Directional Selection Research Articles

Body size evolution in otters distinguished from terrestrial mustelids.

Some taxa of mammals live in water, all of which evolved from land-dwelling ancestors. In the family Mustelidae (Mammalia: Carnivora), most species live on land, while otters, comprising the subfamily Lutrinae, inhabit aquatic environments, which include the almost exclusively aquatic sea otters (Enhydra lutris). Thus, the transition from a terrestrial to an aquatic lifestyle has occurred within this family. Despite potentially different selection pressures on body size in aquatic and terrestrial habitats, no divergence in the evolutionary pattern of body size between otters and other mustelids has previously been shown using models of trait evolution on a phylogeny. We applied models that explicitly incorporated lineage-specific directional selection to the evolution of body mass in living mustelids. Using a simulation-based likelihood and approximate Bayesian computation approach, we demonstrated lineage-specific directional selection for larger body mass in otters, which is distinct from other mustelids. There was no evidence of a difference between sea otters and other otters in the strength of directional selection for larger body mass. Additionally, our analyses supported no difference in the rate at which body mass evolves in both directions between otters and other mustelids. These findings suggest that the evolution of body mass in otters is associated with selective advantages of larger size rather than the relaxation of constraints on body size in aquatic habitats, like other aquatic mammals such as sirenians, cetaceans, and pinnipeds.

A cosmopolitan inversion facilitates seasonal adaptation in overwintering Drosophila.

Fluctuations in the strength and direction of natural selection through time are a ubiquitous feature of life on Earth. One evolutionary outcome of such fluctuations is adaptive tracking, wherein populations rapidly adapt from standing genetic variation. In certain circumstances, adaptive tracking can lead to the long-term maintenance of functional polymorphism despite allele frequency change due to selection. Although adaptive tracking is likely a common process, we still have a limited understanding of aspects of its genetic architecture and its strength relative to other evolutionary forces such as drift. Drosophila melanogaster living in temperate regions evolve to track seasonal fluctuations and are an excellent system to tackle these gaps in knowledge. By sequencing orchard populations collected across multiple years, we characterized the genomic signal of seasonal demography and identified that the cosmopolitan inversion In(2L)t facilitates seasonal adaptive tracking and shows molecular footprints of selection. A meta-analysis of phenotypic studies shows that seasonal loci within In(2L)t are associated with behavior, life history, physiology, and morphological traits. We identify candidate loci and experimentally link them to phenotype. Our work contributes to our general understanding of fluctuating selection and highlights the evolutionary outcome and dynamics of contemporary selection on inversions.

Threshold‐dependent gene regulation and partial assortative mating determine wing dimorphism of an insect

Wing dimorphism is a life‐historical trait of insects which indicates the developmental trend of populations, going as migrants or staying as residents. The alternative wing morph enhances adaptability of insects to changing environments. However, the underlying mechanism for maintaining wing dimorphism remains vague. The brown planthoppers Nilaparvata lugens, a serious pest of rice, are either short‐winged or long‐winged. The shift between two wing morphs is determined by two insulin receptors. So, this pest is a better model organism to explore the mechanism of wing dimorphism. Here, the short‐ and long‐winged strains of N. lugens were selected. Rates of a selected wing morph were linearly increased in populations, and the selection response of the short‐winged morph was stronger than that of the long‐winged. Selection enhanced the migratory or resident propensity. Directional selection for the long‐winged morph resulted in longer and lighter forewings, while selection for the short‐winged morph generated shorter and thicker wings and higher fecundity. Relative expression levels of wing development genes InR1, InR2 and Foxo were positively correlated with the short‐winged rate in the short‐winged strain, while they were negatively correlated with the long‐winged rate in the long‐winged strain at specific stages. The change rate of expression levels was approximately two times as high as that of the wing morph rates in populations, indicating a high threshold‐dependent gene expressed regulation of wing morph. A partial assortative mating behavior occurred between the nearly pure‐bred lineages of short‐ and long‐winged strains. The short‐winged males preferred to mate with short‐winged females while the long‐winged males mated with the short‐ and long‐winged females equally. The threshold‐dependent mode may be more flexible to adjust wing morphs according to environmental conditions and the partial assortative mating promotes the genetic exchange between two wing morphs which drive the maintenance of wing dimorphism.

