RESUMO
Laboratory selection in thermal regimes that differed in the amplitude and the predictability of daily fluctuations had a marked effect on stress resistance and life history traits in Drosophila simulans. The observed evolutionary changes are expected to be the result of both direct and correlated responses to selection. Thus, a given trait might not evolve independently from other traits because of genetic correlations among these traits. Moreover, different test environments can induce novel genetic correlations because of the activation of environmentally dependent genes. To test whether and how genetic correlations among stress resistance and life history traits constrain evolutionary adaptation, we used three populations of D. simulans selected for 20 generations in constant, predictable and unpredictable daily fluctuating thermal regimes and tested each of these selected populations in the same three thermal regimes. We explored the relationship between genetic correlations between traits and the evolutionary potential of D. simulans by comparing genetic correlation matrices in flies selected and tested in different thermal test regimes. We observed genetic correlations mainly between productivity, body size, starvation and desiccation tolerance, suggesting that adaptation to the three thermal regimes was affected by correlations between these traits. We also found that the correlations between some traits such as body size and productivity or starvation tolerance and productivity were determined by test regime rather than selection regime that is expected to limit genetic adaptation to thermal regimes in these traits. The results of this study suggest that several traits and several environments are needed to explore adaptive responses, as genetic and environmentally induced correlations between traits as results obtained in one environment cannot be used to predict the response of the same population in another environment.
Assuntos
Adaptação Fisiológica/genética , Drosophila/genética , Meio Ambiente , Evolução Molecular , Animais , Tamanho Corporal , Desidratação , Privação de Alimentos , Estágios do Ciclo de Vida , Fenótipo , Estresse Fisiológico , TemperaturaRESUMO
Quantitative trait loci (QTL) were mapped for longevity and fecundity at two temperatures, 20 and 30 °C, in two sets of recombinant inbred lines (RIL) highly differing in thermotolerance. Early fecundity (EF) and longevity showed a negative association between temperatures. For instance, longevity was higher and fecundity was lower in the RIL panel showing higher life span at 30 °C. One X-linked QTL (7B3-12E) co-localized for longevity and EF at 20 °C, with one QTL allele showing a positive additive effect on longevity and a negative effect on EF. The across-RIL genetic correlation between longevity and EF was not significant within each temperature, and most QTL that affect life span have no effect on EF at each temperature. EF and longevity can mostly be genetically uncoupled in the thermotolerance-divergent RIL within each temperature as opposed to between temperatures. QTL were mostly temperature specific, although some trait-specific QTL showed possible antagonistic effects between temperatures.
Assuntos
Drosophila melanogaster/genética , Drosophila melanogaster/fisiologia , Fertilidade/genética , Fertilidade/fisiologia , Longevidade/genética , Longevidade/fisiologia , Animais , Mapeamento Cromossômico , Feminino , Temperatura Alta , Masculino , Fenótipo , Locos de Características Quantitativas , Recombinação Genética , TemperaturaRESUMO
The selective past of populations is presumed to affect the levels of phenotypic plasticity. Experimental evolution at constant temperatures is generally expected to lead to a decreased level of plasticity due to presumed costs associated with phenotypic plasticity when not needed. In this study, we investigated the effect of experimental evolution in constant, predictable and unpredictable daily fluctuating temperature regimes on the levels of phenotype plasticity in several life history and stress resistance traits in Drosophila simulans. Contrary to the expectation, evolution in the different regimes did not affect the levels of plasticity in any of the traits investigated even though the populations from the different thermal regimes had evolved different stress resistance and fitness trait means. Although costs associated with phenotypic plasticity are known, our results suggest that the maintenance of phenotypic plasticity might come at low and negligible costs, and thus, the potential of phenotypic plasticity to evolve in populations exposed to different environmental conditions might be limited.
