page_title: Assortative mating
section_title: In non-human animals
hierarchical_section_title: Assortative mating / In non-human animals
caption_attribution_description: アズマヒキガエル 学名：’’Bufo japonicus formosus’’ 英名：Eastern-Japanese Common Toad ペットショップで売られている個体 Location 神戸市中央区 ペットショップにて Source http://opencage.info/pics/large_6403.asp Copyright OpenCage
context_page_description: Assortative mating is a mating pattern and form of sexual selection in which individuals with similar phenotypes mate with one another more frequently than would be expected under a random mating pattern. Some examples of similar phenotypes are body size or skin coloration or pigmentation. Assortative mating can increase genetic relatedness within the family and is the inverse of disassortative mating.
  Disassortative mating means that individuals with dissimilar genotypes or phenotypes mate with one another more frequently than would be expected under random mating. Disassortative mating reduces the genetic similarities within the family. Positive assortative mating occurs more frequently than negative assortative mating. In both cases, the nonrandom mating pattern result in a typical deviation from the Hardy–Weinberg principle.
context_section_description: Assortative mating in animals has been observed with respect to body size and color. Size-related assortative mating is prevalent across many species of vertebrates and invertebrates. 
  It has been found in the simultaneous hermaphrodites such as the land snail Bradybaena pellucida. One reason for its occurrence can be reciprocal intromission (i.e. both individuals provide both male and female gametes during a single mating) that happens in this species. Therefore, individuals with similar body size pair up with one another to facilitate this exchange. Moreover, it is known that larger individuals in such hermaphroditic species produce more eggs, so mutual mate choice is another factor leading to assortative mating in this species.
  Evidence for size-related assortative mating has also been found in the mangrove snail, Littoraria ardouiniana and in the Japanese common toad, Bufo japonicus.
  The second common type of assortative mating occurs with respect to coloration. This type of assortative mating is more common in socially monogamous bird species such as the eastern bluebirds (Sialia sialis) and western bluebirds (Sialia mexicana). In both species more brightly colored males mated with more brightly colored females and less brightly colored individuals paired with one another. Eastern bluebirds also mate assortatively for territorial aggression due to fierce competition for a limited number of nesting sites with tree swallows. Two highly aggressive individuals are better equipped to protect their nest, encouraging assortative mating between such individuals.
  Assortative mating with respect to two common color morphs: striped and unstriped also exists in a polymorphic population of eastern red-backed salamanders (Plethodon cinereus).
  Assortative mating is also found in many socially monogamous species of birds. Monogamous species are often involved in bi-parental care of their offspring. Since males are equally invested in the offspring as the mother, both genders are expected to display mate choice, a phenomenon termed as mutual mate choice. Mutual mate choice occurs when both males and females are searching for a mate that will maximize their fitness. In birds, female and male ornamentation can indicate better overall condition or such individuals might have better genes, or be better suited as parents.
caption: Japanese common toad
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