The timing of reproduction is responding plastically, not genetically, to climate change in yellow-bellied marmots (Marmota flaviventer).

With global climates changing rapidly, animals must adapt to new environmental conditions with altered weather and phenology. The key to adapting to these new conditions is adjusting the timing of reproduction to maximize fitness. Using a long-term dataset on a wild population of yellow-bellied marmots (Marmota flaviventer) at the Rocky Mountain Biological Laboratory (RMBL), we investigated how the timing of reproduction changed with changing spring conditions over the past 50 years. Marmots are hibernators with a 4-month active season. It is thus crucial to reproduce early enough in the season to have time to prepare for hibernation, but not too early, as snow cover prevents access to food. Importantly, climate change in this area has, on average, increased spring temperatures by 5°C and decreased spring snowpack by 50 cm over the past 50 years. We evaluated how female marmots adjust the timing of their reproduction in response to changing conditions and estimated the importance of both microevolution and plasticity in the variation in this timing. We showed that, within a year, the timing of reproduction is not as tightly linked to the date a female emerges from hibernation as previously thought. We reported a positive effect of spring snowpack but not of spring temperature on the timing of reproduction. We found inter-individual variation in the timing of reproduction, including low heritability, but not in its response to changing spring conditions. There was directional selection for earlier reproduction since it increased the number and proportion of pups surviving their first winter. Taken together, the timing of marmot reproduction might evolve via natural selection; however, plastic changes will also be extremely important. Further, future studies on marmots should not operate under the assumption that females reproduce immediately following their emergence.

Performance-based inference of selection on stomatal length and specific leaf area varies with climate-of-origin of the forest tree, Eucalyptus ovata

Understanding how functional traits affect plant performance and fitness is a key step in unravelling the role of natural selection in shaping the evolutionary trajectory of populations. We examined early-age selection acting on leaf traits via their effects on growth performance and fitness, measured in Eucalyptus ovata trees planted in a common-garden field trial embedded in a reforestation planting in Tasmania, Australia. We focused on two important leaf traits - stomatal length and specific leaf area (SLA) - measured two years after planting, and compared interplanted E. ovata groups originating from dry and wet home-site climates, with the trial site having intermediate long-term mean annual rainfall. Two-year height growth was used as the performance attribute, and the time-averaged tree survival over the subsequent six years as the fitness component. There was evidence for performance-based selection on the leaf traits, with the strength and form of selection depending on the trait and climate group being considered. In this sense, selection in the dry group operated mainly on stomatal length where a combination of directional (favouring longer stomata) and stabilizing selection was detected, whereas selection in the wet group acted only on SLA and was purely stabilizing. Estimates of performance-based correlational selection were not statistically significant. For both climate groups, estimates of fitness-based selection gradients provided evidence for significant directional (but not quadratic) selection on height performance, favouring individuals with faster growth, but did not indicate statistical support for direct effects of the leaf traits on tree survival, conditional on measured performance. These results validated qualitative inferences of selection from the performance-based analysis, and suggested that selection on the leaf traits appeared to be mediated by their effects on early-age height performance, which in turn directly influenced later-age survival. We discuss the mechanisms by which the focal traits may have affected height performance, and likely factors contributing to the different patterns of phenotypic selection observed in the two groups experiencing the same environment. We also provide expressions of analytical derivatives that were developed for the estimation of selection gradients based on a logistic regression model relating a binary fitness response to linear and nonlinear covariate terms for the target regressor variables.

Isolation may select for earlier and higher peak viral load but shorter duration in SARS-CoV-2 evolution

During the COVID-19 pandemic, human behavior change as a result of nonpharmaceutical interventions such as isolation may have induced directional selection for viral evolution. By combining previously published empirical clinical data analysis and multi-level mathematical modeling, we find that the SARS-CoV-2 variants selected for as the virus evolved from the pre-Alpha to the Delta variant had earlier and higher peak in viral load dynamics but a shorter duration of infection. Selection for increased transmissibility shapes the viral load dynamics, and the isolation measure is likely to be a driver of these evolutionary transitions. In addition, we show that a decreased incubation period and an increased proportion of asymptomatic infection are also positively selected for as SARS-CoV-2 mutated to adapt to human behavior (i.e., Omicron variants). The quantitative information and predictions we present here can guide future responses in the potential arms race between pandemic interventions and viral evolution.

