RESUMEN
Songbirds have one special accessory chromosome, the so-called germline-restricted chromosome (GRC), which is only present in germline cells and absent from all somatic tissues. Earlier work on the zebra finch (Taeniopygia guttata castanotis) showed that the GRC is inherited only through the female line-like the mitochondria-and is eliminated from the sperm during spermatogenesis. Here, we show that the GRC has the potential to be paternally inherited. Confocal microscopy using GRC-specific fluorescent in situ hybridization probes indicated that a considerable fraction of sperm heads (1 to 19%) in zebra finch ejaculates still contained the GRC. In line with these cytogenetic data, sequencing of ejaculates revealed that individual males from two families differed strongly and consistently in the number of GRCs in their ejaculates. Examining a captive-bred male hybrid of the two zebra finch subspecies (T. g. guttata and T. g. castanotis) revealed that the mitochondria originated from a castanotis mother, whereas the GRC came from a guttata father. Moreover, analyzing GRC haplotypes across nine castanotis matrilines, estimated to have diverged for up to 250,000 y, showed surprisingly little variability among GRCs. This suggests that a single GRC haplotype has spread relatively recently across all examined matrilines. A few diagnostic GRC mutations that arose since this inferred spreading suggest that the GRC has continued to jump across matriline boundaries. Our findings raise the possibility that certain GRC haplotypes could selfishly spread through the population via occasional paternal transmission, thereby outcompeting other GRC haplotypes that were limited to strict maternal inheritance, even if this was partly detrimental to organismal fitness.
Asunto(s)
Cromosomas , Células Germinativas , Herencia Paterna , Pájaros Cantores/genética , Animales , Análisis Citogenético , ADN Mitocondrial , Evolución Molecular , Femenino , Haplotipos , Masculino , Filogenia , Pájaros Cantores/clasificación , EspermatozoidesRESUMEN
The germline-restricted chromosome (GRC) is likely present in all songbird species but differs widely in size and gene content. This extra chromosome has been described as either a microchromosome with only limited basic gene content or a macrochromosome with enriched gene functions related to female gonad and embryo development. Here, we assembled, annotated, and characterized the first micro-GRC in the blue tit (Cyanistes caeruleus) using high-fidelity long-read sequencing data. Although some genes on the blue tit GRC show signals of pseudogenization, others potentially have important functions, either currently or in the past. We highlight the GRC gene paralog BMP15, which is among the highest expressed GRC genes both in blue tits and in zebra finches (Taeniopygia guttata) and is known to play a role in oocyte and follicular maturation in other vertebrates. The GRC genes of the blue tit are further enriched for functions related to the synaptonemal complex. We found a similar functional enrichment when analyzing published data on GRC genes from two nightingale species (Luscinia spp.). We hypothesize that these genes play a role in maintaining standard maternal inheritance or in recombining maternal and paternal GRCs during potential episodes of biparental inheritance.
Asunto(s)
Passeriformes , Pájaros Cantores , Animales , Femenino , Pájaros Cantores/genética , Cromosomas , Células Germinativas , Oocitos , Ovario , Passeriformes/genéticaRESUMEN
Understanding the genomic landscape of adaptation is central to understanding microevolution in wild populations. Genomic targets of selection and the underlying genomic mechanisms of adaptation can be elucidated by genome-wide scans for past selective sweeps or by scans for direct fitness associations. We sequenced and assembled 150 haplotypes of 75 blue tits (Cyanistes caeruleus) of a single Central European population by a linked-read technology. We used these genome data in combination with coalescent simulations (i) to estimate an historical effective population size of ~250,000, which recently declined to ~10,000, and (ii) to identify genome-wide distributed selective sweeps of beneficial variants probably originating from standing genetic variation (soft sweeps). The genes linked to these soft sweeps, but also those linked to hard sweeps based on new beneficial mutants, showed a significant enrichment for functions associated with gene expression and transcription regulation. This emphasizes the importance of regulatory evolution in the population's adaptive history. Soft sweeps were further enriched for genes related to axon and synapse development, indicating the significance of neuronal connectivity changes in the brain potentially linked to behavioural adaptations. A previous scan of heterozygosity-fitness correlations revealed a consistent negative effect on arrival date at the breeding site for a single microsatellite in the MDGA2 gene. Here, we used the haplotype structure around this microsatellite to explain the effect as a local and direct outbreeding effect of a gene involved in synapse development.
