What role does natural selection play in speciation?

If distinct biological species are to coexist in sympatry, they must be reproductively isolated and must exploit different limiting resources. A two-niche Levene model is analysed, in which habitat preference and survival depend on underlying additive traits. The population genetics of preference and viability are equivalent. However, there is a linear trade-off between the chances of settling in either niche, whereas viabilities may be constrained arbitrarily. With a convex trade-off, a sexual population evolves a single generalist genotype, whereas with a concave trade-off, disruptive selection favours maximal variance. A pure habitat preference evolves to global linkage equilibrium if mating occurs in a single pool, but remarkably, evolves to pairwise linkage equilibrium within niches if mating is within those niches—independent of the genetics. With a concave trade-off, the population shifts sharply between a unimodal distribution with high gene flow and a bimodal distribution with strong isolation, as the underlying genetic variance increases. However, these alternative states are only simultaneously stable for a narrow parameter range. A sharp threshold is only seen if survival in the ‘wrong’ niche is low; otherwise, strong isolation is impossible. Gene flow from divergent demes makes speciation much easier in parapatry than in sympatry.

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Review Lecture Disruptive selection

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1972.0070 ◽

1972 ◽

Vol 182 (1067) ◽

pp. 109-143 ◽

Cited By ~ 66

Keyword(s):

Gene Flow ◽

Genetic Variance ◽

Natural Populations ◽

Disruptive Selection ◽

Ecological Niches ◽

Gene Exchange ◽

Bisexual Species ◽

Frequency Dependent ◽

Ecological Conditions ◽

Intermediate Phenotypes

A population is exposed to disruptive selection if more than one phenotype has optimal fitness and intermediate phenotypes have lower fitnesses. Maintenance of the two or more optima may depend upon their relative fitnesses being frequency dependent. Such selection may be expected in two contrasting types of situation. First the two or more optimal phenotypes may depend on one another as do the two sexes in a bisexual species. Secondly the optima may be set by heterogeneity of the environment. Then we may think in terms of a mosaic of ecological niches or a clinal situation, and may expect that gene flow will tend to promote convergence of the sub-populations while disruptive selection tends to promote their divergence. Disruptive selection may therefore be relevant both to the evolution and maintenance of polymorphisms and to the divergence of parts of populations one from another, under the influence of variation of ecological conditions within the range of gametic and/or zygotic dispersal. Disruptive selection has been shown to be capable of increasing phenotypic and genetic variance, of producing and maintaining polymorphisms, of causing divergence of sub-populations between which substantial gene exchange occurs, and of splitting a population into two which are genetically isolated from one another. These results are reviewed and their relevance to natural populations discussed.

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Sympatric ecological divergence with coevolution of niche preference

10.1101/2019.12.20.884817 ◽

2019 ◽

Author(s):

Pavel Payne ◽

Jitka Polechová

Keyword(s):

Genetic Variation ◽

Gene Flow ◽

Assortative Mating ◽

Parameter Space ◽

Sympatric Speciation ◽

Secondary Contact ◽

Disruptive Selection ◽

Ecological Divergence ◽

Trade Off ◽

Speciation Process

AbstractReinforcement, the increase of assortative mating driven by selection against unfit hybrids, is conditional on pre-existing divergence. Yet, for ecological divergence to precede the evolution of assortment, strict symmetries between fitnesses in niches must hold, and/or there must be low gene flow between the nascent species. It has thus been argued that conditions favouring sympatric speciation are rarely met in nature. Indeed, we show that under disruptive selection, violating symmetries in niche sizes and increasing strength of the trade-off in selection between the niches quickly leads to loss of genetic variation, instead of evolution of specialists. The region of the parameter space where polymorphism is maintained further narrows with increasing number of loci encoding the diverging trait and the rate of recombination between them. Yet, evolvable assortment and pre-existing assortment both substantially broaden the parameter space within which polymorphism is maintained. Notably, pre-existing niche preference speeds up further increase of assortment, thus facilitating reinforcement in the later phases of speciation. We conclude that in order for sympatric ecological divergence to occur, niche preference must co-evolve throughout the divergence process. Even if populations come into secondary contact, having diverged in isolation, niche preference substantially broadens the conditions for coexistence in sympatry and completion of the speciation process.

