Sex and Adaptation in a Changing Environment

Genetics ◽  
1999 ◽  
Vol 153 (2) ◽  
pp. 1041-1053 ◽  
Author(s):  
David Waxman ◽  
Joel R Peck
Keyword(s):  
Mathematical Model ◽  
Genetic Variability ◽  
Environmental Change ◽  
Natural Populations ◽  
Changing Environment ◽  
Asexual Population ◽  
Sexual Population ◽  
Large Populations ◽  
Stochastic Forces ◽  
Low Rate

Abstract In this study we consider a mathematical model of a sexual population that lives in a changing environment. We find that a low rate of environmental change can produce a very large increase in genetic variability. This may help to explain the high levels of heritability observed in many natural populations. We also study asexuality and find that a modest rate of environmental change can be very damaging to an asexual population, while leaving a sexual population virtually unscathed. Furthermore, in a changing environment, the advantages of sexuality over asexuality can be much greater than suggested by most previous studies. Our analysis applies in the case of very large populations, where stochastic forces may be neglected.

scholarly journals Genetic variability under the seedbank coalescent

2015 ◽  
Author(s):  
Jochen Blath ◽  
Bjarki Eldon ◽  
Adrian Casanova ◽  
Noemi Kurt ◽  
Maite Wilke-Berenguer
Keyword(s):  
Genetic Variability ◽  
Frequency Spectrum ◽  
Common Ancestor ◽  
Scaling Limit ◽  
Natural Populations ◽  
Recent Common Ancestor ◽  
Most Recent Common Ancestor ◽  
Active Population ◽  
Large Populations ◽  
Site Frequency Spectrum

We analyse patterns of genetic variability of populations in the presence of a large seedbank with the help of a new coalescent structure called the seedbank coalescent. This ancestral process appears naturally as scaling limit of the genealogy of large populations that sustain seedbanks, if the seedbank size and individual dormancy times are of the same order as the active population. Mutations appear as Poisson processes on the active lineages, and potentially at reduced rate also on the dormant lineages. The presence of `dormant' lineages leads to qualitatively altered times to the most recent common ancestor and non-classical patterns of genetic diversity. To illustrate this we provide a Wright-Fisher model with seedbank component and mutation, motivated from recent models of microbial dormancy, whose genealogy can be described by the seedbank coalescent. Based on our coalescent model, we derive recursions for the expectation and variance of the time to most recent common ancestor, number of segregating sites, pairwise differences, and singletons. Estimates (obtained by simulations) of the distributions of commonly employed distance statistics, in the presence and absence of a seedbank, are compared. The effect of a seedbank on the expected site-frequency spectrum is also investigated using simulations. Our results indicate that the presence of a large seedbank considerably alters the distribution of some distance statistics, as well as the site-frequency spectrum. Thus, one should be able to detect from genetic data the presence of a large seedbank in natural populations.

scholarly journals Resampling the pool of genotypic possibilities: an adaptive function of sexual reproduction

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Donal A. Hickey ◽  
G. Brian Golding
Keyword(s):  
Genetic Variation ◽  
Natural Selection ◽  
Sexual Reproduction ◽  
Finite Population ◽  
Natural Populations ◽  
Initial Population ◽  
Adaptive Function ◽  
Asexual Population ◽  
Sexual Population ◽  
The Universe

Abstract Background Natural populations harbor significant levels of genetic variability. Because of this standing genetic variation, the number of possible genotypic combinations is many orders of magnitude greater than the population size. This means that any given population contains only a tiny fraction of all possible genotypic combinations. Results We show that recombination allows a finite population to resample the genotype pool, i.e., the universe of all possible genotypic combinations. Recombination, in combination with natural selection, enables an evolving sexual population to replace existing genotypes with new, higher-fitness genotypic combinations that did not previously exist in the population. This process allows the sexual population to gradually increase its fitness far beyond the range of fitnesses in the initial population. In contrast to this, an asexual population is limited to selection among existing lower fitness genotypes. Conclusions The results provide an explanation for the ubiquity of sexual reproduction in evolving natural populations, especially when natural selection is acting on the standing genetic variation.

scholarly journals Selection against harmful mutations in large sexual and asexual populations

1982 ◽  
Vol 40 (3) ◽  
pp. 325-332 ◽  
Author(s):  
Alexey S. Kondrashov
Keyword(s):  
Reasonable Assumption ◽  
New Mutation ◽  
Asexual Population ◽  
Sexual Population ◽  
A Genome ◽  
Large Populations ◽  
Asexual Populations ◽  
Average Fitness ◽  
Equilibrium Number ◽  
New Mutations

