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Rapid adaptation can prevent extinction when populations are exposed to extremely marginal or stressful environments. Factors that affect the likelihood of evolutionary rescue from extinction have been identified, but much less is known about the evolutionary dynamics (e.g., rates and patterns of allele frequency change) and genomic basis of successful rescue, particularly in multicellular organisms. We conducted an evolve‐and‐resequence experiment to investigate the dynamics of evolutionary rescue at the genetic level in the cowpea seed beetle, Callosobruchus maculatus, when it is experimentally shifted to a stressful host plant, lentil. Low survival (~1%) at the onset of the experiment caused population decline. But adaptive evolution quickly rescued the population, with survival rates climbing to 69% by the F5 generation and 90% by the F10 generation. Population genomic data showed that rescue likely was caused by rapid evolutionary change at multiple loci, with many alleles fixing or nearly fixing within five generations of selection on lentil. Selection on these loci was only moderately consistent in time, but parallel evolutionary changes were evident in sublines formed after the lentil line had passed through a bottleneck. By comparing estimates of selection and genomic change on lentil across five independent C. maculatus lines (the new lentil‐adapted line, three long‐established lines and one case of failed evolutionary rescue), we found that adaptation on lentil occurred via somewhat idiosyncratic evolutionary changes. Overall, our results suggest that evolutionary rescue in this system can be caused by very strong selection on multiple loci driving rapid and pronounced genomic change. [ABSTRACT FROM AUTHOR]

The article focuses on role of structural genomic variants in adaptive evolution and species diversification with single nucleotide polymorphism (SNPs). It mentions comparison of different kind of structural variants in the genome to bioinformatic approaches that can be used to characterize structural variants, experimental approaches that test the role of structural variants in adaptation. It also mentions structural variants offer important sources of genetic fuel for evolutionary processes.

In many insects, X‐linked inversions fix at a higher rate and are much less polymorphic than autosomal inversions. Here, we report that in Drosophila, X‐linked inversions also capture 67% more genes. We estimated the number of genes captured through an approximate Bayesian computational analysis of gene orders in nine species of Drosophila. X‐linked inversions fixed with a significantly larger gene content. Further, X‐linked inversions of intermediate size enjoy highest fixation rate, while the fixation rate of autosomal inversions decreases with size. A less detailed analysis in Anopheles suggests a similar pattern holds in mosquitoes. We develop a population genetic model that assumes the fitness effects of inversions scale with the number of genes captured. We show that the same conditions that lead to a higher fixation rate also produce a larger size for inversions on the X. [ABSTRACT FROM AUTHOR]

Abstract: Urban areas are highly fragmented and thereby exert strong constraints on individual dispersal. Despite this, some species manage to persist in urban areas, such as the garden snail, Cornu aspersum, which is common in cityscapes despite its low mobility. Using landscape genetic approaches, we combined study area replication and multiscale analysis to determine how landscape composition, configuration and connectivity influence snail dispersal across urban areas. At the overall landscape scale, areas with a high percentage of roads decreased genetic differentiation between populations. At the population scale, genetic differentiation was positively linked with building surface, the proportion of borders where wooded patches and roads appeared side by side and the proportion of borders combining wooded patches and other impervious areas. Analyses based on pairwise genetic distances validated the isolation‐by‐distance and isolation‐by‐resistance models for this land snail, with an equal fit to least‐cost paths and circuit‐theory‐based models. Each of the 12 landscapes analysed separately yielded specific relations to environmental features, whereas analyses integrating all replicates highlighted general common effects. Our results suggest that urban transport infrastructures facilitate passive snail dispersal. At a local scale, corresponding to active dispersal, unfavourable habitats (wooded and impervious areas) isolate populations. This work upholds the use of replicated landscapes to increase the generalizability of landscape genetics results and shows how multiscale analyses provide insight into scale‐dependent processes. [ABSTRACT FROM AUTHOR]

Abstract: One of the primary challenges of evolutionary research is to identify ecological factors that favour reproductive isolation. Therefore, studying partially isolated taxa has the potential to provide novel insight into the mechanisms of evolutionary divergence. Our study utilizes an adaptive colour polymorphism in the arc‐eye hawkfish (Paracirrhites arcatus) to explore the evolution of reproductive barriers in the absence of geographic isolation. Dark and light morphs are ecologically partitioned into basaltic and coral microhabitats a few metres apart. To test whether ecological barriers have reduced gene flow among dark and light phenotypes, we evaluated genetic variation at 30 microsatellite loci and a nuclear exon (Mc1r) associated with melanistic coloration. We report low, but significant microsatellite differentiation among colour morphs and stronger divergence in the coding region of Mc1r indicating signatures of selection. Critically, we observed greater genetic divergence between colour morphs on the same reefs than that between the same morphs in different geographic locations. We hypothesize that adaptation to the contrasting microhabitats is overriding gene flow and is responsible for the partial reproductive isolation observed between sympatric colour morphs. Combined with complementary studies of hawkfish ecology and behaviour, these genetic results indicate an ecological barrier to gene flow initiated by habitat selection and enhanced by assortative mating. Hence, the arc‐eye hawkfish fulfil theoretical expectations for the earliest phase of speciation with gene flow. [ABSTRACT FROM AUTHOR]

Abstract: Maternal effects, where the performance of offspring is determined by the condition of their mother, are widespread and may in some cases be adaptive. The crustacean Daphnia magna shows strong maternal effects: offspring size at birth and other proxies for fitness are altered when their mothers are older or when mothers have experienced dietary restriction. The mechanisms for this transgenerational transmission of maternal experience are unknown, but could include changes in epigenetic patterning. MicroRNAs (miRNAs) are regulators of gene expression that have been shown to play roles in intergenerational information transfer, and here, we test whether miRNAs are involved in D. magna maternal effects. We found that miRNAs were differentially expressed in mothers of different ages or nutritional state. We then examined miRNA expression in their eggs, their adult daughters and great granddaughters, which did not experience any treatments. The maternal (treatment) generation exhibited differential expression of miRNAs, as did their eggs, but this was reduced in adult daughters and lost by great granddaughters. Thus, miRNAs are a component of maternal provisioning, but do not appear to be the cause of transgenerational responses under these experimental conditions. MicroRNAs may act in tandem with egg provisioning (e.g., with carbohydrates or fats), and possibly other small RNAs or epigenetic modifications. [ABSTRACT FROM AUTHOR]

