Fitness In Different Environments Research Articles

Hosts, microbiomes, and the evolution of critical windows.

The absence of microbial exposure early in life leaves individuals vulnerable to immune overreaction later in life, manifesting as immunopathology, autoimmunity, or allergies. A key factor is thought to be a "critical window" during which the host's immune system can "learn" tolerance, and beyond which learning is no longer possible. Animal models indicate that many mechanisms have evolved to enable critical windows, and that their time limits are distinct and consistent. Such a variety of mechanisms, and precision in their manifestation suggest the outcome of strong evolutionary selection. To strengthen our understanding of critical windows, we explore their underlying evolutionary ecology using models encompassing demographic and epidemiological transitions, identifying the length of the critical window that would maximize fitness in different environments. We characterize how direct effects of microbes on host mortality, but also indirect effects via microbial ecology, will drive the optimal length of the critical window. We find that indirect effects such as magnitude of transmission, duration of infection, rates of reinfection, vertical transmission, host demography, and seasonality in transmission all have the effect of redistributing the timing and/or likelihood of encounters with microbial taxa across age, and thus increasing or decreasing the optimal length of the critical window. Declining microbial population abundance and diversity are predicted to result in increases in immune dysfunction later in life. We also make predictions for the length of the critical window across different taxa and environments. Overall, our modeling efforts demonstrate how critical windows will be impacted over evolution as a function of both host-microbiome/pathogen interactions and dispersal, raising central questions about potential mismatches between these evolved systems and the current loss of microbial diversity and/or increases in infectious disease.

Plant sex affects plant-microbiome assemblies of dioecious Populus cathayana trees under different soil nitrogen conditions

BackgroundDioecious plants have coevolved with diverse plant microbiomes, which are crucial for the fitness and productivity of their host. Sexual dimorphism in morphology, physiology, or gene expression may relate to different microbial compositions that affect male and female fitness in different environments. However, sex-specific impacts on ecological processes that control the microbiome assembly are not well known. In this study, Populus cathayana males and females were planted in different nitrogen conditions. It was hypothesized that males and females differently affect bacterial and fungal communities in the rhizosphere soil, roots, old leaves, and young leaves. Physiological traits and transcriptome profiles of male and female plants were investigated to reveal potential mechanisms that control the microbiome assembly.ResultsOur results showed strong niche differentiation that shapes microbial communities leading to a rapid loss of diversity along a decreasing pH gradient from the rhizosphere soil to leaves. Sex had different impacts on the microbial assembly in each niche. Especially fungal endophytes showed great differences in the community structure, keystone species, and community complexity between P. cathayana males and females. For example, the fungal co-occurrence network was more complex and the alpha diversity was significantly higher in young female leaves compared to young male leaves. Transcriptome profiles revealed substantial differences in plant-pathogen interactions and physiological traits that clearly demonstrated divergent internal environments for endophytes inhabiting males and females. Starch and pH of young leaves significantly affected the abundance of Proteobacteria, while tannin and pH of roots showed significant effects on the abundance of Chloroflexi, Actinobacteria, and Proteobacteria, and on the bacterial Shannon diversity.ConclusionOur results provided important knowledge for understanding sexual dimorphism that affects microbial assemblies, thus advancing our understanding of plant-microbiome interactions.6fJBNPXyfja-eHSN4N3z_QVideo

Flagellation of Shewanella oneidensis Impacts Bacterial Fitness in Different Environments.

Flagella occur on many prokaryotes, which primarily propel cells to move from detrimental to favorable environments. A variety of species-specific flagellation patterns have been identified. Although it is presumed that for each of these flagellated microorganisms, an evolutionarily fixed flagellation pattern is favored under the normal living conditions, direct evidence is lacking. Here, we use Shewanella oneidensis, a rod-shaped Gram-negative bacterium with a monotrichous polar flagellum (MR-1, the wild-type), as a research model. The investigation has been enabled by multiple mutants with diverse flagellation patterns that had been generated by removing FlhF and FlhG proteins that control flagellar location and number, respectively. Growth assays, as a measure of fitness, revealed that the wild-type strain predominated in spreading on swim plates and in pellicles which form at the air-liquid interface. However, under the pellicles where oxygen is limited, both aflagellated and monotrichous lateral strains showed similar increase in fitness, whereas strains with multiple flagella were less competitive. Moreover, under shaking culturing conditions, the aflagellated strain outcompeted all other strains, including the wild-type, suggesting that cells devoid of flagella would be more likely enriched upon agitation. Overall, these data support the presumption that the monotrichous polar flagellum, as evolutionarily fixed in the wild-type strain, is optimal for the growth fitness of S. oneidensis over any other mutants under most test conditions. However, upon specific changes of environmental conditions, another form could come to predominate. These findings provide insight into the impacts of flagellation patterns and function on bacterial adaptation to differing environments.