Low but significant evolutionary potential for growth, phenology and reproduction traits in European beech

AbstractLocal survival of forest tree populations under climate change depends on existing genetic variation and their adaptability to changing environments. Responses to selection were studied in European beech (Fagus sylvatica) under field conditions. A total of 1087 adult trees, seeds, 1‐year‐old seedlings and established multiyear saplings were genotyped with 16 nuSSRs. Adult trees were assessed for phenotypic traits related to growth, phenology and reproduction. Parentage and paternity analyses were used to estimate effective female and male fecundity as a proxy of fitness and showed that few parents contributed to successful regeneration. Selection gradients were estimated from the relationship between traits and fecundity, while heritability and evolvability were estimated using mixed models and the breeder's equation. Larger trees bearing more fruit and early male flowering had higher total fecundity, while trees with longer growth season had lower total fecundity (directional selection). Stabilizing selection on spring phenology was found for female fecundity, highlighting the role of late frosts as a selection driver. Selection gradients for other traits varied between measurement years and the offspring cohort used to estimate parental fecundity. Compared to other studies in natural populations, we found low to moderate heritability and evolvability for most traits. Response to selection was higher for growth than for budburst, leaf senescence or reproduction traits, reflecting more consistent selection gradients across years and sex functions, and higher phenotypic variability in the population. Our study provides empirical evidence suggesting that populations of long‐lived organisms such as forest trees can adapt locally, even at short‐time scales.

120 Using Simulated Data to Evaluate the Accuracy of Selection Signature Detection Methods in Varying Scenarios

Abstract The identification of molecular signatures of selection has become increasingly important in recent years. The detection of selection signatures can aid in both population characterization as well as the detection and identification of genes and advantageous mutations within populations. Various statistical methodologies have been developed to detect directional selection signatures based on different demographic or selection models. The detection of definite evidence of selection on genomes remains a challenge, as other events in the demographic history of a population under investigation may imitate the effects of selection on the genetic variation in the genome. To accurately detect selection signatures, researchers need to consider the large number of methodologies available as well as the factors influencing the detection of selection signatures. Using simulated data, it is possible to evaluate several methods and factors on a larger number of genotypes without the expense of genotyping several animals. The objective of this study was to simulate several sheep populations that have undergone different selection pressures, with varying parameters that may possibly influence the accuracy of detecting selection signatures and testing multiple methods of selection signature detection to find the most reliable method for each scenario. Sheep populations were simulated with varying numbers of QTL (5, 100, 2000) and h2 (0.15, 0.4). The populations were then expanded through either selection for high, low, or random genetic values. Thereafter the populations were selected for sample sizes of 20, 200 and 1000 individuals, resulting in a total of 54 populations for analysis. The populations were then subjected to ROH, iHS, Fst and XP-EHH analysis. After the most effective method for detection of selection signatures for each scenario was identified, the influence of effective population size, generations of animals included in the sample, relatedness, and sex of individuals on the accuracy of each method was tested. Preliminary results indicated that the accuracy of XP-EHH as well as ROH increased with larger population sizes, as well as greater numbers of QTL. Further results of this study will be presented at the conference.

Problems with studying directional natural selection in humans.

The review describes the main methods for assessing directional selection in human populations. These include bioinformatic analysis of DNA sequences via detection of linkage disequilibrium and of deviations from the random distribution of frequencies of genetic variants, demographic and anthropometric studies based on a search for a correlation between fertility and phenotypic traits, genome-wide association studies on fertility along with genetic loci and polygenic risk scores, and a comparison of allele frequencies between generations (in modern samples and in those obtained from burials). Each approach has its limitations and is applicable to different periods in the evolution of Homo sapiens. The main source of error in such studies is thought to be sample stratification, the small number of studies on nonwhite populations, the impossibility of a complete comparison of the associations found and functionally significant causative variants, and the difficulty with taking into account all nongenetic determinants of fertility in contemporary populations. The results obtained by various methods indicate that the direction of human adaptation to new food products has not changed during evolution since the Neolithic; many variants of immunity genes associated with inflammatory and autoimmune diseases in modern populations have undergone positive selection over the past 2-3 thousand years owing to the spread of bacterial and viral infections. For some genetic variants and polygenic traits, an alteration of the direction of natural selection in Europe has been documented, e. g., for those associated with an immune response and cognitive abilities. Examination of the correlation between fertility and educational attainment yields conflicting results. In modern populations, to a greater extent than previously, there is selection for variants of genes responsible for social adaptation and behavioral phenotypes. In particular, several articles have shown a positive correlation of fertility with polygenic risk scores of attention deficit/hyperactivity disorder.

