Disassortative mating (also known as negative assortative mating or heterogamy) is a mating pattern in which individuals with dissimilar phenotypes mate with one another more frequently than would be expected under random mating. Disassortative mating reduces the mean genetic similarities within the population and produces a greater number of heterozygotes. The pattern is character specific, but does not affect allele frequencies.[1] This nonrandom mating pattern will result in deviation from the Hardy-Weinberg principle (which states that genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences, such as "mate choice" in this case).
Disassortative mating is different from outbreeding, which refers to mating patterns in relation to genotypes rather than phenotypes.
Due to homotypic preference (bias toward the same type), assortative mating occurs more frequently then disassortative mating.[2][3] This is due to the fact that homotypic preferences increase relatedness between mates and between parents and offspring that would promote cooperation and increases inclusive fitness. With disassortative mating, heterotypic preference (bias towards different types) in many cases has been shown to increase overall fitness.[4] When this preference is favored, it allows a population to generate and/or maintain polymorphism (genetic variation within a population).
The fitness advantage aspect of disassortative mating seems straightforward, but the evolution of selective forces involved in disassortative mating are still largely unknown in natural populations.
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Mating behavior and inclusive fitness | Individuals and Society | MCAT | Khan Academy
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Definition of assortative mating
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What is assortative mating?
Transcription
- [Voiceover] Mating is the pairing of opposite sex organisms for the purpose of reproduction, and the subsequent propagation of genetic material. And this includes the actual act of mating, but it can also refer to all of the other behaviors that could be associated with this process. This could include things like elaborate mating dances, and a good example of this is the superb bird of paradise, and yes, that is its real name. When the male superb bird of paradise wants to attract a female, he does kind of a complicated dance that involves him bouncing around, and then fluffing out his feathers in such a way that it kind of looks like a face, and I have a drawing of what it looks like here, but this is something that you should go on YouTube and watch a clip of, because it is really pretty fantastic and ridiculous. Other behaviors that would be included under mating behaviors would be things that happen after mating. Things like nest-building, or feeding the young. In terms of searching for a mate, animals use many different mating strategies. The first one is random mating, which would describe a situation where all individuals within a species are potential partners, meaning that they all are equally likely to mate with each other. And so, random mating is not influenced by environment, or heredity, or any kind of behavioral or a social limitation. And this can be a pretty good strategy, because it ensures a large amount of genetic diversity. There are also a number of non-random mating strategies, or cases where each individual is not equally likely to be chosen as a mate. For example, assortative mating is a strategy where individuals with certain similarities, either in genotypes or phenotypes, or genes or physical appearance, tend to mate with each other at a higher frequency. For example, large animals tend to mate with large animals, and small animals tend to mate with other small animals. And while this can generally be seen as a pretty good mating strategy, the mating of two individuals who are too genetically similar to each other, which is also known as in-breeding, tends to weaken a population overall, because it can increase the likelihood that harmful recessive traits will be passed along to offspring. Disassortative mating, or non-assortative mating, is the opposite of assortative mating. So, with assortative mating, individuals with similar traits were more likely to mate. In contrast, non-assortative mating describes a situation where individuals with different, or diverse, traits mate at a higher frequency than we would see with random mating. And you might be wondering which of these strategies is better. And that's actually kind of an odd question, but in general, I would say that scientists would point to assortative mating, because despite the dangers of in-breeding, it can generally help to increase the inclusive fitness of an organism. And I might as well point out that this concept, inclusive fitness, is one that I struggled with when I was in college, and so I'm going to try to break it down as well as I can. The inclusive fitness of an organism concerns the number of offspring an animal has, how they support them, and how their offspring could support each other. So typically, we think about fitness on an individual level, that an individual creature, on some level, wants to be able to reproduce, and pass on his or her genes. But inclusive fitness is trying to think about this on a slightly larger level. It points out that because close relatives of an individual tend to have similar genes, it would be evolutionarily advantageous for an animal to promote the reproduction and survival of closely related individuals, as well as him or herself, meaning that it is not only our individual genes, but also highly related genes, that it would be advantageous to promote. And that's what we mean when we talk about inclusive fitness. And I think that this concept can help us solve some of the problems that people tend to have with evolution. When people talk about evolution, they tend to focus on things like survival of the fittest, which, if taken literally, would predict that animals, including humans, might be predisposed to act selfishly, to do whatever would be necessary to live the longest, and reproduce the most. But of course, most people don't really act like that. They're kind to other people. They help others. And this is actually what inclusive fitness accounts for, because it predicts that we will behave helpfully and altruistically towards those with genes similar to our own, and that is exactly what we see. Studies about human altruism show that people are more likely to behave altruistically towards people who share the same last name with them, which is a modern cue of possible relatedness, and therefore, shared genetic material.