Assuntos
Adaptação Fisiológica/genética , Evolução Biológica , Drosophila simulans/genética , Drosophila simulans/fisiologia , Ecossistema , Temperatura , Animais , Feminino , Variação Genética , Masculino , Seleção GenéticaRESUMO
Recently, heterogeneity of the environment has been suggested as an important player in the evolution of life span variation. Established ageing theories propose that life span variation is the result of coevolution with other traits, such as stress resistance. This study aimed to compare these alternative hypotheses by examining the relationship between four environmental variables and different types of stress resistance traits with life span in 13 Drosophila species originating from tropical, subtropical and temperate environments (ecotypes). Average life span was found to differ significantly both between species and sexes, but only male life span correlated with the environment and cold resistance. While controlling for phylogeny, the environmental variable precipitation seasonality and resistance against cold-induced stress explained most variation in male life span. Furthermore, male life span varied between species in a manner represented by environmental variables linked to the different ecotypes, such that tropical species lived longer and were less cold resistant. The current results suggest that general mechanisms underlying stress resistance and life span are unlikely. In addition, our results point to the environment independently shaping variation in life span and cold resistance rather than genetic interactions.
Assuntos
Drosophila/fisiologia , Longevidade , Estresse Fisiológico , Animais , Drosophila/classificação , Feminino , Masculino , Especificidade da EspécieRESUMO
Many natural populations experience inbreeding and genetic drift as a consequence of nonrandom mating or low population size. Furthermore, they face environmental challenges that may interact synergistically with deleterious consequences of increased homozygosity and further decrease fitness. Most studies on inbreeding-environment (I-E) interactions use one or two stress levels, whereby the resolution of the possible stress and inbreeding depression interaction is low. Here we produced Drosophila melanogaster replicate populations, maintained at three different population sizes (10, 50 and a control size of 500) for 25 generations. A nutritional stress gradient was imposed on the replicate populations by exposing them to 11 different concentrations of yeast in the developmental medium. We assessed the consequences of nutritional stress by scoring egg-to-adult viability and body mass of emerged flies. We found: (1) unequivocal evidence for I-E interactions in egg-to-adult viability and to a lesser extent in dry body mass, with inbreeding depression being more severe under higher levels of nutritional stress; (2) a steeper increase in inbreeding depression for replicate populations of size 10 with increasing nutritional stress than for replicate populations of size 50; (3) a nonlinear norm of reaction between inbreeding depression and nutritional stress; and (4) a faster increase in number of lethal equivalents in replicate populations of size 10 compared with replicate populations of size 50 with increasing nutritional stress levels. Our data provide novel and strong evidence that deleterious fitness consequences of I-E interactions are more pronounced at higher nutritional stress and at higher inbreeding levels.
Assuntos
Drosophila melanogaster/genética , Aptidão Genética , Endogamia , Estresse Fisiológico/genética , Fenômenos Fisiológicos da Nutrição Animal , Animais , Peso Corporal , Drosophila melanogaster/fisiologia , Feminino , Interação Gene-Ambiente , Masculino , Modelos Genéticos , Densidade DemográficaRESUMO
Fitness decreases associated with inbreeding depression often become more pronounced in a stressful environment. The functional genomic causes of these inbreeding-by-environment (I × E) interactions, and of inbreeding depression in general, are poorly known. To further our understanding of I × E interactions, we performed a genome-wide gene expression study of a single inbred line that suffers from temperature-sensitive lethality. We confirmed that increased differential expression between the thermosensitive line and the control line occurs at the restrictive temperature. This demonstrates that I × E interactions in survival are reflected in similar I × E interactions at the gene expression level. To make an impression of the cellular response associated with the lethal effect, we analysed all functional annotation terms that were overrepresented among the differentially expressed genes. Some sets of differentially expressed genes function in the general stress response, and these are more likely to also be differentially expressed in other studies of inbreeding, inbreeding depression, immunity and heat stress. Other sets of differentially expressed genes are shared with studies of gene expression in inbred lines, but not studies of the response to extrinsic stress, and represent a general transcriptomic signature of inbreeding. Finally, some sets of genes have an annotation that is not reported in other studies. These we consider to be candidates for the genes harbouring the mutations responsible for the thermosensitive phenotype, as these mutations are expected to be unique to this line. These genes may also serve as candidate QTL in studies of thermal tolerance and heat resistance.
