Effects Of Directional Selection Research Articles

Origin, domestication and dog breeds

Aim. Out of 8 thousand species of mammals, dog is the first domesticated animal. Archaeologists studying the process of human evolution and producing excavations of ancient sites, found the bones of animals, which man ate and also bone remains of animals that lived near the sites. Wolf was the first domesticated animal of primitive tribes. This process began in the Mesolithic era 12–15 thousand years ago. Due to domestication of wolf population many indigenous, transitional and other breeds of dogs appeared. Methods. Using morphological, biochemical and genetic methods of research scientists were able to determine genome and karyotype of wild European wolf and domestic dog. Results. Domestication is a process of historical transformation of wild animals into domesticated ones. Nowadays taking into account genetics research, cytology and special experiments, researchers-cynologists came to the conclusion that only wolf is a direct ancestor of modern dogs. This is confirmed by the fact that wolf and dog have 78 chromosomes and after mating we get fertile litter. The domestication of dogs is a complicated process. While domestication of dogs to the new conditions occurred in captivity, genetic mechanisms well-known to us played an important role – mutation, recombination, hidden reserve of heredity, the direct effect of selection. Conclusions.It was proved by our research that the process of breeding in dogs which appeared as a result of domestication and microevolution of animals was accompanied by specialization and genetic differentiation of dog breeds. Кeywords: wolf, dog, domestication, karyotype, breed.

Directional selection in the evolution of elongated upper canines in clouded leopards and sabre-toothed cats.

Extremely developed or specialized traits such as the elongated upper canines of extinct sabre-toothed cats are often not analogous to those of any extant species, which limits our understanding of their evolutionary cause. However, an extant species may have undergone directional selection for a similar extreme phenotype. Among living felids, the clouded leopard, Neofelis nebulosa, has exceptionally long upper canines for its body size. We hypothesized that directional selection generated the elongated upper canines of clouded leopards in a manner similar to the process in extinct sabre-toothed cats. To test this, we developed an approach that compared the effect of directional selection among lineages in a phylogeny using a simulation of trait evolution and approximate Bayesian computation. This approach was applied to analyse the evolution of upper canine length in the Felidae phylogeny. Our analyses consistently showed directional selection favouring longer upper canines in the clouded leopard lineage and a lineage leading to the sabre-toothed cat with the longest upper canines, Smilodon. Most of our analyses detected an effect of directional selection for longer upper canines in the lineage leading to another sabre-toothed cat, Homotherium, although this selection may have occurred exclusively in the primitive species. In all the analyses, the clouded leopard and Smilodon lineages showed comparable directional selection. This implies that clouded leopards share a selection advantage with sabre-toothed cats in having elongated upper canines.

Additive genetic variation in the craniofacial skeleton of baboons (genus Papio) and its relationship to body and cranial size.

Determining the genetic architecture of quantitative traits and genetic correlations among them is important for understanding morphological evolution patterns. We address two questions regarding papionin evolution: (1) what effect do body and cranial size, age, and sex have on phenotypic (VP ) and additive genetic (VA ) variation in baboon crania, and (2) how might additive genetic correlations between craniofacial traits and body mass affect morphological evolution? We use a large captive pedigreed baboon sample to estimate quantitative genetic parameters for craniofacial dimensions (EIDs). Our models include nested combinations of the covariates listed above. We also simulate the correlated response of a given EID due to selection on body mass alone. Covariates account for 1.2-91% of craniofacial VP . EID VA decreases across models as more covariates are included. The median genetic correlation estimate between each EID and body mass is 0.33. Analysis of the multivariate response to selection reveals that observed patterns of craniofacial variation in extant baboons cannot be attributed solely to correlated response to selection on body mass, particularly in males. Because a relatively large proportion of EID VA is shared with body mass variation, different methods of correcting for allometry by statistically controlling for size can alter residual VP patterns. This may conflate direct selection effects on craniofacial variation with those resulting from a correlated response to body mass selection. This shared genetic variation may partially explain how selection for increased body mass in two different papionin lineages produced remarkably similar craniofacial phenotypes.

Genetic Variability and Path Analysis Studies in Hybrid Maize (<i>Zea mays</i> L.)

