Georgia State Biology Prof Studies Sex Changing Fish
By LaTina Emerson
We humans tend to think our way of life is the norm, but compared to the vast number of creatures on the planet, we’re the odd ones. Especially when it comes to sex.
As it turns out, varieties of fishes that can change sex far outnumber humans and other primates that are born either male or female and stay that way, said Matthew Grober, associate professor of biology at Georgia State University.
Grober has devoted decades of work to studying the sex-changing phenomenon in fishes by focusing on the bluebanded goby, a small, bright red fish with blue stripes.
“There are many more species of gobies that change sex than all living primate species combined,” Grober said. “Gobies are the largest family of marine fishes, and most marine gobies change sex.
“What humans do is really not common, or at least not as common as we like to think. To suggest that our species is the norm when looking at the diversity of life on earth, that’s not the case.”
In his latest research, Grober is studying different patterns of gene expression to determine how bluebanded gobies avoid becoming fixed as a male or female early in life.
While other fishes also change sex, bluebanded gobies are “champions” at doing it, which is why Grober has focused on them. These fishes are sequential hermaphrodites, meaning they can move between sexes.
Grober travels to Catalina Island, off the coast of southern California, to study his subjects, which live in small groups with a male as leader of a harem of several females. If the male leaves or dies, the dominant female changes sex to become the new male of the group.
“Sex change is a huge bonus to them in terms of maximizing their reproduction,” Grober said. “They can respond with the right sex to maximize that situation. If maximizing reproduction is the game, they’ve really got it rigged.”
Within 20 minutes of the male being removed, the dominant female transforms her behavior and takes over as the male of the group. In three weeks, faster if the water is warm, the female has physically transformed into a male, developing male sex organs and hormones. The body shape even changes, with the head becoming wider at the bottom.
Grober has been studying the role of two genes involved in sexual differentiation, the androgen receptor gene and DMRT1 gene.
The androgen receptor allows androgens, steroid hormones that control development and maintenance of masculine characteristics, to have their effects in the body. DMRT1 is involved in the production of testes. By looking at changes in the expression of these genes, Grober’s group can better understand how these male typical genes are regulating the female to male transition.
Grober plans to return Catalina Island this winter or spring to continue his work.
And how does he explain his research to non-scientists?
“One of the reasons you would study something as strange as a sex-changing fish is because humans don’t change sex,” he said. “If you want to understand the rules, sometimes you have to go outside the box.”