Small crustaceans transport sperm-like bodies from male to female red seaweed members. Pollination may have evolved in the sea rather than on land, according to Gracilaria gracilis.
A small woodlouse-like crustacean appears to fertilize red seaweed in rock pools in the same way that bees pollinate flowers. This suggests that such behavior is more common in the oceans than previously thought and that animal-mediated pollination may have evolved there as well.
On land, we typically associate pollination with insects such as bees and flowering plants, but crustaceans have been discovered to pollinate seagrass underwater. Myriam Valero of the Sorbonne University’s Roscoff Biological Station in France and her colleagues have now demonstrated that a similar phenomenon occurs with the red seaweed Gracilaria gracilis, which is actually a type of algae.
Individuals can be either male or female during the seaweed’s life cycle. Water currents have previously been shown to transport spermatia, the seaweed’s version of sperm, from male individuals to reproductive organs on nearby female seaweed. Each fertilisation event results in the formation of a cystocarp, a visible bulb-shaped structure on the female seaweed.
To see if a woodlouse-like marine isopod called Idotea balthica could pollinate the seaweed, Valero’s team placed 20 of the animals in an aquarium with one male and one female seaweed member separated by 15 centimeters. I. balthica is a common parasite of G. gracilis. The scientists also used tanks without crustaceans.
The team discovered that there were 20 times more fertilisation events in the presence of the little crustaceans than in their absence by counting the number of cystocarps on female seaweed. This implies that the seaweed was pollinated by the animals.
The team then photographed the crustaceans that interacted with the seaweed and discovered spermatia attached to the animals’ abdomens and legs, indicating that they could carry it around when switching from male to female seaweed.
According to the findings, animal-mediated pollination may have evolved in the sea rather than on land.
“Until recently, it was thought that animal-aided fertilization emerged among plants when they moved ashore 450 million years ago.” “Red algae first appeared over 800 million years ago, and their fertilization through animal intermediaries may predate the origin of pollination on land,” says Valero.
“We cannot, however, rule out the possibility that different animal-mediated fertilization mechanisms evolved independently and repeatedly in terrestrial and marine environments.”
Reference: Science , DOI: 10.1126/science.abo0661