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Characterizing differences in sequences between two conditions, such as with and without drug exposure, using high-throughput sequencing data is a prevalent problem involving quantifying changes in sequence abundances, and predicting such differences for unobserved sequences. A key shortcoming of current approaches is their extremely limited ability to share information across related but non-identical reads. Consequently, they cannot use sequencing data effectively, nor be directly applied in many settings of interest. We introduce model-based enrichment (MBE) to overcome this shortcoming. We evaluate MBE using both simulated and real data. Overall, MBE improves accuracy compared to current differential analysis methods.

Abstract Characterizing differences in sequences between two conditions, such as with and without drug exposure, using high-throughput sequencing data is a prevalent problem involving quantifying changes in sequence abundances, and predicting such differences for unobserved sequences. A key shortcoming of current approaches is their extremely limited ability to share information across related but non-identical reads. Consequently, they cannot use sequencing data effectively, nor be directly applied in many settings of interest. We introduce model-based enrichment (MBE) to overcome this shortcoming. We evaluate MBE using both simulated and real data. Overall, MBE improves accuracy compared to current differential analysis methods.

Trade-offs and constraints are inherent to life, and studies of these phenomena play a central role in both organismal and evolutionary biology. Trade-offs can be defined, categorized, and studied in at least six, not mutually exclusive, ways. (1) Allocation constraints are caused by a limited resource (e.g., energy, time, space, essential nutrients), such that increasing allocation to one component necessarily requires a decrease in another (if only two components are involved, this is referred to as the Y-model, e.g., energy devoted to size versus number of offspring). (2) Functional conflicts occur when features that enhance performance of one task decrease performance of another (e.g., relative lengths of in-levers and outlevers, force-velocity trade-offs related to muscle fiber type composition). (3) Shared biochemical pathways, often involving integrator molecules (e.g., hormones, neurotransmitters, transcription factors), can simultaneously affect multiple traits, with some effects being beneficial for one or more components of Darwinian fitness (e.g., survival, age at first reproduction, fecundity) and others detrimental. (4) Antagonistic pleiotropy describes genetic variants that increase one component of fitness (or a lower-level trait) while simultaneously decreasing another. (5) Ecological circumstances (or selective regime) may impose trade-offs, such as when foraging behavior increases energy availability yet also decreases survival. (6) Sexual selection may lead to the elaboration of (usually male) secondary sexual characters that improve mating success but handicap survival and/or impose energetic costs that reduce other fitness components. Empirical studies of trade-offs often search for negative correlations between two traits that are the expected outcomes of the trade-offs, but this will generally be inadequate if more than two traits are involved and especially for complex physiological networks of interacting traits. Moreover, trade-offs often occur only in populations that are experiencing harsh environmental conditions or energetic challenges at the extremes of phenotypic distributions, such as among individuals or species that have exceptional athletic abilities. Trade-offs may be (partially) circumvented through various compensatory mechanisms, depending on the timescale involved, ranging from acute to evolutionary. Going forward, a pluralistic view of trade-offs and constraints, combined with integrative analyses that cross levels of biological organization and traditional boundaries among disciplines, will enhance the study of evolutionary organismal biology. [ABSTRACT FROM AUTHOR]

Pedigree-derived relationships for individuals from an intercross of several lines cannot easily account for the segregation variance that is mainly caused by loci with alternative alleles fixed in different lines. However, when all founders are genotyped for a large number of markers, such relationships can be derived for descendants as expected genomic relationships conditional on the observed founder allele frequencies. A tabular method was derived in detail for autosomes and the X-chromosome. As a case study, we analyzed litter size and body weights at three different ages in an advanced mouse intercross (29 generations, total pedigree size 19,266) between a line selected for high litter size (FL1) and a highly inbred control line (DUKsi). Approximately 60% of the total genetic variance was due to segregation variance. Estimated heritability values were 0.20 (0.03), 0.34 (0.04), 0.23 (0.03), 0.41 (0.03) and 0.47 (0.02) for litter size, litter weight and body weight at ages of 21, 42 and 63 days, respectively (standard errors in brackets). These values were between 12% and 65% higher than observed in analyses that treated founders as unrelated. Fields of applications include experimental populations (selection experiments or advanced intercross lines) with a limited number of founders, which can be genotyped at a reasonable cost. In principle any number of founder lines can be treated. Additional genotypes from individuals in later generations can be combined into a joint relationship matrix by capitalizing on previously published approaches.

