Many tropical coral reef marine fishes change sex during their lifespan depending on the social conditions. For example, 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. This is one of the most remarkable and dramatic examples of plasticity in nature, the complete morphological sex transformation dependent completely on sensory input that dictates differences in the social environment. Despite a large literature describing the ecology and natural history of this incredible phenomenon, very little is known about how the brain orchestrates the transformation. Presumably, the brain is the organ that initially receives the sensory information from the change in the social environment, and then via unknown changes in neural control, changes the central commands that orchestrate the hormonal signals that ultimately change morphology and sex. The purpose of this research program is to make progress understanding the neurobiology that underlies the sequential hermaphroditism of the clownfish. Currently we are applying similar techniques that we have been using in the mouse to study plasticity and function of the nervous system in the fish, e.g., measuring adult neurogenesis, neural activity using immunohistochemical detection of immediate early genes, and morphology and anatomy using nissl stains, microscopy and image analysis.
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Red Lionfish (Pterois volitans)
Yellow Tang (Zebrasoma flavescens)
Blue Tang (Paracanthurus hepatus)
Queen Coris (Coris frerei)
Red-Knobbed Starfish (Protoreaster linckii)