High connectivity on a global scale in the pelagic wahoo,Acanthocybium solandri (tuna family Scombridae)

The population genetic structure and phylogeography of wahoo, Acanthocybium solandri, were investigated on a global scale with intron six of lactate dehydrogenase‐A (ldhA6, 8 locations, N = 213) and mtDNA cytochrome b (Cytb, 10 locations, N = 322). Results show extensive sharing of haplotypes across the wahoo's entire global range, and analyses were unable to detect significant structure (nuclear F_ST = 0.0125, P = 0.106; mtDNA Φ_ST < 0.0001, P = 0.634). Power analyses indicated 95% confidence in detecting nuclear F_ST ≥ 0.0389 and mtDNA Φ_ST ≥ 0.0148. These findings appear unique, as most other tunas, billfishes, and oceanic sharks exhibit significant population structure on the scale of East–West Atlantic, Atlantic vs. Indian‐Pacific, or East–West Pacific. Overall nuclear heterozygosity (H = 0.714) and mtDNA haplotype diversity (h = 0.918) are both high in wahoo, while overall mtDNA nucleotide diversity (π= 0.006) and nuclear nucleotide diversity (π=0.004) are uniformly low, indicating a recent increase in population size. Coalescence analyses yield an estimate of effective female population size (N_eF) at ~816 000, and a population bottleneck ~690 000 years ago. However, conclusions about population history from our Cytb data set are not concordant with a control region survey, a finding that will require further investigation. This is the first example of a vertebrate with a single globally distributed population, a finding we attribute to extensive dispersal at all life stages. The indications of a worldwide stock for wahoo reinforce the mandate for international cooperation on fisheries issues.     

RAD genotyping reveals fine‐scale genetic structuring and provides powerful population assignment in a widely distributed marine species,the American lobster (Homarus americanus)

Deciphering genetic structure and inferring connectivity in marine species have been challenging due to weak genetic differentiation and limited resolution offered by traditional genotypic methods. The main goal of this study was to assess how a population genomics framework could help delineate the genetic structure of the American lobster (Homarus americanus) throughout much of the species’ range and increase the assignment success of individuals to their location of origin. We genotyped 10 156 filtered SNPs using RAD sequencing to delineate genetic structure and perform population assignment for 586 American lobsters collected in 17 locations distributed across a large portion of the species’ natural distribution range. Our results revealed the existence of a hierarchical genetic structure, first separating lobsters from the northern and southern part of the range (F_CT = 0.0011; P‐value = 0.0002) and then revealing a total of 11 genetically distinguishable populations (mean F_ST = 0.00185; CI: 0.0007–0.0021, P‐value < 0.0002), providing strong evidence for weak, albeit fine‐scale population structuring within each region. A resampling procedure showed that assignment success was highest with a subset of 3000 SNPs having the highest F_ST. Applying Anderson's (Molecular Ecology Resources, 2010, 10, 701) method to avoid ‘high‐grading bias’, 94.2% and 80.8% of individuals were correctly assigned to their region and location of origin, respectively. Lastly, we showed that assignment success was positively associated with sample size. These results demonstrate that using a large number of SNPs improves fine‐scale population structure delineation and population assignment success in a context of weak genetic structure. We discuss the implications of these findings for the conservation and management of highly connected marine species, particularly regarding the geographic scale of demographic independence.     

Unexpected cryptic species diversity in the widespread coral Seriatopora hystrix masks spatial‐genetic patterns of connectivity

Mounting evidence of cryptic species in a wide range of taxa highlights the need for careful analyses of population genetic data sets to unravel within‐species diversity from potential interspecies relationships. Here, we use microsatellite loci and hierarchical clustering analysis to investigate cryptic diversity in sympatric and allopatric (separated by 450 km) populations of the widespread coral Seriatopora hystrix on the Great Barrier Reef. Structure analyses delimited unique genetic clusters that were confirmed by phylogenetic and extensive population‐level analyses. Each of four sympatric yet distinct genetic clusters detected within S. hystrix demonstrated greater genetic cohesion across regional scales than between genetic clusters within regions (<10 km). Moreover, the magnitude of genetic differentiation between different clusters (>0.620 G”_ST) was similar to the difference between S. hystrix clusters and the congener S. caliendrum (mean G”_ST 0.720). Multiple lines of evidence, including differences in habitat specificity, mitochondrial identity, Symbiodinium associations and morphology, corroborate the nuclear genetic evidence that these distinct clusters constitute different species. Hierarchical clustering analysis combined with more traditional population genetic methods provides a powerful approach for delimiting species and should be regularly applied to ensure that ecological and evolutionary patterns interpreted for single species are not confounded by the presence of cryptic species.     

