Relative Fitness Of Genotypes Research Articles

Association of a nonsynonymous substitution in the condensin NCAPG gene with traits of eggs in laying hens

One of the most important areas of research in the biology and genetics of farmed animals is one of identification of genes controlling the expression of traits with practical importance for animal breeding. For most of these characteristic features, the wide variation in gene expression in specific loci, which are called quantitative trait loci (QTL), is typical. Eggs have been researched for decades due to their importance for the reproduction of birds, as well as for its widespread use in pharmaceutical, cosmetic, and food industries. Breeding hens and crosslines are a necessary step for producing eggs with the desired quality. The results of this work are recommended for use to create systems of molecular markers for the marker selection of layers and obtain new lines and cross hens with larger mass eggs. Compared to the existing conventional systems of selecting layers on this basis, this will eliminate the assessment of the genotype of male progeny, which will significantly reduce breeding time. The system of markers will appear as a set of primers for detecting gene alleles that have a significant impact on the characteristics as above. The use of the molecular markers of high-performance systems for direct selection based on domestic chicken eggs should lead to substantial progress in biotechnology poultry and help avoid having to purchase similar systems from outside the country. The association of the condensin NCAPG gene with the egg traits of domestic chicken has been studied. Associations of the SNP alleles of the rs14491030 marker localized in exon 8 of the NCAPG gene with the trait “the weight eggs,” p < 0.001, as well as with the elastic deformation of the egg shell, p < 0.026, have been found. It has been found that a single nucleotide nonsynonymous A → G substitution leads to a significant increase in egg weight. The marker SNP rs14491030 with the observed significant effect on the egg weight trait can be recommended for use in breeding laying hens. The calculations of the relative fitness of genotypes of the SNP rs14491030 marker suggest a natural selection for heterozygotes. The results obtained are discussed in connection with the role of the canonical condensin complex in the compaction of chromatin and segregation of chromosomes.

Association of a non-synonymous substitution in the condensin NCAPG gene with traits of eggs in laying hens

One of the most important areas of research in the biology and genetics of farmed animals is one of identification of genes controlling the expression of traits with practical importance for animal breeding. For most of these characteristic features, wide variation in gene expression in specific loci, which are called quantitative trait loci (QTL), is typical. Eggs have been researched for decades due to their importance for the reproduction of birds, as well as for its widespread use in pharmaceutical, cosmetic and food industries. Breeding hens and cross-lines is a necessary step for producing eggs with desired quality. The results of this work are recommended for use to create systems of molecular markers for marker selection of layers and obtain new lines and cross hens with larger mass eggs. Compared to existing conventional systems of selecting layers on this basis, this will eliminate the assessment of the genotype of male progeny, which will significantly reduce breeding time. The system of markers will appear as a set of primers for detection of gene alleles that have a significant impact on the characteristics as above. The use of the molecular markers of high-performance systems for direct selection on the basis of domestic chicken eggs would lead to substantial progress in biotechnology poultry and help avoid having to purchase similar systems from outside the country. The association of the condensin NCAPG gene with the egg traits of domestic chicken has been studied. Associations of the SNP alleles of the rs14491030 marker localized in exon 8 of the NCAPG gene with the trait “the weight eggs”, p &lt; 0.001, as well as with the elastic deformation of the egg shell, p &lt; 0.026, have been found. It has been found that a single nucleotide nonsynonymous A G substitution leads to a significant increase in egg weight. The marker SNP rs14491030 with the observed significant effect on the trait «egg weight» can be recommended for use in breeding of laying hens. Calculations of the relative fitness of genotypes of the marker SNP rs14491030 suggest natural selection for heterozygotes. The results obtained are discussed in connection with the role of the canonical condensin complex in the compaction of chromatin and segregation of chromosomes.