Polymorphism describes two or more distinct, genetically determined, phenotypes that co-occur in the same population, where the rarest morph is maintained at a frequency above the mutation rate (Ford 1945; Huxley 1955). In a recent opinion piece, we explored a new idea regarding the role of genetic architectures and morph interactions in colour polymorphisms and how this can negatively affect population performance (Bolton et al. 2015). In this issue of Molecular Ecology, Forsman (2016) thoroughly discusses the current evidence for polymorphisms enhancing population performance and critiques the validity of the definitions of polymorphism we use in our original paper. We respond by clarifying that the negative consequences of polymorphisms that we discussed are likely to be most pertinent in species that have a particular set of characteristics, such as strong sexual or social interactions between morphs and discrete genetic architectures. Although it was not our intention to redefine polymorphism, we do believe that there should be further discussion about refining or characterizing balanced polymorphisms with respect to the degree of morph sympatry, discreteness of traits and their underlying genetic architecture, and the types of selection that drive and maintain the variation. The latter describes whether polymorphism is primarily maintained by external factors such as predation pressure or internal factors such as interactions with members of the same species. The contribution of Forsman (2016) is useful to this discussion, and we hope that our exchange of opinions will inspire new empirical and theoretical ideas on the origin and maintenance of colour polymorphisms. [ABSTRACT FROM AUTHOR]

Recent studies have revealed repeated patterns of genomic divergence associated with species formation. Such patterns suggest that natural selection tends to target a set of available genes, but is also indicative that closely related taxa share evolutionary constraints that limit genetic variability. Studying patterns of genomic divergence among populations within the same species may shed light on the underlying evolutionary processes. Here, we examine transcriptome-wide divergence and polymorphism in the marine copepod Tigriopus californicus, a species where allopatric evolution has led to replicate sets of populations with varying degrees of divergence and hybrid incompatibility. Our analyses suggest that relatively small effective population sizes have resulted in an exponential decline of shared polymorphisms during population divergence and also facilitated the fixation of slightly deleterious mutations within allopatric populations. Five interpopulation comparisons at three different stages of divergence show that nonsynonymous mutations tend to accumulate in a specific set of proteins. These include proteins with central roles in cellular metabolism, such as those encoded in mt DNA, but also include an additional set of proteins that repeatedly show signatures of positive selection during allopatric divergence. Although our results are consistent with a contribution of nonadaptive processes, such as genetic drift and gene expression levels, generating repeatable patterns of genomic divergence in closely related taxa, they also indicate that adaptive evolution targeting a specific set of genes contributes to this pattern. Our results yield insights into the predictability of evolution at the gene level. [ABSTRACT FROM AUTHOR]

Recently, there has been increased awareness of the role of background selection (BGS) in both data analysis and modelling advances. However, BGS is still difficult to take into account because of tractability issues with simulations and difficulty with nonequilibrium demographic models. Often, simple rescaling adjustments of effective population size are used. However, there has been neither a proper characterization of how BGS could bias or shift inference when not properly taken into account, nor a thorough analysis of whether rescaling is a sufficient solution. Here, we carry out extensive simulations with BGS to determine biases and behaviour of demographic inference using an approximate Bayesian approach. We find that results can be positively misleading with significant bias, and describe the parameter space in which BGS models replicate observed neutral nonequilibrium expectations. [ABSTRACT FROM AUTHOR]

Understanding the processes underlying speciation has long been a challenge to evolutionary biologists. This spurs from difficulties teasing apart the various mechanisms that contribute to the evolution of barriers to reproduction. The study by Rafati et al. ( ) in this issue of Molecular Ecology combines spatially explicit whole‐genome resequencing with evaluation of differential gene expression across individuals with mixed ancestry to associate the genomic architecture of reproductive barriers with expression of reproductive incompatibilities. In a natural hybrid zone between rabbit subspecies, Oryctolagus cuniculus cuniculus and O. c. algirus (Figure ), Rafati et al. ( ) use landscape‐level patterns of allele frequency variation to identify potential candidate regions of the genome associated with reproductive isolation. These candidate regions are used to test predictions associated with the genomic architecture of reproductive barriers, including the role of structural rearrangements, enrichment of functional categories associated with incompatibilities, and the contribution of protein‐coding versus regulatory changes. A lack of structural rearrangements and limited protein‐coding changes in candidate regions point towards the importance of regulatory variation as major contributors to genetic incompatibilities, while functional enrichments indicate overrepresentation of genes associated with male infertility. To quantify phenotypic expression of proposed incompatibilities, the authors assess gene expression of experimental crosses. Extensive misregulation of gene expression within the testes of backcross hybrids relative to F1 and parental individuals provides an important link between genotype and phenotype, validating hypotheses developed from assessment of genomic architectures. Together, this work shows how pairing natural hybrid zones with experimental crosses can be used to link observations in nature to mechanistic underpinnings that may be tested experimentally. [ABSTRACT FROM AUTHOR]

Geographic patterns of genetic variation are shaped by multiple evolutionary processes, including genetic drift, migration and natural selection. Switchgrass ( Panicum virgatum L.) has strong genetic and adaptive differentiation despite life history characteristics that promote high levels of gene flow and can homogenize intraspecific differences, such as wind-pollination and self-incompatibility. To better understand how historical and contemporary factors shape variation in switchgrass, we use genotyping-by-sequencing to characterize switchgrass from across its range at 98 042 SNPs. Population structuring reflects biogeographic and ploidy differences within and between switchgrass ecotypes and indicates that biogeographic history, ploidy incompatibilities and differential adaptation each have important roles in shaping ecotypic differentiation in switchgrass. At one extreme, we determine that two Panicum taxa are not separate species but are actually conspecific, ecologically divergent types of switchgrass adapted to the extreme conditions of coastal sand dune habitats. Conversely, we identify natural hybrids among lowland and upland ecotypes and visualize their genome-wide patterns of admixture. Furthermore, we determine that genetic differentiation between primarily tetraploid and octoploid lineages is not caused solely by ploidy differences. Rather, genetic diversity in primarily octoploid lineages is consistent with a history of admixture. This suggests that polyploidy in switchgrass is promoted by admixture of diverged lineages, which may be important for maintaining genetic differentiation between switchgrass ecotypes where they are sympatric. These results provide new insights into the mechanisms shaping variation in widespread species and provide a foundation for dissecting the genetic basis of adaptation in switchgrass. [ABSTRACT FROM AUTHOR]

Next-generation sequencing ( NGS) technology is revolutionizing the fields of population genetics, molecular ecology and conservation biology. But it can be challenging for researchers to learn the new and rapidly evolving techniques required to use NGS data. A recent workshop entitled 'Population Genomic Data Analysis' was held to provide training in conceptual and practical aspects of data production and analysis for population genomics, with an emphasis on NGS data analysis. This workshop brought together 16 instructors who were experts in the field of population genomics and 31 student participants. Instructors provided helpful and often entertaining advice regarding how to choose and use a NGS method for a given research question, and regarding critical aspects of NGS data production and analysis such as library preparation, filtering to remove sequencing errors and outlier loci, and genotype calling. In addition, instructors provided general advice about how to approach population genomics data analysis and how to build a career in science. The overarching messages of the workshop were that NGS data analysis should be approached with a keen understanding of the theoretical models underlying the analyses, and with analyses tailored to each research question and project. When analysed carefully, NGS data provide extremely powerful tools for answering crucial questions in disciplines ranging from evolution and ecology to conservation and agriculture, including questions that could not be answered prior to the development of NGS technology. [ABSTRACT FROM AUTHOR]

