Seahorses remain an enigma. These mysterious-looking creatures appear to float around coastal seas with a grace and level of perfection that sucks in observers and admirers from all quarters of society. In ancient Greek and Roman times, seahorses were revered. They were once seen as symbols of power and of authority. Even the Latin taxonomic family name stirs the imagination, as Hippocampus translates as the “horse sea monster”.
The reality is that seahorses are part of the teleost group – the most common type of fish – and so are far more closely related to an Atlantic cod than to any horses, monsters or imaginary creatures. But seahorses also have some very unusual features, from their equine appearance and body armour to the fact that it is the males that carry and give birth to offspring. Now a new analysis of all the genes in the seahorse’s DNA (known as its genome)
Seahorses belong to the syngnathids family of fish, which includes approximately 300 species. Analysing the seahorse’s genes confirmed that it is in a sister group of fishes to that of the stickleback. What makes the particular group, which includes seahorses, unique among vertebrates, however, is their “male pregnancy”. The males nourish developing embryos in a brood pouch until hatching and parturition occurs. The male provides all the parental care and so have adaptations to provide the embryos with the right balance of fluids, oxygen and nourishment.
We think this oddity of evolution came about as a way for male seahorses to ensure they were the fathers of their mate’s children. In some species of seahorse, this phenomenon of male “pregnancy” reverses the usual roles of attracting a mate, with females competing for the males’ attention and evolving their own secondary sexual characteristics to do so.
The new research, from the ASTAR institute in Singapore and published in the journal Nature, shows that this unique feature of seahorses is clearly coded into the male genome. The researchers found that five of the genes responsible for hatching embryos that are usually active in most female fishes are very active in male seahorses and may be involved in male pregnancy.