Calculations of population differentiation based on GST and D: forget GST but not all of statistics!

G _ST‐values and its relatives (F_ST) belong to the most used parameters to define genetic differences between populations. Originally, they were developed for allozymes with very low number of alleles. Using highly polymorphic microsatellite markers it was often puzzling that G_ST‐values were very low but statistically significant. In their papers, Jost (2008) and Hedrick (2005) explained that G_ST‐values do not show genetic differentiation, and Jost suggested calculating D‐values instead. Theoretical mathematical considerations are often difficult to follow; therefore, we chose an applied approach comparing two artificial populations with different number of alleles at equal frequencies and known genetic divergence. Our results show that even for more than one allele per population G_ST‐values do not calculate population differentiation correctly; in contrast, D‐values do reflect the genetic differentiation indicating that data based on G_ST‐values need to be re‐evaluated. In our approach, statistical evaluations remained similar. We provide information about the impact of different sample sizes on D‐values in relation to number of alleles and genetic divergence.     

The empirical Bayes estimators of fine‐scale population structure in high gene flow species

An empirical Bayes (EB) pairwise F_ST estimator was previously introduced and evaluated for its performance by numerical simulation. In this study, we conducted coalescent simulations and generated genetic population structure mechanistically, and compared the performance of the EBF_ST with Nei's G_ST, Nei and Chesser's bias‐corrected G_ST (G_{ST_NC}), Weir and Cockerham's θ (θ_WC) and θ with finite sample correction (θ_{WC_F}). We also introduced EB estimators for Hedrick’ G’_ST and Jost’ D. We applied these estimators to publicly available SNP genotypes of Atlantic herring. We also examined the power to detect the environmental factors causing the population structure. Our coalescent simulations revealed that the finite sample correction of θ_WC is necessary to assess population structure using pairwise F_ST values. For microsatellite markers, EBF_ST performed the best among the present estimators regarding both bias and precision under high gene flow scenarios (). For 300 SNPs, EBF_ST had the highest precision in all cases, but the bias was negative and greater than those for G_{ST_NC} and θ_{WC_F} in all cases. G_{ST_NC} and θ_{WC_F} performed very similarly at all levels of F_ST. As the number of loci increased up to 10 000, the precision of G_{ST_NC} and θ_{WC_F} became slightly better than for EBF_ST for cases with , even though the size of the bias remained constant. The EB estimators described the fine‐scale population structure of the herring and revealed that ~56% of the genetic differentiation was caused by sea surface temperature and salinity. The R package finepop for implementing all estimators used here is available on CRAN.     

Absence of founder effect and evidence for adaptive divergence in a recently introduced insular population of white‐tailed deer (Odocoileus virginianus)

Islands are generally colonized by few individuals which could lead to a founder effect causing loss of genetic diversity and rapid divergence by strong genetic drift. Insular conditions can also induce new selective pressures on populations. Here, we investigated the extent of genetic differentiation within a white‐tailed deer (Odocoileus virginianus) population introduced on an island and its differentiation with its source mainland population. In response to their novel environmental conditions, introduced deer changed phenotypically from mainland individuals, therefore we investigated the genetic bases of the morphological differentiation. The study was conducted on Anticosti Island (Québec, Canada) where 220 individuals were introduced 120 years ago, resulting in a population size over 160,000 individuals. We used genotyping‐by‐sequencing (GBS) to generate 8,518 filtered high‐quality SNPs and compared patterns of genetic diversity and differentiation between the continental and Anticosti Island populations. Clustering analyses indicated a single panmictic island population and no sign of isolation by distance. Our results revealed a weak, albeit highly significant, genetic differentiation between the Anticosti Island population and its source population (mean F_ST = 0.005), which allowed a population assignment success of 93%. Also, the high genetic diversity maintained in the introduced population supports the absence of a strong founder effect due to the large number of founders followed by rapid population growth. We further used a polygenic approach to assess the genetic bases of the divergent phenotypical traits between insular and continental populations. We found loci related to muscular function and lipid metabolism, which suggested that these could be involved in local adaptation on Anticosti Island. We discuss these results in a harvest management context.     

