Historical mating systems and the origin of sexual ornam

Andrew Crompton 

Ornamental traits are commonly interpreted as products of runaway sexual selection or costly signals of male quality, but many ornamental traits appear to be functionally redundant, and, especially in birds, multiple ornaments coexist without clear links to condition or survival. This new proposal explains the evolution of ornament through sexual selection. based on looking for historic circumstances under which such traits might once have been functional. If mating systems are seen on a spectrum between polygyny and monogamy then in an intermediate state, when are both systems are viable, females may benefit from identifying males likely to provide parental care rather than pursue additional mates. Selection may then favour traits that function as signals of fidelity. If mating subsequently resolves into pure polygyny or monogamy these signals may persist through a coupling between female preference and male ornament, as predicted by standard models of sexual selection. Repeated transitions between mating strategies will cause ornament traits to accumulate. Traits may also be vulnerable to deceptive mimicry by males pursuing alternative mating strategies, leading to an evolutionary arms race that selects traits that are costly or difficult to imitate. This helps to explain the extravagance and diversity of plumage and behaviour observed in species such as Birds-of-paradise.