scholarly journals Host races in plant–feeding insects and their importance in sympatric speciation

2002 ◽  
Vol 357 (1420) ◽  
pp. 471-492 ◽  
Author(s):  
Michele Drès ◽  
James Mallet
Keyword(s):  
Linkage Disequilibrium ◽  
Gene Flow ◽  
Natural Selection ◽  
Reproductive Isolation ◽  
Sympatric Speciation ◽  
Accurate Information ◽  
Sympatric Populations ◽  
New Host ◽  
Host Races ◽  
Plant Feeding

The existence of a continuous array of sympatric biotypes—from polymorphisms, through ecological or host races with increasing reproductive isolation, to good species—can provide strong evidence for a continuous route to sympatric speciation via natural selection. Host races in plant–feeding insects, in particular, have often been used as evidence for the probability of sympatric speciation. Here, we provide verifiable criteria to distinguish host races from other biotypes: in brief, host races are genetically differentiated, sympatric populations of parasites that use different hosts and between which there is appreciable gene flow. We recognize host races as kinds of species that regularly exchange genes with other species at a rate of more than ca . 1% per generation, rather than as fundamentally distinct taxa. Host races provide a convenient, although admittedly somewhat arbitrary intermediate stage along the speciation continuum. They are a heuristic device to aid in evaluating the probability of speciation by natural selection, particularly in sympatry. Speciation is thereby envisaged as having two phases: (i) the evolution of host races from within polymorphic, panmictic populations; and (ii) further reduction of gene flow between host races until the diverging populations can become generally accepted as species. We apply this criterion to 21 putative host race systems. Of these, only three are unambiguously classified as host races, but a further eight are strong candidates that merely lack accurate information on rates of hybridization or gene flow. Thus, over one–half of the cases that we review are probably or certainly host races, under our definition. Our review of the data favours the idea of sympatric speciation via host shift for three major reasons: (i) the evolution of assortative mating as a pleiotropic by–product of adaptation to a new host seems likely, even in cases where mating occurs away from the host; (ii) stable genetic differences in half of the cases attest to the power of natural selection to maintain multilocus polymorphisms with substantial linkage disequilibrium, in spite of probable gene flow; and (iii) this linkage disequilibrium should permit additional host adaptation, leading to further reproductive isolation via pleiotropy, and also provides conditions suitable for adaptive evolution of mate choice (reinforcement) to cause still further reductions in gene flow. Current data are too sparse to rule out a cryptic discontinuity in the apparently stable sympatric route from host–associated polymorphism to host–associated species, but such a hiatus seems unlikely on present evidence. Finally, we discuss applications of an understanding of host races in conservation and in managing adaptation by pests to control strategies, including those involving biological control or transgenic parasite–resistant plants.

scholarly journals Ecological Divergence and the Origins of Intrinsic Postmating Isolation with Gene Flow

2011 ◽  
Vol 2011 ◽  
pp. 1-15 ◽  
Author(s):  
Aneil F. Agrawal ◽  
Jeffrey L. Feder ◽  
Patrik Nosil
Keyword(s):  
Linkage Disequilibrium ◽  
Gene Flow ◽  
Natural Selection ◽  
Theoretical Models ◽  
Ecological Speciation ◽  
Divergent Selection ◽  
Postmating Isolation ◽  
Divergent Natural Selection ◽  
Mathematical Exploration ◽  
Neutral Gene

The evolution of intrinsic postmating isolation has received much attention, both historically and in recent studies of speciation genes. Intrinsic isolation often stems from between-locus genetic incompatibilities, where alleles that function well within species are incompatible with one another when brought together in the genome of a hybrid. It can be difficult for such incompatibilities to originate when populations diverge with gene flow, because deleterious genotypic combinations will be created and then purged by selection. However, it has been argued that if genes underlying incompatibilities are themselves subject to divergent selection, then they might overcome gene flow to diverge between populations, resulting in the origin of incompatibilities. Nonetheless, there has been little explicit mathematical exploration of such scenarios for the origin of intrinsic incompatibilities during ecological speciation with gene flow. Here we explore theoretical models for the origin of intrinsic isolation where genes subject to divergent natural selection also affect intrinsic isolation, either directly or via linkage disequilibrium with other loci. Such genes indeed overcome gene flow, diverge between populations, and thus result in the evolution of intrinsic isolation. We also examine barriers to neutral gene flow. Surprisingly, we find that intrinsic isolation sometimes weakens this barrier, by impeding differentiation via ecologically based divergent selection.