The present study was carried out to access correlation coefficient, path analysis and genetic variability among twenty one locally developed maize hybrids for ten characters. Positive and significant genotypic, phenotypic correlation coefficient were recorded for yield with anthesis silking interval (rg = 1.00**, rp = 0.96**), cob diameter (rg = 0.99** and rp = 0.95**) and ear height (rg = 0.98** and rp = 0.94**). But days to 50% tasseling had moderate but significant positive correlation at both phenotypic and genotypic level. High genotypic coefficient of variation (GCV) was obtained from thousand seed weight, days to 50% silking, cob diameter and anthesis silking interval. The highest phenotypic coefficient of variation (PCV) was observed in thousand seed weight followed by days to 50% silking and cob diameter. The highest heritability (Hb) was observed for cob diameter (95.25) followed by days to 50% silking (94.15), days to maturity (93.85) and ear height (93.06). The characters with high GCV and higher values of heritability indicated high potential for selection. Anthesis silking interval (0.79) had the highest positive direct effect on yield followed by cob diameter (0.31), cob length (0.31) and plant height (0.04) indicating the effectiveness of direct selection. While some other characters such as days to 50% tasseling (-0.12), days to 50% silking (-1.78), ear height (-1.16), days to maturity (-0.64) exhibited indirect negative effect on yield indicating the effectiveness of indirect selection.

Genetic sources of individual variation in parental care behavior

Consistent individual differences in behavior exist for many behavioral traits. Several evolutionary hypotheses regarding the maintenance of this variation have been proposed, but they all rest on the relatively untested question of whether this variation has a genetic basis and if so, exactly what genetic mechanisms may be involved. We tested for heritability and the effects of heterozygosity on two measures of parental care behavior (nestling provisioning rate and the likelihood of provisioning with large food items) in a population of wild house sparrows (Passer domesticus), where both behaviors display consistent individual differences across a wide range of contexts. We found no evidence of significant heritability in either measure of parental care behavior. However, in a subset of 46 female sparrows, the likelihood of bringing large food items to the nest, but not provisioning rate, was positively correlated with genetic heterozygosity estimated from 18 polymorphic microsatellite markers. Despite these findings, individual identity continued to explain a significant proportion of the variation in parental care behavior. Our results imply that while the effects of directional selection on traits associated with parental care may be limited in this population, genetic heterozygosity appears to play a role in the maintenance of phenotypic diversity in at least one aspect of parental care behavior.

Experimental evidence of genome‐wide impact of ecological selection during early stages of speciation‐with‐gene‐flow

Theory predicts that speciation‐with‐gene‐flow is more likely when the consequences of selection for population divergence transitions from mainly direct effects of selection acting on individual genes to a collective property of all selected genes in the genome. Thus, understanding the direct impacts of ecologically based selection, as well as the indirect effects due to correlations among loci, is critical to understanding speciation. Here, we measure the genome‐wide impacts of host‐associated selection between hawthorn and apple host races of Rhagoletis pomonella (Diptera: Tephritidae), a model for contemporary speciation‐with‐gene‐flow. Allele frequency shifts of 32 455 SNPs induced in a selection experiment based on host phenology were genome wide and highly concordant with genetic divergence between co‐occurring apple and hawthorn flies in nature. This striking genome‐wide similarity between experimental and natural populations of R. pomonella underscores the importance of ecological selection at early stages of divergence and calls for further integration of studies of eco‐evolutionary dynamics and genome divergence.

A haplotype map of allohexaploid wheat reveals distinct patterns of selection on homoeologous genomes.

BackgroundBread wheat is an allopolyploid species with a large, highly repetitive genome. To investigate the impact of selection on variants distributed among homoeologous wheat genomes and to build a foundation for understanding genotype-phenotype relationships, we performed population-scale re-sequencing of a diverse panel of wheat lines.ResultsA sample of 62 diverse lines was re-sequenced using the whole exome capture and genotyping-by-sequencing approaches. We describe the allele frequency, functional significance, and chromosomal distribution of 1.57 million single nucleotide polymorphisms and 161,719 small indels. Our results suggest that duplicated homoeologous genes are under purifying selection. We find contrasting patterns of variation and inter-variant associations among wheat genomes; this, in addition to demographic factors, could be explained by differences in the effect of directional selection on duplicated homoeologs. Only a small fraction of the homoeologous regions harboring selected variants overlapped among the wheat genomes in any given wheat line. These selected regions are enriched for loci associated with agronomic traits detected in genome-wide association studies.ConclusionsEvidence suggests that directional selection in allopolyploids rarely acted on multiple parallel advantageous mutations across homoeologous regions, likely indicating that a fitness benefit could be obtained by a mutation at any one of the homoeologs. Additional advantageous variants in other homoelogs probably either contributed little benefit, or were unavailable in populations subjected to directional selection. We hypothesize that allopolyploidy may have increased the likelihood of beneficial allele recovery by broadening the set of possible selection targets.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-015-0606-4) contains supplementary material, which is available to authorized users.