Elevated Carbon Dioxide Alters the Relative Fitness of &amp;lt;i&amp;gt;Taraxacum officinale&amp;lt;/i&amp;gt; Genotypes

I tested whether elevated [CO2] affected which genotypes of Taraxacum officinale had highest fitness in two field experiments. In one experiment, T. officinale plants which persisted as weeds in alfalfa plots in open top chambers at ambient and elevated [CO2] were compared. In a second experiment, T. officinale seeds collected from local habitats were mixed and scattered in open top chambers at ambient and elevated [CO2], and plants producing seeds after one and two years in monocultures were compared. In both experiments seeds produced in each chamber were collected, and many plants from the seed lot from each chamber were grown in controlled environment chambers to test whether the [CO2] of the chamber of origin affected the mean value of various plant parameters. In both experiments, the results indicated that field exposure to elevated [CO2] altered the relative fitness of genotypes. Elevated [CO2] favored genotypes which produced biomass more rapidly at elevated [CO2] in both experiments, primarily because of faster rates of leaf initiation. The results suggest that genotypes of this species vary widely in fitness at elevated [CO2] whether grown in monocultures or in mixed communities, and that this species could adapt rapidly to rising atmospheric [CO2].

Genotype‐by‐environment interactions leads to variable selection on life‐history strategy in Common Evening Primrose (Oenothera biennis)

Monocarpic plant species, where reproduction is fatal, frequently exhibit variation in the length of their prereproductive period prior to flowering. If this life-history variation in flowering strategy has a genetic basis, genotype-by-environment interactions (G x E) may maintain phenotypic diversity in flowering strategy. The native monocarpic plant Common Evening Primrose (Oenothera biennis L., Onagraceae) exhibits phenotypic variation for annual vs. biennial flowering strategies. I tested whether there was a genetic basis to variation in flowering strategy in O. biennis, and whether environmental variation causes G x E that imposes variable selection on flowering strategy. In a field experiment, I randomized more than 900 plants from 14 clonal families (genotypes) into five distinct habitats that represented a natural productivity gradient. G x E strongly affected the lifetime fruit production of O. biennis, with the rank-order in relative fitness of genotypes changing substantially between habitats. I detected genetic variation in annual vs. biennial strategies in most habitats, as well as a G x E effect on flowering strategy. This variation in flowering strategy was correlated with genetic variation in relative fitness, and phenotypic and genotypic selection analyses revealed that environmental variation resulted in variable directional selection on annual vs. biennial strategies. Specifically, a biennial strategy was favoured in moderately productive environments, whereas an annual strategy was favoured in low-productivity environments. These results highlight the importance of variable selection for the maintenance of genetic variation in the life-history strategy of a monocarpic plant.

Wright meets AD: not all landscapes are adaptive

Wright meets AD: not all landscapes are adaptive

Introduction: Experimental Approaches to Testing Adaptation

How natural selection acts on traits to produce adaptation to different environments is a central question in evolutionary biology. Recently there has been a revival of interest in this question, in part because of the development of new tools in several fields (Rose and Lauder 1996). Modern methods for phylogenetic analysis now provide a framework for testing the hypothesis that a trait is an adaptation using comparative data (Larson and Losos 1996). It is also possible to test the current adaptive value of specific traits. Within-species phenotypic selection analysis (Lande and Arnold 1983) allows the measurement of direct and indirect selection on correlated characters in natural populations, and it can be combined with quantitative genetic data to predict short-term responses to selection. However, testing hypotheses concerning the ecological causes of natural selection usually requires experimental manipulation (Wade and Kalisz 1990). The objective of this volume is to explore how modern techniques for genetic and physiological manipulation can be used to elucidate the causes and mechanisms of adaptation. Experimental studies of adaptation are not new. The classical approach to testing for intraspecific local adaptation is the reciprocal transplant experiment. If the relative fitness of genotypes from each population is highest in their “home” environment, there is strong evidence for local adaptation. However, classical reciprocal transplant experiments cannot tell us the ecological causes of adaptation or what specific traits are under selection. More recently, evolutionary ecologists have used multivariate selection analysis (Lande and Arnold 1983; Rausher 1992) to examine direct and indirect selection on specific characters. This technique can be combined with experimental manipulation of environmental factors to elucidate the ecological causes of natural selection (Wade and Kalisz 1990). If the strength or direction of selection on a set of

INTERTIDAL MICROHABITAT AND SELECTION AT MPI: INTERLOCUS CONTRASTS IN THE NORTHERN ACORN BARNACLE, SEMIBALANUS BALANOIDES.