Premise: Hybrid gene pools harbor more genetic variation than progenitor populations. Thus, we expect hybrid populations to exhibit more dynamic evolutionary responses to environmental variation. We ask how environmental variation experienced by adapted and transplanted populations influence the success of late‐generation hybrid populations during invasion. Methods: For four generations, 20 wild (Raphanus raphanistrum) and 20 hybrid radish (R. sativus × R. raphanistrum) plant populations evolved under experimentally manipulated moisture conditions (dry, wet, control‐sheltered, or control‐unsheltered plots; i.e., evolutionary environment) in old fields near Toronto, Canada. We planted advanced‐generation wild and hybrid radishes in sheltered plots and exposed them to either an evolutionary or a novel watering environment. To determine how soil moisture would influence invasion success, we compared the phenotype and fecundity of plants grown in these various environments. Results: Hybridization produced larger plants. In wet environments, hybrid seedlings emerged more frequently and expressed higher photosynthetic activity. Low‐moisture, novel conditions delayed and reduced seedling emergence frequency. Hybrid plants and those that evolved under relatively wet environments exhibited higher aboveground biomass. Hybrid plants from control‐sheltered plots colonizing novel moisture environments were more fecund than comparable wild plants. Conclusions: Dry environments are less likely than other evolutionary environments to contribute colonists. However, relatively wet locations support the evolution of relatively fecund plants, especially crop‐wild hybrid populations. Thus, our results provide a strong mechanistic explanation for variation in the relative success of crop‐wild hybrids among study locations and a new standard for studies that assess the risk of crop‐wild hybridization events. [ABSTRACT FROM AUTHOR]

Alcoholic fermentation is fundamentally an adaptation process, in which the yeast Saccharomyces cerevisiae outperforms its competitors and takes over the fermentation process itself. Although wine yeast strains appear to be adapted to the stressful conditions of alcoholic fermentation, nitrogen limitations in grape must cause stuck or slow fermentations, generating significant economic losses for the wine industry. One way to discover the genetic bases that promote yeast adaptation to nitrogen-deficient environments are selection experiments, where a yeast population undergoes selection under conditions of nitrogen restriction for a number of generations, to then identify by sequencing the molecular characteristics that promote this adaptation. In this work, we carried out selection experiments in bioreactors imitating wine fermentation under nitrogen-limited fermentation conditions (SM60), using the heterogeneous SGRP-4X yeast population, to then sequence the transcriptome and the genome of the population at different time points of the selection process. The transcriptomic results showed an overexpression of genes from the NA strain (North American/YPS128), a wild, non-domesticated isolate. In addition, genome sequencing and allele frequency results allowed several QTLs to be mapped for adaptation to nitrogen-limited fermentation. Finally, we validated the ECM38 allele of NA strain as responsible for higher growth efficiency under nitrogen-limited conditions. Taken together, our results revealed a complex pattern of molecular signatures favouring adaptation of the yeast population to nitrogen-limited fermentations, including differential gene expression, allele frequency changes and loss of the mitochondrial genome. Finally, the results suggest that wild alleles from a non-domesticated isolate (NA) may have a relevant role in the adaptation to the assayed fermentation conditions, with the consequent potential of these alleles for the genetic improvement of wine yeast strains.

Alcoholic fermentation is fundamentally an adaptation process, in which the yeast Saccharomyces cerevisiae outperforms its competitors and takes over the fermentation process itself. Although wine yeast strains appear to be adapted to the stressful conditions of alcoholic fermentation, nitrogen limitations in grape must cause stuck or slow fermentations, generating significant economic losses for the wine industry. One way to discover the genetic bases that promote yeast adaptation to nitrogen-deficient environments are selection experiments, where a yeast population undergoes selection under conditions of nitrogen restriction for a number of generations, to then identify by sequencing the molecular characteristics that promote this adaptation. In this work, we carried out selection experiments in bioreactors imitating wine fermentation under nitrogen-limited fermentation conditions (SM60), using the heterogeneous SGRP-4X yeast population, to then sequence the transcriptome and the genome of the population at different time points of the selection process. The transcriptomic results showed an overexpression of genes from the NA strain (North American/YPS128), a wild, non-domesticated isolate. In addition, genome sequencing and allele frequency results allowed several QTLs to be mapped for adaptation to nitrogen-limited fermentation. Finally, we validated the ECM38 allele of NA strain as responsible for higher growth efficiency under nitrogen-limited conditions. Taken together, our results revealed a complex pattern of molecular signatures favouring adaptation of the yeast population to nitrogen-limited fermentations, including differential gene expression, allele frequency changes and loss of the mitochondrial genome. Finally, the results suggest that wild alleles from a non-domesticated isolate (NA) may have a relevant role in the adaptation to the assayed fermentation conditions, with the consequent potential of these alleles for the genetic improvement of wine yeast strains. [ABSTRACT FROM AUTHOR]

