page_title: Sexual dimorphism
section_title: Reproductively advantageous
hierarchical_section_title: Sexual dimorphism / Reproductively advantageous
caption_attribution_description: English: Cryptopsaras couesii File:Cryptopsaras couesii triplewart seadevil.svg is a vector version of this file. It should be used in place of this raster image when not inferior. File:Cryptopsaras couesii (triplewart seadevil).png File:Cryptopsaras couesii triplewart seadevil.svg For more information, see Help:SVG. In other languages Alemannisch&#160;| العربية&#160;| беларуская (тарашкевіца)‎&#160;| български&#160;| বাংলা&#160;| català&#160;| нохчийн&#160;| čeština&#160;| dansk&#160;| Deutsch&#160;| Ελληνικά&#160;| English&#160;| Esperanto&#160;| español&#160;| eesti&#160;| euskara&#160;| فارسی&#160;| suomi&#160;| français&#160;| Frysk&#160;| galego&#160;| עברית&#160;| hrvatski&#160;| magyar&#160;| հայերեն&#160;| Bahasa Indonesia&#160;| italiano&#160;| 日本語&#160;| ქართული&#160;| 한국어&#160;| lietuvių&#160;| македонски&#160;| മലയാളം&#160;| Bahasa Melayu&#160;| norsk bokmål&#160;| Plattdüütsch&#160;| Nederlands&#160;| norsk nynorsk&#160;| norsk&#160;| occitan&#160;| polski&#160;| português&#160;| português do Brasil&#160;| română&#160;| русский&#160;| sicilianu&#160;| Scots&#160;| slovenčina&#160;| slovenščina&#160;| српски / srpski&#160;| svenska&#160;| ไทย&#160;| Türkçe&#160;| татарча/tatarça&#160;| українська&#160;| vèneto&#160;| Tiếng Việt&#160;| 中文&#160;| 中文（中国大陆）‎&#160;| 中文（简体）‎&#160;| 中文（繁體）‎&#160;| 中文（马来西亚）‎&#160;| 中文（台灣）‎&#160;| +/−
context_page_description: Sexual dimorphism is the condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs. The condition occurs in many animals and some plants. Differences may include secondary sex characteristics, size, weight, colour, markings, and may also include behavioral and cognitive differences. These differences may be subtle or exaggerated, and may be subjected to sexual selection and natural selection. The opposite of dimorphism is monomorphism.
context_section_description: In theory, larger females are favored by competition for mates, especially in polygamous species. Larger females offer an advantage in fertility, since the physiological demands of reproduction are limiting in females. Hence there is a theoretical expectation that females tend to be larger in species that are monogamous.
  Females are larger in many species of insects, many spiders, many fish, many reptiles, owls, birds of prey and certain mammals such as the spotted hyena, and baleen whales such as blue whale. As an example, in some species, females are sedentary, and so males must search for them. Fritz Vollrath and Geoff Parker argue that this difference in behaviour leads to radically different selection pressures on the two sexes, evidently favouring smaller males. Cases where the male is larger than the female have been studied as well, and require alternative explanations.
  One example of this type of sexual size dimorphism is the bat Myotis nigricans, (black myotis bat) where females are substantially larger than males in terms of body weight, skull measurement, and forearm length. The interaction between the sexes and the energy needed to produce viable offspring make it favorable for females to be larger in this species. Females bear the energetic cost of producing eggs, which is much greater than the cost of making sperm by the males. The fecundity advantage hypothesis states that a larger female is able to produce more offspring and give them more favorable conditions to ensure their survival; this is true for most ectotherms. A larger female can provide parental care for a longer time while the offspring matures. The gestation and lactation periods are fairly long in M. nigricans, the females suckling their offspring until they reach nearly adult size. They would not be able to fly and catch prey if they did not compensate for the additional mass of the offspring during this time. Smaller male size may be an adaptation to increase maneuverability and agility, allowing males to compete better with females for food and other resources.
  Some species of anglerfish also display extreme sexual dimorphism. Females are more typical in appearance to other fish, whereas the males are tiny rudimentary creatures with stunted digestive systems. A male must find a female and fuse with her: he then lives parasitically, becoming little more than a sperm-producing body in what amounts to an effectively hermaphrodite composite organism. A similar situation is found in the Zeus water bug Phoreticovelia disparata where the female has a glandular area on her back that can serve to feed a male, which clings to her (note that although males can survive away from females, they generally are not free-living). This is taken to the logical extreme in the Rhizocephala crustaceans, like the Sacculina, where the male injects itself into the female's body and becomes nothing more than sperm producing cells, to the point that the superorder used to be mistaken for hermaphroditic.
  Some plant species also exhibit dimorphism in which the females are significantly larger than the males, such as in the moss Dicranum and the liverwort Sphaerocarpos. There is some evidence that, in these genera, the dimorphism may be tied to a sex chromosome, or to chemical signalling from females.
  Another complicated example of sexual dimorphism is in Vespula squamosa, the southern yellowjacket.  In this wasp species, the female workers are the smallest, the male workers are slightly larger, and the female queens are significantly larger than her female worker and male counterparts.
caption: Female triplewart seadevil, an anglerfish, with male attached near vent (arrow)
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