Genetic depletion does not prevent rapid evolution in island-introduced lizards.

Experimental introductions of species have provided some of the most tractable examples of rapid phenotypic changes, which may reflect plasticity, the impact of stochastic processes, or the action of natural selection. Yet to date, very few studies have investigated the neutral and potentially adaptive genetic impacts of experimental introductions. We dissect the role of these processes in shaping the population differentiation of wall lizards in three Croatian islands (Sušac, Pod Kopište, and Pod Mrčaru), including the islet of Pod Mrčaru, where experimentally introduced lizards underwent rapid (~30 generations) phenotypic changes associated with a shift from an insectivorous to a plant-based diet. Using a genomic approach (~82,000 ddRAD loci), we confirmed a founder effect during introduction and very low neutral genetic differentiation between the introduced population and its source. However, genetic depletion did not prevent rapid population growth, as the introduced lizards exhibited population genetic signals of expansion and are known to have reached a high density. Our genome-scan analysis identified just a handful of loci showing large allelic shifts between ecologically divergent populations. This low overall signal of selection suggests that the extreme phenotypic differences observed among populations are determined by a small number of large-effect loci and/or that phenotypic plasticity plays a major role in phenotypic changes. Nonetheless, functional annotation of the outlier loci revealed some candidate genes relevant to diet-induced adaptation, in agreement with the hypothesis of directional selection. Our study provides important insights on the evolutionary potential of bottlenecked populations in response to new selective pressures on short ecological timescales.

The genetic basis of traits associated with the evolution of serpentine endemism in monkeyflowers.

The floras on chemically and physically challenging soils, such as gypsum, shale, and serpentine, are characterized by narrowly endemic species. The evolution of edaphic endemics may be facilitated or constrained by genetic correlations among traits contributing to adaptation and reproductive isolation across soil boundaries. The yellow monkeyflowers in the Mimulus guttatus species complex are an ideal system in which to examine these evolutionary patterns. To determine the genetic basis of adaptive and prezygotic isolating traits, we performed genetic mapping experiments with F2 hybrids derived from a cross between a serpentine endemic, M. nudatus, and its close relative M. guttatus. Few large effect and many small effect QTL contribute to interspecific divergence in life history, floral, and leaf traits, and a history of directional selection contributed to trait divergence. Loci contributing to adaptive traits and prezygotic reproductive isolation overlap, and their allelic effects are largely in the direction of species divergence. These loci contain promising candidate genes regulating flowering time and plant organ size. Together, our results suggest that genetic correlations among traits can facilitate the evolution of adaptation and speciation and may be a common feature of the genetic architecture of divergence between edaphic endemics and their widespread relatives.

Sexually concordant selection on floral traits despite greater opportunity for selection through male fitness.

Pollinators are important drivers of floral trait evolution, yet plant populations are not always perfectly adapted to their pollinators. Such apparent maladaptation may result from conflicting selection through male and female sexual functions in hermaphrodites. We studied sex-specific mating patterns and phenotypic selection on floral traits in Aconitum gymnandrum. After genotyping 1786 offspring, we partitioned individual fitness into sex-specific selfed and outcrossed components and estimated phenotypic selection acting through each. Relative fitness increased with increasing mate number, and more so for male function. This led to greater opportunity for selection through outcrossed male fitness, though patterns of phenotypic selection on floral traits tended to be similar, and with better support for selection through female rather than male fitness components. We detected directional selection through one or more fitness component for larger flower number, larger flowers, and more negative nectar gradients within inflorescences. Our results are consistent with Bateman's principles for sex-specific mating patterns and illustrate that, despite the expected difference in opportunity for selection, patterns of variation in selection across traits can be rather similar for the male and female sexual functions. These results shed new light on the effect of sexual selection on the evolution of floral traits.