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Sympatric ecological divergence with coevolution of niche preference

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2019.0749 ◽

2020 ◽

Vol 375 (1806) ◽

pp. 20190749 ◽

Cited By ~ 2

Author(s):

Pavel Payne ◽

Jitka Polechová

Keyword(s):

Genetic Variation ◽

Gene Flow ◽

Reproductive Isolation ◽

Parameter Space ◽

Sympatric Speciation ◽

Secondary Contact ◽

Disruptive Selection ◽

Theme Issue ◽

Ecological Divergence ◽

Trade Off

Reinforcement, the increase of assortative mating driven by selection against unfit hybrids, is conditional on pre-existing divergence. Yet, for ecological divergence to precede the evolution of assortment, strict symmetries between fitnesses in niches must hold, and/or there must be low gene flow between the nascent species. It has thus been argued that conditions favouring sympatric speciation are rarely met in nature. Indeed, we show that under disruptive selection, violating symmetries in niche sizes and increasing strength of the trade-off in selection between the niches quickly leads to loss of genetic variation, instead of evolution of specialists. The region of the parameter space where polymorphism is maintained further narrows with increasing number of loci encoding the diverging trait and the rate of recombination between them. Yet, evolvable assortment and pre-existing assortment both substantially broaden the parameter space within which polymorphism is maintained. Notably, pre-existing niche preference speeds up further increase of assortment, thus facilitating reinforcement in the later phases of speciation. We conclude that in order for sympatric ecological divergence to occur, niche preference must coevolve throughout the divergence process. Even if populations come into secondary contact, having diverged in isolation, niche preference substantially broadens the conditions for coexistence in sympatry and completion of the speciation process. This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers'.

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Differentiation and Interrelations of Two Representatives of Laudakia stellio Complex (Reptilia: Agamidae) in Israel

Russian Journal of Herpetology ◽

10.30906/1026-2296-1997-4-2-102-114 ◽

2011 ◽

Vol 4 (2) ◽

pp. 102-114 ◽

Cited By ~ 2

Author(s):

Evgenyi N. Panov ◽

Larissa Yu. Zykova

Keyword(s):

Population Structure ◽

Gene Flow ◽

Habitat Preference ◽

Additional Data ◽

Near East ◽

Field Studies ◽

Subspecies Level ◽

Limited Gene Flow ◽

Study Sites ◽

And Behavior

Field studies were conducted in Central Negev within the breeding range of Laudakia stellio brachydactyla and in NE Israel (Qyriat Shemona) in the range of an unnamed form (tentatively “Near-East Rock Agama”), during March – May 1996. Additional data have been collected in Jerusalem at a distance of ca. 110 km from the first and about 170 km from the second study sites. A total of 63 individuals were caught and examined. The animals were marked and their subsequent movements were followed. Social and signal behavior of both forms were described and compared. Lizards from Negev and Qyriat Shemona differ from each other sharply in external morphology, habitat preference, population structure, and behavior. The differences obviously exceed the subspecies level. At the same time, the lizards from Jerusalem tend to be intermediate morphologically between those from both above-named localities, which permits admitting the existence of a limited gene flow between lizard populations of Negev and northern Israel. The lizards from NE Israel apparently do not belong to the nominate subspecies of L. stellio and should be regarded as one more subspecies within the species.

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Faculty Opinions recommendation of Locally adapted traits maintained in the face of high gene flow.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.725223126.793501360 ◽

2014 ◽

Author(s):

Ian Wang

Keyword(s):

Gene Flow ◽

High Gene Flow ◽

The Face ◽

High Gene

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Dispersal and Differentiation of Deep-Sea Mussels of the GenusBathymodiolus(Mytilidae, Bathymodiolinae)

Journal of Marine Biology ◽

10.1155/2009/625672 ◽

2009 ◽

Vol 2009 ◽

pp. 1-15 ◽

Cited By ~ 31

Author(s):

Akiko Kyuno ◽

Mifue Shintaku ◽

Yuko Fujita ◽

Hiroto Matsumoto ◽

Motoo Utsumi ◽

...

Keyword(s):

Gene Flow ◽

Genetic Differentiation ◽

Shallow Water ◽

Deep Sea ◽

Dispersal Ability ◽

Evolutionary Transition ◽

Significant Genetic Differentiation ◽

Evolutionary Processes ◽

High Dispersal ◽

High Gene

We sequenced the mitochondrial ND4 gene to elucidate the evolutionary processes ofBathymodiolusmussels and mytilid relatives. Mussels of the subfamily Bathymodiolinae from vents and seeps belonged to 3 groups and mytilid relatives from sunken wood and whale carcasses assumed the outgroup positions to bathymodioline mussels. Shallow water mytilid mussels were positioned more distantly relative to the vent/seep mussels, indicating an evolutionary transition from shallow to deep sea via sunken wood and whale carcasses.Bathymodiolus platifronsis distributed in the seeps and vents, which are approximately 1500 km away. There was no significant genetic differentiation between the populations. There existed high gene flow betweenB. septemdierumandB. breviorand low but not negligible gene flow betweenB. marisindicusandB. septemdierumorB. brevior, although their habitats are 5000–10 000 km away. These indicate a high adaptability to the abyssal environments and a high dispersal ability ofBathymodiolusmussels.

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