Types of disassortative mating
Imprinting is one example of disassortative mating. A model shows that individuals imprint on a genetically transmitted trait during early ontogeny and choosy females later use those parental images as a basis of mate choice. A viability-reducing trait may be maintained even without the fertility cost of same-type matings.[5] With imprinting, preference can be established even if it is initially rare, when there is a fertility cost of same-type matings.
One uncommon type of disassortative mating is the female preference on rare (or novel) male phenotypes. A study on guppies, Poecilia reticulata, revealed that the female preference was sufficient to tightly maintain polymorphism in male traits.[6] This type of mate choice shows that costly preferences can persist at higher frequencies if mate choice is hindered, which would allow the alleles to approach fixation.
Effects
Disassortative mating may result in balancing selection and the maintenance of high genetic variation in the population. This is due to the excess heterozygotes that are produced from disassortative mating relative to a randomly mating population.
In humans
The best-known example of disassortative mating in humans is preference for genes in the major histocompatibility complex (MHC) region on chromosome 6. Individuals feel more attracted to odors of individuals who are genetically different in this region.[7] This promotes MHC heterozygosity in the children, making them less vulnerable to pathogens.
In non-human species
Evidence from research regarding coloration in Heliconius butterflies suggests that disassortative mating is more likely to emerge when phenotypic variation is based on self-referencing (mate preference depends on phenotype of the choosing individual, therefore dominance in relationships influence the evolution of disassortative mating).[8]
Disassortative mating has been found with traits such as body symmetry in Amphridromus inversus snails. Normally in snails, rarely are individuals of the opposite coil able to mate with individuals of a normal coil pattern. However, it has been discovered that this species of snail frequents mating between individuals of opposing coils. It is said that the chirality of the spermatophore and the females reproductive tract have a greater chance of producing offspring.[9] This example of disassortative mating promotes polymorphism within the population.
In the scale eating predator fish, Perissodus microlepis, disassortative mating allows the individuals with the rare phenotype of mouth-opening direction to have better success as predators.[10]
House mice conduct disassortative mating as they prefer mates genetically dissimilar to themselves. Specifically, odor profiles in mice are strongly linked to genotypes at the MHC loci controlling changes in the immune response. When MHC-heterozygous offspring are produced, it enhances their immunocompetence because of their ability to recognize a large range of pathogens.[11] Thus, the mice tend to prefer providing "good genes" to their offspring so they will mate with individuals with differences at the MHC loci.
In the seaweed fly, Coelopa frigida, heterozygotes at the locus alcohol dehydrogenase (Adh) have been shown to express better fitness by having higher larval density and relative viability.[12] Females displayed disassortative mating in respect to the Adh locus because they would only mate with males of the opposite Adh genotype.[13] It is suspected that they do this to maintain genetic variation in the population.
