Seahorses

Just read an interesting book about seahorses – Poseiden’s Steed: The Story of Seahorses, from Myth to Reality by Dr. Helen Scales – a marine biologist from Cambridge who obviously loves them.

Well worth reading if you want to know more about seahorses – everything from how difficult they are to classify taxonomically to how they’re used in traditional Chinese medicine to how images of them appear as the Rainbow Serpent in 6,000 year old Australian Aboriginal images.

One of the interesting things I learned in the book had to do with seahorse reproduction. I knew male seahorses carried the babies in a special pouch but didn’t know how it worked (scientists didn’t really know, in detail, until recently either).

During the courtship dance, the female seahorse inserts her ovipositor into the male’s brood pouch and inserts some eggs. The male seahorse then ejaculates sperm into the water which must then find its way into the brood pouch to fertilize the eggs. The male then carries the fertilized eggs until they develop into baby seahorses (the only male in the animal kingdom that truly gets pregnant and gives birth to young).

Grotesquely pregnant seahorse from Wikipedia

The interesting thing about this is how inefficient this process is. It would be a much better design to have the male release the sperm directly into the brood pouch with the eggs (because the sperm are exposed to the open water, they’re also exposed to pollutants in the water these days). But nature isn’t designed (intelligently or otherwise). This process is the product of its evolutionary history. Seahorses and their pipefish relatives evolved from fish like sticklebacks (or, more correctly, sticklebacks and seahorses had a common ancestor).

Seahorses release sperm into the water because that’s what their ancestors did when fertilizing fish eggs laid outside the body. It’s an evolutionary holdover from its past. Just another of a million examples of evidence for evolution we see in the natural world (read Your Inner Fish: A Journey into the 3.4 billion year history of the Human Body by Neil Shubin for many more).

Another interesting fact – seahorses are monogamous. Probably due to the fact that they’re poor swimmers, not very common, and spend most of their life attached by their tails to a piece of seagrass. Once you find a mate, it makes sense not to wander off since it’s hard to find another.

Interesting little critters.