Interspecific introgressive origin of genomic diversity in the house mouse.

We report on a genome-wide scan for introgression between the house mouse (Mus musculus domesticus) and the Algerian mouse (Mus spretus), using samples from the ranges of sympatry and allopatry in Africa and Europe. Our analysis reveals wide variability in introgression signatures along the genomes, as well as across the samples. We find that fewer than half of the autosomes in each genome harbor all detectable introgression, whereas the X chromosome has none. Further, European mice carry more M. spretus alleles than the sympatric African ones. Using the length distribution and sharing patterns of introgressed genomic tracts across the samples, we infer, first, that at least three distinct hybridization events involving M. spretus have occurred, one of which is ancient, and the other two are recent (one presumably due to warfarin rodenticide selection). Second, several of the inferred introgressed tracts contain genes that are likely to confer adaptive advantage. Third, introgressed tracts might contain driver genes that determine the evolutionary fate of those tracts. Further, functional analysis revealed introgressed genes that are essential to fitness, including the Vkorc1 gene, which is implicated in rodenticide resistance, and olfactory receptor genes. Our findings highlight the extent and role of introgression in nature and call for careful analysis and interpretation of house mouse data in evolutionary and genetic studies.

The colonization and divergence patterns of Brandt's vole (Lasiopodomys brandtii) populations reveal evidence of genetic surfing.

BACKGROUND: The colonial habit of Brandt's vole (Lasiopodomys brandtii) differs from that of most other species of the genus Microtus. The demographic history of this species and the patterns shaping its current genetic structure remain unknown. Here, we explored patterns of genetic differentiation and infered the demographic history of Brandt's vole populations through analyses of nuclear microsatellite and D-loop sequences. RESULTS: Phylogenetic analyses divided the sampled populations into three main clusters, which represent the southeastern, northeastern and western parts of the total range in Mongolia and China. Molecular data revealed an ancestral area located in the southeast of the extant range, in the Xilinguole District, Inner Mongolia, China, from where Brandt's vole populations began expanding. A gene flow analysis suggested that the most likely colonization route was from the ancestral area and was followed by subsequent northeastward and westward range expansions. We identified decreases in genetic diversity with increasing distance from the founder population within the newly occupied regions (northeastern and western regions), clinal patterns in the allele frequencies, alleles that were rare in the original area that have become common in the newly occupied regions, and higher genetic differentiation in the expanded range compared with the original one. CONCLUSION: Our results indicate that L. brandtii most likely originated from the southeastern part of its current geographic range, and subsequently colonized into the northeastern and western parts by expansion. The genetic patterns among the derived populations and with respect to the original population are consistent with that expected under genetic surfing models, which indicated that genetic drift, rather than gene flow, is the predominant factor underlying the genetic structure of expanding Brandt's vole populations.

An HMM-based comparative genomic framework for detecting introgression in eukaryotes.

One outcome of interspecific hybridization and subsequent effects of evolutionary forces is introgression, which is the integration of genetic material from one species into the genome of an individual in another species. The evolution of several groups of eukaryotic species has involved hybridization, and cases of adaptation through introgression have been already established. In this work, we report on PhyloNet-HMM-a new comparative genomic framework for detecting introgression in genomes. PhyloNet-HMM combines phylogenetic networks with hidden Markov models (HMMs) to simultaneously capture the (potentially reticulate) evolutionary history of the genomes and dependencies within genomes. A novel aspect of our work is that it also accounts for incomplete lineage sorting and dependence across loci. Application of our model to variation data from chromosome 7 in the mouse (Mus musculus domesticus) genome detected a recently reported adaptive introgression event involving the rodent poison resistance gene Vkorc1, in addition to other newly detected introgressed genomic regions. Based on our analysis, it is estimated that about 9% of all sites within chromosome 7 are of introgressive origin (these cover about 13 Mbp of chromosome 7, and over 300 genes). Further, our model detected no introgression in a negative control data set. We also found that our model accurately detected introgression and other evolutionary processes from synthetic data sets simulated under the coalescent model with recombination, isolation, and migration. Our work provides a powerful framework for systematic analysis of introgression while simultaneously accounting for dependence across sites, point mutations, recombination, and ancestral polymorphism.