Assuntos
Drosophila melanogaster/fisiologia , Genes Letais , Temperatura Alta , Estresse Fisiológico , Animais , Drosophila melanogaster/genética , Genes de Insetos , Estudos de Associação Genética , Endogamia , Masculino , Fenótipo , Locos de Características Quantitativas , TranscriptomaRESUMO
The adaptability of organisms to novel environmental conditions depends on the amount of genetic variance present in the population as well as on the ability of individuals to adjust their phenotype through phenotypic plasticity. Here, we investigated the phenotypic plasticity induced by a single generation's exposure to three different temperature regimes with respect to several life-history and stress-resistance traits in a natural population of Drosophila simulans. We studied a constant as well as a predictably and an unpredictably fluctuating temperature regime. We found high levels of phenotypic plasticity among all temperature regimes, suggesting a strong influence of both temperature fluctuations and their predictability. Increased heat tolerance was observed for flies developed in both types of fluctuating thermal environments compared with flies developed in a constant environment. We suggest that this was due to beneficial hardening when developing in either fluctuating temperature environment. To our surprise, flies that developed in constant and predictably changing environments were similar to each other in most traits when compared to flies from the unpredictably fluctuating environment. The unpredictably changing thermal environment imposed the most stressful condition, resulting in the lowest performance for stress-related traits, even though the absolute temperature changes never exceeded that of the predictably fluctuating environment. The overall decreased stress resistance of flies in the unpredictably fluctuating environment may be the consequence of maladaptive phenotypic plasticity in this setting, indicating that the adaptive value of plasticity depends on the predictability of the environment.
Assuntos
Adaptação Fisiológica , Drosophila/fisiologia , Temperatura , Animais , Drosophila/genética , Feminino , FenótipoRESUMO
The ability to respond evolutionarily to increasing temperatures is important for survival of ectotherms in a changing climate. Recent studies suggest that upper thermal limits may be evolutionary constrained. We address this hypothesis in a laboratory evolution experiment, encompassing ecologically relevant thermal regimes. To examine the potential for species to respond to climate change, we exposed replicate populations of Drosophila melanogaster to increasing temperatures (0.3 °C every generation) for 20 generations, whereas corresponding replicate control populations were held at benign thermal conditions throughout the experiment. We hypothesized that replicate populations exposed to increasing temperatures would show increased resistance to warm and dry environments compared with replicate control populations. Contrasting replicate populations held at the two thermal regimes showed (i) an increase in desiccation resistance and a decline in heat knock-down resistance in replicate populations exposed to increasing temperatures, (ii) similar egg-to-adult viability and fecundity in replicate populations from the two thermal regimes, when assessed at high stressful temperatures and (iii) no difference in nucleotide diversity between thermal regimes. The limited scope for adaptive evolutionary responses shown in this study highlights the challenges faced by ectotherms under climate change.
Assuntos
Evolução Biológica , Drosophila melanogaster/fisiologia , Animais , Mudança Climática , Desidratação , Drosophila melanogaster/genética , Meio Ambiente , Feminino , Fertilidade , Aptidão Genética , Variação Genética , Laboratórios , Masculino , Óvulo , Estresse Fisiológico , TemperaturaRESUMO
Theoretical ecologists have long sought to understand how the persistence of populations depends on the interactions between exogenous (biotic and abiotic) and endogenous (e.g., demographic and genetic) drivers of population dynamics. Recent work focuses on the autocorrelation structure of environmental perturbations and its effects on the persistence of populations. Accurate estimation of extinction times and especially determination of the mechanisms affecting extinction times is important for biodiversity conservation. Here we examine the interaction between environmental fluctuations and the scaling effect of the mean population size with its variance. We investigate how interactions between environmental and demographic stochasticity can affect the mean time to extinction, change optimal patch size dynamics, and how it can alter the often-assumed linear relationship between the census size and the effective population size. The importance of the correlation between environmental and demographic variation depends on the relative importance of the two types of variation. We found the correlation to be important when the two types of variation were approximately equal; however, the importance of the correlation diminishes as one source of variation dominates. The implications of these findings are discussed from a conservation and eco-evolutionary point of view.