Asunto(s)
Selección Genética , Pájaros Cantores , Adaptación Fisiológica/genética , Animales , Variación Genética , Genética de Población , Genoma/genética , Haplotipos/genética , Pájaros Cantores/genéticaRESUMEN
The evolutionary consequences of individual genetic diversity are frequently studied by assessing heterozygosity-fitness correlations (HFCs). The prevalence of positive and negative HFCs and the predominance of general versus local effects in wild populations are far from understood, partly because comprehensive studies testing for both inbreeding and outbreeding depression are lacking. We studied a genetically diverse population of blue tits in southern Germany using a genome-wide set of 87 microsatellites to investigate the relationship between proxies of reproductive success and measures of multilocus and single-locus individual heterozygosity (MLH and SLH). We used complimentary measures of MLH and partitioned markers into functional categories according to their position in the blue tit genome. HFCs based on MLH were consistently negative for functional loci, whereas correlations were rather inconsistent for loci found in nonfunctional areas of the genome. Clutch size was the only reproductive variable showing a general effect. We found evidence for local effects for three measures of reproductive success: arrival date at the breeding site, the probability of breeding at the study site and male reproductive success. For these, we observed consistent, and relatively strong, negative effects at one functional locus. Remarkably, this marker had a similar effect in another blue tit population from Austria (~400 km to the east). We suggest that a genetic local effect on timing of arrival might be responsible for most negative HFCs detected, with carry-over effects on other reproductive traits. This effect could reflect individual differences in the distance between overwintering areas and breeding sites.
Asunto(s)
Genética de Población , Pájaros Cantores , Animales , Austria , Alemania , Heterocigoto , Endogamia , Masculino , Repeticiones de Microsatélite/genética , Pájaros Cantores/genéticaRESUMEN
When a species colonizes an urban habitat, differences in the environment can create novel selection pressures. Successful colonization will further lead to demographic perturbations and genetic drift, which can interfere with selection. Here, we test for consistent urban selection signals in multiple populations of the burrowing owl (Athene cunicularia), a species that colonized South American cities just a few decades ago. We sequenced 213 owls from three urban-rural population pairs and performed a genome-wide comparison of urban against rural birds. We further studied genome-wide associations with flight initiation distance, a measure of harm avoidance in which urban and rural birds are known to differ. Based on four samples taken over nine years from one of the urban populations, we investigated temporal allele frequency changes. The genomic data were also used to identify urban-specific signatures of selective sweeps. Single genomic sites did not reach genome-wide significance for any association. However, a gene-set analysis on the strongest signals from these four selection scans suggests a significant enrichment of genes with known functions related to synapses and neuron projections. We identified 98 genes predominantly expressed in the brain, of which many may play a role in the modulation of brain connectivity and consequently in cognitive function and motivational behaviour during urbanization. Furthermore, polymorphisms in the promoter region of the synaptic SERT gene - one of the two candidates known to correlate with urban colonization in birds - associated with the habitat in which individuals lived (urban vs. rural).
