Expectant Fathers

Lesson 7: Pregnancy and Nature

Dads in Nature

Courtship and mating are only two stages in which we see role reversals in nature. Fathering, which has historically occupied a supporting role in our human world, takes center stage for many other species. So Dads, step right up and let’s look at a few examples of fathers, pregnancy, and child care in the world of nature.

Among other creatures, the single-parent family is the overwhelming rule - and that parent is almost always female. From building a nest and gathering food to giving birth and protecting their young, females do it all. Male involvement rarely extends beyond their brief contribution at the moment of conception.

There are however, a few notable exceptions to this rule. In 90 percent of bird species, the male provides some form of parental care. In fishes, males occasionally take on a custodial role at the nest site. And for animals living in harsh environments, the efforts of two parents are usually required for the young to survive.

The sea horse, which we briefly visited before, is very unusual in its custodial habits. It is from a small family of fishes called pipefish. The name is derived from the resemblance of the head to that of a horse. With long, tubular jaws and a compressed body covered with a series of external, large, rectangular bony plates, the male and female are indistinguishable except during time of courtship, mating and pregnancy. Living close to shore in tropical waters, the sea horse is more the rule than the exception when it comes to fish forms of parental care. In those species of fish that care for their young after egg laying, fathers usually do all the caring.

This seems strange until you consider the paternity uncertainty of fish. When fish mate, fertilization occurs outside the female’s body. This external fertilization, as it is called, requires so much synchronization in the mating behavior of males and females that males can usually be sure they are not attempting to fertilize and care for eggs by another male.

The male dwarf sea horse, no bigger than a paper clip, curls his tail tightly around a stem of sea grass in the warm Florida Ocean. His tough, boy skin is exactly the same yellowish green as his grassy home. Amazingly, sea horses can change colors, from yellow to green or even orange, to blend into the coral and grass that grow on the sandy bottom.

The male dwarf sea horse uses this camouflage to hide quietly in his shallow ocean habitat; but on this sunny April day, he isn’t trying to hide from his enemies but wants to attract a mate. A pocket like pouch on the front of his body is filled with water and bulges out like a tiny balloon. The father sea horse will brood the eggs of his mate in this pouch until they hatch. He sways with the sea grass and waits for a willing female to approach.

Nearby, a female dwarf sea horse is feeding hungrily on shrimp larvae by using her tube-like snout to suck in a thousand of these tiny sea creatures each day. Although her back fin is beating rapidly, she swims forward very slowly. Sea horses are the slowest-swimming fish in the world. At top speed, most move only a foot or less in one minute.

Attracted by the male, the little female uses the fins on each side of her head to turn toward him. Her body is full of eggs and she’s in the right mood, and she is ready to mate. She settles next to the male and twists her tail around a piece of coral. With their bodies touching, the female pushes a special egg-laying tube into the male’s pouch. She then releases three dozen eggs through the tube thus impregnating the male.

Eagerly, the male fertilizes the eggs as they enter his pouch. When the female has finished releasing her eggs and withdraws her tube, she slowly swims away. Her job as a parent is complete, but his has just begun.

Soon after the male and female have mated, the father sea horse’s pouch closes with the eggs safely inside. For the next two weeks he stays hidden in the sea grass as the eggs in his pouch develop. Blood vessels in the sea horse’s body carry oxygen and nutrients to the pouch, where they are adsorbed by the eggs. As the babies grow, the pouch gets larger.

Finally the father sea horse is ready to deliver his babies. His muscles jerk suddenly and his whole body strains. The pouch opens and one tiny sea horse pops out, headfirst. It is so small it can barely be seen. For a few seconds, the newborn drifts in the water. Then its little back fin begins to beat, and the youngster swims away.

After a minute’s rest, the father’s body begins to twitch again. Out comes another hatchling and then another. For nearly three hours, the delivery process continues.

Each youngster swims away and wraps its tail around a piece of seaweed or coral. Before long there are several different colors among the newborns as their bodies change to match their first hiding places. Each of these dwarf sea horses is now on its own. Not one will have any further contact with its parents.

Before dismissing the sea horse’s pregnancy as brief, the two week event in the life of a sea horse is equivalent to carrying a baby for 3 years before delivery. And this happens three times in the life of this little fish.

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