Plasticity of Mitochondrial DNA Inheritance and its Impact on Nuclear Gene Transcription in Yeast Hybrids.

Mitochondrial DNA (mtDNA) in yeast is biparentally inherited, but colonies rapidly lose one type of parental mtDNA, thus becoming homoplasmic. Therefore, hybrids between the yeast species possess two homologous nuclear genomes, but only one type of mitochondrial DNA. We hypothesise that the choice of mtDNA retention is influenced by its contribution to hybrid fitness in different environments, and the allelic expression of the two nuclear sub-genomes is affected by the presence of different mtDNAs in hybrids. Saccharomyces cerevisiae/S. uvarum hybrids preferentially retained S. uvarum mtDNA when formed on rich media at colder temperatures, while S. cerevisiae mtDNA was primarily retained on non-fermentable carbon source, at any temperature. Transcriptome data for hybrids harbouring different mtDNA showed a strong environmentally dependent allele preference, which was more important in respiratory conditions. Co-expression analysis for specific biological functions revealed a clear pattern of concerted allelic transcription within the same allele type, which supports the notion that the hybrid cell works preferentially with one set of parental alleles (or the other) for different cellular functions. Given that the type of mtDNA retained in hybrids affects both nuclear expression and fitness, it might play a role in driving hybrid genome evolution in terms of gene retention and loss.

Local versus Generalized Phenotypes in Two Sympatric Aurelia Species: Understanding Jellyfish Ecology Using Genetics and Morphometrics.

For individuals living in environmentally heterogeneous environments, a key component for adaptation and persistence is the extent of phenotypic differentiation in response to local environmental conditions. In order to determine the extent of environmentally induced morphological variation in a natural population distributed along environmental gradients, it is necessary to account for potential genetic differences contributing to morphological differentiation. In this study, we set out to quantify geographic morphological variation in the moon jellyfish Aurelia exposed at the extremes of a latitudinal environmental gradient in the Gulf of Mexico (GoM). We used morphological data based on 28 characters, and genetic data taken from mitochondrial cytochrome oxidase I (COI) and nuclear internal transcribed spacer 1 (ITS-1). Molecular analyses revealed the presence of two genetically distinct species of Aurelia co-occurring in the GoM: Aurelia sp. 9 and Aurelia c.f. sp. 2, named for its divergence from (for COI) and similarity to (for ITS-1) Aurelia sp. 2 (Brazil). Neither species exhibited significant population genetic structure between the Northern and the Southeastern Gulf of Mexico; however, they differed greatly in the degree of geographic morphological variation. The morphology of Aurelia sp. 9 exhibited ecophenotypic plasticity and varied significantly between locations, while morphology of Aurelia c.f. sp. 2 was geographically invariant (i.e., canalized). The plastic, generalist medusae of Aurelia sp. 9 are likely able to produce environmentally-induced, “optimal” phenotypes that confer high relative fitness in different environments. In contrast, the non-plastic generalist individuals of Aurelia c.f. sp. 2 likely produce environmentally-independent phenotypes that provide the highest fitness across environments. These findings suggest the two Aurelia lineages co-occurring in the GoM were likely exposed to different past environmental conditions (i.e., different selective pressures) and evolved different strategies to cope with environmental variation. This study highlights the importance of using genetics and morphometric data to understand jellyfish ecology, evolution and systematics.

Effects of Hybrid and Non-hybrid Epichloë Endophytes and Their Associated Host Genotypes on the Response of a Native Grass to Varying Environments.