Asunto(s)
Estrigiformes , Animales , Ciudades , Humanos , Neuronas , Sinapsis , Población UrbanaRESUMEN
When a species successfully colonizes an urban habitat it can be expected that its population rapidly adapts to the new environment but also experiences demographic perturbations. It is, therefore, essential to gain an understanding of the population structure and the demographic history of the urban and neighbouring rural populations before studying adaptation at the genome level. Here, we investigate populations of the burrowing owl (Athene cunicularia), a species that colonized South American cities just a few decades ago. We assembled a high-quality genome of the burrowing owl and re-sequenced 137 owls from three urban-rural population pairs at 17-fold median sequencing coverage per individual. Our data indicate that each city was independently colonized by a limited number of founders and that restricted gene flow occurred between neighbouring urban and rural populations, but not between urban populations of different cities. Using long-range linkage disequilibrium statistics in an approximate Bayesian computation approach, we estimated consistently lower population sizes in the recent past for the urban populations in comparison to the rural ones. The current urban populations all show reduced standing variation in rare single nucleotide polymorphisms (SNPs), but with different subsets of rare SNPs in different cities. This lowers the potential for local adaptation based on rare variants and makes it harder to detect consistent signals of selection in the genome.
Asunto(s)
Evolución Molecular , Genoma , Estrigiformes/genética , Distribución Animal , Animales , Argentina , CiudadesRESUMEN
Human-induced biological invasions are common worldwide and often have negative impacts on wildlife and human societies. Several studies have shown evidence for selection on invaders after introduction to the new range. However, selective processes already acting prior to introduction have been largely neglected. Here, we tested whether such early selection acts on known behaviour-related gene variants in the yellow-crowned bishop (Euplectes afer), a pet-traded African songbird. We tested for nonrandom allele frequency changes after trapping, acclimation and survival in captivity. We also compared the native source population with two independent invasive populations. Allele frequencies of two SNPs in the dopamine receptor D4 (DRD4) gene-known to be linked to behavioural activity in response to novelty in this species-significantly changed over all early invasion stages. They also differed between the African native population and the two invading European populations. The two-locus genotype associated with reduced activity declined consistently, but strongest at the trapping stage. Overall genetic diversity did not substantially decrease, and there is little evidence for new alleles in the introduced populations, indicating that selection at the DRD4 gene predominantly worked on the standing genetic variation already present in the native population. Our study demonstrates selection on a behaviour-related gene during the first stages of a biological invasion. Thus, pre-establishment stages of a biological invasion do not only determine the number of propagules that are introduced (their quantity), but also their phenotypic and genetic characteristics (their quality).
Asunto(s)
Conducta Animal , Frecuencia de los Genes , Genética de Población , Passeriformes/genética , Receptores de Dopamina D4/genética , Animales , Genotipo , Especies Introducidas , Repeticiones de Microsatélite , Fenotipo , Polimorfismo de Nucleótido Simple , Dinámica Poblacional , Senegal , EspañaRESUMEN
Relatively low numbers of kringle 4 type 2 repeats in apolipoprotein(a) and specific haplotypes of the SLC22A3-LPAL2-LPA region on chromosome 6 are associated with an increased risk of coronary disease. We examined the possibility that rs3798220 and rs10455872, short variations located in LPA [the apolipoprotein(a) gene], and related to the number of kringle 4 type 2 repeats, may serve as markers for the association between haplotypes and acute myocardial infarction. Genotypes were determined with TaqMan assays in a sample of 2136 cases and 1211 controls. The minor alleles of rs3798220 and rs10455872 were associated with increased risks (rs3798220-C: adjusted OR 2.14, 95% CI, 1.37-3.33, P = 0.00080; rs10455872-G: adjusted OR 1.74, 95% CI 1.36-2.24, P < 0.00001). After adjustments were made for potential confounders, none of nine polymorphisms included in a haplotype analysis were singly related to disease. Two risk haplotypes were identified; one (CCTTGTGTG; OR 1.25, 95% CI 1.08-1.45, P = 0.0022) was correlated with rs3798220-C and the other (CCCTGGATC; OR 1.65, 95% CI 1.14-2.38, P = 0.0074) with rs10455872-G. Thus, the findings allowed for a more precise definition of risk-associated markers: specific nucleotides in LPA instead of standard haplotypes defined by noneffective variants from the extensive SLC22A3-LPAL2-LPA region.
