Sexual dimorphism
- Pronunciation
- /SEK-shoo-uhl dye-MOR-fiz-um/
- Category
- General Biology
- Singular
- sexual dimorphism
Definition
Phenotypic differences between males and females of the same beyond the primary reproductive organs. In , dimorphism frequently involves body size, coloration, ornamentation, weaponry, or antennal structure, and may reflect contrasting selection pressures: males often evolve exaggerated traits through intrasexual competition or female choice, while females may be larger due to selection or differential resource allocation. The degree of dimorphism varies from subtle (slight size divergence) to extreme (distinctly different body plans, as in some insects or spiders).
Etymology
From Latin sexualis (of sex) and Greek dimorphos (having two forms), via New Latin dimorphismus.
Example
In many orb-weaving spiders (Araneidae), females are substantially larger and more robust than males, sometimes by an order of magnitude, while males often possess modified for sperm transfer and may exhibit brighter coloration or distinct abdominal patterns. Some , such as the African swallowtail Papilio dardanus, show female-limited with multiple mimetic morphs, while males maintain a single non-mimetic phenotype.
Synonyms
- sexual dichromatism
- sexual dimorphy
Related Terms
- monomorphism
- secondary sexual characteristics
- Sexual selection
- intrasexual selection
- intersexual selection
- gonochorism
- protandry
- protogyny
- Rensch's rule
Usage Notes
Distinguished from seasonal or by its consistent association with genetic sex rather than environmental cues. In entomological literature, "sexual dimorphism" is sometimes used more narrowly to refer specifically to morphological (not behavioral or physiological) differences, though the broader usage is standard in evolutionary . When describing color differences alone, "sexual dichromatism" is more precise. The term applies equally to male-biased and female-biased dimorphism, though male-biased exaggeration is more commonly discussed.