A hyperactive quantitative trait locus allele of Arabidopsis BRX contributes to natural variation in root growth vigor.

Quantitative trait loci analysis of natural Arabidopsis thaliana accessions is increasingly exploited for gene isolation. However, to date this has mostly revealed deleterious mutations. Among them, a loss-of-function allele identified the root growth regulator BREVIS RADIX (BRX). Here we present evidence that BRX and the paralogous BRX-LIKE (BRXL) genes are under selective constraint in monocotyledons as well as dicotyledons. Unexpectedly, however, whereas none of the Arabidopsis orthologs except AtBRXL1 could complement brx null mutants when expressed constitutively, nearly all monocotyledon BRXLs tested could. Thus, BRXL proteins seem to be more diversified in dicotyledons than in monocotyledons. This functional diversification was correlated with accelerated rates of sequence divergence in the N-terminal regions. Population genetic analyses of 30 haplotypes are suggestive of an adaptive role of AtBRX and AtBRXL1. In two accessions, Lc-0 and Lov-5, seven amino acids are deleted in the variable region between the highly conserved C-terminal, so-called BRX domains. Genotyping of 42 additional accessions also found this deletion in Kz-1, Pu2-7, and Ws-0. In segregating recombinant inbred lines, the Lc-0 allele (AtBRX(Lc-0)) conferred significantly enhanced root growth. Moreover, when constitutively expressed in the same regulatory context, AtBRX(Lc-0) complemented brx mutants more efficiently than an allele without deletion. The same was observed for AtBRXL1, which compared with AtBRX carries a 13 amino acid deletion that encompasses the deletion found in AtBRX(Lc-0). Thus, the AtBRX(Lc-0) allele seems to contribute to natural variation in root growth vigor and provides a rare example of an experimentally confirmed, hyperactive allelic variant.

A VKORC1-based SNP survey of anticoagulant rodenticide resistance in the house mouse, Norway rat and roof rat in the USA.

BACKGROUND: We conducted a vitamin K epoxide reductase subcomponent 1 (Vkorc1)-based nonsynonymous Single Nucleotide Polymorphism (nsSNP) screen with focus on the house mouse (Mus musculus domesticus), but that also considered the Norway rat (Rattus norvegicus) and roof rat (R. rattus) in the USA. RESULTS: We detected six Vkorc1 nsSNPs underlying the amino-acid polymorphisms Ala21Thr, Trp59Leu, Ile104Val, Val118Leu, Leu128Ser and Tyr139Cys in house mice (average coverage/SNP; n = 182 individuals), two nsSNPs underlying Arg35Pro and Gly46Ser in the Norway rat (n = 93), with the notable absence of Tyr139Cys (n = 179), and one nsSNP underlying Tyr25Phe in the roof rat (n = 27). Inferred resistance frequency is 29.1% for mice (variability of states 0-98.8%), 6.5% (0-33.3%) for the Norway rat, and 39.3% (0-52.6%) for the roof rat based on Tyr25Phe frequencies. CONCLUSIONS: Resistance detected in the USA in the 1980s likely was the consequence of Vkorc1 mutations in mice (Leu128Ser and Tyr139Cys), Norway rats (Arg35Pro) and roof rats (Tyr25Phe). Patterns of variant sharing between the USA and Europe indicate the importance of convergent evolution and gene flow in spreading resistance. The spread of nsSNPs in mice between continents appears to have been more effective than in Norway rats. We hypothesize that Arg35Pro may have originated in Norway rats in the USA, whereas Tyr139Cys variants originated in Europe. Tyr25Phe is the likely cause for resistance in roof rats. Further genetic testing in the USA is required to close sampling gaps, and population genomic data are needed to study the origin and spread of this adaptive trait.

Functional and evolutionary correlates of gene constellations in the Drosophila melanogaster genome that deviate from the stereotypical gene architecture.

