Sex Reversal in Fish

Sex Reversal in Fish - Sex Reversal in Fish Biological...

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Sex Reversal in Fish Biological Sciences 417 Kathryn Gerber April 30, 2007
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Major Question in Marine Biology: How do social systems help regulate sex change in fishes? The behavior of sex change is affected by the social environment, and requires the reorganization of physiological systems. From gonads being transformed, to changes in body size, these physical changes happen as a fish take cues about the size of conspecifics and their behavior from surrounding social environment. These social behaviors help regulate reproduction and growth rate. The composition of a social group triggers the sex change through encounters with smaller and larger fish, and inhibits change by the continued presence of a large fish conspecific. Hermaphroditic fish function as both male and female either sequentially or simultaneously for some period during their life. The following three papers answer the question of how social systems help regulate sex change in fish through experimentation and by establishing criteria for diagnosis of hermaphroditism in fish. They are summarized below. There are a wide variety of criteria and methods for assessing whether a fish species is a hermaphrodite. After the discovery that sex change in sequential hermaphrodites can be induced by social cues, many various scientists began work on the behavioral, ecological, and evolutionary aspects of hermaphroditism. Many methods and criteria used to diagnose hermaphroditism in older studies needed to be reassessed in light of the knowledge we have today. Thus, the authors set out to determine whether a fish is hermaphroditic. (Sadovy and Shapiro, 1987) Some of the features typically used to establish hermaphroditism are more reliable than others. In addition, there are three forms of hermaphroditism. First, conversions from female to male are known as protogynous. Second, conversions made from male to female are called protandrous, and are less common. The third form, called simultaneous hermaphroditism, occurs when the fish has both male and female organs. Protogyny is strongly suggested by the physical make-up of a reproductive system, the presence of transitional individuals, and through manipulating the social system to experimentally produce sex reversed fish. Bimodal size and age frequency distributions are less reliable as this could result from many causes, only one of which is protogyny. Protandry is more challenging to diagnose because testicular tissues from the previous state of sex are usually gone. Detecting protandry is best done by performing an experimental behavioral induction of sex change as age and size frequency distributors are unreliable indicators of this condition. Simultaneous hermaphroditism is diagnosed by the presence of mature tissue from both sexes in one gonad followed by inducing self-fertilization.
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