Aerobic capacity (VO 2max measured during intensive physical exercise) both trained and intrinsic (i.e. genetically determined) has recently been deemed a good predictor of cardiometabolic risks. However, the underlying mechanisms linking VO 2max and health risk factors are not entirely clear, as it seems that not VO 2max per se, but rather some correlated traits, like spontaneous physical activity (SPA) are responsible for sustaining the lean phenotype. Here we investigated the link between genetically determined aerobic capacity, SPA and resistance to diet-induced health risks using replicated lines of mice selected for high aerobic capacity during swimming in mid-cold water (25 °C) and Randomly Bred control mice. After four months of consumption of the western type HFat and HCarb diets and no forced nor voluntary training, we found no evidence of protective effects of intrinsic high VO 2max . The Selected mice displayed similar levels of blood glucose, cholesterol, triglycerides and body fat as the Random Bred control animals. Most notably we found no correlation between VO 2max and SPA levels. Our results therefore call into question the ubiquity of VO 2max as a predictor of metabolic health and leanness, at least in animal models. [ABSTRACT FROM AUTHOR]

The metabolic capabilities of microbes are the basis for many major biotechnological advances, exploiting microbial diversity by selection or engineering of single strains. However, there are limits to the advances that can be achieved with single strains, and attention has turned towards the metabolic potential of consortia and the field of synthetic ecology. The main challenge for the synthetic ecology is that consortia are frequently unstable, largely because evolution by constituent members affects their interactions, which are the basis of collective metabolic functionality. Current practices in modeling consortia largely consider interactions as fixed circuits of chemical reactions, which greatly increases their tractability. This simplification comes at the cost of essential biological realism, stripping out the ecological context in which the metabolic actions occur and the potential for evolutionary change. In other words, evolutionary stability is not engineered into the system. This realization highlights the necessity to better identify the key components that influence the stable coexistence of microorganisms. Inclusion of ecological and evolutionary principles, in addition to biophysical variables and stoichiometric modeling of metabolism, is critical for microbial consortia design. This review aims to bring ecological and evolutionary concepts to the discussion on the stability of microbial consortia. In particular, we focus on the combined effect of spatial structure (connectivity of molecules and cells within the system) and ecological interactions (reciprocal and non-reciprocal) on the persistence of microbial consortia. We discuss exemplary cases to illustrate these ideas from published studies in evolutionary biology and biotechnology. We conclude by making clear the relevance of incorporating evolutionary and ecological principles to the design of microbial consortia, as a way of achieving evolutionarily stable and sustainable systems.

Competitive interactions shape the evolution of organisms. However, often it is not clear whether competition is the driving force behind the patterns observed. The recent use of experimental evolution in competitive environments can help establish such causality. Unfortunately, this literature is scattered, as competition for food, mates, and hosts are subject areas that belong to different research fields. Here, we group these bodies of literature, extract common processes and patterns concerning the role of competition in shaping evolutionary trajectories, and suggest perspectives stemming from an integrative view of competition across these research fields. This review reinstates the power of experimental evolution in addressing the evolutionary consequences of competition, but highlights potential pitfalls in the design of such experiments. [ABSTRACT FROM AUTHOR]

Abstract Selection programmes are mainly concerned with increasing genetic gain. However, short-term progress should not be obtained at the expense of the within-population genetic variability. Different prediction models for the evolution within a small population of the genetic mean of a selected trait, its genetic variance and its inbreeding have been developed but have mainly been validated through Monte Carlo simulation studies. The purpose of this study was to compare theoretical predictions to experimental results. Two deterministic methods were considered, both grounded on a polygenic additive model. Differences between theoretical predictions and experimental results arise from differences between the true and the assumed genetic model, and from mathematical simplifications applied in the prediction methods. Two sets of experimental lines of chickens were used in this study: the Dutch lines undergoing true truncation mass selection, the other lines (French) undergoing mass selection with a restriction on the representation of the different families. This study confirmed, on an experimental basis, that modelling is an efficient approach to make useful predictions of the evolution of selected populations although the basic assumptions considered in the models (polygenic additive model, normality of the distribution, base population at the equilibrium, etc.) are not met in reality. The two deterministic methods compared yielded results that were close to those observed in real data, especially when the selection scheme followed the rules of strict mass selection: for instance, both predictions overestimated the genetic gain in the French experiment, whereas both predictions were close to the observed values in the Dutch experiment.