Increasing evidence exists that bacterial communities interact with and shape the biology of algae and that their evolutionary histories are connected. Despite these findings, physiological studies were and still are generally carried out with axenic or at least antibiotic-treated cultures. Here, we argue that considering interactions between algae and associated bacteria is key to understanding their biology and evolution. To deal with the complexity of the resulting 'holobiont' system, a metabolism-centred approach that uses combined metabolic models for algae and associated bacteria is proposed. We believe that these models will be valuable tools both to study algal-bacterial interactions and to elucidate processes important for the acclimation of the holobiont to environmental changes. [ABSTRACT FROM AUTHOR]

The article offers information on researcher Laurent Excoffier who has received the 2013 Molecular Ecology Prize. It reflects on the educational and professional life of Excoffier. It discusses the work of Excoffier on different topics including evolutionary histories of bats, the absence of Neanderthal mitochondrial DNA lineages among thousands of contemporary-sampled Europeans implied extremely low levels of admixture with Neanderthal and the evolution of Africans.

A knowledge of intraspecific divergence and range dynamics of dominant forest trees in response to past geological and climate change is of major importance to an understanding of their recent evolution and demography. Such knowledge is informative of how forests were affected by environmental factors in the past and may provide pointers to their response to future environmental change. However, genetic signatures of such historical events are often weak at individual loci due to large effective population sizes and long generation times of forest trees. This problem can be overcome by analysing genetic variation across multiple loci. We used this approach to examine intraspecific divergence and past range dynamics in the conifer Picea likiangensis, a dominant tree of forests occurring in eastern and southern areas of the Qinghai-Tibet Plateau ( QTP). We sequenced 13 nuclear loci, two mitochondrial DNA regions and three plastid (chloroplast) DNA regions in 177 individuals sampled from 22 natural populations of this species, and tested the hypothesis that its evolutionary history was markedly affected by Pliocene QTP uplifts and Quaternary climatic oscillations. Consistent with the taxonomic delimitation of the three morphologically divergent varieties examined, all individuals clustered into three genetic groups with intervariety admixture detected in regions of geographical overlap. Divergence between varieties was estimated to have occurred within the Pliocene and ecological niche modelling based on 20 ecological variables suggested that niche differentiation was high. Furthermore, modelling of population-genetic data indicated that two of the varieties (var. rubescens and var. linzhiensis) expanded their population sizes after the largest Quaternary glaciation in the QTP, while expansion of the third variety (var. likiangensis) began prior to this, probably following the Pliocene QTP uplift. These findings point to the importance of geological and climatic changes during the Pliocene and Pleistocene as causes of intraspecific diversification and range shifts of dominant tree species in the QTP biodiversity hot spot region. [ABSTRACT FROM AUTHOR]

Oceanic islands have been a test ground for evolutionary theory, but here, we focus on the possibilities for evolutionary study created by offshore islands. These can be colonized through various means and by a wide range of species, including those with low dispersal capabilities. We use morphology, modern and ancient sequences of cytochrome b ( cytb) and microsatellite genotypes to examine colonization history and evolutionary change associated with occupation of the Orkney archipelago by the common vole ( Microtus arvalis), a species found in continental Europe but not in Britain. Among possible colonization scenarios, our results are most consistent with human introduction at least 5100 bp (confirmed by radiocarbon dating). We used approximate Bayesian computation of population history to infer the coast of Belgium as the possible source and estimated the evolutionary timescale using a Bayesian coalescent approach. We showed substantial morphological divergence of the island populations, including a size increase presumably driven by selection and reduced microsatellite variation likely reflecting founder events and genetic drift. More surprisingly, our results suggest that a recent and widespread cytb replacement event in the continental source area purged cytb variation there, whereas the ancestral diversity is largely retained in the colonized islands as a genetic 'ark'. The replacement event in the continental M. arvalis was probably triggered by anthropogenic causes (land-use change). Our studies illustrate that small offshore islands can act as field laboratories for studying various evolutionary processes over relatively short timescales, informing about the mainland source area as well as the island. [ABSTRACT FROM AUTHOR]

The functional importance of variable, transcriptional regulatory sequences within and among natural populations is largely unexplored. We analysed the cytochrome P4501A (CYP1A) promoter in three populations of the minnow, Fundulus heteroclitus, because two SNPs in the promoter and first intron of CYP1A are under selection in populations adapted to pollutants. To define the importance of these SNPs, 1630 bp of the CYP1A promoter and first intron and exon were sequenced in eight individuals from three populations: a population from a polluted environment resistant to some aromatic pollutants and two flanking reference populations. CYP1A is induced by many aromatic pollutants, but in populations adapted to pollutants, CYP1A has been shown to be refractory to induction. We were interested in understanding whether variation in the CYP1A promoter explains mechanism(s) of adaptation to these aromatic pollutants. The CYP1A promoter was extremely variable (an average of 9.3% of the promoter nucleotides varied among all populations) and exhibited no fixed differences between populations. As CYP1A is poorly inducible in adapted fish, we hypothesized that CYP1A promoter regions might vary functionally between populations. Unexpectedly, in vitro analysis showed significantly greater transcription from CYP1A promoters found in the population from the polluted environment relative to promoters found in both reference populations. Thus, despite extensive variation among populations and lack of fixed differences between populations, individuals from a polluted environment have significantly enhanced promoter activity. These data demonstrate that intraspecific variation, which provides the raw material for natural selection to act on, can occur while maintaining promoter function. [ABSTRACT FROM AUTHOR]

Aphids are a worldwide pest and an important model in ecology and evolution. Little is known, however, about the genetic structure of their colonies at a microgeographic level. For example, it remains largely unknown whether most species form monoclonal or polyclonal colonies. Here, we present the first detailed study on levels of clonal mixing in a nonsocial facultative ant mutualist, the black bean aphid Aphis fabae. In contrast to the earlier suggestion that colonies of this species are generally monoclonal, we found that across two subspecies of the black bean aphid, A. fabae cirsiiacanthoidis and A. fabae fabae, 32% and 67% of the aphid colonies were in fact polyclonal, consisting of a mix of up to four different clones, which resulted in an overall average relatedness within colonies of 0.90 and 0.79 in the two subspecies. Data further show that the average relatedness in A. f. cirsiiacanthoidis remained relatively constant throughout the season, which means that clonal erosion due to clonal selection more or less balanced with the influx of new clones from elsewhere. Nevertheless, relatedness tended to decrease over the lifetime of a given colony, implying that clonal mixing primarily resulted from the joining of pre-existing colonies as opposed to via simultaneous host colonisation by several foundresses. Widespread clonal mixing is argued to affect the ecology and evolution of the aphids in various important ways, for example with respect to the costs and benefits of group living, the evolution of dispersal and the interaction with predators as well as with the ant mutualists. [ABSTRACT FROM AUTHOR]