Species‐level view of population structure and gene flow for a critically endangered primate (Varecia variegata)

Lemurs are among the world's most threatened mammals. The critically endangered black‐and‐white ruffed lemur (Varecia variegata), in particular, has recently experienced rapid population declines due to habitat loss, ecological sensitivities to habitat degradation, and extensive human hunting pressure. Despite this, a recent study indicates that ruffed lemurs retain among the highest levels of genetic diversity for primates. Identifying how this diversity is apportioned and whether gene flow is maintained among remnant populations will help to diagnose and target conservation priorities. We sampled 209 individuals from 19 sites throughout the remaining V. variegata range. We used 10 polymorphic microsatellite loci and ~550 bp of mtDNA sequence data to evaluate genetic structure and population dynamics, including dispersal patterns and recent population declines. Bayesian cluster analyses identified two distinct genetic clusters, which optimally partitioned data into populations occurring on either side of the Mangoro River. Localities north of the Mangoro were characterized by greater genetic diversity, greater gene flow (lower genetic differentiation) and higher mtDNA haplotype and nucleotide diversity than those in the south. Despite this, genetic differentiation across all sites was high, as indicated by high average F_ST (0.247) and Φ_ST (0.544), and followed a pattern of isolation‐by‐distance. We use these results to suggest future conservation strategies that include an effort to maintain genetic diversity in the north and restore connectivity in the south. We also note the discordance between patterns of genetic differentiation and current subspecies taxonomy, and encourage a re‐evaluation of conservation management units moving forward.     

Exploring a Pool‐seq‐only approach for gaining population genomic insights in nonmodel species

Developing genomic insights is challenging in nonmodel species for which resources are often scarce and prohibitively costly. Here, we explore the potential of a recently established approach using Pool‐seq data to generate a de novo genome assembly for mining exons, upon which Pool‐seq data are used to estimate population divergence and diversity. We do this for two pairs of sympatric populations of brown trout (Salmo trutta): one naturally sympatric set of populations and another pair of populations introduced to a common environment. We validate our approach by comparing the results to those from markers previously used to describe the populations (allozymes and individual‐based single nucleotide polymorphisms [SNPs]) and from mapping the Pool‐seq data to a reference genome of the closely related Atlantic salmon (Salmo salar). We find that genomic differentiation (F_ST) between the two introduced populations exceeds that of the naturally sympatric populations (F_ST = 0.13 and 0.03 between the introduced and the naturally sympatric populations, respectively), in concordance with estimates from the previously used SNPs. The same level of population divergence is found for the two genome assemblies, but estimates of average nucleotide diversity differ ( ≈ 0.002 and  ≈ 0.001 when mapping to S. trutta and S. salar, respectively), although the relationships between population values are largely consistent. This discrepancy might be attributed to biases when mapping to a haploid condensed assembly made of highly fragmented read data compared to using a high‐quality reference assembly from a divergent species. We conclude that the Pool‐seq‐only approach can be suitable for detecting and quantifying genome‐wide population differentiation, and for comparing genomic diversity in populations of nonmodel species where reference genomes are lacking.     

