Darwin’s theory of evolution and natural selection are concepts well known by most people. Evolution being a change in a population over time and natural selection essentially coming down to survival of the fittest and being a key mechanism of evolution. In the case of seahorses, rather the 54 species of marine fishes in the genus Hippocampus, the male and female seahorses have evolved a series of unusual adaptations for the purpose of increasing their overall fitness. A common misconception about seahorses is that the males are the ones to become pregnant, when in reality it is more of a team effort where both the male and female share the energy load. The reason why the male carries the babies is because they are known to be more aggressive. Without this protection, pregnant female seahorses could easily be eaten or injured.
It is the norm that ‘care’ is predominantly a concern for the women and part of life as a female. It is construed as a female gift and suggests that we are more suitable for such endeavors like nursing the babies and childcare overall. However, with seahorses it is an evolutionary adaptation for the males to do the “caring and nursing” of the eggs to protect them and the young as long as possible. The way their relationship works is that the female lays the eggs in the pouch of the male (known as the brood pouch) who looks after them. She produces the eggs in about two weeks, which takes energy on her part. If the role of the male was simply to fertilize those eggs and run off, then the life of the female would be rather tough. She would have to produce the eggs, carry them to birth, give birth (which is a tough process for seahorses), then start producing eggs again and so on. This process would take two weeks to produce the eggs and two weeks to gestate them in the pouch. One month in total, and a lot of energy used up as well.
On the other hand, if the male carries the eggs, then the situation changes. The female produces eggs and the male fertilizes and carries them. Two weeks later he gives birth to them, with a lot of contractions over a lot of hours, which is quite exhausting. However, during those two weeks that he has been carrying the babies, the female has been producing more eggs. Thus, once he has ejected the babies, he is ready to fertilize and carry yet another batch of eggs. The cycle is now two weeks as opposed to four if the female had that responsibility. That is twice as many babies, and twice the chance that some may survive the plankton stage. Based on the poor survival rates of baby seahorses in the ocean, I’m sure they have adapted to do whatever it takes to produce the maximum amount of offspring, overall increasing their fitness.
As mentioned in the previous paragraph, the male seahorses are known to be more aggressive whereas the females could easily be eaten or injured. Thus, the males take care of fertilized eggs in the brood pouch. As the developmental stage continues, the brood pouch gets bigger, making the male seahorses look like they are pregnant (but they aren’t). When the development is complete, the pouch opens, and baby seahorses are released. It all comes back to fitness, survival of the fittest. It’s about developing the most efficient way to produce the maximum amount of offspring for better fitness and to increase their survival rates.
The biological characteristics of pregnancy in male seahorses resembles that of female mammals. This is an example of convergent evolution, where unrelated species find a similar solution to cope with specific evolutionary challenges. In a journal article by Susanne Schmitt, she informs us that “the male’s pouch, just like a kangaroo pouch, provides a protective and nutrient-rich environut in which calcium, lipids, oxygen, and the right salt balance are all provided to ensure normal embryonic development.” This being an example of two unrelated species using a similar method for survival of their young. So long as the male does not get eaten, the eggs will survive to hatch. Below is an evolutionary tree showing some of the major evolutionary changes the seahorse has gone through, making it easier to understand how the seahorse became what it is today.
Taxonomy, the study of how animals are related and categorized, is always changing so we may find new information about these relationships as time goes on. Classifying an animal as a male or female is based on the type of gamete produced. The seahorse or the Hippocampus is very unique. There are many examples in the Animal Kingdom where a male takes care of the fertilized egg, for example the Emperor Penguin. But fertilizing eggs in a male’s body is not that common. This happens to be the method that best works for the seahorses. This guarantees a higher percentage survival rate than a random scattering, indicated by the fact they still do it after a few million years of evolution.
The ultimate cause of extinction is failure to adapt to changes in the environment. The seahorse species has clearly adapted where the end result is better survival of parents and the ability to breed more often. There are K-organisms, such as humans, cats, dogs, etc., where they have small litters, reproduce at a later age, there is slow maturation and a lot of care and effort is put in for the offspring. Then there are R-selected organisms who are short lived, have large litters, reproduce at an early age, there is fast maturation and little to no care for the offspring. For example, the seahorses. In the open ocean where their babies are plankton, they need to produce a lot of them! This is the way they have evolved to ensure efficient protection of the young in the particular environment they live in.