Hybrid speciation has long fascinated evolutionary biologists and laymen alike, presumably because it challenges our classical view of evolution as a 'one-way street' leading to strictly tree-like patterns of ancestry and descent. Homoploid hybrid speciation (HHS) has been a particularly interesting puzzle, as it appears to occur extremely rapidly, perhaps within less than 50 generations (; ). Nevertheless, HHS may sometimes involve extended or repeated periods of recombination and gene exchange between populations subject to strong divergent natural selection (). Thus, HHS provides a highly interesting setting for understanding the drivers and tempo of adaptive divergence and speciation in the face of gene flow (; ; Nolte & Tautz 2009). In the present issue of Molecular Ecology, explore a particularly challenging issue connected to HHS: they attempt to trace the colonization and recombination history of an ancient (several MYA) hybrid species, from admixture and recombination in the ancestral hybrid zone to subsequent range shifts triggered by tectonic events (uplift of the Tibetan plateau) and climatic shifts (Pleistocene ice ages). This work is important because it addresses key issues related to the origin of the standing genetic variation available for adaptive responses (e.g. to climate change) and speciation in temperate species, which are topics of great current interest (; ; ). [ABSTRACT FROM AUTHOR]

Relatedness is a central parameter in the evolution of sociality, because kin selection theory assumes that individuals involved in altruistic interactions are related. At least three reproductive characteristics are known to profoundly affect colony kin structure in social insects: the number of reproductive queens per colony, the relatedness among breeding queens and queen mating frequency. Both the occurrence of multiple queens (polygyny) and multiple mating (polyandry) decrease within-colony relatedness, while mating among sibs increases relatedness between the workers and the brood they rear. Using DNA microsatellites, we performed a detailed genetic analysis of the colony kin structure and breeding system in three ant species belonging to the genus Plagiolepis: P. schmitzii, P. taurica and P. maura. Our data show that queens of the three species mate multiply: queens of P. maura mate with 1-2 males, queens of P. taurica with 3-11 males and queens of P. schmitzii may have 1-14 different mates. Moreover, colonies are headed by multiple queens: P. taurica and P. maura are facultatively polygynous, while P. schmitzii is obligately polygynous. Despite polyandry and polygyny, relatedness within colonies remains high because all species are characterized by sib-mating, with a fixation index Fit = 0.25 in P. taurica, 0.24 in P. schmitzii and 0.26 in P. maura, and because the male mates of a queen are on average closely related. [ABSTRACT FROM AUTHOR]

Wolbachia are maternally inherited endosymbionts that can invade arthropod populations through manipulation of their reproduction. In mosquitoes, Wolbachia induce embryonic death, known as cytoplasmic incompatibility (CI), whenever infected males mate with females either uninfected or infected with an incompatible strain. Although genetic determinants of CI are unknown, a functional model involving the so-called mod and resc factors has been proposed. Natural populations of Culex pipiens mosquito display a complex CI relationship pattern associated with the highest Wolbachia ( wPip) genetic polymorphism reported so far. We show here that C. pipiens populations from La Réunion, a geographically isolated island in the southwest of the Indian Ocean, are infected with genetically closely related wPip strains. Crossing experiments reveal that these Wolbachia are all mutually compatible. However, crosses with genetically more distant wPip strains indicate that Wolbachia strains from La Réunion belong to at least five distinct incompatibility groups (or crossing types). These incompatibility properties which are strictly independent from the nuclear background, formally establish that in C. pipiens, CI is controlled by several Wolbachia mod/ resc factors. [ABSTRACT FROM AUTHOR]

Genome-wide transcriptional profiling shows that reducing gravity levels during Drosophila metamorphosis in the International Space Station (ISS) causes important alterations in gene expression: a large set of differentially expressed genes (DEGs) are observed compared to 1g controls. However, the preparation procedures for spaceflight and the nonideal environmental conditions on board the ISS subject the organisms to additional environmental stresses that demonstrably affect gene expression. Simulated microgravity experiments performed on the ground, under ideal conditions for the flies, using the random position machine (RPM), show much more subtle effects on gene expression. However, when the ground experiments are repeated under conditions designed to reproduce the additional environmental stresses imposed by spaceflight procedures, 79% of the DEGs detected in the ISS are reproduced by the RPM experiment. Gene ontology analysis of them shows they are genes that affect respiratory activity, developmental processes and stress-related changes. Here, we analyse the effects of microgravity on gene expression in relation to the environmental stresses imposed by spaceflight. Analysis using 'gene expression dynamics inspector' (GEDI) self-organizing maps reveals a subtle response of the transcriptome to microgravity. Remarkably, hypergravity simulation induces similar response of the transcriptome, but in the opposite direction, i.e. the genes promoted under microgravity are usually suppressed under hypergravity. These results suggest that the transcriptome is finely tuned to normal gravity and that microgravity, together with environmental constraints associated with space experiments, can have profound effects on gene expression. [ABSTRACT FROM AUTHOR]

Adaptation to cool environments is a common feature in the core group of the grass subfamily Pooideae (Triticeae and Poeae). This suggest an ancient evolutionary origin of low temperature stress tolerance dating back prior to the initiation of taxonomic divergence of core Pooideae species. Viewing the Pooideae evolution in a palaeo-climatic perspective reveals that taxonomic divergence of the core Pooideae group initiated shortly after a global super-cooling period at the Eocene–Oligocene boundary (∼33.5–26 Ma). This global climate cooling altered distributions of plants and animals and must have imposed selection pressure for improved low temperature stress responses. Lineage-specific gene family expansions are known to be involved in adaptation to new environmental stresses. In Pooideae, two gene families involved in low temperature stress response, the C-repeat binding factor ( CBF) and fructosyl transferase ( FT) gene families, has undergone lineage-specific expansions. We investigated the timing of these gene family expansions by molecular dating and found that Pooideae-specific expansion events in CBF and FT gene families took place during Eocene–Oligocene super-cooling period. We hypothesize that the E–O super-cooling exerted selection pressure for improved low temperature stress response and frost tolerance in a core Pooideae ancestor, and that those individuals with multiple copies of CBF and FT genes were favoured. [ABSTRACT FROM AUTHOR]

Press stop, erase everything from now till some arbitrary time in the past and start recording life as it evolves once again. Would you see the same tape of life playing itself over and over, or would a different story unfold every time? The late Steven Jay Gould called this experiment replaying the tape of life and argued that any replay of the tape would lead evolution down a pathway radically different from the road actually taken (Gould 1989). This thought experiment has puzzled evolutionary biologists for a long time: how repeatable are evolutionary events? And if history does indeed repeat itself, what are the factors that may help us predict the path taken? A powerful means to address these questions at a small evolutionary scale is to study closely related populations that have evolved independently, under similar environmental conditions. This is precisely what Pereira et al. () set out to do using marine copepods Tigriopus californicus, and present their results in this issue of Molecular Ecology. They show that evolution can be repeatable and even partly predictable, at least at the molecular level. As expected from theory, patterns of divergence were shaped by natural selection. At the same time, strong genetic drift due to small population sizes also constrained evolution down a similar evolutionary road, and probably contributed to repeatable patterns of genomic divergence. [ABSTRACT FROM AUTHOR]