White-throated sparrows, Zonotrichia albicollis, prefer strong disassortative mating behaviors regarding the color of their head stripe. The single locus that controls this expression is only observed in heterozygotes. Additionally, the heterozygote arrangement of chromosome 2 from disassortative mating produced offspring of high aggression which is shown to be a social behavior that allows them to dominate their opponents.[14]
References
- ^ Lewontin, Richard; Kirk, Dudley; Crow, James (1963). "Selective mating, assortative mating, and inbreeding: Definitions and implications". Eugenics Quarterly. 15 (2): 141–143. doi:10.1080/19485565.1968.9987764. PMID 5702329.
- ^ Thiessen; Gregg (1980). "Human assortative mating and genetic equilibrium: An evolutionary perspective". Ethology and Sociobiology. 1 (2): 111–140. doi:10.1016/0162-3095(80)90003-5.
- ^ Wallace, B (January 1958). The role of heterozygosity in drosophila populations (Technical report). OSTI 4289507.
- ^ Burley, Nancy (1983). "The meaning of assortative mating". Ethology and Sociobiology. 4 (4): 191–203. doi:10.1016/0162-3095(83)90009-2.
- ^ Ihara, Yasuo; Feldman, Marcus (2003). "Evolution of disassortative and assortative mating preferences based on imprinting". Theoretical Population Biology. 64 (2): 193–200. doi:10.1016/s0040-5809(03)00099-6. PMID 12948680.
- ^ Kokko, Hanna; Jennions, Michael; Houde, Anne (2007). "Evolution of frequency-dependent mate choice: keeping up with fashion trends". Proceedings. Biological Sciences. 274 (1615): 1317–1324. doi:10.1098/rspb.2007.0043. PMC 2176183. PMID 17360285.
- ^ Wedekind, Claus (1995). "MHC-dependent mate preferences in humans". Proceedings of the Royal Society of London. Series B: Biological Sciences. 260 (1359): 245–249. doi:10.1098/rspb.1995.0087. PMID 7630893. S2CID 34971350.
- ^ Maisonneuve, Ludovic; Joron, Mathieu; Chouteau, Mathieu; Llaurens, Violaine (2020). "Evolution and genetic architecture of disassortative mating at a locus under heterozygote advantage". Evolution. 75 (1): 149–165. bioRxiv 10.1101/616409. doi:10.1111/evo.14129. PMID 33210282. S2CID 227063195.
- ^ Schilthuizen, M. (2007). "Sexual selection maintains whole-body chiral dimorphism in snails". Journal of Evolutionary Biology. 20 (5): 1941–1949. doi:10.1111/j.1420-9101.2007.01370.x. PMC 2121153. PMID 17714311.
- ^ Hori, Michio (1993). "Frequency-Dependent Natural Selection in the Handedness of Scale-Eating Cichlid Fish". Science. 260 (5105): 216–219. Bibcode:1993Sci...260..216H. doi:10.1126/science.260.5105.216. PMID 17807183. S2CID 33113282.
- ^ Penn, Dustin; Potts, Wayne (1999). "The Evolution of Mating Preferences and Major Histocompatibility Complex Genes". The American Naturalist. 153 (2): 145–164. doi:10.1086/303166. PMID 29578757. S2CID 4398891.
- ^ Butlin, R; Collins, P; Day, T (1984). "The effect of larval density on an inversion polymorphism in the seaweed fly Coelopa frigida". Heredity. 52 (3): 415–423. doi:10.1038/hdy.1984.49. S2CID 20675225.
- ^ Day, T; Butlin, R (1987). "Non-random mating in natural populations of the seaweed fly, Coelopa frigida". Heredity. 58 (2): 213–220. doi:10.1038/hdy.1987.35. S2CID 24811609.
- ^ Horton, Brent (2013). "Behavioral Characterization of a White-Throated Sparrow Homozygous for the ZAL2m Chromosomal Rearrangement". Behavior Genetics. 43 (1): 60–70. doi:10.1007/s10519-012-9574-6. PMC 3552124. PMID 23264208.
This page was last edited on 17 March 2024, at 03:17