Drastic post‐LGM expansion and lack of historical genetic structure of a subtropical fig‐pollinating wasp (Ceratosolen sp. 1) of Ficus septica in Taiwan

The climatic oscillations of the last glacial period have had profound influences on the demography and levels of genetic diversity of extant species. Molecular evidence of glacial effects on temperate species has been well documented, whereas little is known regarding that on subtropical species. Here we present analyses based on partial sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene (1052 bp) and genotypes at 15 microsatellite loci to investigate the historical demography, population structure and ongoing gene flow of an undescribed fig‐pollinating wasp (Ceratosolen sp. 1) of Ficus septica in subtropical Taiwan. Reconstructed historical demography based on the coalescent tree of COI sequences suggests that C. sp. 1 has undergone a drastic population expansion which was tightly coupled with climatic changes since the last glacial maximum (LGM). The magnitude of the population size change was approximately 500‐fold, indicating that the population of this wasp and its host was likely highly compressed during the last glacial period. The lack of significant population differentiation (F_ST < 0.02, for all pairwise F_ST values) may be due to rapid postglacial expansion facilitated by long‐distance dispersal, although a low frequency of first‐generation migrants was detected. Our results clearly demonstrate how recent climatic changes since the LGM and dispersal ability have jointly shaped the genetic composition of a subtropical fig‐pollinating wasp.     

Generation of a neutral FST baseline for testing local adaptation on gill raker number within and between European whitefish ecotypes in the Baltic Sea basin

Divergent selection at ecologically important traits is thought to be a major factor driving phenotypic differentiation between populations. To elucidate the role of different evolutionary processes shaping the variation in gill raker number of European whitefish (Coregonus lavaretus sensu lato) in the Baltic Sea basin, we assessed the relationships between genetic and phenotypic variation among and within three whitefish ecotypes (sea spawners, river spawners and lake spawners). To generate expected neutral distribution of F_ST and to evaluate whether highly variable microsatellite loci resulted in deflated F_ST estimates compared to less variable markers, we performed population genetic simulations under finite island and hierarchical island models. The genetic divergence observed among (F_CT = 0.010) and within (F_ST = 0.014–0.041) ecotypes was rather low. The divergence in gill raker number, however, was substantially higher between sea and river spawners compared to observed microsatellite data and simulated neutral baseline (P_CT > F_CT). This suggests that the differences in gill raker number between sea and river spawners are likely driven by divergent natural selection. We also found strong support for divergent selection on gill raker number among different populations of sea spawners (P_ST > F_ST), most likely caused by highly variable habitat use and diverse diet. The putative role of divergent selection within lake spawners initially inferred from empirical microsatellite data was not supported by simulated F_ST distributions. This work provides a first formal test of divergent selection on gill raker number in Baltic whitefish, and demonstrates the usefulness of population genetic simulations to generate informative neutral baselines for P_ST–F_ST analyses helping to disentangle the effects of stochastic evolutionary processes from natural selection.     

Positive selection of IL‐33 in adaptive immunity of domestic Chinese goats

The identification of the candidate genes that play key role in phenotypic variation in livestock populations can provide new information about evolution and positive selection. IL‐33 (71954) (Interleukin) gene is associated with the increased nematode resistance in small ruminants; however, the role of IL‐33 for the genetic control of different diseases in Chinese goat breeds is poorly described in scientific literature. Therefore, the current investigation was performed for the better understanding of the molecular evolution and the positive selection of single‐nucleotide polymorphism in IL‐33 gene. Fixation Index (F_ST)‐based method was used for the outlier loci determination and found that IL‐33 was present in outlier area with the provisional combined allocation of mean heterozygosity and F_ST. Positively selected IL‐33 gene was significantly, that is, p(Simul F_ST < sample F_ST = 0.98*) present in corresponding positive selection area. Hence, our study provided novel information about the nucleotide variations in IL‐33 gene and found to be nonsynonymous which may helpful for the genetic control of diseases by enhancing the immune system in local Chinese goat breeds as well as in other analyzed vertebrate species.     

Large‐scale connectivity,cryptic population structure,and relatedness in Eastern Pacific Olive ridley sea turtles (Lepidochelys olivacea)