Asunto(s)
Apolipoproteínas A/genética , Infarto del Miocardio/genética , Polimorfismo de Nucleótido Simple , Anciano , Anciano de 80 o más Años , Femenino , Predisposición Genética a la Enfermedad , Haplotipos , Humanos , Masculino , Persona de Mediana EdadRESUMEN
The assessment of genetic architecture and selection history in genes for behavioural traits is fundamental to our understanding of how these traits evolve. The dopamine receptor D4 (DRD4) gene is a prime candidate for explaining genetic variation in novelty seeking behaviour, a commonly assayed personality trait in animals. Previously, we showed that a single nucleotide polymorphism in exon 3 of this gene is associated with exploratory behaviour in at least one of four Western European great tit (Parus major) populations. These heterogeneous association results were explained by potential variable linkage disequilibrium (LD) patterns between this marker and the causal variant or by other genetic or environmental differences among the populations. Different adaptive histories are further hypothesized to have contributed to these population differences. Here, we genotyped 98 polymorphisms of the complete DRD4 gene including the flanking regions for 595 individuals of the four populations. We show that the LD structure, specifically around the original exon 3 SNP is conserved across the four populations and does not explain the heterogeneous association results. Study-wide significant associations with exploratory behaviour were detected in more than one haplotype block around exon 2, 3 and 4 in two of the four tested populations with different allele effect models. This indicates genetic heterogeneity in the association between multiple DRD4 polymorphisms and exploratory behaviour across populations. The association signals were in or close to regions with signatures of positive selection. We therefore hypothesize that variation in exploratory and other dopamine-related behaviour evolves locally by occasional adaptive shifts in the frequency of underlying genetic variants.
Asunto(s)
Adaptación Biológica/genética , Conducta Exploratoria/fisiología , Variación Genética , Passeriformes/genética , Receptores de Dopamina D4/genética , Selección Genética , Animales , Secuencia de Bases , Europa (Continente) , Genotipo , Haplotipos/genética , Desequilibrio de Ligamiento , Modelos Genéticos , Datos de Secuencia Molecular , Passeriformes/fisiología , Fenotipo , Polimorfismo de Nucleótido Simple/genética , Análisis de Secuencia de ADN , Especificidad de la EspecieRESUMEN
The stress hormone-regulating hypothalamic-pituitary-adrenal (HPA) axis has been implicated in the causality as well as the treatment of depression. To investigate a possible association between genes regulating the HPA axis and response to antidepressants and susceptibility for depression, we genotyped single-nucleotide polymorphisms in eight of these genes in depressed individuals and matched controls. We found significant associations of response to antidepressants and the recurrence of depressive episodes with single-nucleotide polymorphisms in FKBP5, a glucocorticoid receptor-regulating cochaperone of hsp-90, in two independent samples. These single-nucleotide polymorphisms were also associated with increased intracellular FKBP5 protein expression, which triggers adaptive changes in glucocorticoid receptor and, thereby, HPA-axis regulation. Individuals carrying the associated genotypes had less HPA-axis hyperactivity during the depressive episode. We propose that the FKBP5 variant-dependent alterations in HPA-axis regulation could be related to the faster response to antidepressant drug treatment and the increased recurrence of depressive episodes observed in this subgroup of depressed individuals. These findings support a central role of genes regulating the HPA axis in the causality of depression and the mechanism of action of antidepressant drugs.
