What would it take to change sexes? In humans, it involves complicated surgeries and rigorous hormonal therapies, not to mention hefty social and psychological ramifications. But in the Eastern Pacific Ocean, tiny orange-and-blue fish are naturally transitioning from female to male, and male to female, all the time.
Bluebanded goby fish, about 2 to 2.5 inches long, are able to change their sex when it suits their position in social hierarchies.
Matthew Grober, associate professor of biology at Georgia State University, has received funding from the National Science Foundation to better understand what mechanisms cause some of these fish to change sexes. In his lab, fluorescent lights accentuate dozens of aquariums lined with grayish-green algae where his bluebanded gobies thrive.
"We can detect within minutes, via changes in behavior, when a fish begins the transition, and it generally takes one to two weeks to complete the transition from female to male," Grober explained.
One indicator of typically male behavior is movements associated with male courtship, such as rapid zig-zag movements called "jerks," as described in a 2007 study that Grober co-authored. Females that become males may also reduce their submissive behaviors.
Although natural sex change is exceedingly rare across the animal kingdom, bluebanded gobies are not the only creatures capable of it. Other examples include the clown fish and the limpet snail.
Groups of these fish have a skewed sex ratio in their natural environment. In other words, goby groups are not 50% male and 50% female, as one might expect. Instead, as Grober explained, "Gobies most often live in groups called harems that usually consist of one male and four to five females."
In a natural setting, if the leading male dies, the most dominant female remaining in the group will take leadership of the harem and then physically change into a male.
Why would the female change her sex? The answer lies in evolutionary biology.
An organism's evolutionary success depends on the number of genetic copies of itself it leaves behind in the population. So, a male fish, which mates with all of its harem's females, has much more success in spreading genes than any given female.
For example, a male in a harem of four females has four times more reproductive success than any of his females because each individual female has only the harem's one male partner with whom to mate.
Just as in humans, in many sex-changing fishes, social context often determines an individual's behavior.
Click here to read more.