In a scientific first, Crustaceans discovered 'pollinating' seaweeds

In a scientific first, Crustaceans discovered 'pollinating' seaweeds ...

Animal pollinators such as bees and birds provide the world's food supply, as well as our cravings for coffee, honey, and macadamia nuts, according to new research.

The research, conducted by research organizations based in France and Chile, is the first to document a seaweed species that relies on small marine crustaceans to reproduce.

The researchers claim that animal-assisted pollination might have arisen about 650 million years ago in the oceans once a suitable pollinator existed.

Male reproductive cells, or gametes, travel in the form of pollen grains, which are carried by wind, water, or aback insects, to hopefully land upon a female counterpart somewhere far away.

Scientists then discovered that mosses and some fungi also use animals and insects to encourage reproduction, bucking their previous beliefs about animal-mediated pollination.

Researchers speculated that it may have evolved in concert with terrestrial plants around 140 million years ago or at least during the Mesozoic, which dates back to roughly 252 million years.

Scientists discovered that foraging marine insects carried seagrass sperm a few years ago, reversing the long-standing view that the oceans were free of pollinators.

Emma Lavaut, an evolutionary biology graduate student at Sorbonne University in Paris, and colleagues, describe how small crustaceans, Idotea balthica, aid in the fertilization of a red seaweed species, G. gracilis, that evolved about one billion years ago, long before land plants first appeared.

In a perspective accompanying the publication, Jeff Ollerton and Zong-Xin Ren, two environmentalists from the Chinese Academy of Sciences' Kunming Institute of Botany, have broadened both the variety and the history of animal-mediated male gamete transfer.

Seaweeds, which are a form of photosynthesizing algae, are only very distant from so-called true plants.

G. gracilis is quite different from most other seaweeds in that their male gametes have no flagellum to propel them through the water, leaving them stuck in the ocean unless they can grab a ridge on a passing critter, as this new investigation suggests.

Lavaut and colleagues demonstrated how small marine isopods that forage along male G. gracilis strands inadvertently collect the seaweed's male gametes (spermatia) as they do, then transfer them to female plants in a series of laboratory experiments.

In the image below, an idotea with fluorescently-stained spermatia is seen, indicating that crustaceans may serve as pollinators.

An idotea appendage covered with spermatia (Sebastien Colin, Max Planck Institute for Biology/CNRS/SU).

"Our findings demonstrate for the first time that biotic interactions greatly increase the probability of fertilization in a seaweed," Lavaut and his colleagues said.

The research suggested that fertility results were about 20 times higher in the presence of I. balthica than without the critters.

But they have yet to compare this crustacean pollination to the dispersal of pollen along water currents to determine which plays a greater role.

The origins of plants pollinated by animals remain unanswered, since the scientists only guessed this from the evolutionary history of the animals involved.

According to Lavaut and colleagues, the seaweed provides food and shelter for grazing idoteas. In return, the small crustaceans assist G. gracilis in reproducing, but their appetite for parasite-like plants that colonize G. gracilis fronds increases the seaweed's growth rate.

Idotea balthica, perched on a red seaweed frond. (CNRS/SU).

Nonetheless, these delicate mutualistic interactions between plants or algae and animals are as jeopardy in a world of rapid human-caused climate change.

When coasts are being battered by storms and sea levels are slowly rising landward, seaweeds such as G. gracilis rely on still coastal waters to reproduce. Moreover, ocean acidification can weaken the exoskeletons of crustaceans, although this must be studied in isopods.

The danger of global warming is evidently clear, but evolutionary-minded ecologists are still unsure what G. gracilis did before I. balthica appeared on the scene, since the isopods aren't nearly as old as the algae, and developed a'mere' 300 million years ago.

Ollerton and Ren think that although they most likely relied on ocean currents, "how these seaweeds developed before this is a mystery."

If science has taught us anything, it's that we should always prepare for additional surprises. Ollerton's findings suggest that only one-tenth of the more than 300,000 known animal-pollinated flowering plants has their pollinators documented.

So which species are doing their magic? "No doubt many more revelations await the attentive observer of species interactions," Ollerton and Ren conclude.

The research was published in Science.

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