Contribution of symbiotic microbiota to adaptation of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> to an unfavorable growth medium

The contribution of symbiotic microbiota to the adaptation of Drosophila melanogaster to fodder with an increased content of NaCl has been analyzed. The reproduction efficiency and the development rate of D. melanogaster on the saline fodder medium, on which a homogenate of flies from laboratory salt-adapted lines and from control lines not adapted to the salt were inoculated, were compared. It was established that inoculating with homogenized salt-adapted flies significantly increased the efficiency of use of salty fodders by flies in comparison with the control flies homogenate, which is manifested in the increased number of offspring produced by a pair of parents over a fixed time, and also in faster larval development. It was noted that the results obtained were consistent with the assumption that the adaptation of D. melanogaster to salted fodder is largely due not to genetic changes in the experimental populations but to changes in the concomitant bacterial and yeast microbiota.     

Adaptive nature of the transition phases in development: the case of Sorghum bicolor

An increase in tolerance to salinity is induced in Sorghum bicolor by exposure to a sublethal concentration of NaCl during early vegetative development. The phase of competence for induction of this response, termed salt adaptation, is well defined in time and it coincides with the emergence of the first adventitious roots. The link between these events was investigated. Competence for salt adaptation varies among genotypes. It is shown that competence is especially high for genotypes in which the link between the seminal root and the shoot is reduced during emergence of the adventitious root. These data relate the capacity for salt adaptation with development in the absence of NaCl, suggesting that: (i) functional integration of the adventitious roots within the whole plant has an adaptive nature in normal development; (ii) salt adaptation results from an integration of the environmental constraint (NaCl) during this developmental readjustment. It is concluded that perturbations generated by emergence of a new organ are the cause of rapid variations in sensitivity required to open a competence window.     

Adaptation of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> to increased NaCl concentration due to dominant beneficial mutations

New beneficial mutations, combined with selection, were responsible for quick adaptation of Drosophila melanogaster to a novel environment. Using a highly inbred homozygous stock of D. melanogaster, we observed that in thirty generations the original stock had evolved to resist a previously toxic level of dietary salt (NaCl) and to produce a significantly higher number of progeny when reared in elevated salt concentrations. Survival in higher salt-stressed environments was due to new dominant genetic changes on the second and third chromosomes.     

LIFE-HISTORY CONSEQUENCES OF ADAPTATION TO LARVAL NUTRITIONAL STRESS IN DROSOPHILA

Many animal species face periods of chronic nutritional stress during which the individuals must continue to develop, grow, and/or reproduce despite low quantity or quality of food. Here, we use experimental evolution to study adaptation to such chronic nutritional stress in six replicate Drosophila melanogaster populations selected for the ability to survive and develop within a limited time on a very poor larval food. In unselected control populations, this poor food resulted in 20% lower egg‐to‐adult viability, 70% longer egg‐to‐adult development, and 50% lower adult body weight (compared to the standard food on which the flies were normally maintained). The evolutionary changes associated with adaptation to the poor food were assayed by comparing the selected and control lines in a common environment for different traits after 29–64 generations of selection. The selected populations evolved improved egg‐to‐adult viability and faster development on poor food. Even though the adult dry weight of selected flies when raised on the poor food was lower than that of controls, their average larval growth rate was higher. No differences in proportional pupal lipid content were observed. When raised on the standard food, the selected flies showed the same egg‐to‐adult viability and the same resistance to larval heat and cold shock as the controls and a slightly shorter developmental time. However, despite only 4% shorter development time, the adults of selected populations raised on the standard food were 13% smaller and showed 20% lower early‐life fecundity than the controls, with no differences in life span. The selected flies also turned out less tolerant to adult malnutrition. Thus, fruit flies have the genetic potential to adapt to poor larval food, with no detectable loss of larval performance on the standard food. However, adaptation to larval nutritional stress is associated with trade‐offs with adult fitness components, including adult tolerance to nutritional stress.     

Pre-exposure affects the olfactory response of Drosophila melanogaster to menthol

A modification of the trap assay (Woodard et al., 1989) was used to evaluate the response of Drosophila melanogaster (Meigen) to food media containing menthol. Dose-response curves for flies to mentholic foods were produced for flies that had been pre-exposed to menthol, during development and adult life, and flies that had not been exposed to menthol before the assay. Mentholic food media were less attractive to Drosophila than plain food medium. Rearing flies on a medium containing menthol reduced their aversion to some concentrations of menthol. The rearing effect was not simply due to lowered general activity levels resulting from developing in a medium containing menthol. There was a threshold concentration of menthol in the rearing medium below which we found no induced behavioural change.     