Assuntos
Evolução Biológica , Ecossistema , Extinção Biológica , Modelos Biológicos , Modelos Estatísticos , Crescimento Demográfico , Comportamento Predatório/fisiologia , Animais , Simulação por Computador , Abastecimento de Alimentos/estatística & dados numéricos , HumanosRESUMO
Heat-induced hormesis, i.e. the beneficial effect of mild heat-induced stress, increases the average lifespan of many organisms. This effect, which depends on the heat shock factor, decreases the log mortality rate weeks after the stress has ceased. To identify candidate genes that mediate this lifespan-prolonging effect late in life, we treated flies with mild heat stress (34 °C for 2 h) 3 times early in life and compared the transcriptomic response in these flies versus non-heat-treated controls 10-51 days after the last heat treatment. We found significant transcriptomic changes in the heat-treated flies. Several hsp70 probe sets were up-regulated 1.7-2-fold in the mildly stressed flies weeks after the last heat treatment (P<0.01). This result was unexpected as the major Drosophila heat shock protein, Hsp70, is reported to return to normal levels of expression shortly after heat stress. We conclude that the heat shock response, and Hsp70 in particular, may be central to the heat-induced increase in the average lifespan in flies that are exposed to mild heat stress early in life.
Assuntos
Drosophila melanogaster/genética , Proteínas de Choque Térmico/fisiologia , Temperatura Alta , Longevidade/fisiologia , Transcriptoma/fisiologia , Animais , Drosophila melanogaster/fisiologia , Regulação da Expressão Gênica/fisiologia , Proteínas de Choque Térmico HSP70/fisiologia , Resposta ao Choque Térmico/fisiologiaRESUMO
The behavior of ectotherm organisms is affected by both abiotic and biotic factors. However, a limited number of studies have investigated the synergistic effects on behavioral traits. This study examined the effect of temperature and density on locomotor activity of Musca domestica (L.). Locomotor activity was measured for both sexes and at four densities (with mixed sexes) during a full light and dark (L:D) cycle at temperatures ranging from 10 to 40°C. Locomotor activity during daytime increased with temperature at all densities until reaching 30°C and then decreased. High-density treatments significantly reduced the locomotor activity per fly, except at 15°C. For both sexes, daytime activity also increased with temperature until reaching 30 and 35°C for males and females, respectively, and thereafter decreased. Furthermore, males showed a significantly higher and more predictable locomotor activity than females. During nighttime, locomotor activity was considerably lower for all treatments. Altogether the results of the current study show that there is a significant interaction of temperature and density on daytime locomotor activity of M. domestica and that houseflies are likely to show significant changes in locomotor activity with change in temperature.
Assuntos
Moscas Domésticas/fisiologia , Atividade Motora , Animais , Ritmo Circadiano , Feminino , Masculino , Densidade Demográfica , Fatores Sexuais , TemperaturaRESUMO
Various compositions of fatty acids can produce cell membranes with disparate fluidity and propensity for oxidation. The latter characteristic, which can be evaluated via the peroxidation index (PI), has a fundamental role in the development of the "membrane-pacemaker theory" of aging. This study tried to evaluate differences between the membrane phospholipid fatty acid (PLFA) profile of longevity-selected (L) and corresponding control (C) lines of Drosophila melanogaster with age (3, 9, 14 and 19 days) and its consequences on phase transition temperature as a function of membrane fluidity. Despite an equal proportion of polyunsaturated fatty acids, PI and double bond index over all ages in both experimental groups, monounsaturated fatty acids showed significant variation with advancement of age in both L and C lines. A significant age-associated elevation of the unsaturation vs. saturation index in parallel with a gradual reduction of the mean melting point was observed in longevous flies. PLFA composition of the L vs. C lines revealed a dissimilarity in 3-day old samples, which was based on the positive loading of C(14:0) and C(18:3) as well as negative loading of C(18:0). The findings of this study are not in agreement with the principle of the "membrane pacemaker theory" linking PI and longevity. However, the physiochemical properties of PLFAs in longevity lines may retard the cells' senescence by maintaining optimal membrane functionality over time. Identical susceptibility to peroxidation of both types of lines underlines the involvement of other mechanisms in protecting the bio-membrane against oxidation, such as the reduced production of mitochondrial reactive oxygen species or improvement of the antioxidant defense system in longer-lived phenotypes. Concurrent assessments of these mechanisms in relation to cell membrane PLFA composition may clarify the cellular basis of lifespan in this species.