Transgenerational sublethal pyrethroid exposure gives rise to insecticide resistance in a pest insect

The evolution of insecticide resistance has been attributed to strong directional selection by lethal concentrations of insecticides, but there is growing evidence that sublethal doses may also modify resistance through the hormetic effects. Hormesis is a beneficial effect caused by exposure to low doses. However, the role of parental (transgenerational) effects on hormesis, and through that on insecticide resistance, is still unclear. We investigated the effects of several sublethal pyrethroid insecticide (Decis) doses on survival, body mass, and reproduction within four generations (F0, F1, F2, and F3) of the Colorado potato beetle (Leptinotarsa decemlineata). We found that insecticide exposure had mostly linear adverse within-generation effects: decreased larva-to-adult survival, adult body mass, and egg hatching. However, transgenerational exposure led to hormetic effects: increased larva-to-adult survival and pre-diapause adult body mass. Moreover, transgenerational effects were even more positive for offspring exposed to insecticides, leading to decreased larva-to-adult survival, increased body mass, and egg hatching. Our results show that despite mostly negative within-generation effects, transgenerational sublethal exposure to insecticide can cause unwanted positive hormetic effects in their offspring, making them to resist or tolerate the insecticides better, even though the underlying mechanisms are still unclear.

Genetic Variance Estimation over Time in Broiler Breeding Programmes for Growth and Reproductive Traits.

Monitoring the genetic variance of traits is a key priority to ensure the sustainability of breeding programmes in populations under directional selection, since directional selection can decrease genetic variation over time. Studies monitoring changes in genetic variation have typically used long-term data from small experimental populations selected for a handful of traits. Here, we used a large dataset from a commercial breeding line spread over a period of twenty-three years. A total of 2,059,869 records and 2,062,112 animals in the pedigree were used for the estimations of variance components for the traits: body weight (BWT; 2,059,869 records) and hen-housed egg production (HHP; 45,939 records). Data were analysed with three estimation approaches: sliding overlapping windows, under frequentist (restricted maximum likelihood (REML)) and Bayesian (Gibbs sampling) methods; expected variances using coefficients of the full relationship matrix; and a "double trait covariances" analysis by computing correlations and covariances between the same trait in two distinct consecutive windows. The genetic variance showed marginal fluctuations in its estimation over time. Whereas genetic, maternal permanent environmental, and residual variances were similar for BWT in both the REML and Gibbs methods, variance components when using the Gibbs method for HHP were smaller than the variances estimated when using REML. Large data amounts were needed to estimate variance components and detect their changes. For Gibbs (REML), the changes in genetic variance from 1999-2001 to 2020-2022 were 82.29 to 93.75 (82.84 to 93.68) for BWT and 76.68 to 95.67 (98.42 to 109.04) for HHP. Heritability presented a similar pattern as the genetic variance estimation, changing from 0.32 to 0.36 (0.32 to 0.36) for BWT and 0.16 to 0.15 (0.21 to 0.18) for HHP. On the whole, genetic parameters tended slightly to increase over time. The expected variance estimates were lower than the estimates when using overlapping windows. That indicates the low effect of the drift-selection process on the genetic variance, or likely, the presence of genetic variation sources compensating for the loss. Double trait covariance analysis confirmed the maintenance of variances over time, presenting genetic correlations >0.86 for BWT and >0.82 for HHP. Monitoring genetic variance in broiler breeding programmes is important to sustain genetic progress. Although the genetic variances of both traits fluctuated over time, in some windows, particularly between 2003 and 2020, increasing trends were observed, which warrants further research on the impact of other factors, such as novel mutations, operating on the dynamics of genetic variance.

Directional selection coupled with kin selection favors the establishment of senescence.

Conventional wisdom in evolutionary theory considers aging as a non-selected byproduct of natural selection. Based on this, conviction aging was regarded as an inevitable phenomenon. It was also thought that in the wild organisms tend to die from diseases, predation and other accidents before they could reach the time when senescence takes its course. Evidence has accumulated, however, that aging is not inevitable and there are organisms that show negative aging even. Furthermore, old age does play a role in the deaths of many different organisms in the wild also. The hypothesis of programmed aging posits that a limited lifespan can evolve as an adaptation (i.e., positively selected for) in its own right, partly because it can enhance evolvability by eliminating "outdated" genotypes. A major shortcoming of this idea is that non-aging sexual individuals that fail to pay the demographic cost of aging would be able to steal good genes by recombination from aging ones. Here, we show by a spatially explicit, individual-based simulation model that aging can positively be selected for if a sufficient degree of kin selection complements directional selection. Under such conditions, senescence enhances evolvability because the rate of aging and the rate of recombination play complementary roles. The selected aging rate is highest at zero recombination (clonal reproduction). In our model, increasing extrinsic mortality favors evolved aging by making up free space, thereby decreasing competition and increasing drift, even when selection is stabilizing and the level of aging is set by mutation-selection balance. Importantly, higher extrinsic mortality is not a substitute for evolved aging under directional selection either. Reduction of relatedness decreases the evolved level of aging; chance relatedness favors non-aging genotypes. The applicability of our results depends on empirical values of directional and kin selection in the wild. We found that aging can positively be selected for in a spatially explicit population model when sufficiently strong directional and kin selection prevail, even if reproduction is sexual. The view that there is a conceptual link between giving up clonal reproduction and evolving an aging genotype is supported by computational results.