Drought is the main selection agent in Mediterranean ecosystems and it has been suggested as an important evolutionary force responsible for population diversification in these types of environments. However, population divergence in quantitative traits can be driven by either natural selection, genetic drift or both. To investigate the roles of these forces on among-population divergence in ecophysiological traits related to drought tolerance (carbon isotope discrimination, specific leaf area, leaf size and leaf nitrogen content), we compared molecular and quantitative genetic differentiation in a common garden experiment including thirteen cork oak ( Quercus suber L.) populations across a gradient of rainfall and temperature. Population differentiation for height, specific leaf area, leaf size and nitrogen leaf content measured during a dry year far exceeded the molecular differentiation measured by six nuclear microsatellites. Populations from dry-cool sites showed the lowest nitrogen leaf content and the smallest and thickest leaves contrasting with those from humid-warm sites. These results suggest (i) these traits are subjected to divergence selection and (ii) the genetic differences among populations are partly due to climate adaptation. By contrast, the low among-population divergence found in basal diameter, annual growth and carbon isotopic discrimination (a surrogate for water use efficiency) suggests low or no divergence selection for these traits. Among-population differentiation for neutral markers was not a good predictor for differentiation regarding the quantitative traits studied here, except for leaf size. The correlation observed between the genetic differentiation for leaf size and that for molecular markers was exclusively due to the association between leaf size and the microsatellite QpZAG46, which suggests a possible linkage between QpZAG46 and genes encoding for leaf size. [ABSTRACT FROM AUTHOR]

Pollution by heavy metals is one of the strongest environmental constraints in human-altered environments that only a handful of species can cope with. Identifying the genes conferring to those species the ability to grow in polluted areas is a first step towards a global understanding of the evolutionary processes involved and will eventually improve phytoremediation practices. We used a genome-scan approach to detect loci under divergent selection among four populations of Arabidopsis halleri growing on either polluted or nonpolluted habitats. Based on a high density of amplified fragment length polymorphism (AFLP) markers (820 AFLP markers, i.e. ~1 marker per 0.3 Mb), evidence for selection was found for some markers in every sampled population. Four loci departed from neutrality in both metallicolous populations and thus constitute high-quality candidates for general adaptation to pollution. Interestingly, some candidates differed between the two metallicolous populations, suggesting the possibility that different loci may be involved in adaptation in the different metallicolous populations. [ABSTRACT FROM AUTHOR]

Dispersal is a life-history trait that plays a fundamental role in population dynamics, influencing evolution, species distribution, and the genetics and structure of populations. In spite of the fact that dispersal has been hypothesized to be an efficient behavioural mechanism to avoid inbreeding, the expected relationship between dispersal and mate relatedness still remains controversial. Here, we examine the genetic consequences of natal dispersal, namely the higher chance of obtaining genetically less similar mates as a result of moving from natal to breeding sites, in a lesser kestrel ( Falco naumanni) population. Relatedness between individuals tended to decrease with distance between their breeding colonies, indicating that the study population follows an ‘isolation-by-distance’ pattern of spatial genetic structure. Such a fine-scale genetic structure generates a scenario in which individuals can potentially increase the chance of obtaining genetically less similar mates by dispersing over larger distances from their natal colony. Using dispersal information and genotypic data, we showed that mate relatedness decreased with natal dispersal distance, an effect that remained significant both while including and excluding philopatric individuals from the data set. These results, together with the well known detrimental consequences of reduced genetic diversity in the study population, suggest that dispersal may have evolved, at least in part, to avoid the negative fitness consequences of mating with genetically similar individuals. [ABSTRACT FROM AUTHOR]

Understanding the evolution of ecological specialization is important for making inferences about the origins of biodiversity. Members of the predatory, marine gastropod genus Conus exhibit a variety of diets and the ability to capture prey is linked to a venom comprised of peptide neurotoxins, termed conotoxins. We identified conotoxin transcripts from Conus leopardus, a species of Conus that uniquely preys exclusively on hemichordates, and compared its venom duct transcriptome to that of four other Conus species to determine whether a shift to a specialized diet is associated with changes in the venom composition of this species. We also examined the secondary structure of predicted amino acid sequences of conotoxin transcripts of C. leopardus to identify substitutions that may be linked to specialization on hemichordates. We identified seven distinct conotoxin sequences from C. leopardus that appear to represent transcripts of seven distinct loci. Expression levels and the diversity of conotoxins expressed by C. leopardus are considerably less than those of other Conus. Moreover, gene products of two transcripts exhibited unique secondary structures that have not been previously observed from other Conus. These results suggest that transition to a specialist diet is associated with reduction in the number of components expressed in venoms of Conus and that diverse venoms of Conus are maintained in species with a broad dietary width. [ABSTRACT FROM AUTHOR]

Alewife, Alosa pseudoharengus, populations occur in two discrete life-history variants, an anadromous form and a landlocked (freshwater resident) form. Landlocked populations display a consistent pattern of life-history divergence from anadromous populations, including earlier age at maturity, smaller adult body size, and reduced fecundity. In Connecticut (USA), dams constructed on coastal streams separate anadromous spawning runs from lake-resident landlocked populations. Here, we used sequence data from the mtDNA control region and allele frequency data from five microsatellite loci to ask whether coastal Connecticut landlocked alewife populations are independently evolved from anadromous populations or whether they share a common freshwater ancestor. We then used microsatellite data to estimate the timing of the divergence between anadromous and landlocked populations. Finally, we examined anadromous and landlocked populations for divergence in foraging morphology and used divergence time estimates to calculate the rate of evolution for foraging traits. Our results indicate that landlocked populations have evolved multiple times independently. Tests of population divergence and estimates of gene flow show that landlocked populations are genetically isolated, whereas anadromous populations exchange genes. These results support a ‘phylogenetic raceme’ model of landlocked alewife divergence, with anadromous populations forming an ancestral core from which landlocked populations independently diverged. Divergence time estimates suggest that landlocked populations diverged from a common anadromous ancestor no longer than 5000 years ago and perhaps as recently as 300 years ago, depending on the microsatellite mutation rate assumed. Examination of foraging traits reveals landlocked populations to have significantly narrower gapes and smaller gill raker spacings than anadromous populations, suggesting that they are adapted to foraging on smaller prey items. Estimates of evolutionary rates (in haldanes) indicate rapid evolution of foraging traits, possibly in response to changes in available resources. [ABSTRACT FROM AUTHOR]