Asexual Epichloë endophytes are prevalent in cool season grasses, and many are of hybrid origin. Hybridization of asexual endophytes is thought to provide a rapid influx of genetic variation that may be adaptive to endophyte-host grass symbiota in stressful environments. For Arizona fescue (Festuca arizonica), hybrid symbiota are commonly found in resource-poor environments, whereas non-hybrid symbiota are more common in resource-rich environments. There have been very few experimental tests where infection, hybrid and non-hybrid status, and plant genotype have been controlled to tease apart their effects on host phenotype and fitness in different environments. We conducted a greenhouse experiment where hybrid (H) and non-hybrid (NH) endophytes were inoculated into plant genotypes that were originally uninfected (E-) or once infected with either the H or NH endophytes. Nine endophyte and plant genotypic group combinations were grown under low and high water and nutrient treatments. Inoculation with the resident H endophyte enhanced growth and altered allocation to roots and shoots, but these effects were greatest in resource-rich environments, contrary to expectations. We found no evidence of co-adaptation between endophyte species and their associated host genotypes. However, naturally E- plants performed better when inoculated with the hybrid endophyte, suggesting these plants were derived from H infected lineages. Our results show complex interactions between endophyte species of hybrid and non-hybrid origin with their host plant genotypes and environmental factors.

Metastable coexistence of multiple genotypes in a constant environment with a single resource through fixed settings of a multiplication-survival trade-off

The biological complexity of trade-offs has been a major obstacle in understanding bacterial diversity and coexistence. Here we reduce the biological complexity by using isogenic Escherichia coli strains differing only in a multiplication-survival trade-off regulated by RpoS. The contribution of trade-off characteristics to fitness in different environments was determined. We then designed an environment with intermediate-stress levels that elicits an equivalent fitness. We found metastable coexistence of three strains in steady-state chemostats until mutations changed the relative fitness of competing strains. Our results help explain the rich intra- and inter-species diversity of bacteria through alternative settings of relatively few trade-offs.

Identification of outliers in a genomic scan for selection along environmental gradients in the bamboo locust, Ceracris kiangsu.

Identification of loci under divergent selection is a key step in understanding the evolutionary process because those loci are responsible for the genetic variations that affect fitness in different environments. Understanding how environmental forces give rise to adaptive genetic variation is a challenge in pest control. Here, we performed an amplified fragment length polymorphism (AFLP) genome scan in populations of the bamboo locust, Ceracris kiangsu, to search for candidate loci that are influenced by selection along an environmental gradient in southern China. In outlier locus detection, loci that demonstrate significantly higher or lower among-population genetic differentiation than expected under neutrality are identified as outliers. We used several outlier detection methods to study the features of C. kiangsu, including method DFDIST, BayeScan, and logistic regression. A total of 97 outlier loci were detected in the C. kiangsu genome with very high statistical supports. Moreover, the results suggested that divergent selection arising from environmental variation has been driven by differences in temperature, precipitation, humidity and sunshine. These findings illustrate that divergent selection and potential local adaptation are prevalent in locusts despite seemingly high levels of gene flow. Thus, we propose that native environments in each population may induce divergent natural selection.

CsrR, a Paralog and Direct Target of CsrA, Promotes Legionella pneumophila Resilience in Water.

ABSTRACTCritical to microbial versatility is the capacity to express the cohort of genes that increase fitness in different environments. Legionella pneumophila occupies extensive ecological space that includes diverse protists, pond water, engineered water systems, and mammalian lung macrophages. One mechanism that equips this opportunistic pathogen to adapt to fluctuating conditions is a switch between replicative and transmissive cell types that is controlled by the broadly conserved regulatory protein CsrA. A striking feature of the legionellae surveyed is that each of 14 strains encodes 4 to 7 csrA-like genes, candidate regulators of distinct fitness traits. Here we focus on the one csrA paralog (lpg1593) that, like the canonical csrA, is conserved in all 14 strains surveyed. Phenotypic analysis revealed that long-term survival in tap water is promoted by the lpg1593 locus, which we name csrR (for “CsrA-similar protein for resilience”). As predicted by its GGA motif, csrR mRNA was bound directly by the canonical CsrA protein, as judged by electromobility shift and RNA-footprinting assays. Furthermore, CsrA repressed translation of csrR mRNA in vivo, as determined by analysis of csrR-gfp reporters, csrR mRNA stability in the presence and absence of csrA expression, and mutation of the CsrA binding site identified on the csrR mRNA. Thus, CsrA not only governs the transition from replication to transmission but also represses translation of its paralog csrR when nutrients are available. We propose that, during prolonged starvation, relief of CsrA repression permits CsrR protein to coordinate L. pneumophila’s switch to a cell type that is resilient in water supplies.