BACKGROUND: The biological dimensions of genes are manifold. These include genomic properties, (e.g., X/autosomal linkage, recombination) and functional properties (e.g., expression level, tissue specificity). Multiple properties, each generally of subtle influence individually, may affect the evolution of genes or merely be (auto-)correlates. Results of multidimensional analyses may reveal the relative importance of these properties on the evolution of genes, and therefore help evaluate whether these properties should be considered during analyses. While numerous properties are now considered during studies, most work still assumes the stereotypical solitary gene as commonly depicted in textbooks. Here, we investigate the Drosophila melanogaster genome to determine whether deviations from the stereotypical gene architecture correlate with other properties of genes. RESULTS: Deviations from the stereotypical gene architecture were classified as the following gene constellations: Overlapping genes were defined as those that overlap in the 5-prime, exonic, or intronic regions. Chromatin co-clustering genes were defined as genes that co-clustered within 20 kb of transcriptional territories. If this scheme is applied the stereotypical gene emerges as a rare occurrence (7.5%), slightly varied schemes yielded between approximately 1%-50%. Moreover, when following our scheme, paired-overlapping genes and chromatin co-clustering genes accounted for 50.1 and 42.4% of the genes analyzed, respectively. Gene constellation was a correlate of a number of functional and evolutionary properties of genes, but its statistical effect was approximately 1-2 orders of magnitude lower than the effects of recombination, chromosome linkage and protein function. Analysis of datasets on male reproductive proteins showed these were biased in their representation of gene constellations and evolutionary rate Ka/Ks estimates, but these biases did not overwhelm the biologically meaningful observation of high evolutionary rates of male reproductive genes. CONCLUSION: Given the rarity of the solitary stereotypical gene, and the abundance of gene constellations that deviate from it, the presence of gene constellations, while once thought to be exceptional in large Eukaryote genomes, might have broader relevance to the understanding and study of the genome. However, according to our definition, while gene constellations can be significant correlates of functional properties of genes, they generally are weak correlates of the evolution of genes. Thus, the need for their consideration would depend on the context of studies.

Noninvasive genome sampling in chimpanzees.

The inevitable has happened: genomic technologies have been added to our noninvasive genetic sampling repertoire. In this issue of Molecular Ecology, Perry et al. (2010) demonstrate how DNA extraction from chimpanzee faeces, followed by a series of steps to enrich for target loci, can be coupled with next-generation sequencing. These authors collected sequence and single-nucleotide polymorphism (SNP) data at more than 600 genomic loci (chromosome 21 and the X) and the complete mitochondrial DNA. By design, each locus was 'deep sequenced' to enable SNP identification. To demonstrate the reliability of their data, the work included samples from six captive chimps, which allowed for a comparison between presumably genuine SNPs obtained from blood and potentially flawed SNPs deduced from faeces. Thus, with this method, anyone with the resources, skills and ambition to do genome sequencing of wild, elusive, or protected mammals can enjoy all of the benefits of noninvasive sampling.

Analysis of vkorc1 polymorphisms in Norway rats using the roof rat as outgroup.

BACKGROUND: Certain mutations in the vitamin K epoxide reductase subcomponent 1 gene (vkorc1) mediate rodent resistance to warfarin and other anticoagulants. Testing for resistance often involves analysis of the vkorc1. However, a genetic test for the roof rat (Rattus rattus) has yet to be developed. Moreover, an available roof rat vkorc1 sequence would enable species identification based on vkorc1 sequence and the evaluation of natural selection on particular vkorc1 polymorphisms in the Norway rat (R. norvegicus). RESULTS: We report the coding sequence, introns and 5' and 3' termini for the vkorc1 gene of roof rats (R. r. alexandrinus and R. r. frugivorus) from Uganda, Africa. Newly designed PCR primers now enable genetic testing of the roof rat and Norway rat. Only synonymous and noncoding polymorphisms were found in roof rats from Uganda. Both nominal subspecies of roof rats were indistinguishable from each other but were distinct from R. losea and R. flavipectus; however, the roof rat also shares at least three coding sequence polymorphisms with R. losea and R. flavipectus. Many of recently published vkorc1 synonymous and non-synonymous single nucleotide polymorphisms (SNPs) in Norway rats are likely SNPs from roof rats and/or other Rattus species. Tests applied to presumably genuine Norway rat vkorc1 SNPs are consistent with a role for selection in two populations carrying the derived Phe63Cys and Tyr139Cys mutations. CONCLUSION: Geographic mapping of vkorc1 SNPs in roof rats should be facilitated by our report. Our assay should be applicable to most species of Rattus, which are intermediate in genetic distance from roof and Norway rats. Vkorc1-mediated resistance due to non-synonymous coding SNPs is not segregating in roof rats from Uganda. By using the roof rat sequence as a reference vkorc1, SNPs now can be assigned to the correct rat species with more confidence. Sampling designs and genotyping strategies employed so far have helped detect candidate mutations underlying vkorc1-mediated resistance, but generally provided unsuitable data to test for selection. We propose that our understanding of vkorc1-mediated evolution of resistance in rodents would benefit from the adoption of sampling and genotyping designs that enable tests for selection on vkorc1.