Trans-Arctic dispersals and population and range expansions during the Pleistocene enhanced opportunities for evolutionary diversification and contributed to the process of speciation within the capelin, a northern marine-fish complex exhibiting a circumpolar distribution. Capelin is composed of four highly divergent and geographically discrete mitochondrial DNA (mtDNA) clades (609 bp; cytochrome b). Two clades occur in the North Atlantic, one associated with Canadian Atlantic waters, including Hudson Bay, and the second distributed from West Greenland to the Barents Sea. Two additional clades occur in the Arctic and northeast Pacific Oceans, representing the most recent divergence within the capelin phylogenetic tree. Judged from mtDNA diversity, capelin populations comprising all clades experienced at least one demographic and spatial reduction–expansion episode during recent Pleistocene glaciations that imprinted their molecular architecture. The large contemporary populations in the northeast Pacific and Arctic Oceans exhibited significant genetic structure whereas no such structure was detected in the equally extensive North Atlantic clades. All clades are characterized by one or two prevalent mtDNA haplotypes distributed over the entire range of the clade. Assuming a Pacific ancestor for capelin, we infer that capelin dispersed on two separate occasions to the North Atlantic. A more recent event resulted in the isolation of eastern Pacific and Arctic clades, with the Arctic clade positioned for a potential third Atlantic invasion, as revealed by the presence of this clade in the Labrador Sea. The Labrador Sea is a potential contact zone for three of the four capelin clades. [ABSTRACT FROM AUTHOR]

We investigate the variation in quantitative and molecular traits in the freshwater snail Galba truncatula, from permanent and temporary water habitats. Using a common garden experiment, we measured 20 quantitative traits and molecular variation using seven microsatellites in 17 populations belonging to these two habitats. We estimated trait means in each habitat. We also estimated the distributions of overall genetic quantitative variation ( QST), and of molecular variation ( FST), within and between habitats. Overall, we observed a lack of association between molecular and quantitative variance. Among habitats, we found QST >  FST, an indication of selection for different optima. Individuals from temporary water habitat matured older, at a larger size and were less fecund than individuals from permanent water habitat. We discuss these findings in the light of several theories for life-history traits evolution. [ABSTRACT FROM AUTHOR]

Sex-biased dispersal is an almost ubiquitous feature of mammalian life history, but the evolutionary causes behind these patterns still require much clarification. A quarter of a century since the publication of seminal papers describing general patterns of sex-biased dispersal in both mammals and birds, we review the advances in our theoretical understanding of the evolutionary causes of sex-biased dispersal, and those in statistical genetics that enable us to test hypotheses and measure dispersal in natural populations. We use mammalian examples to illustrate patterns and proximate causes of sex-biased dispersal, because by far the most data are available and because they exhibit an enormous diversity in terms of dispersal strategy, mating and social systems. Recent studies using molecular markers have helped to confirm that sex-biased dispersal is widespread among mammals and varies widely in direction and intensity, but there is a great need to bridge the gap between genetic information, observational data and theory. A review of mammalian data indicates that the relationship between direction of sex-bias and mating system is not a simple one. The role of social systems emerges as a key factor in determining intensity and direction of dispersal bias, but there is still need for a theoretical framework that can account for the complex interactions between inbreeding avoidance, kin competition and cooperation to explain the impressive diversity of patterns. [ABSTRACT FROM AUTHOR]

The relative importance of the Pleistocene glacial cycles in driving avian speciation remains controversial, partly because species limits in many groups remain poorly understood, and because current taxonomic designations are often based on phenotypic characteristics of uncertain phylogenetic significance. We use mtDNA sequence data to examine patterns of genetic variation, sequence divergence and phylogenetic relationships between phenotypically distinct groups of the yellow-rumped warbler complex. Currently classified as a single species, the complex is composed of two North American migratory forms (myrtle warbler Dendroica coronata coronata and Audubon's warbler Dendroica coronata auduboni), and two largely sedentary forms: Dendroica coronata nigrifrons of Mexico, and Dendroica coronata goldmani of Guatemala. The latter are typically considered to be races of the Audubon's warbler based on plumage characteristics. However, mtDNA sequence data reveal that sedentary Mesoamerican forms are reciprocally monophyletic to each other and to migratory forms, from which they show a long history of isolation. In contrast, migratory myrtle and Audubon's warblers form a single cluster due to high levels of shared ancestral polymorphism as evidenced by widespread sharing of mtDNA haplotypes despite marked phenotypic differentiation. Sedentary and migratory forms diverged in the early Pleistocene, whereas phenotypic differentiation between the two migratory forms has occurred in the Holocene and is likely the result of geographical isolation and subsequent range expansion since the last glaciation. Our results underscore the importance of Quaternary climatic events in driving songbird speciation and indicate that plumage traits can evolve remarkably fast, thus rendering them potentially misleading for inferring systematic relationships. [ABSTRACT FROM AUTHOR]

Recent studies that reveal a correlation between heterozygosity and fitness in natural populations have rekindled interest in whether balancing selection is widespread or an evolutionary oddity. We therefore quantified heterozygote advantage at 12 microsatellite markers in both inbred and outbred crosses of Drosophila grown under different forms of environmental stress. As expected, inbreeding depression reduces fitness relative to the outbred controls. In addition, many loci exhibit heterozygote advantage over and above any effect due to inbreeding, with ∼30% of markers showing an effect in any given culture condition and ∼75% of markers showing an effect in at least one of the four culture conditions. To explore the extent of linkage disequilibrium surrounding these loci we further typed four new markers close to each of the three strongest hits. We find a pattern where the extent of heterozygote excess tends to decline to nonsignificance within around 1.5 megabases (Mb) either side of the original hit. Crude extrapolation suggests 12 genes or regions experience detectable levels of heterozygote advantage in any one condition and as many as 25 overall. Thus, balancing selection is widespread and is likely to play an important role in maintaining genetic variability. [ABSTRACT FROM AUTHOR]

Heritable variation in regulatory or coding regions is the raw material for evolutionary processes. The advent of microarrays has recently promoted examination of the extent of variation in gene expression within and among taxa and examination of the evolutionary processes affecting variation. This review examines these issues. We find: (i) microarray-based measures of gene expression are precise given appropriate experimental design; (ii) there is large inter-individual variation, which is composed of a minor nongenetic component and a large heritable component; (iii) variation among populations and species appears to be affected primarily by neutral drift and stabilizing selection, and to a lesser degree by directional selection; and (iv) neutral evolutionary divergence in gene expression becomes nonlinear with greater divergence times due to functional constraint. Evolutionary analyses of gene expression reviewed here provide unique insights into partitioning of regulatory variation in nature. However, common limitations of these studies include the tendency to assume a linear relationship between expression divergence and species divergence, and failure to test explicit hypotheses that involve the ecological context of evolutionary divergence. [ABSTRACT FROM AUTHOR]