Competence and natural transformation in vibrios

Natural transformation is a major mechanism of horizontal gene transfer in bacteria. By incorporating exogenous DNA elements into chromosomes, bacteria are able to acquire new traits that can enhance their fitness in different environments. Within the past decade, numerous studies have revealed that natural transformation is prevalent among members of the Vibrionaceae, including the pathogen Vibrio cholerae. Four environmental factors: (i) nutrient limitation, (ii) availability of extracellular nucleosides, (iii) high cell density and (iv) the presence of chitin, promote genetic competence and natural transformation in Vibrio cholerae by co-ordinating expression of the regulators CRP, CytR, HapR and TfoX respectively. Studies of other Vibrionaceae members highlight the general importance of natural transformation within this bacterial family.

Multiple approaches to detect outliers in a genome scan for selection in ocellated lizards (Lacerta lepida) along an environmental gradient

Identification of loci with adaptive importance is a key step to understand the speciation process in natural populations, because those loci are responsible for phenotypic variation that affects fitness in different environments. We conducted an AFLP genome scan in populations of ocellated lizards (Lacerta lepida) to search for candidate loci influenced by selection along an environmental gradient in the Iberian Peninsula. This gradient is strongly influenced by climatic variables, and two subspecies can be recognized at the opposite extremes: L.lepida iberica in the northwest and L.lepida nevadensis in the southeast. Both subspecies show substantial morphological differences that may be involved in their local adaptation to the climatic extremes. To investigate how the use of a particular outlier detection method can influence the results, a frequentist method, DFDIST, and a Bayesian method, BayeScan, were used to search for outliers influenced by selection. Additionally, the spatial analysis method was used to test for associations of AFLP marker band frequencies with 54 climatic variables by logistic regression. Results obtained with each method highlight differences in their sensitivity. DFDIST and BayeScan detected a similar proportion of outliers (3-4%), but only a few loci were simultaneously detected by both methods. Several loci detected as outliers were also associated with temperature, insolation or precipitation according to spatial analysis method. These results are in accordance with reported data in the literature about morphological and life-history variation of L.lepida subspecies along the environmental gradient.