Endangered species are grouped into genetically discrete populations to direct conservation efforts. Mitochondrial control region (mtCR) haplotypes are used to elucidate deep divergences between populations, as compared to nuclear microsatellites that can detect recent structuring. When prior populations are unknown, it is useful to subject microsatellite data to clustering and/or ordination population inference. Olive ridley sea turtles (Lepidochelys olivacea) are the most abundant sea turtle, yet few studies have characterized olive ridley population structure. Recently, clustering results of olive ridleys in the Eastern Tropical Pacific Ocean suggested weak structuring (F_ST = 0.02) between Mexico and Central America. We analyzed mtCR haplotypes, new microsatellite genotypes from Costa Rica, and preexisting microsatellite genotypes from olive ridleys across the Eastern Tropical Pacific, to further explore population structuring in this region. We subjected inferred populations to multiple analyses to explore the mechanisms behind their structuring. We found 10 mtCR haplotypes from 60 turtles nesting at three sites in Costa Rica, but did not detect divergence between Costa Rican sites, or between Central America and Mexico. In Costa Rica, clustering suggested one population with no structuring, but ordination suggested four cryptic clusters with moderate structuring (F_ST = 0.08, p < .001). Across the Eastern Tropical Pacific, ordination suggested nine cryptic clusters with moderate structuring (F_ST = 0.103, p < .001) that largely corresponded to Mexican and Central American populations. All ordination clusters displayed significant internal relatedness relative to global relatedness (p < .001) and contained numerous sibling pairs. This suggests that broadly dispersed family lineages have proliferated in Eastern Tropical Pacific olive ridleys and corroborates previous work showing basin‐wide connectivity and shallow population structure in this region. The existence of broadly dispersed kin in Eastern Tropical Pacific olive ridleys has implications for management of olive ridleys in this region, and adds to our understanding of sea turtle ecology and life history, particularly in light of the natal‐homing paradigm.     

Testing hypotheses driving genetic structure in the cooperatively breeding Brown‐headed Nuthatch Sitta pusilla

Habitat fragmentation has often been implicated in the decline of many species. For habitat specialists and/or sedentary species, loss of habitat can result in population isolation and lead to negative genetic effects. However, factors other than fragmentation can often be important and also need to be considered when assessing the genetic structure of a species. We genotyped individuals from 13 populations of the cooperatively breeding Brown‐headed Nuthatch Sitta pusilla in Florida to test three alternative hypotheses regarding the effects that habitat fragmentation might have on genetic structure. A map of potential habitat developed from recent satellite imagery suggested that Brown‐headed Nuthatch populations in southern Florida occupied smaller and more isolated habitat patches (i.e. were more fragmented) than populations in northern Florida. We also genotyped individuals from a small, isolated Brown‐headed Nuthatch population on Grand Bahama Island. We found that populations associated with more fragmented habitat in southern Florida had lower allelic richness than populations in northern Florida (P = 0.02), although there were no differences in heterozygosity. Although pairwise estimates of F_ST were low overall, values among southern populations were generally higher than northern populations. Population assignment tests identified K = 3 clusters corresponding to a northern cluster, a southern cluster and a unique population in southeast Florida; using sampling localities as prior information revealed K = 7 clusters, with greater structure only among southern Florida populations. The Bahamas population showed moderate to high differentiation compared with Florida populations. Overall, our results suggest that fragmentation could affect gene flow in Brown‐headed Nuthatch populations and is likely to become more pronounced over time.     

Genetic differentiation among European samples of the arctic‐alpine leaf beetle,Chrysomela lapponica

Genetic differentiation within and among isolated populations of the arctic‐alpine leaf beetle, Chrysomela lapponica L. (Coleoptera: Chrysomelidae), specialized on either Salix L. (Salicaceae) or Betula L. (Betulaceae) species, was assessed by F‐statistics analysis at seven allozyme loci. Beetles were collected on Salix spp. in lowland Finland (four samples), at mid elevation in the Black Forest in Germany (450 m) and the Massif Central in France (two samples, 930–1 300 m), and at high elevation in the French Alps (2 300 m). Beetles sampled in the Czech Republic (650 m) fed on Betula pubescens Ehrh. Larvae feeding on Salix spp. secreted host‐derived salicylaldehyde as major toxin; those feeding on B. pubescens secreted isobutyrates and 2‐methylbutyrates of mixed plant–insect origin. In all samples, a heterozygote deficit was observed (0.120<F_IS<0.568), in particular in populations collected at mid or high elevation (F_IS>0.4). The estimated mean level of genetic differentiation among all populations was high (F_ST = 0.276). Differentiation was highly variable between pairs of populations (F_ST = 0.093–0.455, all significant) without any correlation with geographic distance. The sample collected in the Czech Republic, from the only population on B. pubescens, was not the most divergent.     