Investigating the geographical distribution of genetic lineages within species is critical to our understanding of how species evolve. As many species inhabit large and complex ranges, it is important that phylogeographical research take into account the entire range of widespread species to clarify how myriad extrinsic variables have affected their evolutionary history. Using phylogenetic, nested clade, and mismatch distribution analyses on a portion of the mitochondrial COI gene, I demonstrate that the wide-ranging freshwater snail Theodoxus fluviatilis possesses in parallel many of the phylogeographical patterns seen in less widespread freshwater species of Europe. Fragmentary forces play a major part in structuring the range of this species, with 12 of 14 geographically structured nested clades displaying a distribution consistent with fragmentation or restricted dispersal. Certain regions of southern Europe harbour the majority of genetic diversity (total haplotype diversity, H = 0.87), particularly Italy ( H = 0.87) and areas surrounding the Black Sea ( H = 0.81). Post-Pleistocene range expansion is pronounced, with the majority of northern European populations (95% of sample sites) having arisen from northern Italian individuals that initially colonized northern Germany. Additionally, two highly divergent haplotype lineages present in northern Germany imply that there were at least two postglacial recolonization routes. Estuaries may also provide a means of dispersal given that no genetic differentiation was found between estuarine populations and neighbouring freshwater populations. Taken together, these data reveal a species with a complex genetic history resulting from the fragmentary effects of European geology as well as continuous and discrete range expansion related to their aquatic biology. [ABSTRACT FROM AUTHOR]

Besides showing an extraordinary degree of phenotypic variability, Capsella bursa-pastoris (Brassicaceae) is also one of the world's most common plant species and a serious weed in many countries. We have employed a coalescent-based Bayesian analysis of chloroplast microsatellite data to infer demographic and evolutionary parameters of this species. Two different demographic models applied to data from seven chloroplast microsatellite loci among 59 accessions show that the effective population size of C. bursa-pastoris is very small indicating a rapid expansion of the species, a result that is in accordance with fossil and historical data. Against this background, analysis of flowering time variation among accessions suggests that ecotypic differentiation in flowering time has occurred recently in the species’ history. Finally, our results also indicate that mononucleotide repeat loci in the chloroplast genome can deteriorate in relatively short periods of evolutionary time. [ABSTRACT FROM AUTHOR]

The traditional view that species are held together through gene flow has been challenged by observations that migration is too restricted among populations of many species to prevent local divergence. However, only very low levels of gene flow are necessary to permit the spread of highly advantageous alleles, providing an alternative means by which low-migration species might be held together. We re-evaluate these arguments given the recent and wide availability of indirect estimates of gene flow. Our literature review of FST values for a broad range of taxa suggests that gene flow in many taxa is considerably greater than suspected from earlier studies and often is sufficiently high to homogenize even neutral alleles. However, there are numerous species from essentially all organismal groups that lack sufficient gene flow to prevent divergence. Crude estimates on the strength of selection on phenotypic traits and effect sizes of quantitative trait loci (QTL) suggest that selection coefficients for leading QTL underlying phenotypic traits may be high enough to permit their rapid spread across populations. Thus, species may evolve collectively at major loci through the spread of favourable alleles, while simultaneously differentiating at other loci due to drift and local selection. [ABSTRACT FROM AUTHOR]

Although analyses of intraspecific variability are an important prerequisite for species identification assays, only a few studies have focused on population genetics and historical biogeography of sturgeon species. Here we present the first study on genetic variability of the last remaining Adriatic sturgeon, Acipenser naccarii, derived from mitochondrial and nuclear DNA. Our mitochondrial DNA analyses arranged individuals into three distinguished mitochondrial DNA haplogroups (Po1, Po2 and Buna). Two haplogroups (Po1 and Buna) were correlated to geographical distribution, whereas the third (Po2) was not. It was, however, very closely related to one lineage of its Ponto-Caspian sister species, A. gueldenstaedtii. The distribution of nuclear markers (microsatellites and amplified fragment length polymorphism) was strongly correlated to geographical distribution. An assignment test based on nuclear data placed no specimen of A. naccarii to A. gueldenstaedtii and vice versa. Therefore, the presence of gueldenstaedtii-like haplotypes within the Po population is either the result of a postglacial introgression or an ancestral polymorphism and does not indicate a hybrid population. The most valuable tool for forensic species identification purposes is one diagnostic deletion separating all A. naccarii from A. gueldenstaedtii. As both A. naccarii populations are genetically differentiated, stocking of sturgeon from the Po River in Italy into waters of the Buna River would jeopardize the genetic differences between both populations and should thus be avoided. [ABSTRACT FROM AUTHOR]

There is substantial debate over the criteria that should be used to group populations of a species into distinct units for conservation (e.g. evolutionarily significant units, management units, distinct population segments). However, in practice molecular genetic differentiation is often the only or main criterion used to identify such units. Most genetic studies attempting to define conservation units in animals use a single molecular marker, most often mitochondrial, and use samples from a limited number of populations throughout the species’ range. Although there are many benefits to using mtDNA, certain features can cause it to show patterns of differentiation among populations that do not reflect the history of differentiation at the nuclear genome where loci controlling traits of adaptive significance presumably occur. Here we illustrate an example of such mitochondrial–nuclear discordance in a ranid frog, and show how using mtDNA or nuclear loci alone could have led to very different conservation recommendations. We also found very high genetic differentiation among populations on a local scale, and discuss the conservation implications of our results. [ABSTRACT FROM AUTHOR]

Recent years have seen a debate over various methods that could objectively prioritize conservation value below the species level. Most prominent among these has been the evolutionarily significant unit (ESU). We reviewed ESU concepts with the aim of proposing a more unified concept that would reconcile opposing views. Like species concepts, conflicting ESU concepts are all essentially aiming to define the same thing: segments of species whose divergence can be measured or evaluated by putting differential emphasis on the role of evolutionary forces at varied temporal scales. Thus, differences between ESU concepts lie more in the criteria used to define the ESUs themselves rather than in their fundamental essence. We provide a context-based framework for delineating ESUs which circumvents much of this situation. Rather than embroil in a befuddled debate over an optimal criterion, the key to a solution is accepting that differing criteria will work more dynamically than others and can be used alone or in combination depending on the situation. These assertions constitute the impetus behind adaptive evolutionary conservation. [ABSTRACT FROM AUTHOR]