Animal personality

What is personality? Human personality is something with which we are all intimately familiar, in that we ‘know it when we see it’. In fact, there is good evidence that personality perception is an innate ability we all share. Defining personality scientifically, however, is far from intuitive or straightforward. In fact, psychologists have worked on this problem for a long time and there is an extensive literature on how to define, classify, and measure human personality traits. Increasingly, the concept of ‘personality’ is being applied to nonhuman animals. Investigating animal personalities is not restricted to animals closely related to humans, such as chimpanzees and other primates; other animals in which the presence of animal personalities have been claimed include dogs, birds, amphibians, fish, and even invertebrates such as ants, squid, spiders and crustaceans. But doesn't ‘personality’, by definition, refer to a ‘person’? Like many terms used in studies of animal behaviour, ‘personality’ is a sort of shorthand which has a meaning that is more specific than its everyday usage. The everyday concept of personality and the idea as applied to animal behaviour do, however, share a fundamental feature: this is that individuals consistently differ from one another in behaviour in such a way that these behaviours can be described as individual traits. This basic definition covers a range of phenomena. Individuals might differ in single behaviours or in correlated groups of behaviours that cluster into ‘behavioural syndromes’. These differences should be consistent across time, contexts or situations, and measures. A ‘context’ is the functional category in which behaviours occur, for example feeding, aggression, and courtship. A ‘situation’ is the environmental or social condition at a particular time, for example the high and low predation risk experienced with movement through a habitat. And a ‘measure’ is a way of measuring personality, for example by behavioural tests, ratings by knowledgeable judges, or observations of naturally occurring behaviour. Measures also refer to different manifestations of behavioural traits assessed by the same approach, such as multiple questionnaire items related to the trait, multiple judges rating the trait, or a series of behavioural tests. Thus, the term does not necessarily suggest that personality in cats, spiders or crabs are homologues of human personality. It is merely less of a mouthful than our broad definition and yet it highlights the possibility that what we call personality in a wide range of species, including humans, may have similar underlying causes. Why do animals have personalities? This is the ‘big question’ that animal personality researchers are starting to turn to. Until recently it was thought that there was no particular reason for animals (including humans) to have personalities. Rather, individual differences in behaviour were assumed to be random variation around an optimal mean response. It is now recognised that consistent individual differences in behaviour could be adaptive. This recognition of personality's potential evolutionary importance has been prompted in part by theoretical work. Models suggest that the benefits of a given personality type might be ‘frequency dependent’, so the benefit of having a particular personality changes with the number of others that show the same personality. Such frequency-dependent selection could maintain variation in the population if personality is heritable, and there is increasing evidence for a strong genetic contribution to personality. For example, variation in great tits' (Parus major) exploratory behaviour is heritable. Also, personality ‘structure’ or the covariation among traits might result from genetic correlations. For example, a human twin study showed that factor analysis of the genetic correlations among traits revealed the same five dimensions — Neuroticism, Extraversion, Openness to Experience, Agreeableness and Conscientiousness — as did factor analysis of the phenotypic correlations. Thus, while it may be optimal for an individual to show infinite plasticity and a full range of possible responses from situation to situation, this may be constrained by genetic correlations. Fitness consequences have now been directly studied in a range of species and a meta-analysis found that the personality trait ‘boldness’ correlates positively with reproductive success in many species. This result was not ubiquitous, however, and while it seems clear that there is a heritable genetic basis for personality, its functions and evolution remain obscure. A possible answer to the question “Why have a personality?”, however, is that personality may arise from ‘compromises’ between different factors that influence Darwinian fitness. So, there may be evolutionary reasons for personality's stability: does this mean it never changes? Not necessarily. Like many aspects of phenotype, personality is subject to developmental plasticity, leading to age- or size-specific boldness and the possibility of similar genotypes giving rise to different behavioural phenotypes. Therefore, a further area of interest for animal personality researchers is one that mirrors the longstanding ‘nature verses nurture debate’ in studies of human personality. Furthermore, behavioural consistency does not preclude the possibility of ‘behavioural plasticity’ — the variation in behaviour that an individual might show between different situations. An individual may show greater amounts of avoidance behaviour in a high risk situation than in a low risk situation, but still be a consistently high responder relative to others in the sample. Indeed, in addition to consistent variation in mean responses, individuals may show different ‘behavioural reaction norms’; that is, individuals may differ in their amount of behavioural plasticity. How do we know that a species has personality? A key element in determining whether animal personalities are present is the degree of consistency or generalizability across time, contexts, situations or measures. We can measure consistency across time, contexts and situations by indices of repeatability and re-test reliability. We can measure the generalizability across measures by indices of internal consistency (how tightly do different measures of a trait ‘hang together’) and inter-observer/inter-rater reliability (to what extent do observers observe and record the same behaviours/do judges give similar ratings on a trait?). Moreover, given the assumed evolutionary significance, it is also desirable to demonstrate that personality traits show ‘external validity’, that is, that they predict real world outcomes such