Climate change does not equally affect temporal patterns of natural selection on reproductive timing across populations in two songbird species.

Climate change has led to changes in the strength of directional selection on seasonal timing. Understanding the causes and consequences of these changes is crucial to predict the impact of climate change. But are observed patterns in one population generalizable to others, and can spatial variation in selection be explained by environmental variation among populations? We used long-term data (1955-2022) on blue and great tits co-occurring in four locations across the Netherlands to assess inter-population variation in temporal patterns of selection on laying date. To analyse selection, we combine reproduction and adult survival into a joined fitness measure. We found distinct spatial variation in temporal patterns of selection which overall acted towards earlier laying, and which was due to selection through reproduction rather than through survival. The underlying relationships between temperature, bird and caterpillar phenology were however the same across populations, and the spatial variation in selection patterns is thus caused by spatial variation in the temperatures and other habitat characteristics to which birds and caterpillars respond. This underlines that climate change is not necessarily equally affecting populations, but that we can understand this spatial variation, which enables us to predict climate change effects on selection for other populations.

A common garden experiment supports a genetic component underlying the increased resilience of common cockle (Cerastoderma edule) to the parasite Marteilia cochillia.

The common cockle is a valuable bivalve species inhabiting the Atlantic European coasts. The parasite Marteilia cochillia has devastated cockle beds in the southern Galician (NW Spain) rias since 2012. Previous data suggested that cockles from Ría de Arousa acquired some resilience to this parasite through natural selection after consecutive annual marteiliosis outbreaks and candidate markers associated with marteiliosis resilience were identified using population genomics and transcriptomics approaches. Here, a common garden experiment was performed using a naïve stock (from Ría de Muros-Noia) and an affected stock (from Ría de Arousa) to test this hypothesis. Breeders from both stocks were used to produce seed cohorts at hatchery, which were pre-grown in a raft (outdoor nursery stage) and deployed in two shellfish beds affected by marteiliosis in Ría de Arousa (growing-out stage). In both beds, the naïve stock showed high marteiliosis prevalence and was fully depleted in a short period, while the affected stock barely showed evidence of marteiliosis. A set of 45 SNPs putatively associated with marteiliosis resilience were fitted for MassARRAY genotyping to check their role in the differential resilience detected between both stocks. Though no significant differentiation was found between the naïve and the affected stocks with neutral markers, 28 SNPs showed significant divergence between them, suggesting that these SNPs were involved in directional selection during eight generations (to the most) of marteiliosis pressure (long-term selection). Furthermore, signals of selection were also detected in the naïve stock along the marteiliosis outbreak in the growing-out stage (short-term selection) and six SNPs, all shared with the long-term evaluation, showed consistent signals of differentiation according to the infection severity. Some of these SNPs were located within immune genes pertaining to families such as proteasome, ubiquitin, tumor necrosis factor, and glutathione S-transferase. These resilience-associated markers will be useful to recover cockle production in Galicia.

Phenotypic Diversity in Domesticated and Wild Timothy Grass, and Closely Related Species for Forage Breeding.