Selection at the Esterase-2 locus of Drosophila buzzatii? Perturbation-reperturbation experiments.

Apparent selection affecting starch gel electrophoretic alleles at the Esterase-2 locus of Drosophila buzzatii has been detected in laboratory and natural populations. Perturbation-reperturbation of allele frequencies in replicated laboratory populations attempts to test direct selective effects at the locus versus effects of linked loci. Sequential gel electrophoresis has identified more alleles within starch classes, and three of these alleles (within the a, b and c starch alleles) were used in cage population experiments. Allele a/1.00/1.00/1.00 was set up in 10 replicate populations with allele c/1.00/1.00/1.00, and in an independent 10 replicate populations with allele b/0.99/1.01/1.00. For each set, three reperturbations were done. Replicate populations generally showed similar patterns of allele frequency change and clear directionality: effects of selection, not drift. However, four populations deviated from their replicates, indicating dissipation of linkage disequilibrium. Estimates of pre-adult viability in the F2 of pair-wise crosses among 12 sequential gel electrophoretic alleles showed very variable modes of inheritance and relative viability fitnesses. Together with the diversity of patterns of allele frequency change in the cage populations, these results suggest a gene complex, with selection acting on an interacting set of loci which may include Esterase-2.

Recurrent Selection for Seedling Growth of Sweet Corn in Cool Temperatures

ABSTRACTEarly spring sweet corn producers would benefit from supersweet cultivars with improved seedling cold tolerance. We performed recurrent selection for improved seedling vigor and germination rates at cool temperatures in three sweet corn populations. The original populations were formed by crossing temperate sweet corn and High‐altitude Mexican germplasm. A sugary1 (su1) and a shrunken2 (sh2) population derived from Cacahuacintle Dulce germplasm were evaluated, as well as a sh2 population derived from ‘Maíz Dulce’. The most uniformly vigorous seedling lots were chosen by replicated visual selection and then intermated to form the next cycle. The direct effects of selection were measured through growth chamber germination tests at 10°C. The indirect effects of selection were assessed through replicated field trials. A positive significant linear response to selection for seedling length was present in the two sh2 populations (R2 = 0.92, P < 0.001; R2 = 0.94, P < 0.001). There was a 71% increase in seedling length over four cycles of selection in one sh2 population, and a 116% increase in the other. Significant linear decreases in the average number of dead kernels were observed in both sh2 populations (R2 = 0.91, P < 0.05; R2 = 0.89, P < 0.05). There were no significant changes in kernel carbohydrate composition in either of the sh2 populations. No linear changes were observed as a direct response to selection in the su1 population. While germination under field conditions improved for both of the sh2 populations, selection had a negative effect on several agronomic traits, including plant height, ear height, and ear weight, suggesting the possibility of inbreeding during recurrent selection.

Comparison of phenotypic value changes in pure lines of Bombyx mori (Lepidoptera: Bombycidae) during consecutive generations following initial selection on cocoon weight.

The experiments reported here were conducted to investigate the effect of selection on three quantitative traits, namely cocoon weight, cocoon shell weight, and cocoon shell percentage, during four generations by rearing six pure breeds of domesticated silkworm, Bombyx mori L. (Lepidoptera: Bombycidae) of Chinese and Japanese origin compared with random unselected groups as controls. All stages of rearing and data recording were performed over four rearing periods, with generations 1–3 during successive spring seasons and generation 4 during the autumn season in year 3. Each pure line contained two groups of selected and random (control) groups. Comparisons included the effect of selection methods, pure line, and generation on the phenotypic values. We found strong main effects of pure line, generation, sex, and group and support for nearly all interactions between these main effects for all three response traits. The results indicated that cocoon weight and cocoon shell weight in the selected group were higher than in the control or nonselected group. Both selected and nonselected groups had the lowest cocoon weight, cocoon shell weight, and cocoon shell percentage in the fourth generation when environmental conditions during the autumn season were less favorable than spring. The cocoon weight and cocoon shell weight averages were higher for nonselected groups in the second and third generations, and for the selected group in the first generation due to the direct effect of selection.

