Kin selection and ethnic group selection

Ethnicity looks something like kinship on a larger scale. The same math can be used to measure genetic similarity within ethnic/racial groups and relatedness within families. For example, members of the same continental race are about as related (r = 0.18–0.26) as half-siblings (r = 0.25). However (contrary to some claims) the theory of kin selection does not apply straightforwardly to ethnicity, because inclusive fitness calculations based on Hamilton's rule break down when there are complicated social interactions within groups, and/or groups are large and long-lasting. A more promising approach is a theory of ethnic group selection, a special case of cultural group selection. An elementary model shows that the genetic assimilation of a socially enforced cultural regime can promote group solidarity and lead to the regulation of recruitment to groups, and to altruism between groups, based on genetic similarity – in short, to ethnic nepotism. Several lines of evidence, from historical population genetics and political psychology, are relevant here.     

Group selection in plant populations

Summary Several mechanisms have been proposed for group selection, to account for the evolution of altruistic traits. One type, Neighbourhood models, suggests that individuals react with those immediately around them, but with no recognition mechanism. The organization of plant populations seems especially favorable for this type of selection. The possibility of Neighbourhood selection was investigated by simulating a plant population. It was possible for an altruistic trait to evolve, though only under restricted conditions. The main requirement was gene flow only by very restricted pollen dispersal, and a high benefit : cost ratio in the altruistic relationship. Under conditions favourable for such evolution, the starting frequency of the allele, the initial pattern, and the population size, had little effect. Inbreeding tended to prevent the increase of the altruism allele, though this depended on the mechanism of selfing. Known ecological features of plants are discussed that could be considered altruistic and hence require some form of group selection for their evolution, and whether the benefit : cost requirements are likely to be met. Neighbourhood models of group selection are a possibility in plant populations, and we therefore cannot exclude the possibility of altruism in plants. However, Neighbourhood selection is weak force, unlikely to be effective in the face of opposing individual selection. It may be more important as reinforcement of individual selection.     

Kin selection may inhibit the evolution of reciprocation

Kin selection and reciprocal cooperation provide two candidate explanations for the evolution of cooperation. Models of the evolution of cooperation have typically focussed on one or the other mechanism, despite claims that kin selection could pave the way for the evolution of reciprocal cooperation. We describe a computer simulation model that explicitly supports both kin selection and reciprocal cooperation. The model simulates a viscous population of discrete individuals with social interaction taking the form of the Prisoner's Dilemma and selection acting on performance in these interactions. We recount how the analytical and empirical study of this model led to the conclusion that kin selection may actually inhibit the evolution of effective strategies for establishing reciprocal cooperation.     

Sexual conflict in viscous populations: the effect of the timing of dispersal

In recent years, there has been increasing theoretical and empirical examination of how sexual conflict can arise between males and females. However, much this work has implicitly assumed that interactions take place in panmictic populations with complete dispersal, where interactions are between unrelated individuals. Here, we examine the consequences of limited dispersal and population structure for the evolution of a male phenotype that is associated with the males pre- and post-copulatory reproductive success, using an inclusive-fitness based analysis applied to group-structured populations. We show that: (i) the sex-specific timing of the dispersal phase of the life cycle can drive the evolution of sexual conflict; (ii) the inclusive fitness of a female in this conflict is determined solely by direct (i.e. personal) effects on its own competitive ability. Our analysis is supported by results from individual-based simulations of multi-level selection. Our results support the suggestion that kin selection can influence the evolution of sexual conflict, but reveal that such a role might be more complex than previously appreciated when sex-specific life histories are taken into consideration. We discuss the implications of our results for sexual conflict in various species of insects, but focus primarily on dipteran flies of the family Sepsidae.     

