Sexual dimorphism
Condition where sexes differ in morphology beyond reproduction.
Sexual dimorphism is the condition where different sexes of the same species exhibit different morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecious species, which consist of most animals and some plants. Differences may include secondary sex characteristics, size, weight, color, markings, or behavioral or cognitive traits. Male–male reproductive competition has evolved a diverse array of sexually dimorphic traits. The opposite of dimorphism is monomorphism, when both biological sexes are phenotypically indistinguishable from each other.
- field
- Biology, evolutionary biology
- known_for
- Condition where sexes of the same species exhibit different morphological characteristics
- examples
- Peafowl, blue tits, frogs, guppies, redlip blennies, Catasetum orchids, Cannabis sativa
- types
- Sexual dichromatism, reversed sexual dimorphism, ontogenetic and dynamic dichromatism
Lore & Background
Sexual dimorphism manifests in many forms, including ornamentation and coloration. A difference in the coloration of sexes within a given species is called sexual dichromatism, commonly seen in many species of birds and reptiles. The peafowl constitute conspicuous illustrations: the ornate plumage of peacocks attracts peahens, while the peahen is of a subdued brown coloration. Similar examples are manifold, such as in birds of paradise and argus pheasants. Another example is nestling blue tits, where males are chromatically more yellow than females, a trait linked to carotenoid intake from green Lepidopteran larvae. Frogs also illustrate the principle, with two types of dichromatism: ontogenetic (permanent color changes) and dynamic (temporary changes during breeding season).
Reader's Guide
Sexual dimorphism is a widespread biological phenomenon with significant evolutionary implications. It arises primarily through sexual selection, where traits such as ornamental feathering or aggressive weapons evolve to improve mating success. The increased fitness resulting from ornamentation offsets its cost to produce or maintain, suggesting complex evolutionary implications. Reversed sexual dimorphism, where females are larger or more ornamented than males, occurs in raptors, spiders, the leopard seal, and certain waders. In plants, sexual dimorphism is common in dioecious species, often associated with wind-pollination due to selection for efficient pollen dispersal in males versus pollen capture in females. The study of sexual dimorphism helps illuminate the interplay between natural and sexual selection, and the diverse strategies organisms use to reproduce.
Did You Know?
- The peacock's ornate plumage increases its vulnerability to predators because it is a hindrance in flight and renders the bird conspicuous.
- Male blue tits have a violet-tinted plumage in the ultraviolet spectrum, thought to be an indicator of male parental abilities.
- In redlip blennies, only the male fish develops an organ that produces antimicrobial substances to protect eggs from microbial infections.
- Catasetum orchids are an exception to the rule that insect-pollinated plants look similar; male flowers violently attach pollinia to bee pollinators.
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