and female tissues in their gonads and produce both gametes. Protogyny Protogynous hermaphrodites are animals that are born female and at some point in their lifespan change sex to male. Protogyny is a more common form of sequential hermaphroditism, especially when compared to protandry. As the animal ages, it shifts sex to become a male animal due to internal or external triggers. Unlike females, male fecundity increases greatly with age, and it is hypothesized that it is more selectively advantageous to be a male when an organism's body is larger. This advantage may cause certain species to be protogynous hermaphrodites as the sex change to male leads to an increased reproductive fitness advantage. Protogynous examples Protogyny is the most common form of hermaphroditism in fish in nature. About 75% of the 500 known sequentially hermaphroditic fish species are protogynous and often have polygynous mating systems. In these systems, large males use aggressive territorial defense to dominate female mating. This causes small males to have a severe reproductive disadvantage, which promotes strong selection of size-based protogyny. Therefore, if an individual is small, it is more reproductively advantageous to be female because they will still be able to reproduce, unlike small males. Common model organisms for this type of sequential hermaphroditism are wrasses. They are one of the largest families of coral reef fish and belong to the family Labridae. Wrasses are found around the world in all marine habitats and tend to bury themselves in sand at night or when they feel threatened. In wrasses, the larger of a mating pair is the male, while the smaller is the female. In most cases, females and immature males have a uniform color while the male has the terminal bicolored phase. Large males hold territories and try to pair spawn, while small to mid-size initial-phase males live with females and group spawn. In other words, both the initial- and terminal-phase males can breed, but they differ in the way they do it. In the California sheephead (Semicossyphus pulcher), a type of wrasse, when the female changes to male, the ovaries degenerate and spermatogenic crypts appear in the gonads. The general structure of the gonads remains ovarian after the transformation and the sperm is transported through a series of ducts on the periphery of the gonad and oviduct. Here, sex change is age-dependent. For example, the California sheephead stays a female for four to