Comparative studies of quantitative genetic and neutral marker differentiation have provided means for assessing the relative roles of natural selection and random genetic drift in explaining among-population divergence. This information can be useful for our fundamental understanding of population differentiation, as well as for identifying management units in conservation biology. Here, we provide comprehensive review and meta-analysis of the empirical studies that have compared quantitative genetic (Q(ST)) and neutral marker (F(ST)) differentiation among natural populations. Our analyses confirm the conclusion from previous reviews - based on ca. 100% more data - that the Q(ST) values are on average higher than F(ST) values [mean difference 0.12 (SD 0.27)] suggesting a predominant role for natural selection as a cause of differentiation in quantitative traits. However, although the influence of trait (life history, morphological and behavioural) and marker type (e.g. microsatellites and allozymes) on the variance of the difference between Q(ST) and F(ST) is small, there is much heterogeneity in the data attributable to variation between specific studies and traits. The latter is understandable as there is no reason to expect that natural selection would be acting in similar fashion on all populations and traits (except for fitness itself). We also found evidence to suggest that Q(ST) and F(ST) values across studies are positively correlated, but the significance of this finding remains unclear. We discuss these results in the context of utility of the Q(ST)-F(ST) comparisons as a tool for inferring natural selection, as well as associated methodological and interpretational problems involved with individual and meta-analytic studies.

Comparisons of neutral marker and quantitative trait divergence can provide important insights into the relative roles of natural selection and neutral genetic drift in population differentiation. We investigated phenotypic and genetic differentiation among Fennoscandian threespine stickleback (Gasterosteus aculeatus) populations, and found that the highest degree of differentiation occurred between sea and freshwater habitats. Within habitats, morphological divergence was highest among the different freshwater populations. Pairwise phenotypic and neutral genetic distances among populations were positively correlated, suggesting that genetic drift may have contributed to the morphological differentiation among habitats. On the other hand, the degree of phenotypic differentiation (PST) clearly surpassed the neutral expectation set by FST, suggesting a predominant role for natural selection over genetic drift as an explanation for the observed differentiation. However, separate PST/FST comparisons by habitats revealed that body shape divergence between lake and marine populations, and even among marine populations, can be strongly influenced by natural selection. On the other hand, genetic drift can play an important role in the differentiation among lake populations.

To assess the population genetic structure of the three-spined stickleback, Gasterosteus aculeatus, variability at 18 microsatellite loci was examined in 1724 individuals from 74 locations covering most of the species distribution range in Europe. The results revealed high overall degree of differentiation (F(ST) = 0.21) but contrasting level of divergence and genetic variability between habitat types. Marine populations were genetically relatively uniform even across great geographical distances as compared to substantial differentiation among freshwater populations. Analysis of molecular variance indicated low but significant (2.7%) variation in allele frequencies between geographical regions, but a negligible effect of habitat type (0.2%). The phylogenetic pattern was not explained by habitat type, but a weak signal of populations clustering according to geographical or water system origin was found. The results support the view that three-spined stickleback marine ancestors colonized northern European fresh waters during the postglacial marine submergence c. 10,000 years ago, whereas in the Mediterranean region colonization probably dates back to the Pleistocene. The independent origins of river and lake populations indicate that they originate from multiple colonizations rather than sharing common ancestry. In the continuous marine environment, the low degree of differentiation among populations can be explained by gene flow among subpopulations and large effective population size buffering divergence in neutral markers. In contrast, among postglacially established freshwater populations differentiation appears to be driven by genetic drift and isolation. The stepwise mutations appear to have contributed to the population differentiation in the southern part of the three-spined stickleback distribution range.

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Aim The geographical distributions of animal and plant species endemic to the Iberian Peninsula and Balearic Islands were analysed to locate and designate areas of endemicity.Location The Iberian Peninsula and the three largest Balearic Islands (Mallorca, Menorca and Ibiza) in the western Mediterranean, West Palaearctic region. MethodsThe information analysed consisted of presence/absence data of animal and plant species, recorded on a 100´100 km grid based on the UTM projection system. From a larger initial data set, a simpli®ed matrix of 480 species present in at least two quadrats was obtained, and processed to estimate the overall similarity patterns across land squares, and the areas of endemism. Two methods were employed to detect areas of endemism: Wagner Parsimony (PAE, or parsimony analysis of endemicity) and compatibility. A modi®cation of PAE, PAE±PCE (Parsimony analysis of endemicity with progressive character elimination) was applied to overcome some of the potential shortcomings of the method. ResultsThe results represent the ®rst attempt for a combined analysis of animal and plant distributions in the western Mediterranean. The proposed PAE±PCE procedure proved useful to identify areas of endemism that would have been otherwise overlooked. Up to thirty-six different areas of endemisms were identi®ed. Some of these represent concentric (hierarchically nested) structures, while other are partly overlapping sectors. The endemism areas, as derived from parsimony and compatibility analyses, generally ®t within the frame of the overall similarity approach.Main conclusions The areas of endemicity identi®ed often coincide with mountain sectors, and this may be of incidental interest for conservation policies as most natural preserves in the study area are located in mountain ranges. The conclusions are of interest for large scale approaches to the biogeography of the Mediterranean Basin, facilitating the selection of endemism areas for operative purposes. However, most of the best supported areas of endemism detected are relatively small, or overlap with neighbouring endemism areas. Hence, adopting large area units such as`Iberia' for historical analysis at a wider geographical scale may be risky, because such units may actually represent composite sectors of an heterogeneous nature. The distribution of the areas of endemism, as well as the results of the overall similarity classi®cation, share a number of features with previous sectorizations from independent, mostly phytogeographical, approaches. Parsimony analysis of endemicity is a potentially useful tool for identifying areas designated by species with congruent distributions, but (1) the results Correspondence: Enrique Garcõ Âa-Barros, have no direct historical implications (for phylogenetic information is not incorporated), and (2) unless modi®cations such as the PAE±PCE procedure are applied, the number of potential areas of endemism (in the sense stated above) will often be underestimated. It is also shown that, in a PAE, a`total evidence' approac...