This paper considers how polygenic local adaptation and reproductive isolation between hybridizing populations is influenced by linkage disequilibria (LD) between loci, in scenarios where both gene flow and genetic drift counteract selection. It shows that the combined effects of multi-locus LD and genetic drift on allele frequencies at selected loci and on heterozygosity at neutral loci are predicted accurately by incorporating (deterministic) effective migration rates into the diffusion approximation (for selected loci) and into the structured coalescent (for neutral loci). Theoretical approximations are tested against individual-based simulations and used to investigate conditions for the maintenance of local adaptation on an island subject to one-way migration from a differently adapted mainland, and in an infinite-island population with two habitats under divergent selection. The analysis clarifies the conditions under which LD between sets of locally deleterious alleles allows these to be collectively eliminated despite drift, causing sharper and (under certain conditions) shifted migration thresholds for loss of adaptation. Local adaptation also has counter-intuitive effects on neutral (relative) divergence: FST is highest for a pair of subpopulations belonging to the same (rare) habitat, despite the lack of reproductive isolation between them.

Being able to properly quantify genetic differentiation is key to understanding the evolutionary potential of a species. One central parameter in this context is FST, the mean coancestry within populations relative to the mean coancestry between populations. Researchers have been estimating FST globally or between pairs of populations for a long time. More recently, it has been proposed to estimate population-specific FST values, and population-pair mean relative coancestry. Here, we review the several definitions and estimation methods of FST, and stress that they provide values relative to a reference population. We show the good statistical properties of an allele-sharing, method of moments based estimator of FST (global, population-specific and population-pair) under a very general model of population structure. We point to the limitation of existing likelihood and Bayesian estimators when the populations are not independent. Last, we show that recent attempts to estimate absolute, rather than relative, mean coancestry fail to do so.

This study compares theoretical and simulated properties of two estimators of fixation indices F(ST) for multiallelic data from a single locus. The estimators are due to Weir and Cockerham (straight theta(WC)) and to Robertson and Hill (;straight theta(RH)), respectively. Both estimators are linear combinations of biallelic estimators which differ in the way frequent and rare alleles are weighted. Consequently, their sampling properties differ as far as bias and variance are concerned. In the infinite island model at migration-drift equilibrium, in the case of one multiallelic locus, we analytically approximate the bias of the two estimators and show that;straight theta(WC) is nearly unbiased, whereas;straight theta(RH) is negatively biased. Hence, we propose a correction of bias of the latter. Moreover, we reexamine the properties of variance of the initial estimators: due to their construction, their variances are minimal, each over different parameter ranges,;straight theta(RH) performing better for low differentiation and;straight theta(WC) for high differentiation. These theoretical properties are confirmed by simulations, which show that our correction of bias of;straight theta(RH) performs well and does not affect its property of minimal variance for low differentiation. Hence, we advocate the use of;straight theta(WC) for high values of differentiation, and the use of;straight theta(RH), with our correction of bias, for low or moderate differentiation.

F(st) is a measure of genetic differentiation in a subdivided population. Sewall Wright observed that F(st)=1/1+2Nm in a haploid diallelic infinite island model, where N is the effective population size of each deme and m is the migration rate. In demonstrating this result, Wright relied on the infinite size of the population. Natural populations are not infinite and therefore they change over time due to genetic drift. In a finite population, F(st) becomes a random variable that evolves over time. In this work we ask, given an initial population state, what are the dynamics of the mean and variance of F(st) under the finite island model? In application both of these quantities are critical in the evaluation of F(st) data. We show that after a time of order N generations the mean of F(st) is slightly biased below 1/1+2Nm. Further we show that the variance of F(st) is of order 1/d where d is the number of demes in the population. We introduce several new mathematical techniques to analyze coalescent genealogies in a dynamic setting.

We investigated the effect of nonadditive genetic variance on the amount of additive genetic variance within local populations in an infinite-allele, infinite-island model with migration, extinction, and recolonization, using two-locus descent measures. For an island model with extinction, one- and two-locus descent measures are expressed in a matrix form that allows equilibrium solutions to be calculated similar to previous work on Wright's F-statistics. In a subdivided population, the additive genetic variation within a local deme depends on the dominance and epistatic genetic variation in the species. Moreover, to a good approximation, the amount of additive variance within a deme is a simple function of Fst , which is twice the demic fraction of genic variance. At equilibrium, it is equal to (1 - Fst ) VA plus 4 Fst (1 - Fst ) VA×A , where VA and VA×A are the additive and additive × additive epistatic variances at the level of the species, respectively, plus a contribution from the dominance variance and other terms including dominance. Paradoxically, with nonadditive genetic effects, drift on average increases the amount of additive genetic variance within populations, whereas migration decreases the equilibrium amount. In the presence of nonadditive genetic effects, measurements of additive genetic variance in natural populations must be taken at the proper spatial scale with respect to natural selection, or they will provide an inaccurate description of evolutionary po

Genetic studies in four populations of the northern Aegean Sea, Greece. A total of 945 non-related individuals from four isolated population groups from the Northern Aegean Sea (Greece)--Alonissos, Oxilithos, Skopelos, and Glossa, has been typed for 16 polymorphic systems of the blood, namely A1A2B0, MNS., Rhesus (C, c, Cw, D, E, e), Kell, Duffy (a,b), Kidd (a); Hp, Tf subtypes, Gc, Gm (1, 2, 3, 5, 13), Km (1); aP, AK, PGM1, EsD, and 6-PGD. The distribution of phenotype and gene/haplotype frequencies shows a considerable interpopulational variability, which is discussed considering the history of these populations as well as the impact of locally acting microevolutionary factors such as drift and founder effects. The average coefficient of gene diversity GST comes to 0.0147, whereas Wahlund's variance is on average 0.0154, and Wright's Fst = 0.0147. Genetic distance analysis reveals a pattern of similarities, which is in conformity with the history of the populations under study. Published in Zeitschrift fur Morphologie und Anthropologie (1989)