as how other individuals react to an individual, through to differences in survival and reproductive success. So, now that we know what personality is and whether it is present, how do we investigate its causes and consequences? These questions have been tackled from varied perspectives. Behavioural ecologists might study how individual differences in the exploratory behaviour of birds impact their fitness in different environments. Comparative psychologists have investigated how the clustering of ratings — for example, quitting, erratic or reckless — differ among nonhuman primates. Evolutionary biologists have tried to understand why aggression can be displayed in multiple contexts, even though it would seemingly be more adaptive for the animal to adjust its behaviour according to context. Behavioural geneticists have assessed the proportion of variance underlying a trait which can be explained by additive genetic, maternal, and permanent environment effects and whether there are any gene x environment interactions. Can different species really be studied in the same way? While the concepts might be similar, behavioural measures can certainly vary between species, often out of necessity. When studying free-ranging animals that are difficult to observe over long periods, researchers may use behavioural tests that rapidly score a small number of traits or a single trait. On the other hand, if the same individuals are likely to be encountered multiple times, it may be possible to measure several traits by behavioural tests, long-term behavioural observations, ratings or a combination of all three. For example, boldness in American red squirrels was assessed by the quick measure of trapability, whereas personality in a population of free-ranging Hanuman langurs was assessed more broadly, by a combination of behavioural observations and ratings. Which traits are studied might be influenced by the ease with which they can be measured in the study species. As in humans, one can obtain reliable ratings of chimpanzees and other nonhuman primates on traits such as ‘inventive,’ which is not surprising given the behavioural and genetic similarities between humans and nonhuman primates. On the other hand, trying to assess the ‘inventiveness’ of hermit crabs does not make as much sense. However, hermit crabs hide inside their shells when threatened before re-emerging; the duration of these startle responses can be readily measured and easily studied across situations of high and low predation risk. In fact, measuring predator avoidance responses or response to novel stimuli (boldness) across different levels of risk is an approach that has been used to study personality in diverse groups of animals. And how are data collected and analysed? Depending on how personality was measured, data can consist of the frequency of specific activities that occur during an observation period, the ratings made during or shortly after an observation period, or the ratings formed after long periods of informal observation. Although these data seem different, where multiple approaches have been used, there is often strong congruence among them. Statistical approaches can be straightforward. At the simplest level one can test for a correlation between the responses of individuals in a sample of animals, where the same behaviour is measured in each individual on two or more occasions. To test for behavioural syndromes, one needs to look for correlations between behavioural responses in different contexts. In cases where many traits, situations or contexts are examined, more complex approaches such as exploratory or confirmatory factor analysis, which model correlations among variables as arising from one or more common latent variables, may be used. This seems straightforward but what's that noise I can hear? The range of perspectives from which personality is studied, not to mention the range of species studied, can complicate the interpretation of data and synthesis between studies. A crucial issue is the terminology used to describe traits. For example, what is referred to as ‘boldness’ in one study may also be called ‘emotional stability’, ‘risk taking’ or ‘fast’ by others. And one cannot assume that labels applied to measures of personality traits are more than hypothetical constructs. To do otherwise could lead to an ‘ethological fallacy’. This is a variant of the well-known ‘jingle and jangle’ fallacies identified in human personality research where one assumes that two traits are similar because they have similar labels or assumes that two traits are different because they have dissimilar labels. To avoid this and truly determine whether traits in various species are similar or dissimilar requires showing that they do or do not, respectively, predict the same outcomes or have the same causes. Shouldn't we be worried about anthropomorphism? Anthropomorphism might pose a problem, especially when working with very human-like species and naive raters/observers. The possibility that anthropomorphism influences studies of animal personality has not been addressed in detail but, if anything, current data suggest that it does not. For example, the personality dimensions of Hanuman langurs obtained by detailed behavioural observations and ratings are highly similar. In another example, humans do not project their personalities onto their dogs (in fact they project their dog's personality onto themselves). What we should always appreciate, however, is that while it may be valid to assume that the personality dimensions found in one species might also be present in closely related species, such as humans and chimpanzees, when two species are more distantly related, this assumption is less tenable. “To boldly go……” While personality is being demonstrated in an ever increasing array of taxa, we still are not clear why consistent individual differences are present. One direction for theory development and testing is to incorporate the social context of personalities. A recent model has invoked the ideas of ‘trust’ and ‘social awareness’, and recent analysis of long-term data revealed consistent between-individual differences in the cooperative behaviour of meerkats. More effort will undoubtedly be focused on understanding the proximate mechanisms of personality. This might include analysis of the hormonal underpinnings of social structure (for example, dominance hierarchies) and between-individual differences and a better understanding of the developmental links between phenotypic plasticity, pleiotropy, and the constraints on behavioural plasticity. Finally, it will also be essential to develop and validate measures of personality for later within- and cross-species studies.