scholarly journals Incomplete reproductive isolation following host shift in brood parasitic indigobirds

2008 ◽  
Vol 276 (1655) ◽  
pp. 219-228 ◽  
Author(s):  
Christopher N Balakrishnan ◽  
Kristina M Sefc ◽  
Michael D Sorenson
Keyword(s):  
Gene Flow ◽  
Reproductive Isolation ◽  
Host Shift ◽  
Plumage Colour ◽  
Common Ancestry ◽  
Host Races ◽  
Host Shifts ◽  
Molecular Studies ◽  
Close Relatives ◽  
Incomplete Reproductive Isolation

Behavioural and molecular studies suggest that brood parasitic indigobirds ( Vidua spp.) rapidly diversified through a process of speciation by host shift. However, behavioural imprinting on host song, the key mechanism promoting speciation in this system, may also lead to hybridization and gene flow among established indigobird species when and if female indigobirds parasitize hosts already associated with other indigobird species. It is therefore not clear to what extent the low level of genetic differentiation among indigobird species is due to recent common ancestry versus ongoing gene flow. We tested for reproductive isolation among three indigobird species in Cameroon, one of which comprises two morphologically indistinguishable host races. Mimicry of host songs corresponded with plumage colour in 184 male indigobirds, suggesting that females rarely parasitize the host of another indigobird species. Paternity analyses, however, suggest that imperfect specificity in host and/or mate choice allows for continuing gene flow between recently formed host races of the Cameroon Indigobird Vidua camerunensis ; while 63 pairs of close relatives were associated with the same host, two strongly supported father–son pairs included males mimicking the songs of the two different hosts of V. camerunensis . Thus, complete reproductive isolation is not necessarily an automatic consequence of host shifts, a result that suggests an important role for natural and/or sexual selection in indigobird speciation.

scholarly journals Evidence for natural selection and barrier leakage in candidate loci underlying speciation in wood ants

2018 ◽  
Author(s):  
J Kulmuni ◽  
P Nouhaud ◽  
L Pluckrose ◽  
I Satokangas ◽  
K Dhaygude ◽  
...  
Keyword(s):  
Survival Analysis ◽  
Gene Flow ◽  
Natural Selection ◽  
Reproductive Isolation ◽  
Temporal Variation ◽  
Real Time ◽  
Genome Scans ◽  
Wood Ants ◽  
Selection For ◽  
Candidate Loci

AbstractWhile speciation underlies novel biodiversity, it is poorly understood how natural selection shapes genomes during speciation. Selection is assumed to act against gene flow at barrier loci, promoting reproductive isolation and speciation. However, evidence for gene flow and selection is often indirect. Here we utilize haplodiploidy to identify candidate barrier loci in hybrids between two wood ant species and integrate survival analysis to directly measure if natural selection is acting at candidate barrier loci. We find multiple candidate barrier loci but surprisingly, proportion of them show leakage between samples collected ten years apart, natural selection favoring leakage in the latest sample. Barrier leakage and natural selection for introgressed alleles could be due to environment-dependent selection, emphasizing the need to consider temporal variation in natural selection in future speciation work. Integrating data on survival allows us to move beyond genome scans, demonstrating natural selection acting on hybrid genomes in real-time.

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

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.

scholarly journals Barriers to gene flow play an important role in miantaining reproductive isolation between two closely related Populus (Salicaceae) species

2020 ◽  
Author(s):  
Yang Tian ◽  
Shuyu Liu ◽  
Pär K. Ingvarsson ◽  
Dandan Zhao ◽  
Li Wang ◽  
...  
Keyword(s):  
Gene Flow ◽  
Natural Selection ◽  
Reproductive Isolation ◽  
Chromosomal Rearrangements ◽  
Tibet Plateau ◽  
Sequencing Data ◽  
Genome Wide ◽  
Or Gene ◽  
Genome Heterogeneity ◽  
Qinghai Tibet Plateau

AbstractIn most species, natural selection plays a key role in genomic heterogeneous divergence. Additionally, barriers to gene flow, such as chromosomal rearrangements or gene incompatibilities, can cause genome heterogeneity. We used genome-wide re-sequencing data from 27 Populus alba and 28 P. adenopoda individuals to explore the causes of genomic heterogeneous differentiation in these two closely related species. In highly differentiated regions, neutrality tests (Tajima’s D and Fay & Wu’s H) revealed no difference while the absolute divergence (dxy) were significantly higher than genome background, which indicates that natural selection did not play a major role but barriers to gene flow play an important role in generating genomic heterogeneous divergence and reproductive isolation. The two species diverged ∼5-10 million years ago (Mya), when the Qinghai-Tibet Plateau reached a certain height and the inland climate of the Asian continent became arid. We further found some genes that are related to reproduction.

