In some species females compete for food, foraging territories, mating, and nesting sites. Competing females can exhibit morphological, physiological and behavioral adaptations typical of males, which are commonly considered as secondary sexual traits. Competition and the development of traits increasing competitiveness require much energy and may exert adverse effects on fecundity and survival. From an evolutionary perspective, positive selection for increased competitiveness would then result in evolution of reduced values for traits related to fitness...