Whole animal physiological performance is highly polygenic and highly plastic, and the same is generally true for the many subordinate traits that underlie performance capacities. Quantitative genetics, therefore, provides an appropriate framework for the analysis of physiological phenotypes and can be used to infer the microevolutionary processes that have shaped patterns of trait variation within and among species. In cases where specific genes are known to contribute to variation in physiological traits, analyses of intraspecific polymorphism and interspecific divergence can reveal molecular mechanisms of functional evolution and can provide insights into the possible adaptive significance of observed sequence changes. In this review, we explain how the tools and theory of quantitative genetics, population genetics, and molecular evolution can inform our understanding of mechanism and process in physiological evolution. For example, lab-based studies of polygenic inheritance can be integrated with field-based studies of trait variation and survivorship to measure selection in the wild, thereby providing direct insights into the adaptive significance of physiological variation. Analyses of quantitative genetic variation in selection experiments can be used to probe interrelationships among traits and the genetic basis of physiological trade-offs and constraints. We review approaches for characterizing the genetic architecture of physiological traits, including linkage mapping and association mapping, and systems approaches for dissecting intermediary steps in the chain of causation between genotype and phenotype. We also discuss the promise and limitations of population genomic approaches for inferring adaptation at specific loci. We end by highlighting the role of organismal physiology in the functional synthesis of evolutionary biology. [ABSTRACT FROM AUTHOR]

Abstract: Sex determination in Nile tilapia is very labile. It was shown that the sex ratio in temperature treated groups (36°C, 10days) of Oreochromis niloticus can be selected for as a quantitative trait. The standardized test procedure involved the artificial reproduction of breeders with nine days of egg incubation at 28°C and subsequent testing of fry at an elevated temperature of 36°C for 10days. Family selection was carried out upon the male percentages in treatment groups (high-line>80%, low-line<60%). Selected candidates were taken from corresponding full sib control groups, which were kept at 28°C. After two generations of divergent selection for the male proportion in temperature treated groups, male percentages of 90% and 54% were obtained in the high- and low-line, respectively. Herein, the data for a third generation of selection are presented. Twelve families in the high-line and 20 in the low-line were tested. Average male percentages in the treatment groups of 92.7% and 50.4% were obtained. After three generations of selection the cumulated realized heritabilities for the temperature dependent sex ratio were 0.63 in the high- and 0.84 in the low-line, still indicating good potential for selection. Two families in the high-line exhibited only males, whereas in the low-line two families showed a feminising effect in the treatment groups. Generally elevated temperatures (>34°C) are considered to be masculinising in Nile tilapia, feminising effects so far have only been reported in genetic all-male progenies (YY, XY). In the third generation of selection, it could be shown that elevated temperatures might take over a feminising role through selection in genetically mixed sex (XX/XY) progenies. Consequently both, temperature-masculinising and -feminising genes, exist in the same population and can be accumulated through selection. However, the load of temperature-masculinising genes of dams from the high- or low-line had no effect on mean sex ratios in temperature treated groups when a YY-male was used as a sire. From an evolutionary point of view, the prevalence of both temperature-masculinising and -feminising effects might allow the sex ratio to equilibrate at the population level if random mating occurs. This in turn might counteract the evolution of sex chromosomes. [Copyright &y& Elsevier]

During the Last Glacial Maximum (LGM; 18 000-20 000 yr ago) and previous glacial periods, atmospheric [CO2] dropped to 180-190 ppm, which is among the lowest concentrations that occurred during the evolution of land plants. Modern atmospheric CO2 concentrations ([CO2]) are more than twice those of the LGM and 45% higher than pre-industrial concentrations. Since CO2 is the carbon source for photosynthesis, lower carbon availability during glacial periods likely had a major impact on plant productivity and evolution. From the studies highlighted here, it is clear that the influence of low [CO2] transcends several scales, ranging from physiological effects on individual plants to changes in ecosystem functioning, and may have even influenced the development of early human cultures (via the timing of agriculture). Through low-[CO2] studies, we have determined a baseline for plant response to minimal [CO2] that occurred during the evolution of land plants. Moreover, an increased understanding of plant responses to low [CO2] contributes to our knowledge of how natural global change factors in the past may continue to influence plant responses to future anthropogenic changes. Future work, however, should focus more on the evolutionary responses of plants to changing [CO2] in order to account for the potentially large effects of genetic change. [ABSTRACT FROM AUTHOR]