Divergence population genetic analysis of hybridization between rhesus and cynomolgus macaques.

The geographic ranges of rhesus (Macaca mulatta) and cynomolgus (M. fascicularis) macaques adjoin in Indochina where they appear to hybridize. We used published and newly generated DNA sequences from 19 loci spanning approximately 20 kb to test whether introgression has occurred between these macaque species. We studied introgression at the level of nuclear DNA and distinguished between incomplete lineage sorting of ancestral polymorphisms or interspecific gene flow. We implemented a divergence population genetics approach by fitting our data to an isolation model implemented in the software IMa. The model that posits no gene flow from the rhesus into the cynomolgus macaque was rejected (P = 1.99 x 10(-8)). Gene flow in this direction was estimated as 2Nm approximately 1.2, while gene flow in the reverse direction was nonsignificantly different from zero (P = 0.16). The divergence time between species was estimated as approximately 1.3 million years. Balancing selection, a special case of incomplete sorting, was taken into consideration, as well as potential crossbreeding in captivity. Parameter estimates varied between analyses of subsets of data, although we still rejected isolation models. Geographic sampling of the data, where samples of cynomolgus macaques derived from Indochina were excluded, revealed a lost signature of gene flow, indicating that interspecific gene flow is restricted to mainland Indochina. Our results, in conjunction with those by others, justify future detailed analyses into the genetics of reproductive barriers and reticulate evolution in these two genome-enabled primates. Future studies of the natural hybridization between rhesus and cynomolgus macaques would expand the repertoire of systems available for speciation studies in primates.

Decoupled differentiation of gene expression and coding sequence among Drosophila populations.

Owing to the relevance to evolutionary theories of genotypic and phenotypic evolution, the correspondence of differentiation among natural populations in complex phenotypic traits and genetic markers has been studied extensively, and generally found to be poor. In contrast, the correspondence of differentiation among natural populations in gene expression, now often considered a genomic era proxy for the phenotype, and genetic markers, remains largely unexplored. Here, an analysis of expression and nucleotide sequence polymorphism of 106 genes in Drosophila melanogaster strains of the Cosmopolitan (M) and Zimbabwe, Africa (Z) mating races showed that differentiation of gene expression and of coding sequences, measured as QST and GST, respectively, were uncorrelated and, generally, QST > GST. However, an exploratory analysis showed that GST of the 5 prime sequences of genes was correlated with QST calculated from expression data, while GST of the coding sequences remained uncorrelated with QST. This scenario is consistent with the population differentiation at cis-regulatory regions that is decoupled from differentiation of the coding regions. However, despite evidence for selection on global levels of gene expression (deduced from QST > GST), 5 prime sequence polymorphisms generally were compatible with selective neutrality, suggesting differentiation in cis-regulated gene expression for these genes has been promoted by drift or selection too weak or too long ago to be detected, or higher organizational levels underlying the genetic architecture of expression are targets of selection. In all, this raises the question how selection on the expression changes (i.e. the phenotype) can be so obvious yet elusive at the level of the nucleotide sequence. Our contrasts between genetic differentiation of populations in expression and sequences revealed that even when genotype and phenotype can be connected the sources of variation that are the target of selection remain to be identified.