Speciation

2003 ◽  
Author(s):  
Mary Jane West-Eberhard
Keyword(s):  
Gene Flow ◽  
Reproductive Isolation ◽  
Developmental Plasticity ◽  
Sympatric Speciation ◽  
Similar Species ◽  
Host Shifts ◽  
Phenotypic Divergence ◽  
Alternative Phenotypes ◽  
Living Things ◽  
As Species

In sexually reproducing organisms, speciation is lineage branching—the origin of reproductive isolation between sister populations descended from a single interbreeding parent population. Obviously, speciation is a process of fundamental importance in evolution. In sexually reproducing organisms, every persistent branching point of a phylogenetic tree, whether between very similar species or higher taxa, reflects a speciation event. Because complete reproductive isolation means the end of gene flow between populations, there is no doubt that it can facilitate genetic and phenotypic divergence. So speciation is a major cause of the diversification of living things. In nonsexual or uniparental populations, isolation between divergent populations may also be called speciation, but reduced gene flow can play no role. Such populations may become genetically distinctive and divergent due to differences in mutation, selection, and drift and thereby qualify as species under some definitions (see M. B. Williams, 1992, for a discussion of the species concept in asexual organisms). This chapter deals only with speciation in sexually reproducing organisms. By the usual view of speciation, some barrier to interbreeding comes first, followed or accompanied by genetic and phenotypic divergence. Reproductive isolation leads to divergence. Here I argue that the reverse may sometimes occur—that divergence, mediated by developmental plasticity and selection, may sometimes originate first and contribute to the evolution of reproductive isolation. As discussed in part III, evolution by disruptive and frequencydependent selection can produce a developmental switch between alternative phenotypes rather than loss of intermediate genotypes. This is particularly well documented in insects, often leading to misidentification of intraspecific morphs as species. Since polymorphic insects may have host-associated morphs, host shifts accompanied by distinctive morphology cannot be assumed to represent sympatric speciation or host-race formation, and sympatric speciation hypotheses need to decisively eliminate the possibility of a role for sympatric divergence in the form of polymorphism or behavioral and physiological plasticity. Such intraspecific host shifts may contribute to speciation, whether sympatric or allopatric, as discussed further below.

scholarly journals Sympatric ecological divergence with coevolution of niche preference

2020 ◽  
Vol 375 (1806) ◽  
pp. 20190749 ◽  
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'.

George Romanes, William Bateson, and Darwin's ‘weak point’

2009 ◽  
Vol 64 (2) ◽  
pp. 139-154 ◽  
Author(s):  
Donald R. Forsdyke
Keyword(s):  
Gene Flow ◽  
Natural Selection ◽  
Reproductive Isolation ◽  
Reproductive System ◽  
Distinct Species ◽  
Sterile Hybrid ◽  
Weak Point ◽  
William Bateson ◽  
Thomas Huxley

Thomas Huxley identified as Darwin's ‘weak point’ the failure of breeders when crossing varieties within a species to simulate the sterility of hybrids derived from crosses between allied species. As a result of the sterility, the parents of a hybrid were, in an evolutionary sense, reproductively isolated from each other, so they would be members of distinct species. In his theory of ‘physiological selection’, Romanes postulated germline ‘collective variations’ that accumulate in certain members of a species; these members are thus ‘physiological complements’ producing fertile offspring when mutually crossed, but sterile offspring when crossed with others. Unlike Darwin's natural selection, which secured reproductive isolation of the fit by elimination of the unfit, physiological selection postulated variations in the reproductive system that were not targets of natural selection; these sympatrically isolated the fit from the fit, leaving two species where initially there had been one. Bateson approved of physiological selection. He noted that Mendel's ‘unit characters’ were ‘sensible manifestations’ of what we now refer to as ‘genes’, but postulated a ‘residue’, distinct from genes, that might affect gene flow between organisms and so originate species. The reproductive isolation of the parents of a sterile hybrid was due to two complementing non-genic factors (the ‘residue’) separately introduced into the hybrid by each parent. Modern studies, especially of yeast hybrids, support the Romanes–Bateson viewpoint.

