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PIPEFISH SOCIAL LIFEIn pipefish (shown), mom transfers her eggs to dad, who carries the embryos and gives birth.Siam Ocean World Aquarium in Bangkok, NSF

Broad-nosed pipefish are curious little creatures. They’re close cousins of seahorses, and they look like straws with eyes. They’re tiny and narrow, and their slender bodies mean they can easily hide from predators by swimming into underwater grasses. And like seahorses, pipefish reproduce in an unusual way: The female puts eggs into a pouch in the male, and the male carries the embryos and gives birth.

In a recent study, researchers studied the sex life of pipefish and observed that when a female mated with a small-sized male, her eggs contained an extra amount of protein. The father supplies some protein to his young, but the new research shows that if the father is small, the fertilized eggs he’s carrying contain additional protein — at least 10 percent more than in larger males, says Gry Sagebakken, who helped with the study. These proteins are like food: The embryos need proteins in order to grow into full-fledged pipefish.

Sagebakken is an ecologist at the University of Gothenburg in Sweden who helped with the study. Ecologists study how organisms, including animals such as pipefish, and their environments influence each other. Previous studies have shown that large pipefish males produce large offspring, so Sagebakken suggests that the females add extra protein to the eggs to make up for when their mates are smaller.

Sex can be tricky for pipefish. Females compete fiercely with each other for the chance to deposit their eggs in the males. And it may take days for a female to successfully deposit eggs in the male. Once the eggs are in place, the female swims away — to start the cycle again and look for another male.

Inês Braga Gonçalves is an ecologist who is also at Gothenburg and was part of the study. Gonçalves, Sagebakken and their colleagues captured wild pipefish and gave each of 29 females two chances to mate: once with a large male, and once with a smaller male. Once the female had deposited her eggs into the male’s pouch, the researchers captured the male and examined the fertilized eggs. In smaller males, the eggs had more protein than the eggs in the larger males.

Some scientists study sexual selection — in this case, that’s the study of why female pipefish mate with some males but not with others. One goal for these scientists is to understand how sexual selection affects evolution. Evolution is the process by which organisms change over long periods of time. When an organism reproduces, its offspring may be slightly different from the parents. When those offspring mature and reproduce, their offspring may be slightly different, and so on. Over time, these small changes add to up to bigger changes, and these bigger changes may give it a better chance of survival.

So when the female gives extra protein to eggs deposited in smaller males, it could be that she has evolved to do it. In other words, female broad-nosed pipefish have developed a way to give their offspring a better chance of survival — by giving those offspring more food than the father might offer. Since females compete for males, this extra protein could be a way to make up for the fact that not every female manages to mate with a large male.

For scientists who want to understand the role sexual selection plays in evolution, this study “is a nice example to illustrate how complicated sexual selection is,” Elisabeth Bolund told Science News. Bolund is an evolutionary ecologist in Germany. She points out this study is a good first step, but that scientists need to do more experiments on the pipefish to understand the process of sexual selection.

POWER WORDS (adapted from Yahoo! Kids Dictionary)

ecology The science of the relationships between organisms and their environments.

environment The combination of external physical conditions that affect and influence the growth, development and survival of organisms.

biological evolution The process of physical change in living things across generations.

proteins Molecules that contain carbon, hydrogen, oxygen, nitrogen and usually sulfur and are composed of one or molecules called amino acids. Proteins are fundamental components of all living cells and include many substances that are necessary for the proper functioning of an organism.

reproduce To generate offspring by sexual or asexual means.

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