Locus-specific genetic differentiation at Rw among warfarin-resistant rat (Rattus norvegicus) populations.

Populations may diverge at fitness-related genes as a result of adaptation to local conditions. The ability to detect this divergence by marker-based genomic scans depends on the relative magnitudes of selection, recombination, and migration. We survey rat (Rattus norvegicus) populations to assess the effect that local selection with anticoagulant rodenticides has had on microsatellite marker variation and differentiation at the warfarin resistance gene (Rw) relative to the effect on the genomic background. Initially, using a small sample of 16 rats, we demonstrate tight linkage of microsatellite D1Rat219 to Rw by association mapping of genotypes expressing an anticoagulant-rodenticide-insensitive vitamin K 2,3-epoxide reductase (VKOR). Then, using allele frequencies at D1Rat219, we show that predicted and observed resistance levels in 27 populations correspond, suggesting intense and recent selection for resistance. A contrast of F(ST) values between D1Rat219 and the genomic background revealed that rodenticide selection has overwhelmed drift-mediated population structure only at Rw. A case-controlled design distinguished these locus-specific effects of selection at Rw from background levels of differentiation more effectively than a population-controlled approach. Our results support the notion that an analysis of locus-specific population genetic structure may assist the discovery and mapping of novel candidate loci that are the object of selection or may provide supporting evidence for previously identified loci.

Mitochondrial DNA phylogeography of the Norway rat.

Central Eastern Asia, foremost the area bordering northern China and Mongolia, has been thought to be the geographic region where Norway rats (Rattus norvegicus) have originated. However recent fossil analyses pointed to their origin in southern China. Moreover, whereas analyses of fossils dated the species' origin as ∼ 1.2-1.6 million years ago (Mya), molecular analyses yielded ∼ 0.5-2.9 Mya. Here, to study the geographic origin of the Norway rat and its spread across the globe we analyzed new and all published mitochondrial DNA cytochrome-b (cyt-b; N = 156) and D-loop (N = 212) sequences representing wild rats from four continents and select inbred strains. Our results are consistent with an origin of the Norway rat in southern China ∼ 1.3 Mya, subsequent prehistoric differentiation and spread in China and Asia from an initially weakly structured ancestral population, followed by further spread and differentiation across the globe during historic times. The recent spreading occurred mostly from derived European populations rather than from archaic Asian populations. We trace laboratory strains to wild lineages from Europe and North America and these represent a subset of the diversity of the rat; leaving Asian lineages largely untapped as a resource for biomedical models. By studying rats from Europe we made the observation that mtDNA diversity cannot be interpreted without consideration of pest control and, possibly, the evolution of rodenticide resistance. However, demographic models explored by forward-time simulations cannot fully explain the low mtDNA diversity of European rats and lack of haplotype sharing with their source from Asia. Comprehensive nuclear marker analyses of a larger sample of Norway rats representing the world are needed to better resolve the evolutionary history of wild rats and of laboratory rats, as well as to better understand the evolution of anticoagulant resistance.

Vkorc1 variation in house mice during warfarin and difenacoum field trials.

BACKGROUND: Field studies guided by genetic monitoring of Vkorc1 need to be done to implicate mutations conclusively with rodent control problems due to the presence of animals resistant to anticoagulant rodenticides. Rodent control success in relation to Vkorc1 genotypes in house mice (Mus musculus domesticus) was studied on two farms (I and II) in Germany. Tests were carried out to determine whether certain resistance profiles and Vkorc1 genotypes displayed dynamics over the course of sequential treatments with warfarin and difenacoum that were consistent with single nucleotide polymorphisms (SNPs) in Vkorc1 as indicators of resistance. RESULTS: On farms I and II, respectively, three (A to C) and two (A and B) types of control problem with anticoagulants (i.e. proxies for resistance) were encountered in spatially segregated subunits: A = none; B = control problems with warfarin but not with difenacoum; C = control problems with both anticoagulants. Unexpectedly, resistance was encountered in a population where only Vkorc1 wild-type mice were detected. In addition, the Arg58Gly Vkorc1 variant was found not to correlate with observed control failures. CONCLUSION: Control problems were encountered that cannot be explained by Vkorc1 coding or intronic SNPs, and therefore are likely due to non-coding Vkorc1 SNPs or due to other genetic or non-genetic factors.