Tissue specimens from four species of Neotropical small cats (Oncifelis geoffroyi, N = 38; O. guigna, N = 6; Leopardus tigrinus, N = 32; Lynchailurus colocolo, N = 22) collected from throughout their distribution were examined for patterns of DNA sequence variation using three mitochondrial genes, 16S rRNA, ATP8, and NADH-5. Patterns between and among O. guigna and O. geoffroyi individuals were assessed further from size variation at 20 microsatellite loci. Phylogenetic analyses using mitochondrial DNA sequences revealed monophyletic clustering of the four species, plus evidence of natural hybridization between L. tigrinus and L. colocolo in areas of range overlap and discrete population subdivisions reflecting geographical isolation. Several commonly accepted subspecies partitions were affirmed for L. colocolo, but not for O. geoffroyi. The lack of geographical substructure in O. geoffroyi was recapitulated with the microsatellite data, as was the monophyletic clustering of O. guigna and O. geoffroyi individuals. L. tigrinus forms two phylogeographic clusters which correspond to L.t. oncilla (from Costa Rica) and L.t. guttula (from Brazil) and which have mitochondrial DNA (mtDNA) genetic distance estimates comparable to interspecific values between other ocelot lineage species. Using feline-specific calibration rates for mitochondrial DNA mutation rates, we estimated that extant lineages of O. guigna diverged 0.4 million years ago (Ma), compared with 1.7 Ma for L. colocolo, 2.0 Ma for O. geoffroyi, and 3.7 Ma for L. tigrinus. [ABSTRACT FROM AUTHOR]

Nuclear ribosomal DNA (nrDNA) internal transcribed spacer (ITS) sequences from artificial hybrids and backcrosses between Armeria villosa ssp. longiaristata and A. colorata were studied to assess the possible effects of concerted evolution in natural hybrids. F[sub1] artificial hybrids show the expected pattern of additive polymorphisms for five of six variable sites as estimated from direct sequences. However, homogenization of polymorphism is already observed in the F[sub2], and is biased towards A. colorata except for one site. In backcrosses, an expected tendency towards homogenization of polymorphic sites in the direction of the recurrent parent is observed for five sites, although this does not necessarily imply concerted evolution. Conversely, the sixth site appears to elude such a mechanism and thus provides additional support for the occurrence of biased concerted evolution. Our findings are relevant to interpreting phylogeographic patterns involving gene flow and are also consistent with the hypothesis of a hybrid origin of A. villosa ssp. carratracensis. [ABSTRACT FROM AUTHOR]

One of the most promising hypotheses for the evolution of sex is that sexual reproduction is adventageous because it increases the rate of adaptive evolution in response to parasites. To investigate this advantage of sex, we compared genetic variation of gemini-virsuses infecting sexual and asexual populations of Eupatorium (Asteraceae). The infection frequency was 37.5% in the sexual population and 87.8% in the asexual population. The lower infection frequency in the sexual population might be the result of higher genetic diversity of host plants. If geminiviruses have diverged to counter defence systems of genetically variable hosts, genetic diversity of viruses is expected to be higher in sexual host populations than in asexual host populations. To test this expectation, we used single-strand conformation polymorphism (SSCP) analysis to examine genetic diversity of the geminiviruses in a DNA region containing the open-reading frame (ORF) C4 gene, which is known to function as a host range determinant. As predicted, higher genetic diversity of viruses was observed in the sexual population: three SSCP types were found in the asexual population while six types were found in the sexual population. Sequencing of the polymerase chain reaction (PCR) products revealed further genetic diversity. Phylogenetic analysis of the sequences showed that the SSCP types belonged to four different clades. Several SSCP types from the same clade were found in the sexual population, whereas the asexual population included only one SSCP type from each clade. Amino acid replacements of ORF C4 suggested to be accelerated in the sexual population. This evidence supports the hypothesis that sexual reproduction is advantageous as a defence against epidemic disease. [ABSTRACT FROM AUTHOR]

Postglacial migration is a major factor responsible for the patterns of genetic variation we see in natural populations. Fossil pollen data indicate that early postglacial colonists such as oak, were able to take both western and eastern migration routes into Britain. Analysis at a finer level is now permitted by the use of modem molecular techniques. A 13-bp duplication in the chloroplast tRNALeu1 intron occurs in natural populations of East Anglian oaks, but is not found in other parts of Britain or from mainland Europe. The distribution of this marker suggests that the mutation occurred either in southern England, or during migration from the mainland, and became fixed in a source population from which East Anglia was colonized. Planting of non-native trees for roadside boundaries and in the grounds of old houses and estates, explains the absence of the marker from some East Anglian oaks. [ABSTRACT FROM AUTHOR]

The early period of genetics is closely associated with the study of chromosomal inversions. For almost a century, evolutionary biologists found evidence for the role of inversions in central processes such as adaptation and speciation. In spite of huge efforts, many questions remain about the evolutionary forces underlying the distribution and dynamics of inversions in natural populations. Fortunately, old problems can be solved with new tools. In this issue, Kapun et al. () present a remarkable combination of resources and techniques, including publicly available data, karyotyping, statistical estimation of haplotypes, Pool- Seq data and experimental evolution, setting the ground for exciting developments in the field. [ABSTRACT FROM AUTHOR]

Explaining the maintenance of genetic variation in characters associated with Darwinian fitness is a preoccupation of evolutionary biologists. Spatial or temporal variation in the environment can certainly promote polymorphism, yet even populations of 'model organisms', like fruit flies, kept on invariant protocols for hundreds of generations in the laboratory often show fitness variation that exceeds what would be expected from the input of new mutations alone. Such observations suggest either complexities of selection or of genetic architecture, and offer a powerful tool for the study of mechanisms that promote stable polymorphism. In this issue of Molecular Ecology, Zhang et al. () report examples of nontransitivity in the outcome of postcopulatory sexual selection in the fruit fly, Drosophila, that follow the rules of the popular stalemate-breaking game roshambo - or rock, paper, scissors ( RPS). The important feature of RPS is that while each strategy beats one other, it in turn is beaten by the third. Using chromosome extraction lines, the authors confirm earlier findings that the outcome of postcopulatory sexual selection via sperm competition for a male depends, in part, upon the competitor male's genotype. But taking it one step further, they demonstrate the nontransitivities between males required for circular RPS cycles in sperm competition between males, and are able to identify at least four associated loci. Because the postmating phenotype involves hundreds of potentially interacting peptides and receptors, this is an important step to understanding the persistence of variation in a critical component of male fitness. [ABSTRACT FROM AUTHOR]

The term 'phenotypic capacitance' was introduced nearly 15 years ago to describe the strain-specific effects of impairing Hsp90, a molecular chaperone, in the fly Drosophila melanogaster (Rutherford & Lindquist ). In one genetic background, Hsp90 depletion caused deformed eyes, whereas in other genetic backgrounds, the wings or abdomens or other aspects of morphology were affected. Hsp90 was therefore viewed as acting like a capacitor, allowing genetic differences to build up and to be released at a later time. In the years since, it has been debated whether capacitance is a laboratory curiosity or a major force in evolution. In this issue of Molecular Ecology, Takahashi () presents evidence, from high-resolution morphometric analysis of fly wings, that a large number of other capacitors exist in D. melanogaster, and that the variation they reveal can be quite subtle. His results advance our understanding of capacitance and contribute to a new view of its role in evolutionary adaptation. [ABSTRACT FROM AUTHOR]