development
The new findings suggest that animal-mediated fertilization evolved much earlier than previously thought. The genus to which red algae belong arose about 1 billion years ago, and crustaceans about 600 million years ago. So it’s possible that algae were actually pollinated by animals before the first land plants appeared about 450 million years ago – and long before flowering plants appeared about 140 million years ago.
“The study by Laffaut and colleagues expands the concept of pollination from terrestrial plants to algae and probably goes back to the earliest evolution of marine invertebrates,” wrote Jeff Ollerton and Zhong Shen Ren of the Chinese Academy of Sciences, who are not affiliated with the Chinese Science Organization. With the Chinese Academy of Sciences study, in a commentary also published in the journal Science.
Source: Emma Lavaut (Centre National de la Recherche Scientifique, CNRS) et al., Science, doi: 10.1126/science.abo6661
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