Spawning Characteristics of Sympatric Populations of Steelhead Trout (Salmo gairdneri): Evidence for Partial Reproductive Isolation

1984 ◽  
Vol 41 (10) ◽  
pp. 1454-1462 ◽  
Author(s):  
Steven A. Leider ◽  
Mark W. Chilcote ◽  
John J. Loch
Keyword(s):  
Gene Flow ◽  
Racial Identity ◽  
Reproductive Isolation ◽  
Reproductive Activity ◽  
Salmo Gairdneri ◽  
Steelhead Trout ◽  
Natural Conditions ◽  
Sympatric Populations ◽  
Flow Restriction ◽  
Substantial Degree

We differentially tagged upstream migrant adult summer and winter steelhead trout (Salmo gairdneri) of hatchery and wild origin in the Kalama River, Washington, and subsequently observed them spawning under natural conditions in a tributary. We found that summer steelhead spawned within the study stream on a spatially random basis. The steelhead spawning interval was 6 mo long, during which hatchery summer steelhead spawned first, followed by wild summer, hatchery winter, and wild winter steelhead. Significant temporal spawning differences were found between hatchery summer and wild winter fish, and between wild summer and wild winter steelhead. We developed estimates of potential reproductive overlap between spawner groups that indicated that most reproductive activity involved members of the same spawner group. Estimated genetic exchange among groups was primarily between hatchery and wild fish within races. Of all possible spawner group comparisons, the smallest potential reproductive overlap estimated was between wild summer and wild winter steelhead. We concluded that, although wild summer and wild winter steelhead were not completely reproductively isolated, a substantial degree of successful gene flow restriction occurred, thereby providing a mechanism for the maintenance of racial identity. Additionally, spatial and temporal spawner segregation was of insufficient magnitude to prevent the potential infusion of hatchery steelhead genes into the wild summer steelhead population.

scholarly journals Sympatric speciation revealed by genome-wide divergence in the blind mole rat Spalax

2015 ◽  
Vol 112 (38) ◽  
pp. 11905-11910 ◽  
Author(s):  
Kexin Li ◽  
Wei Hong ◽  
Hengwu Jiao ◽  
Guo-Dong Wang ◽  
Karl A. Rodriguez ◽  
...  
Keyword(s):  
Gene Flow ◽  
Natural Selection ◽  
Enrichment Analysis ◽  
Habitat Choice ◽  
Breeding Population ◽  
Sympatric Speciation ◽  
Population Divergence ◽  
Genome Wide ◽  
Population Structure Analysis ◽  
Genome Analyses

Sympatric speciation (SS), i.e., speciation within a freely breeding population or in contiguous populations, was first proposed by Darwin [Darwin C (1859) On the Origins of Species by Means of Natural Selection] and is still controversial despite theoretical support [Gavrilets S (2004) Fitness Landscapes and the Origin of Species (MPB-41)] and mounting empirical evidence. Speciation of subterranean mammals generally, including the genus Spalax, was considered hitherto allopatric, whereby new species arise primarily through geographic isolation. Here we show in Spalax a case of genome-wide divergence analysis in mammals, demonstrating that SS in continuous populations, with gene flow, encompasses multiple widespread genomic adaptive complexes, associated with the sharply divergent ecologies. The two abutting soil populations of S. galili in northern Israel habituate the ancestral Senonian chalk population and abutting derivative Plio-Pleistocene basalt population. Population divergence originated ∼0.2–0.4 Mya based on both nuclear and mitochondrial genome analyses. Population structure analysis displayed two distinctly divergent clusters of chalk and basalt populations. Natural selection has acted on 300+ genes across the genome, diverging Spalax chalk and basalt soil populations. Gene ontology enrichment analysis highlights strong but differential soil population adaptive complexes: in basalt, sensory perception, musculature, metabolism, and energetics, and in chalk, nutrition and neurogenetics are outstanding. Population differentiation of chemoreceptor genes suggests intersoil population's mate and habitat choice substantiating SS. Importantly, distinctions in protein degradation may also contribute to SS. Natural selection and natural genetic engineering [Shapiro JA (2011) Evolution: A View From the 21st Century] overrule gene flow, evolving divergent ecological adaptive complexes. Sharp ecological divergences abound in nature; therefore, SS appears to be an important mode of speciation as first envisaged by Darwin [Darwin C (1859) On the Origins of Species by Means of Natural Selection].

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