Kin groups and trait groups: population structure and epidemic disease selection

A Monte Carlo simulation based on the population structure of a small-scale human population, the Semai Senoi of Malaysia, has been developed to study the combined effects of group, kin, and individual selection. The population structure resembles D.S. Wilson's structured deme model in that local breeding populations (Semai settlements) are subdivided into trait groups (hamlets) that may be kin-structured and are not themselves demes. Additionally, settlement breeding populations are connected by two-dimensional stepping-stone migration approaching 30% per generation. Group and kin-structured group selection occur among hamlets the survivors of which then disperse to breed within the settlement population. Genetic drift is modeled by the process of hamlet formation; individual selection as a deterministic process, and stepping-stone migration as either random or kin-structured migrant groups. The mechanism for group selection is epidemics of infectious disease that can wipe out small hamlets particularly if most adults become sick and social life collapses. Genetic resistance to a disease is an individual attribute; however, hamlet groups with several resistant adults are less likely to disintegrate and experience high social mortality. A specific human gene, hemoglobin E, which confers resistance to malaria, is studied as an example of the process. The results of the simulations show that high genetic variance among hamlet groups may be generated by moderate degrees of kin-structuring. This strong microdifferentiation provides the potential for group selection. The effect of group selection in this case is rapid increase in gene frequencies among the total set of populations. In fact, group selection in concert with individual selection produced a faster rate of gene frequency increase among a set of 25 populations than the rate within a single unstructured population subject to deterministic individual selection. Such rapid evolution with plausible rates of extinction, individual selection, and migration and a population structure realistic in its general form, has implications for specific human polymorphisms such as hemoglobin variants and for the more general problem of the tempo of evolution as well.     

Mutation accumulation in selfing populations under fluctuating selection

Selfing species are prone to extinction, possibly because highly selfing populations can suffer from a continuous accumulation of deleterious mutations, a process analogous to Muller's ratchet in asexual populations. However, current theory provides little insight into which types of genes are most likely to accumulate deleterious alleles and what environmental circumstances may accelerate genomic degradation. Here, we investigate temporal changes in the environment that cause fluctuations in the strength of purifying selection. We simulate selfing populations with genomes containing a mixture of loci experiencing constant selection and loci experiencing selection that fluctuates in strength (but not direction). Even when both types of loci experience the same average strength of selection, loci under fluctuating selection contribute disproportionately more to deleterious mutation accumulation. Moreover, the presence of loci experiencing fluctuating selection in the genome increases the deleterious fixation rate at loci under constant selection; under most realistic scenarios, this effect of linked selection can be attributed to a reduction in N_e. Fluctuating selection is particularly injurious when selective environments are strongly autocorrelated over time and when selection is concentrated into rare bouts of strong selection. These results imply that loci under fluctuating selection are likely important drivers of extinction in selfing species.     

Diffusion approximations for one-locus multi-allele kin selection,mutation and random drift in group-structured populations: a unifying approach to selection models in population genetics

Diffusion approximations are ascertained from a two-time-scale argument in the case of a group-structured diploid population with scaled viability parameters depending on the individual genotype and the group type at a single multi-allelic locus under recurrent mutation, and applied to the case of random pairwise interactions within groups. The main step consists in proving global and uniform convergence of the distribution of the group types in an infinite population in the absence of selection and mutation, using a coalescent approach. An inclusive fitness formulation with coefficient of relatedness between a focal individual J affecting the reproductive success of an individual I, defined as the expected fraction of genes in I that are identical by descent to one or more genes in J in a neutral infinite population, given that J is allozygous or autozygous, yields the correct selection drift functions. These are analogous to the selection drift functions obtained with pure viability selection in a population with inbreeding. They give the changes of the allele frequencies in an infinite population without mutation that correspond to the replicator equation with fitness matrix expressed as a linear combination of a symmetric matrix for allozygous individuals and a rank-one matrix for autozygous individuals. In the case of no inbreeding, the mean inclusive fitness is a strict Lyapunov function with respect to this deterministic dynamics. Connections are made between dispersal with exact replacement (proportional dispersal), uniform dispersal, and local extinction and recolonization. The timing of dispersal (before or after selection, before or after mating) is shown to have an effect on group competition and the effective population size. In memory of Sam Karlin.     