Assuntos
Envelhecimento/metabolismo , Drosophila melanogaster/metabolismo , Longevidade/fisiologia , Lipídeos de Membrana/metabolismo , Animais , Ácidos Graxos/química , Ácidos Graxos/metabolismo , Feminino , Peroxidação de Lipídeos , Masculino , Fluidez de Membrana , Lipídeos de Membrana/química , Mitocôndrias/metabolismo , Transição de Fase , Fosfolipídeos/química , Fosfolipídeos/metabolismo , Espécies Reativas de Oxigênio/metabolismoRESUMO
In sexually reproducing species, increased homozygosity often causes a decline in fitness, called inbreeding depression. Recently, researchers started describing the functional genomic changes that occur during inbreeding, both in benign conditions and under environmental stress. To further this aim, we have performed a genome-wide gene expression study of inbreeding depression, manifesting as cold sensitivity and conditional lethality. Our focus was to describe general patterns of gene expression during inbreeding depression and to identify specific processes affected in our line. There was a clear difference in gene expression between the stressful restrictive environment and the benign permissive environment in both the affected inbred line and the inbred control line. We noted a strong inbreeding-by-environment interaction, whereby virtually all transcriptional differences between lines were found in the restrictive environment. Functional annotation showed enrichment of transcripts coding for serine proteases and their inhibitors (serpins and BPTI/Kunitz family), which indicates activation of the innate immune response. These genes have previously been shown to respond transcriptionally to cold stress, suggesting the conditional lethal effect is associated with an exaggerated cold stress response. The set of differentially expressed genes significantly overlapped with those found in three other studies of inbreeding depression, demonstrating that it is possible to detect a common signature across different genetic backgrounds.
Assuntos
Temperatura Baixa , Drosophila melanogaster/imunologia , Regulação da Expressão Gênica/imunologia , Imunidade Inata/imunologia , Endogamia , Estresse Fisiológico/genética , Animais , Análise por Conglomerados , Biologia Computacional , Drosophila melanogaster/genética , Masculino , Análise de Sequência com Séries de Oligonucleotídeos , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
The impact of landscape structure and land management on dispersal of populations of wild species inhabiting the agricultural landscape was investigated focusing on the field vole (Microtus agrestis) in three different areas in Denmark using molecular genetic markers. The main hypotheses were the following: (i) organic farms act as genetic sources and diversity reservoirs for species living in agricultural areas and (ii) gene flow and genetic structure in the agricultural landscape are influenced by the degree of landscape complexity and connectivity. A total of 443 individual voles were sampled within 2 consecutive years from two agricultural areas and one relatively undisturbed grassland area. As genetic markers, 15 polymorphic microsatellite loci (nuclear markers) and the central part of the cytochrome-b (mitochondrial sequence) were analysed for all samples. The results indicate that management (that is, organic or conventional management) was important for genetic population structure across the landscape, but that landscape structure was the main factor shaping gene flow and genetic diversity. More importantly, the presence of organically managed areas did not act as a genetic reservoir for conventional areas, instead the most important predictor of effective population size was the amount of unmanaged available habitat (core area). The relatively undisturbed natural area showed a lower level of genetic structuring and genetic diversity compared with the two agricultural areas. These findings altogether suggest that political decisions for supporting wildlife friendly land management should take into account both management and landscape structure factors.
