Adaptive Diversification Due to Resource Competition in Sexual Models

2011 ◽  
Author(s):  
Michael Doebeli
Keyword(s):  
Reproductive Isolation ◽  
Sexual Reproduction ◽  
Assortative Mating ◽  
Resource Competition ◽  
Disruptive Selection ◽  
Evolutionary Branching ◽  
Adaptive Diversification ◽  
Intermediate Phenotypes ◽  
Branching Point ◽  
Adaptive Speciation

This chapter examines evolutionary branching in sexual populations. As sexual populations converge to what would be a branching point in clonal models, splitting obviously becomes a problem, because mating between different marginal phenotypes generally creates intermediate phenotypes. Through segregation and recombination, sexual reproduction can prevent the establishment of diverging phenotypic clusters in randomly mating populations. To allow for a phenotypic split, mating needs to be assortative with respect to the ecological trait that is under disruptive selection. Thus, the question of evolutionary branching in sexual populations, that is, of adaptive speciation, is intimately tied to questions about the evolution of assortative mating. If evolutionary branching occurs in sexual populations due to the presence of assortative mating mechanisms, the diverging phenotypic clusters will show prezygotic reproductive isolation at least to some extent, and hence they can be viewed as representing incipient species.

scholarly journals Unparallel diversification in bacterial microcosms

2005 ◽  
Vol 272 (1570) ◽  
pp. 1393-1398 ◽  
Author(s):  
Jabus Tyerman ◽  
Naomi Havard ◽  
Gerda Saxer ◽  
Michael Travisano ◽  
Michael Doebeli
Keyword(s):  
Escherichia Coli ◽  
Frequency Dependence ◽  
Growth Characteristics ◽  
Colony Morphology ◽  
Disruptive Selection ◽  
Adaptive Diversification ◽  
Fundamental Process ◽  
Adaptive Speciation

Adaptive speciation has gained popularity as a fundamental process underlying the generation of diversity. We tested whether populations respond to similar forms of disruptive selection by diversifying in similar or parallel ways by investigating diversified populations of Escherichia coli B evolved in glucose and glucose–acetate environments. In both environments, the populations have differentiated into two phenotypes, named for their characteristic colony morphologies: large (L) and small (S). Each type is heritable and this polymorphism (or ‘diversified pair’) appears to be maintained by negative frequency dependence. The L and S phenotypes from different environments are convergent in their colony morphology and growth characteristics. We tested whether diversification was parallel by conducting competition experiments between L and S types from different environments. Our results indicate that replicate diversified pairs from different environments have not diversified in parallel ways and suggest that subtle differences in evolutionary environment can crucially affect the outcome of adaptive diversification.

scholarly journals EFFECTS OF POPULATION SIZE AND SELECTION INTENSITY ON RESPONSES TO DISRUPTIVE SELECTION IN DROSOPHILA MELANOGASTER

Genetics ◽  
1974 ◽  
Vol 78 (2) ◽  
pp. 715-735
Author(s):  
J S F Barker ◽  
L J E Karlsson
Keyword(s):  
Assortative Mating ◽  
Random Mating ◽  
Female Parent ◽  
Disruptive Selection ◽  
Lethal Gene ◽  
Selection Intensity ◽  
Bristle Number ◽  
Isolation Index ◽  
Selection Intensities ◽  
High Selection

ABSTRACT Disruptive selection for sternopleural bristle number with opportunity for random mating was done in the four treatment combinations of two population sizes (40 pairs and 8 pairs of selected parents) and two selection intensities (1 in 40 and 1 in 2). In each generation, matings among selected parents were observed in a mating chamber, and progeny collected separately from each female parent. In the high number, high selection intensity treatment, divergence between the high and low parts ceased about generation 11. The isolation index increased rapidly to generation 3, but then fluctuated to termination of the population at generation 17. The overall isolation index was significant, indicating a real tendency to assortative mating. The failure of the isolation index to increase after generation 3 was attributed to lower average mating fitness of high males (due to inbreeding) and reduced receptivity of low females (due to a homozygous lethal gene with a large effect on sternopleural bristle number in heterozygotes). In the two low number treatments, isolation indices fluctuated from generation to generation with no obvious trends, and none of the overall isolation indices were significantly different from zero. The high number, low selection intensity treatment showed very little divergence, and one of the replicates showed, in contrast with expectation and the high number, high selection intensity treatment, a significant tendency to disassortative mating. Intense disruptive selection may lead to assortative mating.

