Crustaceans discovered “pollinating” algae in Scientific First

Pollination is the trademark of flowering plants, with animal pollinators like bees and birds supporting the world’s food supplies, not to mention our cravings for coffee, honey, and macadamia nuts. But new research raises the possibility that animal-assisted pollination may have emerged in the sea, long before plants moved ashore.

The study, conducted by research groups based in France and Chile, is the first to document a species of seaweed that depends on small marine crustaceans stained with pollen spores to reproduce.

Since the red algae Gracilaria gracilis evolved long before the appearance of terrestrial plants, the researchers say their study shows that animal-assisted pollination could have arisen in the oceans around 650 million years ago once a suitable pollinator appeared.

On land in seed-bearing flowering plants and gymnosperms, male reproductive cells, or gametes, take flight in the form of pollen grains, which are carried by the wind, through water, or insects off guard, to hopefully land. , on a female counterpart somewhere far away.

Scientists later found that mosses (a type of rootless, non-flowering plant classified as bryophytes) and some fungi also use animals and insects to facilitate reproduction, reversing what they knew about animal-mediated pollination.

Although often debated, researchers thought it originated in concert with terrestrial plants around 140 million years ago, or at least during the Mesozoic, which dates back to around 252 million years ago.

Just a few years ago, scientists discovered the foraging of marine invertebrates that carry seagrass sperm, launching the long-standing theory that oceans were free of pollinators overboard.

Now, this new study by Emma Lavaut, a graduate student in evolutionary biology at the Sorbonne University in Paris, and colleagues, describes how small crustaceans called isopods, Baltic idoteathey help to fertilize a kind of red algae, G. punywhich evolved about 1 billion years ago, long before 500 million years ago, when terrestrial plants appeared.

“The study by Lavaut et al. Expanded both the variety and history of animal-mediated male gamete transfer, taking the concept of pollination from [land] plants to algae and potentially pushing it back to the early evolution of marine invertebrates, “write Jeff Ollerton and Zong-Xin Ren, two ecologists at the Kunming Institute of Botany of the Chinese Academy of Sciences, in a perspective that accompanies the paper in Science.

A type of photosynthesizing algae, algae are only very distantly related to so-called true plants.

G. puny it also differs from most other algae in that their male gametes have no flagellum to push them through the water, left adrift in the ocean, unless they manage to entangle a crest on a passing creature, as this often suggests new job.

In a series of laboratory experiments, Lavaut and colleagues showed how small marine isopods, which feed along threads of G. punythey inadvertently collect the male gametes of the algae (spermatia) as they make their own, transferring them to the female plants.

You can see in the image below, an idothea decorated with fluorescently colored sperms, which suggests that the crustaceans may act as pollinators.

CloseUpOfIdoteaCoveredInSporesAn appendix of idotea covered with spermathy. (Sebastien Colin, Max Planck Institute of Biology / CNRS / SU).

“Our results demonstrate for the first time that biotic interactions significantly increase the likelihood of fertilization in an alga,” write Lavaut and colleagues.

The success of fertilization was about 20 times higher in the presence of I. Baltic that without the creatures, the team found.

But they have not yet compared this pollination of crustaceans to the dispersion of pollen along water currents to know which plays a greater role.

The origins of plants using animal pollinators also remain largely open, considering that researchers only deduced this based on the evolutionary history of the animals involved.

Lavaut and colleagues think algae provide abundant habitat, shelter, and food for grazing idots. In return, not only small crustaceans help G. puny they reproduce, but their appetite for pest-like plants they colonize G. puny the fronds actually increase the growth rates of the algae, the researchers found.

A brown and white spotted Balthica Idotea perched on a frond of red algae.Baltic idotea, perched on a frond of red algae. (Wilfried Thomas, CNRS / SU).

However, in a world of rapid human-caused climate change, these delicate mutualistic relationships between plants or algae and animals are just as threatened as the ecosystems they support.

Algae like G. puny rely on still coastal waters to reproduce when coasts are hit by storms and sea levels are slowly rising towards land. Meanwhile, ocean acidification can weaken crustacean exoskeletons, although this needs to be studied in isopods.

While the threat of global warming is largely clear, evolutionary-minded ecologists are still puzzled as to what G. puny done before I. Baltic appeared on the scene, as isopods are not as old as algae, evolving “only” 300 million years ago.

Although they were most likely based solely on ocean currents, “how these algae reproduced before this is a mystery,” explain Ollerton and Ren.

If science has taught us anything, it is that we should always be prepared for other surprises. Recent estimates by Ollerton suggest that only one-tenth of the more than 300,000 known species of animal-pollinated flowering plants have had their documented pollinators.

So which species are doing their magic? “No doubt many other revelations await the keen observer of interactions between species,” conclude Ollerton and Ren.

The study was published in Science.

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