Socially Influenced Sex Change in Anemonefishes

Clownfishes typically live most of their life on or in very close proximity to a sea anemone in small groups from 3 up to 6 or 7 depending on the size of the anemone. In these groups, the largest is usually the reproductive female, the second largest, the male and the smaller individuals are undifferentiated. If the female is removed, the male will transform into a female in a matter of weeks. Immediately, within the first few minutes, the male will begin to display female-typical behavior, e.g., court the other smaller fish. Within a few weeks, the testes of the male will have been absorbed, and ovaries will replace them. In addition, the size of the fish will increase, and the genitalia will change shape to allow for the passage of eggs instead of sperm through the genital duct. At the same time, the largest of the undifferentiated fish will transform into a male following a similar time course.

 

The phenomenon of neuroplasticity is perhaps no better exemplified than in the anemonefishes and many other coral reef marine fishes which change sex depending on the outcome of territorial contests.  For the past 5 years, I have been maintaining a colony of Amphiprion ocellaris, a species of anemonefish easily kept and bred in the laboratory, to study how the brain, pituitary, and gonadal tissues of these fishes coordinate a complete and seamless sex transformation.  So far we discovered that arginine vasotocin signaling at V1a receptors is necessary for males to exert aggression and dominance in dyadic contests which precedes sex change in our species.  Moreover, we discovered that males are the primary care-givers of the eggs, and that isotocin and arginine vasotocin play opposing roles in the regulation of paternal care.