Fitness-Associated Sexual Reproduction in a Filamentous Fungus

Sex is a long-standing evolutionary enigma. Although the majority of eukaryotes reproduce sexually at least sometimes [1-3], the evolution of sex from an asexual ancestor has been difficult to explain because it requires sexually reproducing lineages to overcome the manifold costs of sex, including the destruction of favorable gene combinations created by selection [4, 5]. Conditions for the evolution of sex are much broader if individuals can reproduce either sexually or asexually (i.e., facultative sex) and allocate disproportionately more resources to sex when their fitness is low (fitness-associated-sex or FAS [6-10]). Although facultatively sexual organisms have been shown to engage in more sex when stressed [11], direct evidence for FAS is lacking. We provide evidence using 53 genotypes of the filamentous fungus Aspergillus nidulans in a reciprocal transplant experiment across three environments. Different genotypes achieved highest fitness in different environments and genotypes invested relatively more in sex in environments in which their fitness was lower, showing that allocation to sexual reproduction is a function of how well-adapted a genotype is to its environment. FAS in A. nidulans is unlikely to have evolved as a strategy to resist or avoid stress because asexual spores are more dispersive and equally resistant [12, 13].

Quantitative Trait Locus Mapping of Genes Under Selection Across Multiple Years and Sites inAvena barbata: Epistasis, Pleiotropy, and Genotype-by-Environment Interactions

The genetic architecture of variation in evolutionary fitness determines the trajectory of adaptive change. We identified quantitative trait loci (QTL) affecting fitness in a mapping population of recombinant inbred lines (RILs) derived from a cross between moist- and dry- associated ecotypes of Avena barbata. We estimated fitness in 179 RILs in each of two natural environments in each of 4 years. Two loci account for over half of the variation in geometric mean fitness across environments. These loci are associated in repulsion phase in the wild ecotypes, suggesting the potential for strong transgressive segregation, but also show significant epistasis giving hybrid breakdown. This epistasis is the result of sharply lower fitness in only one of the recombinant genotypes, suggesting that the loci may contain synergistically acting mutations. Within each trial (year/site combination), we can explain less of the variation than for geometric mean fitness, but the two major loci are associated with variation in fitness in most environments. Tests for pleiotropic effects of QTL on fitness in different environments reveal that the same loci are under selection in all trials. Genotype-by-environment interactions are significant for some loci, but this reflects variation in the strength, not the direction of selection.

Socially Mediated Trade‐Offs between Aggression and Parental Effort in Competing Color Morphs

Individuals often face trade-offs between investment in parental care and alternative investments of time, energy, and resources into other life-history components, such as dominance, attractiveness, and health. Selection is thought to promote the optimal balance between the costs and the benefits of these conflicting activities by favoring individuals that adopt different tactics to maximize their overall evolutionary fitness in different environments. To test this, we experimentally manipulate both aggression (i.e., competitive environment) and parental effort (i.e., brood size) in red and black morphs of the Gouldian finch (Erythrura gouldiae). Although aggressive red males provide parental effort comparable to that of black males in environments where competition is low, irrespective of their relative brood size, they severely reduce or abandon parental investment in highly competitive environments. In contrast, nonaggressive black males are largely unaffected by the competitive environment and instead adaptively adjust their provisioning effort to the relative demands of their brood. Consequently, in highly competitive environments, although dominant red males defend higher-quality nest sites, they produce fewer and lower-quality offspring (in terms of mass and immunocompetence) than black males do. These opposing effects of frequency-dependent competitive environments on red and black males underlie their differential trade-offs between the costs and the benefits of aggression and parental effort.

Relaxed Selection on the CBF/DREB1 Regulatory Genes and Reduced Freezing Tolerance in the Southern Range of Arabidopsis thaliana