Adaptive introgression of anticoagulant rodent poison resistance by hybridization between old world mice.

Polymorphisms in the vitamin K 2,3-epoxide reductase subcomponent 1 (vkorc1) of house mice (Mus musculus domesticus) can cause resistance to anticoagulant rodenticides such as warfarin [1-3]. Here we show that resistant house mice can also originate from selection on vkorc1 polymorphisms acquired from the Algerian mouse (M. spretus) through introgressive hybridization. We report on a polymorphic introgressed genomic region in European M. m. domesticus that stems from M. spretus, spans >10 Mb on chromosome 7, and includes the molecular target of anticoagulants vkorc1 [1-4]. We show that in the laboratory, the homozygous complete vkorc1 allele of M. spretus confers resistance when introgressed into M. m. domesticus. Consistent with selection on the introgressed allele after the introduction of rodenticides in the 1950s, we found signatures of selection in patterns of variation in M. m. domesticus. Furthermore, we detected adaptive protein evolution of vkorc1 in M. spretus (Ka/Ks = 1.54-1.93) resulting in radical amino acid substitutions that apparently cause anticoagulant tolerance in M. spretus as a pleiotropic effect. Thus, positive selection produced an adaptive, divergent, and pleiotropic vkorc1 allele in the donor species, M. spretus, which crossed a species barrier and produced an adaptive polymorphic trait in the recipient species, M. m. domesticus.

Vitamin K epoxide reductase complex subunit 1 (Vkorc1) haplotype diversity in mouse priority strains.

BACKGROUND: Polymorphisms in the vitamin K-epoxide reductase complex subunit 1 gene, Vkorc1, could affect blood coagulation and other vitamin K-dependent proteins, such as osteocalcin (bone Gla protein, BGP). Here we sequenced the Vkorc1 gene in 40 mouse priority strains. We analyzed Vkorc1 haplotypes with respect to prothrombin time (PT) and bone mineral density and composition (BMD and BMC); phenotypes expected to be vitamin K-dependent and represented by data in the Mouse Phenome Database (MPD). FINDINGS: In the commonly used laboratory strains of Mus musculus domesticus we identified only four haplotypes differing in the intron or 5' region sequence of the Vkorc1. Six haplotypes differing by coding and non-coding polymorphisms were identified in the other subspecies of Mus. We detected no significant association of Vkorc1 haplotypes with PT, BMD and BMC within each subspecies of Mus. Vkorc1 haplotype sequences divergence between subspecies was associated with PT, BMD and BMC. CONCLUSION: Phenotypic variation in PT, BMD and BMC within subspecies of Mus, while substantial, appears to be dominated by genetic variation in genes other than the Vkorc1. This was particularly evident for M. m. domesticus, where a single haplotype was observed in conjunction with virtually the entire range of PT, BMD and BMC values of all 5 subspecies of Mus included in this study. Differences in these phenotypes between subspecies also should not be attributed to Vkorc1 variants, but should be viewed as a result of genome wide genetic divergence.

A cardiovascular phenotype in warfarin-resistant Vkorc1 mutant rats.