Dietary salt levels affect salt preference and learning in larval Drosophila

Drosophila larvae change from exhibiting attraction to aversion as the concentration of salt in a substrate is increased. However, some aversive concentrations appear to act as positive reinforcers, increasing attraction to an odour with which they have been paired. We test whether this surprising dissociation between the unconditioned and conditioned response depends on the larvae's experience of salt concentration in their food. We find that although the point at which a NaCl concentration becomes aversive shifts with different rearing experience, the dissociation remains evident. Testing larvae using a substrate 0.025 M above the NaCl concentration on which the larvae were reared consistently results in aversive choice behaviour but appetitive reinforcement effects.     

苜蓿悬浮细胞对盐胁迫的反应和适应

苜蓿悬浮细胞能够适应200mmol/L NaCl及其以下盐浓度的胁迫,适应细胞中游离脯氨酸、还原糖和Na~ 积累增加。400mmol/LNaCl对细胞生长明显抑制。细胞对盐胁迫的反应和适应中PM-ATPase和TM-ATPase起到重要作用,在适应细胞中两者的活力都明显增加。PM-ATPase活力的增加可受CHX的明显抑制。     

The importance of pre-and postcopulatory sexual selection promoting adaptation to increasing temperatures

Global temperatures are increasing rapidly affecting species globally. Understanding if and how different species can adapt fast enough to keep up with increasing temperatures is of vital importance. One mechanism that can accelerate adaptation and promote evolutionary rescue is sexual selection. Two different mechanisms by which sexual selection can facilitate adaptation are pre- and postcopulatory sexual selection. However, the relative effects of these different forms of sexual selection in promoting adaptation are unknown. Here, we present the results from an experimental study in which we exposed fruit flies Drosophila melanogaster to either no mate choice or 1 of 2 different sexual selection regimes (pre- and postcopulatory sexual selection) for 6 generations, under different thermal regimes. Populations showed evidence of thermal adaptation under precopulatory sexual selection, but this effect was not detected in the postcopulatory sexual selection and the no choice mating regime. We further demonstrate that sexual dimorphism decreased when flies evolved under increasing temperatures, consistent with recent theory predicting more sexually concordant selection under environmental stress. Our results suggest an important role for precopulatory sexual selection in promoting thermal adaptation and evolutionary rescue.     

Natural selection in a bottle

The study of natural selection in laboratory systems undergoing experimental evolution can provide important insights into the relationship between natural selection and adaptation. We studied selection on the norm of reaction of age at first reproduction in a laboratory population of Drosophila melanogaster. This population had been selected on a discrete generation schedule in the laboratory for more than 600 generations. Using genetically marked strains, we studied development time, size, female fecundity, and viability of flies that began development at different times relative to the initiation of each bottle. Only flies that began development within 30 h of the initiation of the bottle were reliably able to eclose before the next transfer. Theory predicts that flies initiating development around this critical time should decrease size at maturity to ensure eclosion by the 14-d deadline, but late flies are not smaller. This result suggests an unknown constraint on response to selection on age at maturity in this population. Ultimately, laboratory systems provide the best opportunity for the study of natural selection, genetic variation, and evolutionary response in the same population.     

Natural and artificial selection on a deviant character of the anal papillae in Drosophila melanogaster and their significance for salt adaptation

Artificial selection was carried out on a deviant character of remnants of the anal papillae in pupae of Drosophila melanogaster, i. e. stretched (S) instead of the normal retracted (R) papillae. A chromosomal interchange between the R- and S-selection lines revealed the polygenic determination of the S-character. A comparison of lines with a different number of chromosomes of the S-line shows the importance of properties of the anal papillae for salt adaptation. By a comparison of populations obtained by artificial selection for anal papillae and by natural selection for salt adaptation we could analyse the significance of the deviant character under natural selection on media with increasing percentages of salt. Our results shows that taking into account only one character in natural selection is often a simplification. However, applying artificial selection on components of the phenotype contributing to the adaptation make an important contribution to the analysis of adaptive processes.     