Adaptive Diversification Due to Resource Competition in Asexual Models

2011 ◽  
Author(s):  
Michael Doebeli
Keyword(s):  
Resource Selection ◽  
Evolutionary Dynamics ◽  
Resource Competition ◽  
Single Species ◽  
Character Displacement ◽  
Adaptive Diversification ◽  
Ecological Character ◽  
Ecological Character Displacement ◽  
Phenotypic Diversification ◽  
Established Species

This chapter focuses on evolutionary branching in niche position due to frequency-dependent competition. When the majority phenotype of a population is competing for one type of resource, selection may favor minority phenotypes that consume different types of resources, which could result in phenotypic differentiation and divergence. The idea of divergence due to competition is also the basis for the well-known concept of ecological character displacement, although here the focus is not so much on the origin of diversity arising in a single species, but rather on the evolutionary dynamics of existing diversity between different and already established species. Ecological character displacement embodies the possibility that competition between species can drive divergence in characters determining resource use. However, there are alternative evolutionary scenarios for phenotypic diversification. In the context of resource competition, one such alternative is that individuals diversify their diet by evolving a wider niche.

Selection

1996 ◽  
Author(s):  
Thomas Bäck
Keyword(s):  
Model Selection ◽  
Evolutionary Algorithms ◽  
Evolutionary Biology ◽  
Disruptive Selection ◽  
Stabilizing Selection ◽  
Intermediate Phenotypes ◽  
Biological Reality ◽  
Survival And Reproduction ◽  
Implementation Models ◽  
Selection Operator

The genetic operators summarized in the set Ω, i.e. mutation and recombination (and probably others, e.g. inversion) create new individuals in a completely undirected way. In Evolutionary Algorithms, the selection operator plays a major role by imposing a direction on the search process, i.e. a clear preference of those individuals which perform better according to the fitness measure Φ. Selection is the only component of Evolutionary Algorithms where the fitness of individuals has an impact on the evolution process. The practical implementations of selection as discussed in sections 2.1.4, 2.2.4, and 2.3.4 seemingly contradict the biological viewpoint presented in section 1.1, where natural selection was emphasized not to be an active force but instead to be characterized by different survival and reproduction rates. However, artificial implementation models and biological reality are not necessarily contradicting each other. While in biological systems fitness can only be measured indirectly by differences in growth rates, fitness in Evolutionary Algorithms is a direct, well-defined and evaluable property of individuals. The biological struggle for existence (e.g. by predator-prey interactions, capabilities of somatic adaptation, and the particular physical properties of individuals) has no counterpart in computer implementations of standard Evolutionary Algorithms. Therefore, an artificial abstraction of these mechanisms can use fitness measures to determine survival and reproduction a posteriori, since the struggle for existence is completely hidden in the evaluation process of individuals. The fact that different survival and reproduction constitute selection is valid in both cases, but in Evolutionary Algorithms fitness is measurable and implies the survival and reproduction behavior, which is just opposite to biological reality. This is simply an implication of the fitness-centered intention which necessarily prevails design and application of these algorithms. Therefore, it is just a logic consequence to model selection as an active, fitness-based component of Evolutionary Algorithms. However, how to model selection is by no means a simple problem. In evolutionary biology, it is usually distinguished between stabilizing, directed, and disruptive selection (see [Fut90], pp. 174–175). In the case of stabilizing selection, intermediate phenotypes have best fitness values, while disruptive selection is characterized by two or more distinct phenotypes that are highly fit and by intermediate phenotypes of low fitness (this assumes an - albeit unknown - ordering of phenotypes).