Inferring Selection Intensity and Allele Age from Multilocus Haplotype Structure

It is a challenging task to infer selection intensity and allele age from population genetic data. Here we present a method that can efficiently estimate selection intensity and allele age from the multilocus haplotype structure in the vicinity of a segregating mutant under positive selection. We use a structured-coalescent approach to model the effect of directional selection on the gene genealogies of neutral markers linked to the selected mutant. The frequency trajectory of the selected allele follows the Wright-Fisher model. Given the position of the selected mutant, we propose a simplified multilocus haplotype model that can efficiently model the dynamics of the ancestral haplotypes under the joint influence of selection and recombination. This model approximates the ancestral genealogies of the sample, which reduces the number of states from an exponential function of the number of single-nucleotide polymorphism loci to a quadratic function. That allows parameter inference from data covering DNA regions as large as several hundred kilo-bases. Importance sampling algorithms are adopted to evaluate the probability of a sample by exploring the space of both allele frequency trajectories of the selected mutation and gene genealogies of the linked sites. We demonstrate by simulation that the method can accurately estimate selection intensity for moderate and strong positive selection. We apply the method to a data set of the G6PD gene in an African population and obtain an estimate of 0.0456 (95% confidence interval 0.0144−0.0769) for the selection intensity. The proposed method is novel in jointly modeling the multilocus haplotype pattern caused by recombination and mutation, allowing the analysis of haplotype data in recombining regions. Moreover, the method is applicable to data from populations under exponential growth and a variety of other demographic histories.

Microevolution in time and space: SNP analysis of historical DNA reveals dynamic signatures of selection in Atlantic cod

Little is known about how quickly natural populations adapt to changes in their environment and how temporal and spatial variation in selection pressures interact to shape patterns of genetic diversity. We here address these issues with a series of genome scans in four overfished populations of Atlantic cod (Gadus morhua) studied over an 80-year period. Screening of >1000 gene-associated single-nucleotide polymorphisms (SNPs) identified 77 loci that showed highly elevated levels of differentiation, likely as an effect of directional selection, in either time, space or both. Exploratory analysis suggested that temporal allele frequency shifts at certain loci may correlate with local temperature variation and with life history changes suggested to be fisheries induced. Interestingly, however, largely nonoverlapping sets of loci were temporal outliers in the different populations and outliers from the 1928 to 1960 period showed almost complete stability during later decades. The contrasting microevolutionary trajectories among populations resulted in sequential shifts in spatial outliers, with no locus maintaining elevated spatial differentiation throughout the study period. Simulations of migration coupled with observations of temporally stable spatial structure at neutral loci suggest that population replacement or gene flow alone could not explain all the observed allele frequency variation. Thus, the genetic changes are likely to at least partly be driven by highly dynamic temporally and spatially varying selection. These findings have important implications for our understanding of local adaptation and evolutionary potential in high gene flow organisms and underscore the need to carefully consider all dimensions of biocomplexity for evolutionarily sustainable management.

Keeping pace with climate change: what is wrong with the evolutionary potential of upper thermal limits?

The potential of populations to evolve in response to ongoing climate change is partly conditioned by the presence of heritable genetic variation in relevant physiological traits. Recent research suggests that Drosophila melanogaster exhibits negligible heritability, hence little evolutionary potential in heat tolerance when measured under slow heating rates that presumably mimic conditions in nature. Here, we study the effects of directional selection for increased heat tolerance using Drosophila as a model system. We combine a physiological model to simulate thermal tolerance assays with multilocus models for quantitative traits. Our simulations show that, whereas the evolutionary response of the genetically determined upper thermal limit (CTmax) is independent of methodological context, the response in knockdown temperatures varies with measurement protocol and is substantially (up to 50%) lower than for CTmax. Realized heritabilities of knockdown temperature may grossly underestimate the true heritability of CTmax. For instance, assuming that the true heritability of CTmax in the base population is h2 = 0.25, realized heritabilities of knockdown temperature are around 0.08–0.16 depending on heating rate. These effects are higher in slow heating assays, suggesting that flawed methodology might explain the apparently limited evolutionary potential of cosmopolitan D. melanogaster.

