To Kill A Mockingbird Sexual Selection Examples

Sexual Selection Examples

Acoustic signaling in the Japanese bush warbler, Cettia diphone Differences in bird songs are a phenotypic trait that is under intersexual selection [4]. Bird songs on islands are often reported to be simpler than bird songs on mainland [1]. Hamao (2013) [11] compared differences in songs of populations of Japanese bush warbler on islands and the mainland using frequency-modulation proportions. Hamao found male songs on island populations to be simpler and shorter compared to mainland population. He hypothesized that the higher complexity of songs on the mainland is due to stronger intersexual selection. He used sexual dimorphism as a proxy for intersexual selection and found mainland population to have higher sexual dimorphism in body weight compared to island populations. There is higher intersexual selection on mainland because males are highly polygynous;

Hamao mentioned that the difference in song between island and mainland populations could be due to founder’s effect and a reduced song repertoire in island populations as a result. However, the significant difference in body size supports the presence of higher sexual dimorphism in mainland population that can be explained by stronger sexual selection. More complex songs in mainland population is likely due to stronger intersexual selection (i.e. female preference) because of higher male polygyny; complex songs serves no practical function in the exclusion of rival males. Although it is not explicitly experimented, we know that females on the mainland do not prefer male songs (i.e. less complex songs) from the island populations. This is evidence for assortative mating in at least the mainland population and the behavioural isolation could be the result of intersexual selection on male songs. However, not all species’ male songs are solely under intersexual