Barnacles were sampled from various microhabitats in the rocky intertidal at multiple sites in two years. At sites in which there were large differences among microhabitats in temperature profiles, Mpi genotype frequencies were consistently and significantly different. Genotype frequencies for another allozyme locus (Gpi) as well as a DNA marker shown to be neutral (the mtDNA control region) were statistically homogeneous among thermal microhabitats at all sites in both years. The data indicate that temperature and/or desiccation mediated selection is operating at Mpi or a linked locus and that Mpi genotypes experience differential mortality in the various habitat types. If the relative fitness of genotypes is dependent on habitat type, the Mpi polymorphism may be actively maintained by a Levene model of balancing selection (Levene 1953). Because barnacle larvae are produced in abundance each year and spend five to eight weeks dispersing in the water column, there is little opportunity for the accumulation of adaptive divergence over the environmental grain size relevant in intertidal habitats. The Mpi polymorphism may be an important component of a suite of traits involved in the adaptation of barnacles to heterogeneous environments. Due to the relatively high concentration of mannose in a variety of algal groups, the metabolism of mannose may substantially affect individual performance and fitness in this and other species that feed on algae and phytoplankton. Because the Mpi locus is one of the most strongly polymorphic in marine organisms, these findings may be relevant for a diversity of other such species.

Further Comments on Models of Pathogen Evolution in Cultivar Mixtures and the Definition of Pathogen Fitness

Further Comments on Models of Pathogen Evolution in Cultivar Mixtures and the Definition of Pathogen Fitness

FINE-GRAINED SPATIAL AND TEMPORAL VARIATION IN SELECTION DOES NOT MAINTAIN GENETIC VARIATION IN ERIGERON ANNUUS.

Because interactions among plants are spatially local, the scale of environmental heterogeneity can have large effects on evolutionary dynamics. However, very little is known about the spatial patterns of variation in fitness and the relative magnitude of spatial and temporal variation in selection. Replicates of 12 genotypes of Erigeron annuus (Asteraceae) were planted in 288 locations within a field, separated by distances of 0.1 to 30.0 m, and replicated in two years. In a given year, most spatial variation in relative fitness (genotype-environment [G × E] interactions for fitness) occurred over distances of only 50 cm. Year effects were as large or larger than the spatial variation in fitness; in particular there was a large, three-way, genotype-year-environment interaction at the smallest spatial scale. The genetic correlation of fitness across years at a given location was near zero, 0.03. Thus, the relative fitness of genotypes is spatially unpredictable and a map of the selective environment has constantly shifting locations of peaks and valleys. Including measurements of soil nutrients as covariates in the analysis removed most of the spatial G × E interaction. Vegetation and microtopography had no effect on the G × E terms, suggesting that differential response to soil nutrients is the cause of spatial variation in fitness. However, the slope of response to NH4 and P04 was negative; therefore the soil nutrients are probably just indicators of other, unknown, environmental factors. We explored via simulation the evolutionary consequences of spatial and temporal variation in fitness and showed that, for this system, the spatial scale of variation was too fine grained (by a factor of 3 to 5) to be a powerful force maintaining genetic variation in the population. The inclusion of both spatial and temporal variation in fitness actually reduced the coexistence of genotypes compared to pure spatial models. Thus the presence of spatial or temporal variation in selection does not guarantee that it is an effective evolutionary force maintaining diversity. Instead the pattern of selection favors generalist genotypes.

GENOTYPE-BY-ENVIRONMENT INTERACTIONS FOR FITNESS OF ERIGERON ANNUUS SHOW FINE-SCALE SELECTIVE HETEROGENEITY.

The results of natural selection depend critically on whether variation in fitness is finegrained or coarse-grained with respect to dispersal, but little is known of the spatial scale of fitness variation in natural populations. For most evolutionary questions, environmental heterogeneity must be defined by reversals in the relative fitness of genotypes; absolute fitness may vary, but if genotypes respond in parallel then selection is uniform. Thus, measurements of genotype-by-environment (G × E) interactions for fitness are necessary to understand patterns of variation in natural selection.