Establishment of new mutations under divergence and genome hitchhiking

Theoretical models addressing genome-wide patterns of divergence during speciation are needed to help us understand the evolutionary processes generating empirical patterns. Here, we examine a critical issue concerning speciation-with-gene flow: to what degree does physical linkage (r < 0.5) of new mutations to already diverged genes aid the build-up of genomic islands of differentiation? We used simulation and analytical approaches to partition the probability of establishment for a new divergently selected mutation when the mutation (i) is the first to arise in an undifferentiated genome (the direct effect of selection), (ii) arises unlinked to any selected loci (r = 0.5), but within a genome that has some already diverged genes (the effect of genome-wide reductions in gene flow for facilitating divergence, which we term 'genome hitchhiking'), and (iii) arises in physical linkage to a diverged locus (divergence hitchhiking). We find that the strength of selection acting directly on a new mutation is generally the most important predictor for establishment, with divergence and genomic hitchhiking having smaller effects. We outline the specific conditions under which divergence and genome hitchhiking can aid mutation establishment. The results generate predictions about genome divergence at different points in the speciation process and avenues for further work.

Call diversity in the North Pacific killer whale populations: implications for dialect evolution and population history

Although killer whale, Orcinus orca, dialects have been studied in detail in several populations, little attempt has been made to compare dialect characteristics between populations. In this study we investigated geographical variation in monophonic and biphonic calls among four resident populations from the North Pacific Ocean: Northern and Southern residents from British Columbia and Washington State, southern Alaska residents, and eastern Kamchatka residents. We tested predictions generated by the hypothesis that call variation across populations is the result of an accumulation of random errors and innovation by vertical cultural transmission. Call frequency contours were extracted and compared using a dynamic time-warping algorithm. We found that the diversity of monophonic calls was substantially higher than that of biphonic calls for all populations. Repertoire diversity appeared to be related to population size: in larger populations, monophonic calls were more diverse and biphonic calls less diverse. We suggest that the evolution of both monophonic and biphonic calls is caused by an interaction between stochastic processes and directional selection, but the relative effect of directional selection is greater for biphonic calls. Our analysis revealed no direct correlation between call repertoire similarity and geographical distance. Call diversity within predefined call categories, types and subtypes, showed a high degree of correspondence between populations. Our results indicate that dialect evolution is a complex process influenced by an interaction among directional selection, horizontal transmission and founder effects. We suggest several scenarios for how this might have arisen and the implications of these scenarios for call evolution and population history.

Long-term impacts of genome-enabled selection

The objective was to evaluate the effects of directional selection based on estimated genomic breeding values (GEBVs) for a quantitative trait. Selection affects GEBV prediction accuracy as well as genetic architecture via changes in allelic frequencies and linkage disequilibrium (LD), and the resulting changes are different from those in the absence of selection. How marker density affects long-term GEBV accuracy and selection response needs to be understood as well. Simulations were used to characterize the impact of selection based on GEBVs over generations. Single-nucleotide polymorphism (SNP) marker effects were estimated with the Bayesian Lasso method in the base generation, and these estimates were used to calculate the GEBVs in subsequent generations. GEBV accuracy decreased over generations of selection, and it was lower than under random selection, where a decay took place as well. In the long term, selection response tended to reach a plateau, but, at higher marker density, both the magnitude and duration of the response were larger. Selection changed quantitative trait loci (QTL) allele frequencies and generated new but unfavorable LD for prediction. Family effects had a considerable contribution to GEBV accuracy in early generations of selection.