Assuntos
Arvicolinae/genética , Ecossistema , Fluxo Gênico , Agricultura , Animais , Dinamarca , Marcadores Genéticos , Variação Genética , Repetições de Microssatélites , Dados de Sequência MolecularRESUMO
This investigation presents results from a genetic characterization of 5 Danish dog breeds genotyped on the CanineHD BeadChip microarray with 170,000 SNP. The breeds investigated were 1) Danish Spitz (DS; n=8), 2) Danish-Swedish Farm Dog (DSF; n=18), 3) Broholmer (BR; n=22), 4) Old Danish Pointing Dog (ODP; n=24), and 5) Greenland Dog (GD; n=23). The aims of the investigation were to characterize the genetic profile of the abovementioned dog breeds by quantifying the genetic differentiation among them and the degree of genetic homogeneity within breeds. The genetic profile was determined by means of principal component analysis (PCA) and through a Bayesian clustering method. Both the PCA and the Bayesian clustering method revealed a clear genetic separation of the 5 breeds. The level of genetic variation within the breeds varied. The expected heterozygosity (HE) as well as the degree of polymorphism (P%) ranked the dog breeds in the order DS>DSF>BR>ODP>GD. Interestingly, the breed with a tenfold higher census population size compared to the other breeds, the Greenland Dog, had the lowest within-breed genetic variation, emphasizing that census size is a poor predictor of genetic variation. The observed differences in variation among and within dog breeds may be related to factors such as genetic drift, founder effects, genetic admixture, and population bottlenecks. We further examined whether the observed genetic patterns in the 5 dog breeds can be used to design breeding strategies for the preservation of the genetic pool of these dog breeds.
Assuntos
Cruzamento , Cães/genética , Variação Genética , Genótipo , Transcriptoma , Animais , DNA/genética , Dinamarca , Polimorfismo GenéticoRESUMO
In insects, pre-adult stages of the life cycle are exposed to variation in temperature that may differ from that in adults. However, the genetic basis for adaptation to environmental temperature could be similar between the pre-adult and the adult stages of the life cycle. Here, we tested quantitative trait loci (QTL) for heat-stress survival in larvae of Drosophila melanogaster, with and without a mild-heat-stress pre-treatment. Two sets of recombinant inbred lines derived from lines artificially selected for high and low levels of knockdown resistance to high temperature in young flies were used as the mapping population. There was no apparent increase in heat-shock survival between heat-pretreated and non-pretreated larvae. There was a positive correlation between the two experimental conditions of heat-shock survival (with and without a heat pre-treatment) except for males from one set of lines. Several QTL were identified involving all three major chromosomes. Most QTL for larval thermotolerance overlapped with thermotolerance QTL identified in previous studies for adults, indicating that heat-stress resistance is not genetically independent between life cycle stages because of either linkage or pleiotropy. The sign of the effects of some QTL alleles differed both between the sexes and between life stages.
Assuntos
Drosophila melanogaster/crescimento & desenvolvimento , Drosophila melanogaster/fisiologia , Resposta ao Choque Térmico/fisiologia , Endogamia , Recombinação Genética/genética , Análise de Variância , Animais , Drosophila melanogaster/genética , Feminino , Estágios do Ciclo de Vida , Funções Verossimilhança , Masculino , Locos de Características Quantitativas/genéticaRESUMO
The American mink (Neovison vison) was introduced to Danish fur farms in the 1930s. An unknown number of mink have managed to escape these farms over the years. Today feral mink are found in the wild in most parts of Denmark. A population viability analysis (PVA) was performed using VORTEX, a stochastic population simulation software, to 1) predict the viability and potential population expansion from different sizes of founding populations of farm escapees, 2) investigate which parameters mostly affect the viability, 3) assess the effects of continuous escapes on the feral populations and how the feral populations are affected by management programs, and 4) discuss eradication strategies and their efficiency in management of the feral American mink population in Denmark. The simulations showed that juvenile mortality had the greatest effect on population viability followed by fecundity, adult mortality, and initial population size. Populations supplemented yearly by escapees all reached the carrying capacity and gained genetic variability over the years. Harvesting was modeled as the yearly number of mink caught in Denmark. Most of the simulated harvested populations crashed within few years after the first harvesting event. This indicates that the feral number of mink in Denmark is sustained due to supplements from mink farms and no true feral population exists. To manage the number of feral mink in Denmark it is essential to prevent escapees. The eradication effort would be most effective if focused on late summer and autumn when juvenile mink leave the maternal territory.