Asunto(s)
Antidepresivos/uso terapéutico , Depresión/genética , Proteínas HSP90 de Choque Térmico/genética , Sistema Hipotálamo-Hipofisario/metabolismo , Sistema Hipófiso-Suprarrenal/metabolismo , Polimorfismo de Nucleótido Simple/genética , Receptores de Glucocorticoides/genética , Adulto , Análisis de Varianza , Antidepresivos/administración & dosificación , Western Blotting , Hormona Liberadora de Corticotropina/genética , Depresión/tratamiento farmacológico , Fluorescencia , Frecuencia de los Genes , Genotipo , Alemania , Proteínas HSP90 de Choque Térmico/metabolismo , Humanos , Linfocitos/metabolismo , Neurofisinas/genética , Precursores de Proteínas/genética , Receptores de Glucocorticoides/metabolismo , Análisis de Regresión , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Vasopresinas/genéticaRESUMEN
Genetic conflicts can arise between components of the genome with different inheritance strategies. The germline-restricted chromosome (GRC) of songbirds shows unusual mitotic and meiotic transmission compared with the rest of the genome. It is excluded from somatic cells and maintained only in the germline. It is usually present in one copy in the male germline and eliminated during spermatogenesis, while in the female germline, it usually occurs in two copies and behaves as a regular chromosome. Here, we review what is known about the GRC's evolutionary history, genetic content, and expression and discuss how it may be involved in different types of genetic conflicts. Finally, we interrogate the potential role of the GRC in songbird germline development, highlighting several unsolved mysteries.
Asunto(s)
Pájaros Cantores , Animales , Masculino , Pájaros Cantores/genética , Cromosomas , Células Germinativas , GenomaRESUMEN
Numerous studies have reported associations between heterozygosity in microsatellite markers and fitness-related traits (heterozygosity-fitness correlations, HFCs). However, it has often been questioned whether HFCs reflect general inbreeding depression, because a small panel of microsatellite markers does not reflect very well an individual's inbreeding coefficient (F) as calculated from a pedigree. Here, we challenge this prevailing view. Because of chance events during Mendelian segregation, an individual's realized proportion of the genome that is identical by descent (IBD) may substantially deviate from the pedigree-based expectation (i.e. F). This Mendelian noise may result in a weak correlation between F and multi-locus heterozygosity, but this does not imply that multi-locus heterozygosity is a bad estimator of realized IBD. We examined correlations between 11 fitness-related traits measured in up to 1192 captive zebra finches and three measures of inbreeding: (i) heterozygosity across 11 microsatellite markers, (ii) heterozygosity across 1359 single-nucleotide polymorphism (SNP) markers and (iii) F, based on a 5th-generation pedigree. All 11 phenotypic traits showed positive relationships with measures of heterozygosity, especially traits that are most closely related to fitness. Remarkably, the small panel of microsatellite markers produced equally strong HFCs as the large panel of SNP markers. Both marker-based approaches produced stronger correlations with phenotypes than the pedigree-based F, and this did not seem to result from the shortness of our pedigree. We argue that a small panel of microsatellites with high allelic richness may better reflect an individual's realized IBD than previously appreciated, especially in species like the zebra finch, where much of the genome is inherited in large blocks that rarely experience cross-over during meiosis.
Asunto(s)
Pinzones/genética , Aptitud Genética , Genética de Población , Heterocigoto , Repeticiones de Microsatélite , Animales , Femenino , Endogamia , Patrón de Herencia , Masculino , Modelos Genéticos , Linaje , Fenotipo , Polimorfismo de Nucleótido SimpleRESUMEN
Understanding the targets of selection associated with changes in behavioral traits represents an important challenge of current evolutionary research. Owls (Strigiformes) are a diverse group of birds, most of which are considered nocturnal raptors. However, a few owl species independently adopted a diurnal lifestyle in their recent evolutionary history. We searched for signals of accelerated rates of evolution associated with a diurnal lifestyle using a genome-wide comparative approach. We estimated substitution rates in coding and noncoding conserved regions of the genome of seven owl species, including three diurnal species. Substitution rates of the noncoding elements were more accelerated than those of protein-coding genes. We identified new, owl-specific conserved noncoding elements as candidates of parallel evolution during the emergence of diurnality in owls. Our results shed light on the molecular basis of adaptation to a new niche and highlight the importance of regulatory elements for evolutionary changes in behavior. These elements were often involved in the neuronal development of the brain.