SUMMARYSelection against harmful mutations in large populations is studied assuming that the rate of fitness decrease grows with every new mutation added to a genome. Under this reasonable assumption (Mayr, 1970) the average fitness of a sexual population, without linkage between the loci, is higher, and the average equilibrium number of harmful mutations per individual lower, than in an asexual population. If a gamete contains on the average one or more new mutations, the resulting advantage of sexual reproduction and recombination seems to be sufficient to counterbalance the double advantage of parthenogenesis. Moreover, selection against harmful mutations is probably the most powerful factor preventing linkage disequilibrium even with epistatic interaction between the loci.

scholarly journals Fitness-valley crossing in subdivided asexual populations

2016 ◽  
Author(s):  
Michael R. McLaren
Keyword(s):  
Quantitative Description ◽  
Natural Populations ◽  
Asexual Population ◽  
Migration Rates ◽  
Large Populations ◽  
Subdivided Populations ◽  
The Mean ◽  
And Migration ◽  
Asexual Populations ◽  
Mean Time

AbstractAdaptations may require multiple mutations that are beneficial only in combination. To adapt, a lineage must acquire mutations that are individually neutral or deleterious before gaining the beneficial combination, thereby crossing a plateau or valley, respectively, in the mapping from genotype to fitness. Spatial population structure can facilitate plateau and valley crossing by allowing neutral and deleterious lineages to survive longer and produce more beneficial mutants. Here, we analyze adaptation across a two-mutation plateau or valley in an asexual population that is subdivided into discrete subpopulations, or demes, connected by migration. We describe how subdivision alters the dynamics of adaptation from those in an equally sized unstructured population and give a complete quantitative description of these dynamics for the island migration model. Subdivision can significantly decrease the waiting time for the adaptation if demes and migration rates are small enough that single-mutant lineages fix in one or more demes before producing the beneficial double mutant. But, the potential decrease is small in very large populations and may also be limited by the slow spread of the beneficial mutant in extremely subdivided populations. Subdivision has a smaller effect on the probability that the population adapts very quickly than on the mean time to adapt, which has important consequences in some applications, such as the development of cancer. Our results provide a general and intuitive framework for predicting the effects of spatial structure in other models and in natural populations.

scholarly journals THE PARTHENOGENETIC CAPACITIES AND GENETIC STRUCTURES OF SYMPATRIC POPULATIONS OF DROSOPHILA MERCATORUM AND DROSOPHILA HYDEI

Genetics ◽  
1979 ◽  
Vol 92 (4) ◽  
pp. 1283-1293
Author(s):  
Alan R Templeton
Keyword(s):  
Natural Populations ◽  
Population Increase ◽  
Sympatric Populations ◽  
Sexual Population ◽  
Garbage Dump ◽  
Drosophila Hydei ◽  
Drosophila Mercatorum ◽  
Hardy Weinberg Equilibrium ◽  
Genetic Structures ◽  
Low Rate

ABSTRACT Drosophila mercatorum is a sexual species that can reproduce parthenogenetically in the laboratory. A previous study showed that a natural population of D. mercatorum inhabiting the Kamuela garbage dump on the Island of Hawaii could produce both viable parthenogenetic adults and self-sustaining parthenogenetic lines. The present study deals with a second screen for parthenogenesis and an isozyme survey performed on natural populations of D. mercatorum and D. hydei caught in patches of Opuntia tuna about 10 kilometers from Kamuela. Both cactus-patch species produced viable partheno-genetic adults, but only D. mercatorum produced parthenogenetic females themselves capable of parthenogenesis. Moreover, D. mercatorum produced several "hot" lines characterized by high parthenogenetic rates, while all lines of D. hydei had a homogenous low rate. The parthenogenetic capacity of the cactus-patch D. mercaiorum was lower than that of the garbage-dump D. mercatorum. Moreover, both the cactus-patch D. mercatorum and D. hydei had lower levels of polymorphism (26% and 22%, respectively) then the garbage-dump D. mercatorum (44%), and both cactus-patch populations had heterozygote deficiencies with respect to Hardy-Weinberg equilibrium, unlike the garbage-dump population. Consequently, these data do not support the idea that decreased levels of heterozygosity in a sexual population increase the chance that sexual females will produce totally homozygous, parthenogenetic progeny.

scholarly journals Differentiation and genetic variability in natural populations of Anopheles (N.) triannulatus (Neiva& Pinto, 1922) of Brazilian Amazonia

2004 ◽  
Vol 64 (2) ◽  
pp. 327-336 ◽  
Author(s):  
J. M. M. Santos ◽  
J. F. Maia ◽  
W. P. Tadei
Keyword(s):  
Genetic Variability ◽  
Natural Populations ◽  
Isozyme Analysis ◽  
Brazilian Amazonia ◽  
F Statistics

