Protandrous

Protandrous describes organisms that begin life as males and later become females. The term is derived from Greek protos (“first”) and aner/andros (“man”) and describes a form of sequential hermaphroditism. In protandry, individuals function as males for part of their life before their gonads transform to support female reproduction.

Protandry is best documented in certain fish, especially some reef species such as clownfishes (Amphiprioninae) and several damselfishes and wrasses. In these species, social structure and size influence sex role: a smaller or subordinate individual will develop as a male, but as opportunities for female reproduction become advantageous, a dominant individual may transition to female to maximize reproductive output.

The change involves gonadal transformation and hormonal reorganization. During the transition, the testes regress and ovaries develop, and associated changes in secondary sexual traits may occur. The process typically unfolds over weeks to months and can be influenced by factors such as social hierarchy, population density, and environmental conditions. In most protandrous species, the transition is not easily reversible, though the degree of reversibility varies among taxa.

Ecological and evolutionary implications include impacts on population sex ratios, mating systems, and recruitment dynamics. Protandry affects how populations respond to changes in social structure or environmental pressures and is relevant to conservation, fisheries management, and aquaculture, where understanding sex change helps predict breeding success. Protandry is contrasted with protogyny, in which individuals begin life as females and become males.