What prompted the birth of dicromatism in evolution?

2020/11/04 Agirre Ruiz de Arkaute, Aitziber - Elhuyar Zientzia Iturria: Elhuyar aldizkaria

The male and female butterfly Ornithoptera goliath (left to right). Ed. Wikimedia Wikimedia

Males and females of many animal species are usually dimorphic, differentiated both in their appearance and in their functioning (basic metabolic functions, immune system, behavior, etc. ). Dichromatism of birds and butterflies is one of the most striking dimorphisms, where males and females have different colors. Charles Darwin proposed that sexual selection has driven in evolution dicromatism before the preference of females by colored males. Somehow, the males developed dichromatism away from the low colors of the females. Alfred Russel Wallace's hypothesis was that females need colors that go unnoticed to transport eggs or to care for their offspring. And he argued that they were females, but they moved away from those striking colors. What is the evolutionary motor that caused dichromatism? 150 years ago it provoked a debate between Darwin and Wallace and the answer was given by the zoologists of the University of Stockholm.

From the point of view of the European butterflies, the phylogenetic branches have analysed the direction and speed of the changes in the colors of the species and the sexes, modeling the change of the colors throughout the evolution. Calculated the ancestors and evolutionary vectors of both sexes, conclude that although the color evolved 26% faster than that of the females, it is possible that the chromatic lineages are a consequence of a strong directional selection. Thus, they conclude that sexual selection was the main driver of dicromatism in European butterflies in evolution. That is, Darwin was right.

According to the researchers, although it does not seem that it is the competition between them that guided dichromism, but the tastes of females. It seems that female butterflies prefer bright and saturated colors, since they guarantee that males are young.