Prediction of rates of inbreeding in populations undergoing index selection

For populations undergoing mass selection, previous studies have shown that the rate of inbreeding is directly related to the mean and variance of long-term contributions from ancestors to descendants, and thus prediction of the rate of inbreeding can be achieved via the prediction of long-term contributions. In this paper, it is shown that the same relationship between the rate of inbreeding and long-term contributions is found when selection is based on an index of individual and sib records (index selection) and where sib records may be influenced by a common environment. In these situations, rates of inbreeding may be considerably higher than under mass selection. An expression for the rate of inbreeding is derived for populations undergoing index selection based on variances of (one-generation) family size and incorporating the concept of long-term selective advantage. When the mating structure is hierarchical, and when half-sib records are included in the index, the correlation between parental breeding values and the index values of their offspring is higher for male parents than female parents. This introduces an important asymmetry between the contributions of male and female ancestors to the evolution of inbreeding which is not present when selection is based on individual and/or full-sib records alone. The prediction equation for index selection accounts for this asymmetry. The prediction is compared to rates of inbreeding calculated from simulation. The prediction is good when family size is small relative to the number selected. The reasons for overprediction in other situations are discussed.     

Kin encounter rate and inbreeding avoidance in canids

Mating with close kin can lead to inbreeding depression through the expression of recessive deleterious alleles and loss of heterozygosity. Mate selection may be affected by kin encounter rate, and inbreeding avoidance may not be uniform but associated with age and social system. Specifically, selection for kin recognition and inbreeding avoidance may be more developed in species that live in family groups or breed cooperatively. To test this hypothesis, we compared kin encounter rate and the proportion of related breeding pairs in noninbred and highly inbred canid populations. The chance of randomly encountering a full sib ranged between 1-8% and 20-22% in noninbred and inbred canid populations, respectively. We show that regardless of encounter rate, outside natal groups mates were selected independent of relatedness. Within natal groups, there was a significant avoidance of mating with a relative. Lack of discrimination against mating with close relatives outside packs suggests that the rate of inbreeding in canids is related to the proximity of close relatives, which could explain the high degree of inbreeding depression observed in some populations. The idea that kin encounter rate and social organization can explain the lack of inbreeding avoidance in some species is intriguing and may have implications for the management of populations at risk.     

Exact inbreeding coefficients in populations with overlapping generations

A theory is given that allows inbreeding coefficients to be calculated exactly for populations with overlapping generations. Emphasis is placed on providing equations well suited for computer iteration. Both monoecious and dioecious populations are considered and family size is not restricted to being Poisson. One-locus and two-locus inbreeding coefficients are evaluated, although the reader may omit the two-locus sections. The exact treatment is shown to be preferable to approximate treatments in that it applies to both early and late generations for all populations sizes. Inbreeding effective numbers found by the exact treatment are compared to various approximate numbers, and the approximate values are found to be generally very good.     

The different limits of weak selection and the evolutionary dynamics of finite populations

Evolutionary theory often resorts to weak selection, where different individuals have very similar fitness. Here, we relate two ways to introduce weak selection. The first considers evolutionary games described by payoff matrices with similar entries. This approach has recently attracted a lot of interest in the context of evolutionary game dynamics in finite populations. The second way to introduce weak selection is based on small distances in phenotype space and is a standard approach in kin-selection theory. Whereas both frameworks are interchangeable for constant fitness, frequency-dependent selection shows significant differences between them. We point out the difference between both limits of weak selection and discuss the condition under which the differences vanish. It turns out that this condition is fulfilled by the popular parametrization of the prisoner's dilemma in benefits and costs. However, for general payoff matrices differences between the two frameworks prevail.     

植物的亲缘选择

亲缘选择是指在一个随机交配群体中的个体基于亲缘关系而以一种非随机性的方式相互作用,其作用结果是亲缘个体得到更大的广义适合度。综述了亲缘选择和亲缘竞争两种观点以及各自的试验支持证据;分析了导致亲缘选择试验结果出现分歧的原因,认为这主要是由于对亲缘选择理解上的模糊以及试验设计的不严谨所致。植物间的亲缘选择研究不仅相对较少,对亲缘选择的机制研究更为欠缺,这就造成了目前对此问题在科学认识上出现不少盲点。综合前期研究,提出今后对亲缘选择的研究应该首先界定"亲缘"程度,同时改良试验设计方案,选择多种不同生境下的物种对亲缘选择进行深入研究,并且考虑环境因子对植物亲缘选择的影响。同时,对植物亲缘识别机制的研究应该从生理生化方面出发,通过定性定量地分析探索植物根系分泌物在植物亲缘识别中的作用和作用途径。     