The ecology and genetics of fitness in Chlamydomonas . I. Genotype-by-environment interaction among pure strains

Strains of Chlamydomonas were cultured in different macroenvironments created by manipulating levels of nitrate, phosphate and bicarbonate in liquid growth media. Cell density, measured by optical transmittance, increased in a density-regulated manner, permitting the logistic par­ameters r and K to be estimated for each genotype–environment combination. The main empirical results of a factorial experiment were as follows. (i) A large proportion of the overall genotypic variance in fitness measures was attributable to genotype-by-environment (G × E) interaction: 65 % for r and 50 % for K . Variance components for r and K were uncorrelated, but components of the interaction variance may have been correlated with corresponding components of the environmental variance, such that the relative fitness of genotypes was most strongly affected by environmental factors that have the greatest effect on average fitness. Higher-order interactions were as large as lower-order interactions, so that relative fitness was sensitive to particular combinations of environmental factors as well as to their main effects. The covariance of r with K also showed strong G × E interaction, being negative in some macroenvironments and zero in others. (ii) An ‘environmental’ decomposition of the G × E interaction vari­ance separates ‘inconsistency’, due to lack of complete correlation between genotypes over macroenvironments, from ‘responsiveness’, due to differences between environmental variances among genotypes. Inconsistency was much the larger component for both r and K , showing that the greater part of the interaction variance was created by changes in the ranking of genotypes with respect to fitness between macroenvironments. When reaction norms were defined as the linear regressions of genotypic value on mean environmental value, substantial variance among reaction norms was detected : nonlinear effects were also large. (ii) A ‘genetic’ decomposition of the G × E interaction variance separates a component due to lack of complete genetic correlation from one due to differences in genetic variance. Incomplete genetic correlation was much the larger effect, the mean correlation between genotypes in two macroenvironments being only about +0.23 for r and +0.45 for K . A very striking observation was that the genetic correlation decreased as the difference between environments increased. It declined from +0.31 (for r ; + 0.58 for K ) when one factor differed between macroenvironments to +0.18 ( + 0.40) when two factors differed, and to +0.13 ( + 0.24) when all three factors differed. Furthermore, the genetic correlation varied inversely with the difference between environmental values, approaching zero when this difference was maximal. A measure of environmental consistency was obtained by plotting the score of a genotype in a given macroenvironment on its mean score over all macroenvironments, to identify environments in which generally inferior genotypes performed relatively well and vice versa. This analysis revealed some differences between macroenvironments, but nonlinear effects were again large. (iv) The two major empirical results of this investigation were ( a ) that much of the variance in fitness among genotypes is due to G × E inter­action caused by incomplete genetic correlation, and ( b ) that genetic correlation is smaller between environments that are less similar. Both the relevance and the limitations of these findings with respect to the interpretation of diversity are discussed.

Stability and harvesting of competing populations with genetic variation in life history strategy

The dynamics of competing populations are investigated using discrete non-linear models with age structure. Necessary and sufficient stability conditions for the coexistence equilibrium between two competing non-interbreeding species are developed. An extension of this result shows that coexistence, which is not necessarily stable, occurs in terms of a simple geometric rule on a two dimensional phase plane, provided that each species reaches a stable equilibrium state in the absence of the other species. In the interbreeding case, analytical results are derived for a one locus, two allele model. Sufficient conditions for the stability of polymorphic equilibria are obtained. It is also shown that if both the homozygous genotypes have stable equilibria at fixation, then genetic coexistence occurs when the equilibrium heterozygous zygote production rate is overdominant. Harvesting can lead to the extinction of one of a pair of competing species, or to loss of genetic diversity in a panmictic population. When catchability increases sufficiently with body size, then harvesting preferentially removes the most productive genotypes, and this causes a reduction in the maximum sustainable yield of the population. Harvesting can also reverse the relative fitness of genotypes, since a rare inferior genotype in an unexploited population may be more fit under fishing.

Can Fitness be Aggregated?

A fitness-ranking compares the fitness of two genotypes or, more generally, traits. A species' fitness-ranking describes the relative fitness of genotypes in an aggregated species as a whole. An environmental fitness-ranking describes the relative fitness of genotypes in a particular population of the species in a particular environment. A set of axioms is proposed to describe what might plausibly be desired of the relation between a species' fitness-ranking and environmental fitness-rankings. There is no way in general to construct a species' fitness-ranking that satisfies all of these axioms. Hope that a single natural measure of the "fitness" of genotypes exists for a species as a whole must be replaced by attention to the dynamics of multiple populations in multiple environments.

