auxosporulation

Auxosporulation is a reproductive process in certain algae, most notably diatoms (Bacillariophyta), that serves to restore cell size after successive divisions reduce the size of the vegetative cells. It occurs as part of the sexual phase of the life cycle and is triggered when cells become too small to continue normal asexual reproduction.

During auxosporulation, sexual recombination forms a zygote, which then develops into an auxospore. The auxospore is typically a larger, often non-siliceous cell that expands and grows by deposition of new valve material as it enlarges. Through a series of growth steps, an initial cell with the maximum species-specific size is produced. After this enlargement, the life cycle returns to vegetative, silica-based cell division, and the cycle of size reduction begins again.

The process helps overcome the size limitation imposed by diatom frustule construction and mitotic division. The auxospore stage may involve distinct developmental forms and periodic growth phases, and in many diatoms, the enlargement resumes with fresh valve formation around a expanding cytoplasm, resulting in a fully formed initial cell that can undergo standard reproduction and division.

Significance lies in maintaining functional cell size and frustule architecture within populations, influencing ecological success and fossil record interpretation. While most detailed descriptions come from centric and some araphid diatoms, auxosporulation is recognized as a key mechanism by which diatoms sustain their characteristic life cycle and size distribution. See also diatom life cycle, sexual reproduction, and frustule formation.