Elucidating the molecular basis of adaptive phenotypic variation represents a central aim in evolutionary biology. Traits exhibiting patterns of clinal variation represent excellent models for studies of molecular adaptation, especially when variation in phenotype can be linked to organismal fitness in different environments. Natural accessions of the model plant species Arabidopsis thaliana exhibit clinal variation in freezing tolerance that follows a gradient of temperature variability across the species' native range (Zhen Y, Ungerer MC. 2008. Clinal variation in freezing tolerance among natural accessions of A. thaliana. New Phytol. 177:419-427). Here, we report that this pattern of variation is attributable, at least in part, to relaxed purifying selection on members of a small family of transcriptional activators (the CBF/DREB1s) in the species' southern range. These regulatory genes play a critical role in the ability of A. thaliana plants to undergo cold acclimation and thereby achieve maximum freezing tolerance. Relative to accessions from northern regions, accessions of A. thaliana from the southern part of their geographic range exhibit levels of nonsynonymous nucleotide polymorphism that are approximately 2.8-fold higher across this small gene subfamily. Relaxed selection on the CBF/DREB1s in southern accessions also has resulted in multiple mutations in regulatory regions resulting in abrogated expression of particular subfamily members in particular accessions. These coding-region and regulatory mutations compromise the ability of these genes to act as efficient transcriptional activators during the cold acclimation process, as determined by reductions in rates of induction and maximum levels of expression in the downstream genes they regulate. This study highlights the potential role of regulatory genes in underlying adaptive phenotypic variation in nature.

Hybridization, recombination, and the genetic basis of fitness variation across environments in Avena barbata

We created Recombinant Inbred Lines (RILs) derived from a cross between ecotypes of Avena barbata associated with moist (mesic) and dry (xeric) habitats in California. Traits which were correlated with fitness across RILs mapped to the same Quantitative Trait Loci (QTLs) as fitness. However, different QTL affected fitness in different environments so that fitness was weakly correlated across environments. Recombination released considerable heritable variation both in fitness, and in ecologically relevant traits. Many traits showed transgressive segregation caused by recombination of QTL associated in repulsion phase in the parents. In addition, some traits were uncorrelated, allowing novel combinations of those traits to be created. Recombination also created heritable variation in reaction norms for at least one trait (root allocation). Altogether these results suggest that recombination can combine the most selectively advantageous genes and traits of the parents to produce broadly adapted genotypes that are capable of outperforming the parents. Indeed, two of the RILs showed higher fitness than the parental ecotypes across a range of environmental treatments in the greenhouse, but their superiority was less pronounced in the field. Although late-generation recombinants exhibited hybrid breakdown, being less fit, on average, than the mid-parent, early generation hybrids appear to exhibit hybrid vigour through the expression of dominance effects in the heterozyotes. This vigour may offset the effects of hybrid breakdown in the early generations following a cross, enhancing the opportunity for recombination to create broadly adapted genotypes. We discuss the implications of these findings to the evolution of colonizing species.

Evolution of antifungal-drug resistance: mechanisms and pathogen fitness

Like other microorganisms, fungi exist in populations that are adaptable. Under the selection imposed by antifungal drugs, drug-sensitive fungal pathogens frequently evolve resistance. Although the molecular mechanisms of resistance are well-characterized, there are few measurements of the impact of these mechanisms on pathogen fitness in different environments. To predict resistance before a new drug is prescribed in the clinic, the full spectrum of potential resistance mutations and the interactions among combinations of divergent mechanisms can be determined in evolution experiments. In the search for new strategies to manage drug resistance, measuring the limits of adaptation might reveal methods for trapping fungal pathogens in evolutionary dead ends.

The Red Queen Beats the Jack-Of-All-Trades: The Limitations on the Evolution of Phenotypic Plasticity and Niche Breadth

The evolution of niche breadth or phenotypic plasticity is often assumed to be limited by negative genetic correlations among fitness in different environments, but these trade-offs are rarely observed. Many other constraints can reduce the mean niche breadth of species. This article discusses one of these limitations-that species with broader niche breadths can have a slower rate of evolutionary response. Species with narrower niche breadths have higher probabilities of fixing beneficial alleles, taking less time to do so; they have fewer deleterious alleles drifting to fixation (a lighter drift load) and a lower frequency of deleterious alleles at mutation-selection equilibrium (a lighter mutation load). These patterns are true even with no correlation at all between fitness in different environments; no trade-offs are assumed. Furthermore, niche breadth is likely to evolve to be more narrow, because of the association between location and alleles favored in local habitats for individuals with reduced migration, assortative mating, or habitat selection. The evolution of niche breadth and plasticity is not a simple function of the fitness in different environments; understanding niche breadth evolution requires consideration of the limitations of the evolutionary process per se.