Effects of spatial pattern and relatedness in an experimental plant community

Many plant species show limited dispersal resulting in spatial and genetic substructures within populations. Consequently, neighbours are often related between each other, resulting in sibling competition. Using seed families of the annuals Capsella bursa-pastoris and Stachys annua we investigated effects of spatial pattern (i.e. random versus aggregated) on total and individual performance at the level of species and seed families under field conditions. At the level of species, we expected that inferior competitors increase, while superior competitors decrease their performance within neighbourhoods of conspecifics. Thus, we expected a species by spatial pattern interaction. Sibling competition, however, might reduce the performance of competitors, when genetically related, rather than non-related individuals are competing. Therefore, aggregations at the level of seed families could decrease the performance of competitors. Alternatively, if the opposite outcome would be observed, kin selection might be hypothesized to have occurred in the past. Because heavy seeds are expected to disperse less than light seeds, we further hypothesized that kin selection might be more likely to occur in superior competitors with heavy, locally dispersed seeds (e.g. Stachys) compared to inferior competitors with light, more distantly dispersed seeds (e.g. Capsella). We found a significant species by spatial pattern interaction. Indeed, the inferior competitor, Capsella, showed increased reproductive biomass production in aggregated compared to random patterns. Whereas, the performance of the superior competitor, Stachys, was to some extent decreased by intraspecific aggregation. Although statistically not significant, effects of intrafamily aggregations tended to be rather negative in Capsella but positive in Stachys. Our results confirmed that spatial patterns affect growth and reproduction of plant species promoting coexistence in plant communities. Although, we could not provide strong evidence for sibling competition or kin selection, our results suggested that competition among relatives was more severe for Capsella (lighter seeds) compared to Stachys (heavier seeds).     

Kin discrimination and sex ratios in a parasitoid wasp

Sex ratio theory provides a clear and simple way to test if nonsocial haplodiploid wasps can discriminate between kin and nonkin. Specifically, if females can discriminate siblings from nonrelatives, then they are expected to produce a higher proportion of daughters if they mate with a sibling. This prediction arises because in haplodiploids, inbreeding (sib-mating) causes a mother to be relatively more related to her daughters than her sons. Here we formally model this prediction for when multiple females lay eggs in a patch, and test it with the parasitoid wasp Nasonia vitripennis. Our results show that females do not adjust their sex ratio behaviour dependent upon whether they mate with a sibling or nonrelative, in response to either direct genetic or a range of indirect environmental cues. This suggests that females of N. vitripennis cannot discriminate between kin and nonkin. The implications of our results for the understanding of sex ratio and social evolution are discussed.     

Effective size of populations under partial inbreeding and selection on a set of linked additive genes

The prediction theory of effective population size (Ne) is extended to cover selection on a set of linked additive genes and partial inbreeding (partial selfing or partial full-sib mating). Ne under selection is generally expressed as a function of the cumulative change in frequency of a neutral gene due to the random association between the neutral and selected genes generated by finite sampling. In this study, the association under partial selfing was classified into two types, the association between the neutral and selected genes on the same gamete, and the association between the neutral and selected genes each on the different gametes in the same parent. For partial full-sib mating, an additional association, i.e., the association between the neutral and selected genes each in the different parents in the same family, was included in the model. According to this classification of the association, the coefficient accounting for the cumulative change in frequency of the neutral gene was partitioned into two or three components. A method for computing the partitioned coefficients was obtained from the transition matrix approach, in which the joint effect of linkage, selection and partial inbreeding was taken into account. To assess the joint effects of linkage, selection and partial inbreeding on Ne, numerical computations with the obtained expressions were carried out. The effect of linkage on Ne was generally small, except for an extremely small genome size, while the partial inbreeding resulted in a drastic reduction in Ne. For a given genome size, Ne was essentially independent of the length and number of chromosomes. Some of these results were verified by stochastic simulations.     

The accuracy of prediction of genomic selection in elite hybrid rye populations surpasses the accuracy of marker-assisted selection and is equally augmented by multiple field evaluation locations and test years

Background

Marker-assisted selection (MAS) and genomic selection (GS) based on genome-wide marker data provide powerful tools to predict the genotypic value of selection material in plant breeding. However, case-to-case optimization of these approaches is required to achieve maximum accuracy of prediction with reasonable input.