Populations of Anopheles triannulatus from Macapá (AP), Aripuanã (MT), Ji-Paraná (RO), and Manaus-Janauari Lake (AM) were studied using 16 enzymatic loci. The results of the isozyme analysis showed that the population of Macapá presented higher polymorphism (56.3%). The lowest variability was observed in the population of Manaus (p = 25.0; Ho = 0.077 ± 0.046). The results of Wright's F statistics showed unbalance due to excess of homozygotes (Fis > Fst), denoting a certain intrapopulational differentiation. Although the populations are genetically very close (D = 0.003 - 0.052), the dendrogram separates the populations in two groups: Macapá separated from that of Manaus, Ji-Paraná, and Aripuanã. This result may suggest a reduction in the genic flow, which possibly had some influence in the substructuration of the populations.

Social Responses to a Changing Environment

2021 ◽  
Author(s):  
Lisa Reyes Mason ◽  
Susan P. Kemp ◽  
Lawrence A. Palinkas ◽  
Amy Krings
Keyword(s):  
Social Work ◽  
Environmental Change ◽  
Social Vulnerability ◽  
Cultural Relevance ◽  
Social Acceptability ◽  
Water Shortages ◽  
Changing Environment ◽  
Social Responses ◽  
Key Concepts ◽  
Technical Solutions

Communities worldwide are facing environmental crises such as air pollution, water shortages, climate change, and other forms of environmental change and degradation. While technical solutions for environmental change are essential, so too are solutions that consider social acceptability, value cultural relevance, and prioritize equity and social justice. Social work has a critical and urgent role in creating and implementing macrolevel social responses to environmental change. The key concepts of environmental change, environmental and ecological justice, social vulnerability, and social responses are discussed. A description of the roles and skills unique to macro social workers for this effort is given, followed by examples of macrolevel strategies and interventions. Opportunities and directions for future social work responses to a changing environment are identified.

scholarly journals Genetic variability of brycon orbignyanus (valenciennes, 1850) (characiformes: characidae) in cultivated and natural populations of the upper paraná river, and implications for the conservation of the species

2011 ◽  
Vol 54 (4) ◽  
pp. 839-848 ◽  
Author(s):  
Renata de Souza Panarari-Antunes ◽  
Alberto José Prioli ◽  
Sônia Maria Alves Pinto Prioli ◽  
Alexsandro Sobreira Galdino ◽  
Horácio Ferreira Julio Junior ◽  
...  
Keyword(s):  
Genetic Variability ◽  
Natural Populations ◽  
Paraná River ◽  
Parana River ◽  
Upper Paraná River

Genetic variability in the natural populations of Lasioderma serricorne (F.) (Coleoptera: Anobiidae), detected by RAPD markers and by esterase isozymes

2015 ◽  
Vol 106 (1) ◽  
pp. 47-53 ◽  
Author(s):  
T. Coelho-Bortolo ◽  
C.A. Mangolin ◽  
A.S. Lapenta
Keyword(s):  
Genetic Variability ◽  
Random Amplified Polymorphic Dna ◽  
Natural Populations ◽  
Electrophoretic Analysis ◽  
Effective Control ◽  
Lasioderma Serricorne ◽  
Control Programs ◽  
Dried Fruit ◽  
High Level ◽  
High Degree

AbstractLasioderma serricorne (F.) is a small cosmopolitan beetle regarded as a destructive pest of several stored products such as grains, flour, spices, dried fruit and tobacco. Chemical insecticides are one of the measures used against the pest. However, intensive insecticide use has resulted in the appearance of resistant insect populations. Therefore, for the elaboration of more effective control programs, it is necessary to know the biological aspects of L. serricorne. Among these aspects, the genetic variability knowledge is very important and may help in the development of new control methods. The objective of this study was to evaluate the genetic variability of 11 natural populations of L. serricorne collected respectively in three and four towns in the states of Paraná and São Paulo, Brazil, using 20 primers random amplified polymorphic DNA (RAPD) and polymorphisms of esterases. These primers produced 352 polymorphic bands. Electrophoretic analysis of esterases allowed the identification of four polymorphic loci (Est-2, Est-4, Est-5 and Est-6) and 18 alleles. Results show that populations are genetically differentiated and there is a high level of genetic variability within populations. The high degree of genetic differentiation is not directly correlated to geographical distance. Thus, our data indicate that movement of infested commodities may contribute to the dissemination of L. serricorne, facilitating gene flow.

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