Cultivated plants that cannot survive on their own often have maladaptive domestication traits. Unharvested crop seeds may generate feral populations, at times causing serious weed problems, but little is known about the evolution of ferality. We explored the potential for cultivated radish, Raphanus sativus, to become feral, given that closely related taxa (e.g., R. raphanistruin and crop-wild hybrids) are well-documented weeds. First, we measured the population growth of five experimental, cultivated, self- seeding radish populations in Michigan, USA, for three generations. Three late-flowering populations went extinct, and two others apparently hybridized with local R. raphanistrum. A common garden experiment showed that the two surviving populations had earlier flowering, smaller root diameters, and greater individual fecundity than did nonhybridized populations. We also used artificial selection to measure the evolutionary potential for earlier flowering. After two generations of strong selection, two of three lineages flowered earlier and produced more seeds than control lineages, but insufficient genetic variation prevented dramatic evolution of crop phenotypes. In summary, it seems unlikely that radishes could spontaneously become feral in our study area without gene flow from R. raphanistrum. Applying these approaches to other cultivated species may provide a better understanding of mechanisms promoting the evolution of feral weeds. [ABSTRACT FROM AUTHOR]

Adaptation is back on the research schedules of evolutionists and ecologists. This renewed interest is driven by global change, to which species, in particular arctic and alpine ones, either react by migration or adaptation. In this overview, we give a brief introduction to the use of genome scans along with environmental data to identify molecular markers of adaptive relevance. This approach encompasses the sampling of many populations along ecological gradients or from different habitat types combined with genome scans using presumably neutral markers such as amplified fragment length polymorphisms or microsatellites. To identify markers linked to genes under selection, two different methods (besides others) are particularly relevant. (1) One searches for markers exhibiting higher genetic differentiation among populations than expected under neutrality. The frequencies of alleles at such outlier loci can then be related to ecological factors. (2) The other method uses logistic regression between allele presence/absence and ecological factors (i.e. an allele distribution model). It thus directly links marker occurrence with environmental data. We illustrate these two methods with examples from the literature. The strength of genome scans used in parallel with environmental data is that they provide distinct clues for selective forces acting on molecular markers of adaptive relevance in real landscapes. We further discuss limitations of genome scans (e.g. sensitivity to phylogeographic structure and bottlenecks) and of other genomic approaches to detect adaptive molecular markers such as candidate genes, quantitative trait loci or transcription profiling. We stress that the selective advantage of particular alleles has to be proven in selection experiments. We conclude that combining studies on adaptive and neutral molecular markers will largely contribute to our understanding of how species react to global change and will allow us to investigate the 'migration of adaptation'. [ABSTRACT FROM AUTHOR]

An absence of genetic variance in traits under selection is perhaps the oldest explanation for a limit to evolutionary change, but has also been the most easily dismissed. We review a range of theoretical and empirical results covering single traits to more complex multivariate systems, and show that an absence of genetic variance may be more common than is currently appreciated. From a single-trait perspective, we highlight that it is becoming clear that some trait types do not display significant levels of genetic variation, and we raise the possibility that species with restricted ranges may differ qualitatively from more widespread species in levels of genetic variance in ecologically important traits. A common misconception in many life-history studies is that a lack of genetic variance in single traits, and genetic constraints as a consequence of bivariate genetic correlations, are different causes of selection limits. We detail how interpretations of bivariate patterns are unlikely to demonstrate genetic limits to selection in many cases. We advocate a multivariate definition of genetic constraints that emphasizes the presence (or otherwise) of genetic variance in the multivariate direction of selection. For multitrait systems, recent results using longer term studies of organisms, in which more is understood concerning what traits may be under selection, have indicated that selection may exhaust genetic variance, resulting in a limit to the selection response. [ABSTRACT FROM AUTHOR]