Selection for Earlier Flowering Crop Associated with Climatic Variations in the Sahel

Climate changes will have an impact on food production and will require costly adaptive responses. Adapting to a changing environment will be particularly challenging in sub-Saharan Africa where climate change is expected to have a major impact. However, one important phenomenon that is often overlooked and is poorly documented is the ability of agro-systems to rapidly adapt to environmental variations. Such an adaptation could proceed by the adoption of new varieties or by the adaptation of varieties to a changing environment. In this study, we analyzed these two processes in one of the driest agro-ecosystems in Africa, the Sahel. We performed a detailed study in Niger where pearl millet is the main crop and covers 65% of the cultivated area. To assess how the agro-system is responding to recent recurrent drought, we analyzed samples of pearl millet landraces collected in the same villages in 1976 and 2003 throughout the entire cultivated area of Niger. We studied phenological and morphological differences in the 1976 and 2003 collections by comparing them over three cropping seasons in a common garden experiment. We found no major changes in the main cultivated varieties or in their genetic diversity. However, we observed a significant shift in adaptive traits. Compared to the 1976 samples, samples collected in 2003 displayed a shorter lifecycle, and a reduction in plant and spike size. We also found that an early flowering allele at the PHYC locus increased in frequency between 1976 and 2003. The increase exceeded the effect of drift and sampling, suggesting a direct effect of selection for earliness on this gene. We conclude that recurrent drought can lead to selection for earlier flowering in a major Sahelian crop. Surprisingly, these results suggest that diffusion of crop varieties is not the main driver of short term adaptation to climatic variation.

Positively Selected G6PD -Mahidol Mutation Reduces Plasmodium vivax Density in Southeast Asians

Glucose-6-phosphate dehydrogenase (G6PD) deficiency--the most common known enzymopathy--is associated with neonatal jaundice and hemolytic anemia usually after exposure to certain infections, foods, or medications. Although G6PD-deficient alleles appear to confer a protective effect against malaria, the link with clinical protection from Plasmodium infection remains unclear. We investigated the effect of a common G6PD deficiency variant in Southeast Asia--the G6PD-Mahidol(487A) variant--on human survival related to vivax and falciparum malaria. Our results show that strong and recent positive selection has targeted the Mahidol variant over the past 1500 years. We found that the G6PD-Mahidol(487A) variant reduces vivax, but not falciparum, parasite density in humans, which indicates that Plasmodium vivax has been a driving force behind the strong selective advantage conferred by this mutation.

COMBINING SELECTIVE EPISODES TO ESTIMATE LIFETIME NONLINEAR SELECTION

Studies measuring natural selection acting via different components of fitness may provide insight into such central questions in evolutionary biology as the evolution of life histories and sexual dimorphism. It is often desirable to combine estimates of selection at different episodes to understand how they interact to produce total lifetime selection. When selective episodes are sequential, total directional selection may be calculated by summing directional selection across episodes. However, it is unclear whether lifetime nonlinear (e.g., stabilizing, disruptive, or correlational) selection may be similarly calculated using estimates of quadratic selection from sequential episodes. Here, I show that lifetime quadratic selection depends not only upon the sum total of quadratic selection across episodes but also upon the pattern of directional selection across episodes. In certain cases, the effects of directional selection across episodes may cancel one another, leading to no net directional selection but strong stabilizing selection. This result suggests that true stabilizing selection may be more common than previously thought, especially when the entire life cycle is considered. The equations derived here are easily applicable to empirical data, as is illustrated both with a simulated dataset and with a reanalysis of a study of quadratic selection in dark-eyed juncos.

Effect of directional selection for body size on fluctuating asymmetry in certain morphological traits in Drosophila ananassae

Variation in the subtle differences between the right and left sides of bilateral characters or fluctuating asymmetry (FA) has been considered as an indicator of an organism's ability to cope with genetic and environmental stresses during development. However, due to inconsistency in the results of empirical studies, the relationship between FA and stress has been the subject of intense debate. In this study, we investigated whether stress caused by artificial bidirectional selection for body size has any effect on the levels of FA of different morphological traits in Drosophila ananassae. The realised heritability (h2) was higher in low-line females and high-line males, which suggests an asymmetrical response to selection for body size. Further, the levels of FA were compared across 10 generations of selection in different selection lines in both sexes for sternopleural bristle number, wing length, wing-to-thorax ratio, sex combtooth number and ovariole number. The levels of FA differed significantly among generations and selection lines but did not change markedly with directional selection. However, the levels of FA were higher in the G10 generation (at the end of selection) than G0 (at the start of selection) but lower than the G5 generation in different selection lines, suggesting that the levels of FA are not affected by the inbreeding generated during the course of selection. Also, the levels of FA in the hybrids of high and low lines were signifi cantly lower than the parental selection lines, suggesting that FA is influenced by hybridisation. These results are discussed in the framework of the literature available on FA and its relationship with stress.