THE RESPONSES OF DROSOPHILA MELANOGASTER TO ARTIFICIAL SELECTION ON BODY WEIGHT AND ITS PHENOTYPIC PLASTICITY IN TWO LARVAL FOOD ENVIRONMENTS

To investigate the potential response to natural selection of reaction norms for age and size at maturity, fresh body weight at eclosion was mass selected under rich and poor larval food conditions in Drosophila melanogaster. The sensitivity of dry weight at eclosion to the difference between rich and poor larval food was selected using differences in sensitivities among families. For both experiments, the correlated response to selection of age at eclosion was examined. The flies were derived from wild populations and had been mass cultured in the lab for more than six months before the experiments started. These flies responded to selection on body weight upwards and downwards on both rich and poor larval food. Selection on increased or decreased sensitivity of body weight was also successful in at least one direction. Sensitivity was reduced by selection upwards in a poor environment and downwards in a rich environment.     

Cooperation between Drosophila flies in searching behavior

In Drosophila melanogaster food search behaviour, groups of flies swarm around and aggregate on patches of food. We wondered whether flies explore their environment in a cooperative way as interactions between individual flies within a population might influence the flies' ability to locate food sources. We have shown that the food search behavior in the fruit fly Drosophila is a two-step process. Firstly, 'primer' flies search the environment and randomly land on different food patches. Secondly, the remaining group of flies move to the most favorable food source and aggregate there. We call this a 'search–aggregation' cycle. Our data demonstrate that flies do not individually assess all available food resources. Rather, social interactions between flies appear to affect their choice of a specific food patch. A genetic analysis of this 'search–aggregation' behavior shows that flies carrying mutations in specific genes (for example, the dunce ( dnc ) gene which codes for a phosphodiesterase) were defective in this search–aggregation behavior when compared to normal flies. Future investigations of the neuronal signaling involved in this behavior will help us to understand the complexities of this aspect of Drosophila social behaviour.     

The response of the filamentous cyanobacterium Spirulina platensis to salt stress

The responses of the filamentous cyanobacterium Spirulina platensis to increased NaCl concentrations (0.25–1.0 M) in addition to the concentration of sodium in the growth medium were studied. A two stage response to the salt stress was observed. This consisted of a relatively short shock stage, followed by adaptation process. It was shown that upon exposure to high salt concentrations of 0.5 M and above, immediate inhibition of photosynthesis and respiration, and complete cessation of growth occurred. After a time lag, the energy-yielding processes exhibited restored activity. At 0.5 and 1.0M NaCl photosynthesis reached 80% and 50% that of the control, while respiration was enhanced by 140 and 200%, respectively. The time lags were longer when the cells were exposed to higher NaCl concentrations. The resumption of growth and the establishment of new steady state growth rates were found to be correlated to the recovery in respiration. The relationship between the growth rates after adaptation and the increased NaCl concentrations was found to be inversely linear. The cellular sodium content was maintained at a constant low level, regardless of the external NaCl concentration, while potassium content declined linearly vs. the external NaCl concentration. The carbohydrate content of the cells rose exponentially with the increase in NaCl concentration.Publication No. 34 from the Micro-Algal Biotechnology Lab.     

Evolution of increased adult longevity in Drosophila melanogaster populations selected for adaptation to larval crowding

In holometabolous animals such as Drosophila melanogaster, larval crowding can affect a wide range of larval and adult traits. Adults emerging from high larval density cultures have smaller body size and increased mean life span compared to flies emerging from low larval density cultures. Therefore, adaptation to larval crowding could potentially affect adult longevity as a correlated response. We addressed this issue by studying a set of large, outbred populations of D. melanogaster, experimentally evolved for adaptation to larval crowding for 83 generations. We assayed longevity of adult flies from both selected (MCUs) and control populations (MBs) after growing them at different larval densities. We found that MCUs have evolved increased mean longevity compared to MBs at all larval densities. The interaction between selection regime and larval density was not significant, indicating that the density dependence of mean longevity had not evolved in the MCU populations. The increase in longevity in MCUs can be partially attributed to their lower rates of ageing. It is also noteworthy that reaction norm of dry body weight, a trait probably under direct selection in our populations, has indeed evolved in MCU populations. To the best of our knowledge, this is the first report of the evolution of adult longevity as a correlated response of adaptation to larval crowding.     