Asunto(s)
Estrigiformes , Adaptación Fisiológica/genética , Animales , Genoma , Genómica , Fenotipo , Estrigiformes/genéticaRESUMEN
Bird migration is one of the most spectacular and best-studied phenomena in behavioural biology. Yet, while the patterns of variation in migratory behaviour and its ecological causes have been intensively studied, its genetic, physiological and neurological control remains poorly understood. The lack of knowledge of the molecular basis of migration is currently not only limiting our insight into the proximate control of migration, but also into its evolution. We investigated polymorphisms in the exons of six candidate genes for key behavioural traits potentially linked to migration, which had previously been identified in several bird species, and eight control loci in 14 populations of blackcaps (Sylvia atricapilla), representing the whole range of geographical variation in migration patterns found in this species, with the aim of identifying genes controlling variation in migration. We found a consistent association between a microsatellite polymorphism and migratory behaviour only at one candidate locus: the ADCYAP1 gene. This polymorphism explained about 2.6 per cent of the variation in migratory tendency among populations, and 2.7-3.5% of variation in migratory restlessness among individuals within two independent populations. In all tests, longer alleles were associated with higher migratory activity. The consistency of results among different populations and levels of analysis suggests that ADCYAP1 is one of the genes controlling the expression of migratory behaviour. Moreover, the multiple described functions of the gene product indicate that this gene might act at multiple levels modifying the shift between migratory and non-migratory states.
Asunto(s)
Migración Animal/fisiología , Conducta Animal/fisiología , Passeriformes/genética , Passeriformes/fisiología , Polipéptido Hipofisario Activador de la Adenilato-Ciclasa/genética , Animales , Repeticiones de Microsatélite , Polimorfismo GenéticoRESUMEN
The relationship between genetic diversity and fitness has important implications in evolutionary and conservation biology. This relationship has been widely investigated at the individual level in studies of heterozygosity-fitness correlations (HFC). General effects caused by inbreeding and/or local effects at single loci have been used as explanations of HFC, but the debate about the causes of HFC in open, natural populations is still ongoing. Study designs that control for variation in the inbreeding level of the individuals, and knowledge on the function and location of the markers used to measure heterozygosity, are fundamental to understand the causes of HFC. Here we investigated correlations between individual heterozygosity and estimates of survival at different life-history stages in an open population of blue tits (Cyanistes caeruleus). For survival at the embryo, nestling and fledgling stage, we used a full-sibling approach, i.e. we controlled for the level of inbreeding. We genotyped 1496 individuals with 79 microsatellites mapped across 25 chromosomes in the zebra finch (Taeniopygia guttata) that were classified either as potentially functional (58 loci) or as neutral (21 loci). We found different effects of standardized multilocus heterozygosity (SH): SH(functional) had a negative effect on the probability of hatching and local recruitment of females, whereas SH(neutral) had a positive effect on adult survival. The negative effects of functional loci are better explained by local effects, whereas the positive effects of neutral markers could reflect inbreeding effects in the population. Our results highlight the importance of considering the characteristics of the markers used in HFC studies and confirm the mixed effects of heterozygosity in different contexts (e.g. sex and life-history stage).
