Is Mating Different in Monogamous Species? The Midas Cichlid Fish as a Case Study

Monogamous species are typically sexually isomorphic, pair well before spawning is imminent, take much time to pair, are discerning about pairing, and appear to weigh multiple sources of information about species, sex, and quality of mate. The monogamous and polychromatic Midas cichlid (Cichlasoma citrinellum) distinguished between its own and a highly similar heterospecific behind a one-way mirror only when visual and chemical cues matched. Likewise, recognition of sex was hindered when interaction was precluded, even in the presence of chemical cues. Female choice of mate was most strongly influenced by the “normal, ” primitive, color and to a lesser degree by color of parents and siblings, making it difficult to account for positive color-assortative mating in the field. Females also selected the largest and the most aggressive males; size predicted a good defender of territory, and aggressiveness foretold effective protection of the young. Males, however, were not choosy. Pair formation features much aggression between the large male and smaller female, and gold-colored morphs (G) dominate normal (N) ones. That made it difficult for an N female to pair with a G male; using an N female the same size as the G male, however, resulted in the usual proportion of successful pairings. I propose three testable models of pair compatibility: complementarity, parity, and maximum male aggressiveness.