Results

Based on extended field evaluation data for grain yield, plant height, starch content and total pentosan content of elite hybrid rye derived from testcrosses involving two bi-parental populations that were genotyped with 1048 molecular markers, we compared the accuracy of prediction of MAS and GS in a cross-validation approach. MAS delivered generally lower and in addition potentially over-estimated accuracies of prediction than GS by ridge regression best linear unbiased prediction (RR-BLUP). The grade of relatedness of the plant material included in the estimation and test sets clearly affected the accuracy of prediction of GS. Within each of the two bi-parental populations, accuracies differed depending on the relatedness of the respective parental lines. Across populations, accuracy increased when both populations contributed to estimation and test set. In contrast, accuracy of prediction based on an estimation set from one population to a test set from the other population was low despite that the two bi-parental segregating populations under scrutiny shared one parental line. Limiting the number of locations or years in field testing reduced the accuracy of prediction of GS equally, supporting the view that to establish robust GS calibration models a sufficient number of test locations is of similar importance as extended testing for more than one year.

Conclusions

In hybrid rye, genomic selection is superior to marker-assisted selection. However, it achieves high accuracies of prediction only for selection candidates closely related to the plant material evaluated in field trials, resulting in a rather pessimistic prognosis for distantly related material. Both, the numbers of evaluation locations and testing years in trials contribute equally to prediction accuracy.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-556) contains supplementary material, which is available to authorized users.     

Genetic relatedness in viscous populations

Summary Hamilton's inclusive fitness rule shows that the evolution of altruism is facilitated by high genetic relatedness of altruists to their beneficiaries. But the evolution of altruism is inhibited when the beneficiaries are also close competitors of the altruist, as will often be true in structured or viscous populations. However, Hamilton's rule still gives the correct condition for the evolution of altruism if relatedness is measured with respect to the local competitive neighbourhood.     

The interpretation of selection coefficients

Evolutionary biologists have an array of powerful theoretical techniques that can accurately predict changes in the genetic composition of populations. Changes in gene frequencies and genetic associations between loci can be tracked as they respond to a wide variety of evolutionary forces. However, it is often less clear how to decompose these various forces into components that accurately reflect the underlying biology. Here, we present several issues that arise in the definition and interpretation of selection and selection coefficients, focusing on insights gained through the examination of selection coefficients in multilocus notation. Using this notation, we discuss how its flexibility—which allows different biological units to be identified as targets of selection—is reflected in the interpretation of the coefficients that the notation generates. In many situations, it can be difficult to agree on whether loci can be considered to be under “direct” versus “indirect” selection, or to quantify this selection. We present arguments for what the terms direct and indirect selection might best encompass, considering a range of issues, from viability and sexual selection to kin selection. We show how multilocus notation can discriminate between direct and indirect selection, and describe when it can do so.     

Predicting rates of inbreeding in populations undergoing selection

Tractable forms of predicting rates of inbreeding (DeltaF) in selected populations with general indices, nonrandom mating, and overlapping generations were developed, with the principal results assuming a period of equilibrium in the selection process. An existing theorem concerning the relationship between squared long-term genetic contributions and rates of inbreeding was extended to nonrandom mating and to overlapping generations. DeltaF was shown to be approximately (1)/(4)(1 - omega) times the expected sum of squared lifetime contributions, where omega is the deviation from Hardy-Weinberg proportions. This relationship cannot be used for prediction since it is based upon observed quantities. Therefore, the relationship was further developed to express DeltaF in terms of expected long-term contributions that are conditional on a set of selective advantages that relate the selection processes in two consecutive generations and are predictable quantities. With random mating, if selected family sizes are assumed to be independent Poisson variables then the expected long-term contribution could be substituted for the observed, providing (1)/(4) (since omega = 0) was increased to (1)/(2). Established theory was used to provide a correction term to account for deviations from the Poisson assumptions. The equations were successfully applied, using simple linear models, to the problem of predicting DeltaF with sib indices in discrete generations since previously published solutions had proved complex.