Mechanisms of Assortative Mating in Speciation with Gene Flow: Connecting Theory and Empirical Research

Hybridization and subsequent genetic introgression are now known to be common features of the histories of many species, including our own. Following hybridization, post-zygotic selection tends to purge introgressed DNA genome-wide. While mate choice can prevent hybridization in the first place, it is also known to play an important role in post-zygotic selection against hybrids, and thus the purging of introgressed DNA. However, this role is usually thought of as a direct one: a mating preference for conspecifics reduces the sexual fitness of hybrids, reducing the transmission of introgressed ancestry. Here, we explore a second, indirect role of mate choice as a barrier to gene flow. Under assortative mating, parents covary in their ancestry, causing ancestry to be "bundled" in their offspring and later generations. This bundling effect increases ancestry variance in the population, enhancing the efficiency with which post-zygotic selection purges introgressed DNA. Using whole-genome simulations, we show that the bundling effect can comprise a substantial portion of mate choice's overall effect as a postzygotic barrier to gene flow, and that it is driven by ancestry covariances both between and within maternally and paternally inherited genomes. Using estimates of the strength of assortative mating in avian hybrid zones, we calculate that the bundling effect of mate choice may increase the amount of purging of introgressed DNA by 40-80%, contributing substantially to the genetic isolation of species.

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Variation in sexual dimorphism and assortative mating do not predict genetic divergence in the sexually dimorphic Goodeid fish Girardinichthys multiradiatus

Current Zoology ◽

10.1093/czoolo/58.3.440 ◽

2012 ◽

Vol 58 (3) ◽

pp. 440-452 ◽

Cited By ~ 8

Author(s):

C. Macías Garcia ◽

G. Smith ◽

C. González Zuarth ◽

J. A. Graves ◽

M. G. Ritchie

Keyword(s):

Sexual Selection ◽

Gene Flow ◽

Sexual Dimorphism ◽

Assortative Mating ◽

Genetic Divergence ◽

Isolation By Distance ◽

Morphological Differentiation ◽

Morphological Differences ◽

Or Gene ◽

Male Morphology

Abstract Sexual dimorphism is often used as a proxy for the intensity of sexual selection in comparative studies of sexual selection and diversification. The Mexican Goodeinae are a group of livebearing freshwater fishes with large variation between species in sexual dimorphism in body shape. Previously we found an association between variation in morphological sexual dimorphism between species and the amount of gene flow within populations in the Goodeinae. Here we have examined if morphological differentiation within a single dimorphic species is related to assortative mating or gene flow between populations. In the Amarillo fish Girardinichthys multiradiatus studies have shown that exaggerated male fins are targets of female preferences. We find that populations of the species differ in the level of sexual dimorphism displayed due to faster evolution of differences in male than female morphology. However, this does not predict variation in assortative mating tests in the laboratory; in fact differences in male morphology are negatively correlated with assortative mating. Microsatellite markers reveal significant genetic differences between populations. However, gene flow is not predicted by either morphological differences or assortative mating. Rather, it demonstrates a pattern of isolation by distance with greater differentiation between watersheds. We discuss the caveats of predicting behavioural and genetic divergence from so-called proxies of sexual selection.

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Learning decreases heterospecific courtship and mating in fruit flies

Biology Letters ◽

10.1098/rsbl.2008.0437 ◽

2008 ◽

Vol 4 (6) ◽

pp. 645-647 ◽

Cited By ~ 48

Author(s):

Reuven Dukas

Keyword(s):

Gene Flow ◽

Assortative Mating ◽

Sexual Behaviour ◽

Fruit Flies ◽

Recent Theory ◽

Incipient Speciation ◽

Adaptive Use ◽

Drosophila Persimilis

Recent theory and data suggest that adaptive use of learning in the context of sexual behaviour could contribute to assortative mating. Experiments examining this issue indicated that male Drosophila persimilis that experienced courtship and rejection by heterospecific females exhibited significantly lower levels of heterospecific courtship and mating compared with those of inexperienced males. These results indicate that experience in the context of sexual behaviour in fruit flies could reduce gene flow between diverging populations, which may contribute to incipient speciation.

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Pairing dynamics and the origin of species

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2011.1549 ◽

2011 ◽

Vol 279 (1731) ◽

pp. 1085-1092 ◽

Cited By ~ 25

Author(s):

Oscar Puebla ◽

Eldredge Bermingham ◽

Frédéric Guichard

Keyword(s):

Sexual Selection ◽

Gene Flow ◽

Mate Choice ◽

Assortative Mating ◽

Evolutionary Biology ◽

Population Genetic Analysis ◽

Flow Through ◽

Individual Based Simulation ◽

The Stability ◽

Standing Question

Whether sexual selection alone can drive the evolution of assortative mating in the presence of gene flow is a long-standing question in evolutionary biology. Here, we report a role for pairing dynamics of individuals when mate choice is mutual, which is sufficient for the evolution of assortative mating by sexual selection alone in the presence of gene flow. Through behavioural observation, individual-based simulation and population genetic analysis, we evaluate the pairing dynamics of coral reef fish in the genus Hypoplectrus (Serranidae), and the role these dynamics can play for the evolution of assortative mating. When mate choice is mutual and the stability of mating pairs is critical for reproductive success, the evolution of assortative mating in the presence of gene flow is not only possible, but is also a robust evolutionary outcome.

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Assortative mating, sexual selection and their consequences for gene flow in Littorina

10.1101/2020.01.28.922658 ◽

2020 ◽

Author(s):

Samuel Perini ◽

Marina Rafajlović ◽

Anja M. Westram ◽

Kerstin Johannesson ◽

Roger K. Butlin

Keyword(s):

Sexual Selection ◽

Gene Flow ◽

Natural Selection ◽

Reproductive Isolation ◽

Assortative Mating ◽

Small Male ◽

Mating Pattern ◽

Barrier Effects ◽

Divergent Natural Selection ◽

Coastal Marine

AbstractWhen divergent populations are connected by gene flow, the establishment of complete reproductive isolation usually requires the joint action of multiple barrier effects. One example where multiple barrier effects are coupled consists of a single trait that is under divergent natural selection and also mediates assortative mating. Such multiple-effect traits can strongly reduce gene flow. However, there are few cases where patterns of assortative mating have been described quantitatively and their impact on gene flow has been determined. Two ecotypes of the coastal marine snail, Littorina saxatilis, occur in North Atlantic rocky-shore habitats dominated by either crab predation or wave action. There is evidence for divergent natural selection acting on size, and size-assortative mating has previously been documented. Here, we analyze the mating pattern in L. saxatilis with respect to size in intensively-sampled transects across boundaries between the habitats. We show that the mating pattern is mostly conserved between ecotypes and that it generates both assortment and directional sexual selection for small male size. Using simulations, we show that the mating pattern can contribute to reproductive isolation between ecotypes but the barrier to gene flow is likely strengthened more by sexual selection than by assortment.

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