Spatio‐temporal genetic structure and the effects of long‐term fishing in two partially sympatric offshore demersal fishes

Environmental gradients have been shown to disrupt gene flow in marine species, yet their influence in structuring populations at depth remains poorly understood. The Cape hakes (Merluccius paradoxus and M. capensis) are demersal species co‐occurring in the Benguela Current system, where decades of intense fishing resulted in severely depleted stocks in the past. Previous studies identified conflicting mtDNA genetic substructuring patterns and thus contrasting evolutionary trajectories for both species. Using 10 microsatellite loci, the control region of mtDNA and employing a seascape genetics approach, we investigated genetic connectivity and the impact of prolonged exploitation in the two species, which are characterized by different patterns of fishing pressure. Three consecutive years were sampled covering the entire distribution (N = 2100 fishes). Despite large estimated population sizes, both species exhibited low levels of contemporary genetic diversity (0.581 < H_E < 0.692), implying that fishing has had a significant impact on their genetic composition and evolutionary trajectories. Further, for M. paradoxus, significant temporal, but not spatial, divergence points to the presence of genetic chaotic patchiness. In contrast, M. capensis exhibited a clear latitudinal cline in genetic differentiation between Namibia and South Africa (F_ST = 0.063, P < 0.05), with low (0.2% per generation) estimates of contemporary gene flow. Seascape analyses reveal an association with bathymetry and upwelling events, suggesting that adaptation to local environmental conditions may drive genetic differentiation in M. capensis. Importantly, our results highlight the need for temporal sampling in disentangling the complex factors that impact population divergence in marine fishes.     

Familial social structure and socially driven genetic differentiation in Hawaiian short‐finned pilot whales

Social structure can have a significant impact on divergence and evolution within species, especially in the marine environment, which has few environmental boundaries to dispersal. On the other hand, genetic structure can affect social structure in many species, through an individual preference towards associating with relatives. One social species, the short‐finned pilot whale (Globicephala macrorhynchus), has been shown to live in stable social groups for periods of at least a decade. Using mitochondrial control sequences from 242 individuals and single nucleotide polymorphisms from 106 individuals, we examine population structure among geographic and social groups of short‐finned pilot whales in the Hawaiian Islands, and test for links between social and genetic structure. Our results show that there are at least two geographic populations in the Hawaiian Islands: a Main Hawaiian Islands (MHI) population and a Northwestern Hawaiian Islands/Pelagic population (F_ST and Φ_ST p < .001), as well as an eastern MHI community and a western MHI community (F_ST p = .009). We find genetically driven social structure, or high relatedness among social units and clusters (p < .001), and a positive relationship between relatedness and association between individuals (p < .0001). Further, socially organized clusters are genetically distinct, indicating that social structure drives genetic divergence within the population, likely through restricted mate selection (F_ST p = .05). This genetic divergence among social groups can make the species less resilient to anthropogenic or ecological disturbance. Conservation of this species therefore depends on understanding links among social structure, genetic structure and ecological variability within the species.     

Pervasive selection or is it…? why are FST outliers sometimes so frequent?

It is now common for population geneticists to estimate F_ST for a large number of loci across the genome, before testing for selected loci as being outliers to the F_ST distribution. One surprising result of such F_ST scans is the often high proportion (>1% and sometimes >10%) of outliers detected, and this is often interpreted as evidence for pervasive local adaptation. In this issue of Molecular Ecolog, Fourcade et al. ( 2013 ) observe that a particularly high rate of F_ST outliers has often been found in river organisms, such as fishes or damselflies, despite there being no obvious reason why selection should affect a larger proportion of the genomes of these organisms. Using computer simulations, Fourcade et al. ( 2013 ) show that the strong correlation in co‐ancestry produced in long one‐dimensional landscapes (such as rivers, valleys, peninsulas, oceanic ridges or coastlines) greatly increases the neutral variance in F_ST, especially when the landscape is further reticulated into fractal networks. As a consequence, outlier tests have a high rate of false positives, unless this correlation can be taken into account. Fourcade et al.'s study highlights an extreme case of the general problem, first noticed by Robertson ( 1975a , b ) and Nei & Maruyama ( 1975 ), that correlated co‐ancestry inflates the neutral variance in F_ST when compared to its expectation under an island model of population structure. Similar warnings about the validity of outlier tests have appeared regularly since then but have not been widely cited in the recent genomics literature. We further emphasize that F_ST outliers can arise in many different ways and that outlier tests are not designed for situations where the genetic architecture of local adaptation involves many loci.     