HETEROZYGOTE ADVANTAGE AT THE FRUIT WING LOCUS IN PLECTRITIS CONGESTA (VALERIANACEAE).

The genus Plectritis consists of four species of winter annual plants occurring along the Pacific coast of North America and intermittently inland as far as the Rocky Mountains, with an additional disjunct species occurring in Chile. The North American species exhibit a characteristic dimorphism in the fruits, with individual plants producing either winged or wingless fruits (Neilsen, 1949; Dempster, 1958; Morey, 1959, 1962). Populations may be either monomorphic or polymorphic for this fruit wing character. In the two closely related species P. congesta (Lindl.) DC. and P. brachystemon F. & M., the fruit wing phenotype is controlled by two alleles at a single locus, with the allele for winged fruits dominant to the allele for wingless fruits (Ganders et al., 1977a, 1977b). Presumably this is the case in the other species as well. A very similar fruit wing polymorphism also occurs in some species of the related genus Valerianella. In V. ozarkana the polymorphism is also controlled by a single locus with the allele for winged fruits dominant (Ware, 1969). Progeny tests using the fruit polymorphism as a genetic marker have provided estimates of outcrossing rates and genotype frequencies in several natural populations of P. congesta. Comparisons of observed with expected genotype frequencies showed that heterozygote frequencies were higher than expected at the estimated outcrossing rates, and in some cases higher than expected even if the outcrossing rate had been 100% (Ganders et al., 1977b). Ganders et al. (1977b) concluded that heterozygote advantage at the winged fruit locus was responsible for maintaining the polymorphism in populations. Subsequent progeny tests of other populations have produced estimates of outcrossing rate in good agreement with previous studies, and have also indicated excess heterozygotes in populations (Table 1). The method used to estimate expected and observed genotype frequencies, and hence relative fitness of genotypes, was that of Harding (1970). Such fitness estimates obtained by comparing observed and expected genotype frequencies are subject to a number of assumptions and problems. One is that the joint estimate of outcrossing rate and genotype frequencies is for a single year. Since the observed genotype frequencies in a population of annuals are a function of the outcrossing rate the previous year, while the expected genotype frequencies are based on the current year outcrossing rate, the method therefore assumes that outcrossing rate, are essentially constant from year to year. If the outcrossing rate had been higher the previous year, there would be more heterozygotes than expected at the current year outcrossing rate. The observed excess of heterozygotes in P. congesta is unlikely to be the result of fluctuating outcrossing rates for two reasons. First, it seems highly unlikely that either a random or systematic reduction in outcrossing rate would have occurred in all seven populations sampled in three different years (Table 1). Second, in some populations heterozygotes were present at frequencies higher than expected even if outcrossing had been 100% (Ganders et al., 1977b). Demonstrating excess heterozygotes by comparing observed and expected genotype frequencies also assumes that the polymorphism is stable and not transient. Continuing selection against one homo-

Relative fitness of genotypes in a population of Rattus norvegicus polymorphic for warfarin resistance

Resistance to warfarin and an increased vitamin K requirement appear to be pleiotropic effects of the same allele (Rw2). In a natural population containing resistant individuals where the use of warfarin is discouraged the change in the frequency of resistance should reflect the relative fitnesses of the three possible genotypes. A large polymorphic population of rats was extensively poisoned with warfarin and the level of resistance monitored regularly for a period of 18 months after withdrawal of the poison. During this period the proportion of resistant animals in live-capture samples decreased significantly from approximately 80 per cent to 33 per cent. This decline is consistent with a hypothesis of reduced fitness of both Rw2Rw2 and Rw1Rw2 genotypes relative to Rw1Rw1 under natural conditions. The relative fitnesses of these genotypes were calculated using an optimisation method based on least squares analysis. These estimates were: Rw2Rw2 (0.46), Rw1Rw2 (0.77) and Rw1Rw1 (1.00). Homozygous resistant individuals were found in some of the samples, confirming that the Rw2 allele does not act as a recessive lethal, although it must be extremely disadvantageous. Some heterogeneity was observed in the proportion of resistant animals in samples taken from different areas of the farm building complex. This could reflect stochastic processes influencing the Rw2 allele frequency in small peripheral populations.

