Gonochoristic- fish that maintain the same sex throughout their entire lifespan.

Induction- When one member changes sex due to lack (or removal) of the other sex; often when that individual is placed in a new environment.

Polygyny- a single, dominant male reproducing with a group of females (a harem).

Protandry- beginning life as a male and then changing to female.

Protogyny- beginning life as a female and then switching to male.

Secondary Male- A male that began life as a female (protogynous in origin).

Simultaneous Hermaphroditism- the sex organ is partitioned into both male and females (only seen in the Serranidae, genus Hypoplectrus, the Hamlets)

Size advantage model (Ghiselin 1969)- if an individual of a certian sex could significantly increase its reproductive success after reaching a certain size, it would be to their advantage to switch to that sex.

For example, a female with a larger body cavity can produce and more eggs per reproductive episode, and the more eggs produced increases her potential reproductive success. In such an instance, it would me beneficial for males after reaching a certain size to change to female. Such circumstances would predict protandry within a species.

Conversely, if a male above a certain size were to have greatly increased reproductive success (i.e. gain control of a harem), females would switch to males. This scenario would predict protogyny.

The size advantage model can be more clearly illustrated in the following figures:

Sneaker Male (also known as initial phase males, primary males, streaker males)- Born as males in a protogynous species, and stay as males. In fact, they will pretend to be females, and through this behavior, they can get close enough to a harem of females without being percieved as a threat, and fertilize the females eggs before the dominant secondary male has a chance to. Some of the most violent interactions on reefs are between secondary and primary males.

Suppression- In protogyny, when the presence of a male prevents females from changing sex. The females will then change sex upon removal of the male.



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