Thousands of mating types in split-gill fungi: what does that mean?

The number concerns partner compatibility

The split-gill mushroom, Schizophyllum commune, produces small fruiting bodies on wood, but its reproductive genetics is unusually elaborate. The frequently repeated figure of 23,328 refers to possible mating types. It is neither a catalogue of that many mushroom shapes nor a count of individuals found in a single woodland.

In the classical account, two genetic systems, A and B, participate in partner recognition and subsequent mycelial development. Their different variants generate numerous combinations. A recent study of mating subtypes explains the basis of the familiar number: it estimates possible combinations of variants. It does not demonstrate that every combination occurs with equal frequency in natural populations.

Two nuclei can remain separate

After compatible hyphae fuse, these fungi can develop a mycelium whose cells maintain two separate nuclei. This is the dikaryotic stage. Later reproductive processes lead to nuclear fusion and eventually to a new generation of spores. Saying simply that “two fungi joined together” therefore leaves out much of the underlying biology.

Functional research on mating-related genes separates the contributions of different parts of the system. Meanwhile, experimental evolution of mating success asks questions that compatibility alone cannot answer. Being genetically capable of mating does not settle the outcome of competition, subsequent growth or transmission of genetic material. Those processes require their own observations and experiments.

Why “thousands of sexes” needs an explanation

The popular phrase can spark an interest in fungi, but without context it mixes distinct concepts. A mating type is a category of reproductive compatibility. It should not automatically inherit every characteristic associated with sex in animals, nor be mapped onto human identity. Explaining the genetic system is more informative than treating the number as an isolated record.

The ecological question is what this elaborate system allows fungal partners to do. Recognition structures the exchange of genes between mycelia, yet the system cannot be read from a photograph. Colour, size and the distinctive split gills describe a fruiting body. Establishing its mating type requires crossing experiments or suitable genetic analyses. Two mushrooms that look nearly identical may therefore represent different compatibility types, while differences in appearance need not indicate different mating types at all.