肠道微生物群加重黑腹果蝇盐胁迫反应

【背景】高盐饮食目前引起普遍关注,肠道微生物与盐胁迫的相互作用正成为研究热点之一。【目的】以黑腹果蝇为宿主模型,探讨肠道微生物对果蝇盐胁迫反应的影响与潜在机理。【方法】利用平板计数法和定量PCR法检测果蝇肠道载菌量;利用存活率和运动能力测定装置测定果蝇适合度;用化学试剂和抗生素处理建立无菌果蝇,测定肠道菌对果蝇盐胁迫反应的影响;利用亮蓝食用色素染料渗透性实验检测果蝇肠道屏障的完整性;应用实时定量PCR检测先天免疫系统的活性。【结果】高盐处理引起果蝇肠道菌群失调,导致其肠道载菌量显著增加。此外,高盐饮食(high salt diet,HSD)降低了黑腹果蝇成虫的存活率和运动能力。经0.75 mol/L NaCl处理,雌性GF (germ-free)果蝇存活率比对照组升高了11%,同时混合抗生素有效地提高了高盐处理后果蝇的存活率。肠道微生物加剧了肠道屏障功能损伤,雌性GF果蝇出现染料渗透性实验现象的百分率比对照组降低了8%。在分子水平上,盐胁迫下雌性GF果蝇体内Attacin-C、Duox基因表达水平分别是CR(conventionally reared)果蝇的2.5倍和1.7倍。【结论】肠道微生物加重果蝇盐胁迫反应,引发高盐诱导的肠屏障功能紊乱,并且抑制高盐诱导的先天免疫活性。     

Behavioral, physical, and demographic changes in Drosophila populations through dietary restriction

Dietary restriction (DR) is a valuable experimental tool for studying the aging process. Primary advancement of research in this area has relied on rodent models, but attention has recently turned toward Drosophila melanogaster. However, little is known about the baseline effects of DR on wild-type Drosophila and continued experimentation requires such information. The findings described here survey the effects of DR on inbred, wild-type populations of Canton-S fruit flies and demonstrate a robust effect of diet on longevity. Over a circumscribed range of dietary conditions, healthy lifespan varies by as much as 121% for wild-type Drosophila females. Significant differences are also observed for male flies, but the magnitude of the DR effect is less robust. Mortality analyses of the survivorship data reveal that this variation in lifespan can be attributed to a modulation of the rate parameter for the mortality function - a change in the demographic rate of aging. Since the feeding of fruit flies is less easily controlled than that of rodents, this research also addresses the validity of applying a DR model to Drosophila populations. Feeding and body weight data for flies given the various dietary conditions surveyed indicate that Drosophila on higher-calorie diets consume a similar volume of food to those on a low-calorie diet, resulting in different levels of calorie intake. Fertility and activity levels demonstrate that the diets surveyed are comparable, and that increasing the calorie content of laboratory food up to twice the normal concentration is not pathologic for experimental fly populations.     

Indirect selection of thermal tolerance during experimental evolution of Drosophila melanogaster

Natural selection alters the distribution of a trait in a population and indirectly alters the distribution of genetically correlated traits. Long‐standing models of thermal adaptation assume that trade‐offs exist between fitness at different temperatures; however, experimental evolution often fails to reveal such trade‐offs. Here, we show that adaptation to benign temperatures in experimental populations of Drosophila melanogaster resulted in correlated responses at the boundaries of the thermal niche. Specifically, adaptation to fluctuating temperatures (16–25°C) decreased tolerance of extreme heat. Surprisingly, flies adapted to a constant temperature of 25°C had greater cold tolerance than did flies adapted to other thermal conditions, including a constant temperature of 16°C. As our populations were never exposed to extreme temperatures during selection, divergence of thermal tolerance likely reflects indirect selection of standing genetic variation via linkage or pleiotropy. We found no relationship between heat and cold tolerances in these populations. Our results show that the thermal niche evolves by direct and indirect selection, in ways that are more complicated than assumed by theoretical models.     

Alcohol dehydrogenase and adaptation to ethanol in Drosophila

The subject of this research is activity and allozyme spectra of alcohol dehydrogenase (ADH), and survival of mutant strains of Drosophila kept in standard nutrient medium with added ethanol. In all experiments the ADH of flies revealed greater affinity to isopropanol than ethanol. The mutant strains considerably differed from one another and from the wild type of flies in the level of enzyme activity, which may be connected with genotypic properties in the mutants studied. The ADH variability in mutant strains seems to be caused by different alleles of the structural ADH gene, which was established as a result of investigation of activity, electrophoretic mobility and thermostability of corresponding allozymes. As follows from experiments on the genotypical structure of populations in the conditions of fly selection in the medium containing ethanol (10%), the adaptation of flies to exogenous ethanol takes place via mechanisms of allele control of the ADH activity. Phenotypical manifestation of the ADH locus and its effect on the resistance of Drosophila to alcohol are supposed to depend on complex gene interactions determined by the genotype as a whole.     

