ABSTRACT
While the most noteworthy feature of annual shes may be their unusual life history, these animals have long been appreciated by scientists and hobbyists for the striking sexual dimorphism and dichromatism they share with other cyprinodontiforms. Indeed, one of the rst studies on sexual selection in shes was on the African annual Nothobranchius guentheri (Haas, 1976a). Males of most annual sh species are larger than females, exhibit bright coloration in the body anks and have strongly pigmented unpaired ns, perform elaborate courtship displays, and engage in ritualized aggressive contests with other males for access to mates. By contrast, females are small and cryptic with few distinguishing characteristics across species and express behavioral preferences for distinct male phenotypes (Figure 12.1). This pronounced sexual dimorphism suggests that sexual selection shapes the reproductive behavior in this clade (Box 12.1) and that direct and indirect competition for mates should be intense.