Assuntos
Criação de Animais Domésticos , Conservação dos Recursos Naturais , Variação Genética , Vison/fisiologia , Animais , Dinamarca , Espécies Introduzidas , Vison/genética , Modelos Biológicos , Densidade Demográfica , Dinâmica PopulacionalRESUMO
This article documents the addition of 83 microsatellite marker loci and 96 pairs of single-nucleotide polymorphism (SNP) sequencing primers to the Molecular Ecology Resources Database. Loci were developed for the following species: Bembidion lampros, Inimicus japonicus, Lymnaea stagnalis, Panopea abbreviata, Pentadesma butyracea, Sycoscapter hirticola and Thanatephorus cucumeris (anamorph: Rhizoctonia solani). These loci were cross-tested on the following species: Pentadesma grandifolia and Pentadesma reyndersii. This article also documents the addition of 96 sequencing primer pairs and 88 allele-specific primers or probes for Plutella xylostella.
Assuntos
Primers do DNA/genética , Bases de Dados Genéticas , Repetições de Microssatélites/genética , Polimorfismo de Nucleotídeo Único/genética , Animais , Sequência de Bases , Ecologia/métodos , Biologia Molecular/métodos , Dados de Sequência Molecular , Análise de Sequência de DNA , Especificidade da EspécieRESUMO
Laboratory experiments on Drosophila have often demonstrated increased heritability for morphological and life-history traits under environmental stress. We used parent-offspring comparisons to examine the impact of humidity levels on the heritability of a physiological trait, resistance to heat, measured as knockdown time at constant temperature. Drosophila melanogaster were reared under standard nonstressful conditions and heat-shocked as adults at extreme high or low humidity. Mean knockdown time was decreased in the stressful dry environment, but there was a significant sex-by-treatment interaction: at low humidity, females were more heat resistant than males, whereas at high humidity, the situation was reversed. Phenotypic variability of knockdown time was also lower in the dry environment. The magnitude of genetic correlation between the sexes at high humidity indicated genetic variation for sexual dimorphism in heat resistance. Heritability estimates based on one-parent-offspring regressions tended to be higher under desiccation stress, and this could be explained by decreased environmental variance of heat resistance at low humidity. There was no indication that the additive genetic variance and evolvability of heat resistance differed between the environments. The pattern of heritability estimates suggests that populations of D. melanogaster may have a greater potential for evolving higher thermal tolerance under arid conditions.
Assuntos
Adaptação Fisiológica , Drosophila melanogaster/genética , Umidade , Temperatura , Animais , Drosophila melanogaster/fisiologia , Feminino , Variação Genética , Padrões de Herança , Masculino , Fenótipo , Análise de Regressão , Caracteres Sexuais , Estresse Fisiológico , Fatores de TempoRESUMO
It has frequently been suggested that trait heritabilities are environmentally sensitive, and there are genetic trade-offs between tolerating different environments such as hot and cold or constant and fluctuating temperatures. Future climate predictions suggest an increase in both temperatures and their fluctuations. How species will respond to these changes is uncertain, particularly as there is a lack of studies which compare genetic performances in constant vs. fluctuating environments. In this study, we used a nested full-sib/half-sib breeding design to examine how the genetic variances and heritabilities of egg-to-adult viability differ at high and low temperatures with and without daily fluctuations in temperatures using Drosophila melanogaster as a model organism. Although egg-to-adult viability was clearly sensitive to developmental temperatures, heritabilities were not particularly sensitive to developmental temperatures. Moreover, we found that egg-to-adult viabilities at different developmental temperatures were positively correlated, suggesting a common genetic background for egg-to-adult viability at different temperatures. Finding both a uniform genetic background coupled with rather low heritabilities insensitive to temperatures, our results suggest evolutionary responses are unlikely to be limited by temperature effects on genetic parameters or negative genetic correlations, but by the direct effects of stressful temperatures on egg-to-adult viability accompanied with low heritabilities.