苜蓿愈伤组织盐适应过程中的溶质积累

通过一步筛选获得耐1.0％NaCl的苜蓿愈伤组织(S-1)。比较盐适应(S-1)和未经适应愈伤组织(S-0)在1.0％NaCl培养基上溶质积累的情况,渗透势的下降S-0略低于S-1;S-0细胞变小,S-1细胞无明显变化,含水量S-0比S-1下降多,Na~ 和Cl~-大量积累,S-0低于S-1,K~ 浓度升高,但含量下降,S-0比S-1下降多,脯氨酸和可溶性还原糖含量的增加S-0远高于S-1。对于含盐培养基上S-0和S-1渗透调节模式的差异及溶质积累与盐适应的关系,可以认为增加Na~ 和Cl~-积累是苜蓿愈伤组织盐适应的主要方面,脯氨酸和可溶性还原糖的增加在渗透适应上只起部分作用。     

黑腹果蝇对高盐的产卵避性反应及其生物学意义

【目的】研究黑腹果蝇Drosophila melanogaster对高盐的产卵避性,并通过高盐下后代生存率和发育历期的变化来揭示这一现象的生物学意义。【方法】应用产卵双选择装置,检测黑腹果蝇和雅库巴果蝇D. yakuba雌成虫分别对含有0. 25和1 mol/L NaCl的培养基的产卵选择性;利用产卵装置,检测黑腹果蝇对1 mol/L NaCl的位置效应;通过强迫产卵实验检测钠盐胁迫下黑腹果蝇的产卵能力;通过毛细管摄食法和观察口器延伸,检测钠盐胁迫下黑腹果蝇的摄食行为。利用黑暗条件和突变体Orco2分别探究视觉和嗅觉对高盐的产卵选择性。通过外科手术法摘除黑腹果蝇前足部分味觉感受器,并使用咸味突变体Ionotropic Receptor 76b (IR76b),研究介导该行为的感觉系统。在含有不同浓度NaCl (0,0. 25,0. 50,0. 75和1 mol/L)的培养基上培养黑腹果蝇,探究NaCl对黑腹果蝇后代的发育历期和存活率的影响。【结果】雌性黑腹果蝇产卵对高盐产生避性反应,对0. 25和1 mol/L NaCl的产卵偏嗜指数分别为-0. 45和-0. 59;雅库巴果蝇对高盐的反应与黑腹果蝇相同,对0. 25和1 mol/L NaCl的产卵偏嗜指数分别为-0. 78和-0. 99;并且两种果蝇均对0. 25和1 mol/L KCl和CaCl2产生产卵避性反应。黑腹果蝇避开含0. 25和1 mol/L NaCl培养基,位置指数分别为-0. 74和-0. 88。高盐不影响黑腹果蝇的生育能力,其对0,0. 25和1 mol/L NaCl的产卵指数分别为5. 59,6. 63和5. 41。黑腹果蝇对0. 25和1 mol/L NaCl摄食产生明显排斥反应,摄食指数分别为-0. 37和-0. 41,且随浓度增大食欲越低。同时在黑暗条件下,黑腹果蝇对0. 25和1 mol/L NaCl仍产生了显著的避性反应,产卵偏嗜指数分别为-0. 49和-0. 59,摘除前足的黑腹果蝇对0. 25 mol/L NaCl的产卵偏嗜指数为-0. 05,IR76b突变体对高盐的产卵避性反应消失,对0. 25和1 mol/L NaCl的产卵偏嗜指数分别为0. 46和0. 39。0. 25 mol/L NaCl明显延长了后代成蛹时间0. 40 d,后代幼虫存活率降低了16. 5%,而在1 mol/L NaCl上后代卵完全不能形成蛹和成虫。【结论】黑腹果蝇雌成虫通过咸味感觉器官感知高盐而产生产卵避性反应,以促进后代的生长发育和提高后代的幼虫存活率。