The effects of selection,drift and genetic variation on life‐history trait divergence among insular populations of natterjack toad,Bufo calamita

Although loss of genetic variation is frequently assumed to be associated with loss of adaptive potential, only few studies have examined adaptation in populations with little genetic variation. On the Swedish west coast, the northern fringe populations of the natterjack toad Bufo calamita inhabit an atypical habitat consisting of offshore rock islands. There are strong among‐population differences in the amount of neutral genetic variation, making this system suitable for studies on mechanisms of trait divergence along a gradient of within‐population genetic variation. In this study, we examined the mechanisms of population divergence using Q_ST–F_ST comparisons and correlations between quantitative and neutral genetic variation. Our results suggest drift or weak stabilizing selection across the six populations included in this study, as indicated by low Q_ST–F_ST values, lack of significant population × temperature interactions and lack of significant differences among the islands in breeding pond size. The six populations included in this study differed in both neutral and quantitative genetic variation. Also, the correlations between neutral and quantitative genetic variation tended to be positive, however, the relatively small number of populations prevents any strong conclusions based on these correlations. Contrary to the majority of Q_ST–F_ST comparisons, our results suggest drift or weak stabilizing selection across the examined populations. Furthermore, the low heritability of fitness‐related traits may limit evolutionary responses in some of the populations.     

Selection on life‐history traits and genetic population divergence in rotifers

A combination of founder effects and local adaptation – the Monopolization hypothesis – has been proposed to reconcile the strong population differentiation of zooplankton dwelling in ponds and lakes and their high dispersal abilities. The role genetic drift plays in genetic differentiation of zooplankton is well documented, but the impact of natural selection has received less attention. Here, we compare differentiation in neutral genetic markers (F_ST) and in quantitative traits (Q_ST) in six natural populations of the rotifer Brachionus plicatilis to assess the importance of natural selection in explaining genetic differentiation of life‐history traits. Five life‐history traits were measured in four temperature × salinity combinations in common‐garden experiments. Population differentiation for neutral genetic markers – 11 microsatellite loci – was very high (F_ST = 0.482). Differentiation in life‐history traits was higher in traits related to sexual reproduction than in those related to asexual reproduction. Q_ST values for diapausing egg production (a trait related to sexual reproduction) were higher than their corresponding F_ST in some pairs of populations. Our results indicate the importance of divergent natural selection in these populations and suggest local adaptation to the unpredictability of B. plicatilis habitats.     

Temporal shifts of DNA‐microsatellite allele profiles in roe deer (Capreolus capreolus L.) within three decades

DNA‐microsatellite polymorphism (four loci) was studied in 56 male roe deer (Capreolus capreolus) from a 900‐ha hunting territory in the Vosges du Nord Mountains (France), culled over 34 years (1956–1990). Changed allele frequencies at two loci within this period, and increased allelic diversity, were traced to a phase of reduced population density and subsequent immigration. Decadic population samples collected within 900‐ha were distinguished by higher genetic variability measures than were certain geographical samples across Central Europe (4–900 km). On average, the decadic cohorts were distinguished by a gene diversity index of G_ST = 0.0286, and a genetic distance of D = 0.0938, which reflect 54% (G_ST) and 69% (D) of the respective geographic (350 km) differentiation indices of roe deer in Central Europe. The importance of demography and population ecology effects for microevolution in a large mammal is demonstrated, as is the risk of artefact by composing population samples of deer over several years. Population genetic screening should cover various demes of roe deer from the same general region, and be based on many unlinked polymorphic loci, to minimize the distorting effects of genetic dynamics at the small spatial scale.