scholarly journals Spatial swarm segregation and reproductive isolation between the molecular forms of Anopheles gambiae

2009 ◽  
Vol 276 (1676) ◽  
pp. 4215-4222 ◽  
Author(s):  
Abdoulaye Diabaté ◽  
Adama Dao ◽  
Alpha S. Yaro ◽  
Abdoulaye Adamou ◽  
Rodrigo Gonzalez ◽  
...  
Keyword(s):  
Reproductive Isolation ◽  
Anopheles Gambiae ◽  
Assortative Mating ◽  
Molecular Form ◽  
Mate Recognition ◽  
Spatial Segregation ◽  
Molecular Forms ◽  
Ecological Niches ◽  
Ecological Criteria ◽  
Underlying Mechanisms

Anopheles gambiae , the major malaria vector in Africa, can be divided into two subgroups based on genetic and ecological criteria. These two subgroups, termed the M and S molecular forms, are believed to be incipient species. Although they display differences in the ecological niches they occupy in the field, they are often sympatric and readily hybridize in the laboratory to produce viable and fertile offspring. Evidence for assortative mating in the field was recently reported, but the underlying mechanisms awaited discovery. We studied swarming behaviour of the molecular forms and investigated the role of swarm segregation in mediating assortative mating. Molecular identification of 1145 males collected from 68 swarms in Donéguébougou, Mali, over 2 years revealed a strict pattern of spatial segregation, resulting in almost exclusively monotypic swarms with respect to molecular form. We found evidence of clustering of swarms composed of individuals of a single molecular form within the village. Tethered M and S females were introduced into natural swarms of the M form to verify the existence of possible mate recognition operating within-swarm. Both M and S females were inseminated regardless of their form under these conditions, suggesting no within-mate recognition. We argue that our results provide evidence that swarm spatial segregation strongly contributes to reproductive isolation between the molecular forms in Mali. However this does not exclude the possibility of additional mate recognition operating across the range distribution of the forms. We discuss the importance of spatial segregation in the context of possible geographic variation in mechanisms of reproductive isolation.

scholarly journals Acoustic discrimination of sympatric morphs in Darwin's finches: a behavioural mechanism for assortative mating?

2010 ◽  
Vol 365 (1543) ◽  
pp. 1031-1039 ◽  
Author(s):  
Jeffrey Podos
Keyword(s):  
Assortative Mating ◽  
Disruptive Selection ◽  
Evolutionary Divergence ◽  
Santa Cruz Island ◽  
Evolutionary Diversification ◽  
Acoustic Discrimination ◽  
Behavioural Types ◽  
Geospiza Fortis ◽  
Beak Size ◽  
Behavioural Mechanism

Populations with multiple morphological or behavioural types provide unique opportunities for studying the causes and consequences of evolutionary diversification. A population of the medium ground finch ( Geospiza fortis ) at El Garrapatero on Santa Cruz Island, Galápagos, features two beak size morphs. These morphs produce acoustically distinctive songs, are subject to disruptive selection and mate assortatively by morph. The main goal of the present study was to assess whether finches from this population are able to use song as a cue for morph discrimination. A secondary goal of this study was to evaluate whether birds from this population discriminate songs of their own locality versus another St Cruz locality, Borrero Bay, approximately 24 km to the NW. I presented territorial males with playback of songs of their own morph, of the other morph, and of males from Borrero Bay. Males responded more strongly to same-morph than to other-morph playbacks, showing significantly shorter latencies to flight, higher flight rates and closer approaches to the playback speaker. By contrast, I found only minor effects of locality on responsiveness. Evidence for morph discrimination via acoustic cues supports the hypothesis that song can serve as a behavioural mechanism for assortative mating and sympatric evolutionary divergence.

Review Lecture Disruptive selection

1972 ◽  
Vol 182 (1067) ◽  
pp. 109-143 ◽  
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.

Sign in / Sign up

Export Citation Format

Share Document