GENETIC VARIATION AND HOST PLANT RELATIONS IN A PARTHENOGENETIC MOTH.

Ecological genetics is the investigation of the influence of ecological factors on the genetic properties of populations, and the influence of genetic structure on their ecological properties. Ideally, these studies should determine how genetic variation is affected by selection and by the size, dynamics, and degree of subdivision of populations; what ecological factors determine the relative fitness of genotypes; and what effect the genetic composition of a population has on such ecological parameters as its density, stability, and ecological amplitude. Many studies have demonstrated selection in natural populations; indeed, the widespread existence of selection is perhaps the only generalization that can be made about ecological genetics. But most studies are incomplete. A few, such as the analysis of inversion karyotypes in Drosophila pseudoobscura by Dobzhansky

Fitness of allozyme variants in Drosophila pseudoobscura. I. Selection at the PGM-1 and Me-2 loci.

We have studied in Drosophila pseudoobscura the effect of allozyme variation on seven fitness components: female fecundity, egg hatchability, egg-to-adult survival under near-optimal and under competitive conditions, rate of development under near-optimal and under competitive conditions, and mating capacity of males. Three genotypes at each of two loci, Pgm-1 and Me-2, have been studied in various combinations. These two loci are highly polymorphic in natural populations of D. pseudoobscura. Statistically significant differences involving one or more genotypes exist for all components of fitness. No single genotype is best for all fitness components; rather the relative fitnesses of genotypes are reversed when different parameters are considered, or when they are studied in different environmental conditions. Also, the average egg-to-adult survival and rate of development are better when different genotypes are reared together than when they occur in pure culture. Four different modes of selection have been uncovered by our experiments. These forms of selection may account for the persistence of the two allozyme polymorphisms in nature, and for previously observed seasonal fluctuations of the allelic frequencies in natural populations.

A Fundamental Theorem of Natural Selection for Sex Linkage or Arrhenotoky

Equation (11) is a general equation for the change in geometric mean fitness at a male haploid or sex-linked locus when the selection intensity is small. The rate of change in fitness depends on the additive genetic variance in fitness, which is defined as the variance of the additive genotypic values when the additive model of gene action assumes no dominance in females and complete dosage compensation in males. If the relative fitnesses of genotypes are constant, then under slow selection the increment in fitness is equal to the additive variance if either (1) the population is in random mating or (2) there is no dominance in females and complete dosage compensation in males. If both conditions hold, then a male haploid population evolves one-third faster than the corresponding diploid population and one-third slower than the corresponding haploid population. In computer-simulated populations undergoing random mating, the additive variance is a good approximation to actual fitness changes over a wide ra...

A Comparison of the Relative Fitness of Genotypes Segregating for the tw2Allele in Laboratory Stock and Its Possible Effect on Gene Frequency in Mouse Populations

A Comparison of the Relative Fitness of Genotypes Segregating for the t^w2Allele in Laboratory Stock and Its Possible Effect on Gene Frequency in Mouse Populations

Effects of Partial Isolation (Distance), Migration, and Different Fitness Requirements among Environmental Pockets upon Steady State Gene Frequencies

Expected gene frequencies are described for a simple genetic system. The development emphasizes the effects of different fitness requirements among environmental pockets, associated groups of individuals (colonies), and migration. The effects of isolation and migration are reflected as translations of the xi and x2 displacement distances. The net effect of finite colony size is to reduce the magnitude of change in expected gene frequency per generation as compared to that obtained by infinite theory. For two special cases, a clinal variation in fitness and a pocket of differential fitness, a detailed analysis is given, including results of computer analyses. In general, a clinal variation in fitness yields a narrow hybrid belt. Peripheral areas of differential fitness for a genotype (the region being primarily neutral with respect to relative fitness of genotypes) or differences in fitness considerably less than those considered can lead to an extended belt. Migration can mask a pocket of differential fitness. Some critical pocket sizes corresponding to selected differential fitnesses are given. Interpretations for selected biological systems are made.