An ocean of pheromones

Human pheromones have been the source of quite a bit of speculation, and while they may have some effect on sexual attraction, it certainly doesn’t appear that they are required for mating. The story for diatoms, though, is exactly the opposite, according to a study published today.

These tiny unicellular creatures live in the ocean, where it is easy to imagine that an egg and sperm might have trouble finding each other. To solve this problem, they have evolved a system where pheromones actually orchestrate the whole process, so that egg and sperm are only released on cue, hopefully making it easier for them to connect.

Here’s how it works. The females release their sex pheromone, called ph-1, constantly. Then, when a male is nearby, he senses the pheromone, which triggers him to make and release sperm. At the same time, he also begins to produce his own sex pheromone, called ph-2, which makes the female produce and release her eggs. The researchers suspect that there is yet a third pheromone, called ph-3, that is then released by the eggs to continue attracting the sperm. However, while they detected ph-1 and ph-2 in their experiments, ph-3 was not directly observed.

By relying on these chemical signals, the diatoms make sure that they are only releasing their gametes when a potential partner is nearby, which keeps them from wasting lots of energy. This elegant solution so far appears unique among related organisms.

The researchers also found some other cool elements of the diatom’s reproductive cycle, like “threads” on the sperm that help it move and grab things, and “blobs” on the sperm with unknown function. Check out these movies for a look!

This post was written by Rachel Bernstein, an associate editor at PLoS ONE.