The evolution of sexual dichromatism in a large radiation of landfowls: re-examining the female-biased selection in Wallace's model

Sexual dichromatism is generally thought to arise from sexual selection favouring elaborately coloured males, as proposed in Darwins model. Wallace offers an expanded perspective, emphasising that the evolution of cryptic and dim female colouration to evade nest predation significantly contributed to the origin of sexual dichromatism. However, previous studies on the evolutionary forces of sexual dichromatism examining Darwins and Wallaces models have produced mixed results. Here, we re-examined Wallaces model of female-biased selection using the largest and most ecologically diverse family of landfowl (Phasianidae), known for its wide-ranging distribution and striking plumage patterns. Our results demonstrate that the level of sexual dichromatism is negatively correlated with colour contrasts in females but not males, and the evolutionary rates of sexual dichromatism are positively correlated with the evolutionary rates of colour contrasts in both sexes. Furthermore, we show that species with lower nest safety have significantly reduced female colour contrasts and sexual dichromatism, supporting Wallaces model by highlighting the role of nest predation in driving evolutionary changes in sexual dichromatism within the Phasianidae family.