Asunto(s)
Heterocigoto , Passeriformes/genética , Animales , Mapeo Cromosómico , Femenino , Pinzones/genética , Marcadores Genéticos , Genotipo , Endogamia , Longevidad , Masculino , Repeticiones de Microsatélite , Passeriformes/fisiologíaRESUMEN
In vertebrates, including humans, the relative length of the second to the fourth digit correlates with sex hormone-dependent behavioural, psychological and physiological traits. However, despite a decade of research, the underlying mechanism linking digit ratio to these sex hormone-dependent traits remains unclear. Previous work suggests that during embryo development, circulating levels of plasma androgens or oestrogens may act through their receptors to affect transcription levels of posterior HOX genes in the developing digits, thereby possibly influencing their relative length. The correlation between digit ratio and sex hormone-dependent traits might thus stem from variation in expression or sensitivity of the sex hormone receptors, or from variation in sex hormone levels in the embryo. Here, we show that in a population of 1156 zebra finches Taeniopygia guttata, a polymorphism in the oestrogen receptor α gene (ESR1) explains 11.3 per cent of the variation in digit ratio, and is also associated with male and female-mating behaviour. By contrast, we found no associations between digit ratio or mating behaviours and polymorphisms in the androgen receptor gene. Thus, our results (i) provide an explanation for the observed significant genetic covariance between digit ratio and male and female mating behaviour and (ii) strongly confirm the indicator function of digit ratio through the oestrogen pathway. Finally, we note that the commonly invoked effect of foetal testosterone on human digit ratio seems to be substantially weaker than the effect described here.
Asunto(s)
Receptor alfa de Estrógeno/fisiología , Receptores Androgénicos/fisiología , Pájaros Cantores/fisiología , Dedos del Pie/anatomía & histología , Animales , Conducta de Elección/fisiología , ADN/química , ADN/genética , Receptor alfa de Estrógeno/genética , Femenino , Variación Genética , Haplotipos , Masculino , Repeticiones de Microsatélite/genética , Reacción en Cadena de la Polimerasa , Polimorfismo Genético , Receptores Androgénicos/genética , Análisis de Regresión , Conducta Sexual Animal/fisiología , Pájaros Cantores/anatomía & histología , Pájaros Cantores/genética , Vocalización Animal/fisiologíaRESUMEN
Polymorphisms in the dopamine receptor D4 gene (DRD4) have been related to individual variation in novelty-seeking or exploratory behaviour in a variety of animals, including humans. Recently, the human DRD4 orthologue was sequenced in a wild bird, the great tit (Parus major) and a single nucleotide polymorphism in exon 3 of this gene (SNP830) was shown to be associated with variation in exploratory behaviour of lab-raised individuals originating from a single wild population. Here we test the generality of this finding in a large sample of free-living individuals from four European great tit populations, including the originally sampled population. We demonstrate that the association between SNP830 genotype and exploratory behaviour also exists in free-living birds from the original population. However, in the other three populations we found only limited evidence for an association: in two populations the association appeared absent; while in one there was a nonsignificant tendency. We could not confirm a previously demonstrated interaction with another DRD4 polymorphism, a 15 bp indel in the promoter region (ID15). As yet unknown differences in genetic or environmental background could explain why the same genetic polymorphism (SNP830) has a substantial effect on exploratory behaviour in one population, explaining 4.5-5.8% of the total variance-a large effect for a single gene influencing a complex behavioural trait-but not in three others. The confirmation of an association between SNP830 genotype and personality-related behaviour in a wild bird population warrants further research into potential fitness effects of the polymorphism, while also the population differences in the strength of the association deserve further investigation. Another important future challenge is the identification of additional loci influencing avian personality traits in the wild.
