Sexual Dimorphism Articles from SEXGRINDER.COM Free Article Directory

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Sexual dimorphism is the systematic difference in form between individuals of different sex in the same species. Examples include size, color, and the presence or absence of parts of the body used in courtship displays or fights, such as ornamental feathers, horns, antlers or tusks.

Dimorphism comes from two Greek words, di meaning two and morph meaning form. Thus, sexual dimorphism basically refers to two forms of sex, male and female.

In many species, including most mammals, the male is larger than the female. In others, such as most insects, spiders, birds, reptiles and amphibians, many fish, and certain mammals such as the spotted hyena, the female is larger than the male. Other sex-specific differences include differences in colouration (sexual dichromatism), presence vs. absence of certain body parts such as horns, antlers, tusks or display feathers; size of the eyes (some insects); possession of stings (various kinds of Hymenoptera), and different thresholds for certain behaviors (aggression, infant care, etc).

Among vertebrates, sexual dimorphism is particularly apparent in ducks, and most gamefowl perhaps most dramatically including peafowl. Male pheasants are notably larger than females and possess bright plumage; females are usually a drab brown irrespective of the particular species. In some birds (most of which are waders such as the phalaropes and painted snipes), females have brighter colors than males. As this is the opposite of the usual sexual dichromatism, it is termed reverse sexual dimorphism. In many predatory birds females are larger than males, often considerably so. This seems to reduce competition between members of a pair, as they have different optimal prey sizes. Some cases of sexual dimorphism in birds are so striking that males and females of the same species were originally taken to be members of entirely different species, as in the case of the Eclectus Parrot (Eclectus roratus), where the male is predominantly green with an orange beak and the female scarlet and deep blue with a black beak.

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