A short-term selection experiment for increasing the first-day litter size (LS1) and 28-day litter weight (LW28) was conducted with three populations of mice over 8 generations. Different methods of litter size manipulation were used for the populations - in S the litter size was standardized to 8 (4 ♂ ♂, 4 ♀♀) on the first day, in LA it was adjusted to the average size of all litters born on the same day and NL had the natural litter size. To eliminate temporary environmental effects, a control population was kept in each case. The selection results per generation were, for LS 1 b=0.30 (S, NL) and 0.20 (LA), and for LW28 b=5.62 g (S), 5.26 g (NL), and 4.32 g (LA). The heritability obtained was between 0.18 and 0.13 for LS 1 and from 0.42 to 0.12 for LW28. The populations differed in the correlated responses for body weight parameters (litter weight gain). The implantation rate increased in populations S and NL (b=0.19, 0.37), but not in population LA. Postnatal mortality went down (b=-0.07) and the dam's milk production rose (b=1.11 g) only in population LA. The estimated partial regression coefficient linking body weight at mating (BWM) for the dam and the daughter's litter size showed an effect on the litter size. [ABSTRACT FROM AUTHOR]

A long-term experiment for increasing the traits first day litter size (LS1) and litter weight (LW1) was conducted with two populations for 33 generations. The selection plateau was reached in population DU-C (selection and estrus synchronization (h = 0.02±0.01); in population DU-K (selection) the plateau (h = 0.05±0.2) was nearly reached. Selection progress per generation was in LS1 b = 0.11±0.02; b = 0.12±0.04 (1st to 18th generation DU-K, DU-C) and b = 0.10±0.03; b = 0.07±0.05 (19th to 33rd generation, DU-K, DU-C) in LW1 b = 0.16±0.04 g; 0.19±0.07 g (DU-K, DU-C) b = 0.20±0.09 g; 0.001±0.09 g (DU-K, DU-C). Reverse and relaxe selection as well as systematic inbreeding was applied for 10 generations. Reverse selection yielded h = 0.28±0.11 (R-DU-K) and h = 0.17±0.05 (R-DU-C) and showed that there was still additive genetic variance. Relaxe selection did not cause alterations in the selection parameters, whereas inbreeding lead to inbred depressions (b = LS1 = −0.42±0.15; −0.45±0.12; b = LW1 = −1.13±0.20; −0.82±0.18 I-DU-K, I-DU-C). The plateau was based upon the heterozygote advantage. Several methods for overcoming the plateau were applied. A new selective useful variance could be created by crossing the plateau populations (h = 0.14±0.04). A short-term progress in overcoming the plateau (1st to 3rd generation) could be obtained by litter size standardization (LS = 388). Tandem selection (selection for body weight - BW42) as well as crossing of inbred strains were not suitable for overcoming the selection plateau. Altering the environmental conditions as a possibility for overcoming the plateau has been discussed. [ABSTRACT FROM AUTHOR]

Abstract: A two generation selection experiment in Nile tilapia (O. niloticus, Lake Manzala, Egypt) was carried out to test whether the proportion of males after temperature treatment could be sustainably influenced by selection. Starting with 45 families as a base population the families were tested for their thermal sensitivity in the following way. After a 9-day incubation period at 28 °C, fry of each family were subdivided into a control (28 °C) and a treatment group, each consisting of 110 fish. The treatment group was kept at a temperature of 36 °C for 10 days. Thereafter treated fry were gradually adapted to 28 °C again. Each treatment and corresponding control group was raised separately until sexing (by microscopic inspection of gonad squashes at a minimum age of 90 days). A random sample of ten males and females from control groups of each family was kept for later selection decisions. The percentage of males in treatment groups was the selection criterion and the families showing more than 80% males or less than 60% after temperature treatment were selected. Over two generations (G0 and G1) around 14% of the tested families were selected to produce two divergent lines (high and low line) which showed a high or low response to temperature treatment regarding their sex ratios. In the first and second generation of selection 66 and 26 families were tested in the high line and 72 and 13 families in the low line, respectively. After two generations of selection the temperature treated groups in the high line showed a male percentage of 90%, whereas the weakly sensitive low line showed an average male proportion of 54%. The realized heritability estimated from the cumulated realized selection response and -differential in successive generations was 0.69 in the high line and 0.86 in the low line. This study provides the first evidence that a surplus of males in temperature treated groups can be selected for as a quantitative trait. Thus, temperature sensitive lines could be produced as a consumer- and environment-friendly approach to significantly increase the proportion of males in Nile tilapia, if large numbers of broodstock could be tested. [Copyright &y& Elsevier]