BACKGROUND: The inhibition of the vitamin K cycle by warfarin promotes arterial calcification in the rat. Conceivably, genetically determined vitamin K-deficiency owing to a mutant epoxide reductase subcomponent 1 (Vkorc1) gene, a key component of the vitamin K cycle, might also promote arterial calcification. In the absence of an available Vkorc1 gene knockout model we used a wild-derived Vkorc1 mutant rat strain (Rattus norvegicus) to explore the validity of this hypothesis. METHODS: We provide histopathological descriptions of a naturally occurring Vkorc1 gene knockdown: wild-derived lab-reared rats that are resistant to the anticoagulant warfarin owing to a non-synonymous mutation in the Vkorc1 gene (Vkorc1(Y->C)), which, in vitro, reduces the basal activity of the vitamin K epoxide reductase enzyme complex by ~52%. H&E stained sections of heart and kidney were compared between homozygous Vkorc1(Y->C/ Y->C), heterozygous Vkorc1(Y->C/+) and wildtype Vkorc1(+/+) rats of both sexes. RESULTS: We observed that the aorta of the heart was mineralized in the Vkorc1(Y->C/ Y->C) male rats but lesions were virtually absent from Vkorc1(Y->C/+) and Vkorc1(+/+) male and all female rats. The renal arteries were mineralized in Vkorc1(Y->C/ Y->C) and Vkorc1(Y->C/+) mutant rats, regardless of sex. CONCLUSIONS: Results support a hypothesis that posits that Vkorc1 genetic polymorphisms reducing basal enzyme activity could affect cardiovascular health, with dependencies on genotype, sex, and tissue. The undercarboxylation of the vitamin K-dependent Matrix Gla protein may be the crucial component of the pathway promoting this mineralization.

Annotating ebony on the fly.

The distinctive black phenotype of ebony mutants has made it one of the most widely used phenotypic markers in Drosophila genetics. Without doubt, ebony showcases the fruits of the fly community's labours to annotate gene function. As of this writing, FlyBase lists 142 references, 1277 fly stocks, 15 phenotypes and 44 alleles. In addition to its namesake pigmentation phenotype, ebony mutants affect other traits, including phototaxis and courtship. With phenotypic consequences of ebony variants readily apparent in the laboratory, does natural selection also see them in the wild? In this issue of Molecular Ecology, Pool & Aquadro investigate this question and found signs of natural selection on the ebony gene that appear to have resulted from selection for darker pigmentation at higher elevations in sub-Saharan populations of Drosophila melanogaster. Such findings from population genomic analysis of wild-derived strains should be included in gene annotations to provide a more holistic view of a gene's function. The evolutionary annotation of ebony added by Pool & Aquadro substantiates that pigmentation can be adaptive and implicates elevation as an important selective factor. This is important progress because the selective factors seem to differ between populations and species. In addition, the study raises issues to consider when extrapolating from selection at the molecular level to selection at the phenotypic level.

Genomic inferences of the cis-regulatory nucleotide polymorphisms underlying gene expression differences between Drosophila melanogaster mating races.

Nucleotide sequence polymorphisms affecting gene expression occur in the regulatory region of genes (in cis) and elsewhere in the genome (in trans). Further study is required to weigh the relative importance of cis- and trans-acting mutations in mediating gene expression differences within and between species. Here, microarray hybridization experiments were used to isolate 363 gene expression differences between the female fly head transcriptomes of 2 Drosophila melanogaster strains. One strain (French) represented the cosmopolitan M mating race and the other strain (ZS30) represented the Z mating race derived from Zimbabwe, Africa. From chromosomal substitution strains engineered from the 2 strains, we inferred that the expression differences between M and Z alleles largely could be attributed to the genotype of the chromosomes where the differentially expressed genes were located, that is, cis-regulatory polymorphisms prominently influence gene expression differences between M and Z. The effects of trans-regulatory polymorphisms were apparent yet difficult to quantify. Results have implications for models of gene regulatory evolution as well as experimental studies trying to identify the nucleotide sequence polymorphisms underlying gene expression differences between Drosophila strains.

Genomics and conservation genetics.

In large part, the relevance of genetics to conservation rests on the premise that neutral marker variation in populations reflects levels of detrimental and adaptive genetic variation. Despite its prominence, this tenet has been difficult to evaluate, until now. As we discuss here, genome sequence information and new technological and bioinformatics platforms now enable comprehensive surveys of neutral variation and more direct inferences of detrimental and adaptive variation in species with sequenced genomes and in 'genome-enabled' endangered taxa. Moreover, conservation schemes could begin to consider specific pathological genetic variants. A new conservation genetic agenda would utilize data from enhanced surveys of genomic variation in endangered species to better manage functional genetic variation.