Asunto(s)
Conducta Exploratoria , Genética de Población , Passeriformes/genética , Personalidad/genética , Receptores de Dopamina D4/genética , Animales , Genotipo , Polimorfismo de Nucleótido Simple , Regiones Promotoras Genéticas , Análisis de Secuencia de ADNRESUMEN
It has been suggested that positive selection, in particular selection favoring a change in the protein sequence, plays a role in the evolution of olfactory receptor (OR) gene repertoires in fish and mammals. ORs are 7-transmembrane domain (TM) proteins, members of the G-protein-coupled receptor superfamily in vertebrate genomes, and responsible for odorant binding and discrimination. OR gene repertoires in birds are surprisingly large and diverse, suggesting that birds have a keen olfactory sense. The aim of this study is to investigate signatures of positive selection in an expanded OR clade (group-gamma-c) that seems to be a characteristic of avian genomes. Using maximum-likelihood methods that estimate the d(N)/d(S) ratios and account for the effects of recombination, we show here that there is evidence for positive selection in group-gamma-c partial OR coding sequences of 9 bird species that are likely to have different olfactory abilities: the blue tit (Cyanistes caeruleus), the black coucal (Centropus grillii), the brown kiwi (Apteryx australis), the canary (Serinus canaria), the galah (Eolophus roseicapillus), the kakapo (Strigops habroptilus), the mallard (Anas platyrhynchos), the red jungle fowl (Gallus gallus), and the snow petrel (Pagodroma nivea). Positively selected codons were predominantly located in TMs, which in other vertebrates are involved in odorant binding. Our data suggest that 1) at least some avian OR genes have been subjected to adaptive evolution, 2) the extent of such adaptive evolution differs between bird species, and 3) positive selective pressures may have been stronger on the group-gamma-c OR genes of species that have well-developed olfactory abilities.
Asunto(s)
Adaptación Biológica/genética , Aves/genética , Evolución Molecular , Receptores Odorantes/genética , Animales , Secuencia de Bases , Aves/clasificación , Datos de Secuencia Molecular , Filogenia , Recombinación Genética , Selección Genética , Análisis de Secuencia de ADNRESUMEN
Owls (Strigiformes) evolved specific adaptations to their nocturnal predatory lifestyle, such as asymmetrical ears, a facial disk, and a feather structure allowing silent flight. Owls also share some traits with diurnal raptors and other nocturnal birds, such as cryptic plumage patterns, reversed sexual size dimorphism, and acute vision and hearing. The genetic basis of some of these adaptations to a nocturnal predatory lifestyle has been studied by candidate gene approaches but rarely with genome-wide scans. Here, we used a genome-wide comparative analysis to test for selection in the early history of the owls. We estimated the substitution rates in the coding regions of 20 bird genomes, including 11 owls of which five were newly sequenced. Then, we tested for functional overrepresentation across the genes that showed signals of selection. In the ancestral branch of the owls, we found traces of positive selection in the evolution of genes functionally related to visual perception, especially to phototransduction, and to chromosome packaging. Several genes that have been previously linked to acoustic perception, circadian rhythm, and feather structure also showed signals of an accelerated evolution in the origin of the owls. We discuss the functions of the genes under positive selection and their putative association with the adaptation to the nocturnal predatory lifestyle of the owls.
Asunto(s)
Adaptación Biológica/genética , Evolución Biológica , Conducta Predatoria , Selección Genética , Estrigiformes/genética , Animales , Ritmo Circadiano/genética , Genoma , Audición/genética , Filogenia , Visión Ocular/genéticaRESUMEN
Understanding the population genetic consequences of habitat heterogeneity requires assessing whether patterns of gene flow correspond to landscape configuration. Studies of the genetic structure of populations are still scarce for Neotropical forest birds. We assessed range-wide genetic structure and contemporary gene flow in the thorn-tailed rayadito (Aphrastura spinicauda), a passerine bird inhabiting the temperate forests of South America. We used 12 microsatellite loci to genotype 582 individuals from eight localities across a large latitudinal range (30°S-56°S). Using population structure metrics, multivariate analyses, clustering algorithms, and Bayesian methods, we found evidence for moderately low regional genetic structure and reduced gene flow towards the range margins. Genetic differentiation increased with geographic distance, particularly in the southern part of the species' distribution where forests are continuously distributed. Populations in the north seem to experience limited gene flow likely due to forest discontinuity, and may comprise a demographically independent unit. The southernmost population, on the other hand, is genetically depauperate and different from all other populations. Different analytical approaches support the presence of three to five genetic clusters. We hypothesize that the genetic structure of the species follows a hierarchical clustered pattern.