Table 1.

Simplified characterization of mating systems (monogamous, polygynous, promiscuous; see text for full definitions), spawning mode (pair spawning or group spawning), sperm competition (classified as low or high) and gonadosomatic index, GSI (classified as low or high) for each sexual system (G = Gonochorism; PA = Protandry; PG = Protogyny). In bold: most common type.

Sexual System	Mating System	Spawning mode	Sperm competition	GSI	Prediction
PG	Harem polygyny	Pair	Low	Low	Low
	Lek polygyny	Pair	Low	Low
	Promiscuous large groups*	Group	High	High
PA	Monogamy	Pair	Low	Low	Low
	Random pair mating	Pair	Low	Low
	Promiscuous small groups	Small group	Low	Low
	Promiscuous large groups**	Group	High	High
G	Promiscuous large groups	Group	High	High	High
	Monogamy (size assortative mating)	Pair	Low	Low
	Monogamy (random pair mating)	Pair	Low	Low

The prediction column summarizes the overall expectation on sperm competition (and thus GSI) for the sexual system, based on the most common mating and spawning mode, according to the SAM^23,24.

*Protogynous group spawners should be favoured as large males can produce more sperm²⁸.

**Promiscuous large groups are not common, but still present in protandrous species (see text for examples).