Timothy grass (Phleum pratense L.) is one of the most important forage crops in temperate regions. Forage production, however, faces many challenges, and new cultivars adapted to a changing climate are needed. Wild populations and relatives of timothy may serve as valuable genetic resources in the breeding of improved cultivars. The aim of our study is to provide knowledge about the phenotypic diversity in domesticated (cultivars, breeding lines and landraces) and wild timothy and two closely related species, P. nodosum (lowland species) and P. alpinum, (high altitude species) to identify potential genetic resources. A total of 244 accessions of timothy and the two related species were studied for growth (plant height, fresh and dry weight) and plant development (days to stem elongation, days to booting and days to heading) in the field and in a greenhouse. We found a large diversity in development and growth between the three Phleum species, as well as between the accessions within each species. Timothy showed the highest growth, but no significant difference was found between wild accessions and cultivars of timothy in fresh and dry weight. However, these two groups of accessions showed significant differences in plant development, where timothy cultivars as a group reached flowering earlier than the wild accessions. This suggests that there has not been a strong directional selection towards increased yield during the domestication and breeding of timothy; rather, timothy has been changed for other traits such as earlier heading. Principal component analysis and cluster analysis based on all traits revealed distinct clusters. Accessions falling within the same cluster showed similarities in the development and growth rather than the type of accession. The large diversity found in this study shows the potential of using timothy accessions as genetic resources in crosses with existing cultivars. Also, accessions of P. nodosum with favorable traits can be candidates for the domestication of a novel forage crop, and the high-altitude relative P. alpinum may be a source of genes for the development of more cold and stresstolerant cultivars.

Major histocompatibility complex complement (MHC) Bf alleles show trans species evolution between man and chimpanzee

HLA and disease studies by using single allele statistics have been fruitless during the last 40 years for explaining association pathogenesis of the associated diseases.Other approaches are necessary to untangle this puzzle. We aim to revisit complement alleleism in humans and primates for both studying MHC and disease association to complotypes and extended MHC haplotypes in order to also explain the positive directional selection of maintaining immune response genes (complement, MHC adaptive and MHC non-specific genes) that keeps these three type of genes together in a short chromosome stretch (MHC) for million years. These genes may be linked to conjointly avoid microbes attack and autoimmunity. In the present paper, it is obtained a new Bf chimpanzee allele, provisionaly named Patr-Bf*A:01,that differs from other Bf alleles by having CTG at eleventh codon of exon 2 in order to start the newly suggested methodology and explain functional and evolutionary MHC obscure aspects. Exons 1 to 6 of Ba fragment of Bf gene were obtained from chimpanzee. This new chimpanzee Factor B allele (Patr-Bf*A:01) is to be identical to a infrequent human Bf allele (SNP rs641153); it stresses the strong evolutive pressure upon certain alleles that are trans specific. It also may apply to MHC extended haplotipes which may conjointly act to start an adequate immune response. It is the first time that a complement MHC class III allele is described to undergo trans species evolution,in contrast to class I and class II alleles which had already been reported . Allelism of complement factors are again proposed for studying MHC complement genes, complotypes, and extended MHC haplotypes which may be more informative that single MHC marker studies.

Modeling heterothermic fitness landscapes in a marsupial hibernator using changes in body composition.

Hibernation is an adaptive strategy that allows animals to enter a hypometabolic state, conserving energy and enhancing their fitness by surviving harsh environmental conditions. However, addressing the adaptive value of hibernation, at the individual level and in natural populations, has been challenging. Here, we applied a non-invasive technique, body composition analysis by quantitative magnetic resonance (qMR), to calculate energy savings by hibernation in a population of hibernating marsupials (Dromiciops gliroides). Using outdoor enclosures installed in a temperate rainforest, and measuring qMR periodically, we determined the amount of fat and lean mass consumed during a whole hibernation cycle. With this information, we estimated the daily energy expenditure of hibernation (DEEH) at the individual level and related to previous fat accumulation. Using model selection approaches and phenotypic selection analysis, we calculated linear (directional, β), quadratic (stabilizing or disruptive, γ) and correlational (ρ) coefficients for DEEH and fat accumulation. We found significant, negative directional selection for DEEH (βDEEH = - 0.58 ± 0.09), a positive value for fat accumulation (βFAT = 0.34 ± 0.07), and positive correlational selection between both traits (ρDEEH × FAT = 0.24 ± 0.07). Then, individuals maximizing previous fat accumulation and minimizing DEEH were promoted by selection, which is visualized by a bi-variate selection surface estimated by generalized additive models. At the comparative level, results fall within the isometric allometry known for hibernation metabolic rate in mammals. Thus, by a combination of a non-invasive technique for body composition analysis and semi-natural enclosures, we were characterized the heterothermic fitness landscape in a semi-natural population of hibernators.