Trade-off of energy metabolites as well as body color phenotypes for starvation and desiccation resistance in montane populations of Drosophila melanogaster

Storage of energy metabolites has been investigated in different sets of laboratory selected desiccation or starvation resistant lines but few studies have examined such changes in wild-caught populations of Drosophila melanogaster. In contrast to parallel selection of desiccation and starvation tolerance under laboratory selection experiments, opposite clines were observed in wild populations of D. melanogaster. If resistance to desiccation and starvation occurs in opposite directions under field conditions, we may expect a trade-off for energy metabolites but such correlated changes are largely unknown. We tested whether there is a trade-off for storage as well as actual utilization of carbohydrates (trehalose and glycogen), lipids and proteins in D. melanogaster populations collected from different altitudes (512-2500 m). For desiccation resistance, darker flies (> 50% body melanization) store more body water content and endure greater loss of water (higher dehydration tolerance) as compared to lighter flies (< 30% body melanization). Based on within population analysis, we found evidence for coadapted phenotypes i.e. darker flies store and actually utilize more carbohydrates to confer greater desiccation resistance. In contrast, higher starvation resistance in lighter flies is associated with storage and actual utilization of greater lipid amount. However, darker and lighter flies did not vary in the rate of utilization of carbohydrates under desiccation stress; and of lipids under starvation stress. Thus, we did not find support for the hypothesis that a lower rate of utilization of energy metabolites may contribute to greater stress resistance. Further, for increased desiccation resistance of darker flies, about two-third of total energy budget is provided by carbohydrates. By contrast, lighter flies derive about 66% of total energy content from lipids which sustain higher starvation tolerance. Our results support evolutionary trade-off for storage as well as utilization of energy metabolites for desiccation versus starvation resistance in D. melanogaster.     

Genetic load and viability studies in Korean natural populations of Drosophila melanogaster

Further studies about the amount of genetic load in the Korean Anyang and Cheju (Sughipo) Island populations of Drosophila melanogaster were performed. In total 1630 second chromosomes were extracted from the Anyang opulation between 1983 and 1985; 19.0 % of the chromosomes proved lethal, 8.8 % semilethal in homozygous condition. From the island oulation, 504 wild second chromosomes were analysed in 1986; 24.2 % were lethal, 4.6 % subleiaf A slight increase of lethal and semilethal frequencies between 1976 and 1986 can be observed. Mean viabilities of “all homozy-gotes”, “quasinormal-homozygotes”, and “random heterozygotes” were estimated from crossin experiments with marker strains. Random heterozygotes were always more viable than quasinormal homozygotes. An analysis for correlation between random heterozgous and homozygous viabilities gave values significantly different from zero only for the 1985 kyang sample (r =—0.4625, P < 0.01), but no significances could be observed for all other Anyang samples from 1983, 1984, and 1986, respectively. he effective population sizes were estimated to be between 2000 and 6300 individuals for the Anyan and 4200 individuals for the island population, using Nel's formula (1968). It is sugested that baknced natural selection is mainly responsible for the maintenance of genetic load in the Anyang natural populations of D. melanogaster.     

黑带食蚜蝇体色变异的研究

通过对黑带食蚜蝇Episyrphus balteatus(De Geer)体色变异的研究,发现黑带食蚜蝇存在深色型和浅色型2种基本形式,体色变异具有明显的季节性,深色型个体出现在温度较低的秋季及早春,浅色型个体发生在温度较高的春夏季节;在腹部色斑方面,深色型和浅色型个体中均存在变异,可划分为8种类型,腹部色斑的变异在浅色型个体中较为丰富,腹部不同体节背板上色斑的变异程度不同;黑带食蚜蝇在体型大小方面同样存在差异,这些变异的多态性可能是食蚜蝇系统学研究中异名产生的一个重要原因。因此,食蚜蝇类群的个体体色变异在系统学研究中是一个必须特别注意的问题。     

Phenotypic plasticity in morphological traits in two populations of Drosophila melanogaster

Isofemale lines of two populations of Drosophila melanogaster, originating from France and Tanzania, were examined over a range of temperatures. Morphological traits showed distinct patterns in phenotypic plasticity; flies of the two populations differed in shape. Genotype-by-Environment (G*E) interactions were frequently found in the Tanzania population, but were hardly present in the France population. If G*E interaction was present over temperature, estimates of additive genetic variance and additive genetic covariance were made to compare theoretical models with our data. The conclusion is that in France Drosophila melanogaster has been selected over a wider range of temperatures, resulting in parallel reaction norms of more optimal slope. In contrast, selection must have taken place over a narrower temperature range in Tanzanian flies, and will have exerted no direct influence on the slope of the reaction norm.     

不同地理种群和红色及绿色麦长管蚜遗传多样性分析

麦长管蚜Sitobion avenae(Fabricius)体色变异(红色和绿色)是一种常见的生物学现象,揭示其体色的转换机制对该类害虫的防控和测报具有潜在意义。本文利用微卫星标记技术,对麦长管蚜种群进行聚类分析和分子方差分析,从群体遗传学角度研究了不同地理种群和不同色型之间遗传多样性差异。研究结果表明,麦长管蚜的遗传分化主要以种群内的变异为主,种群间的变异占总变异的比例很小。此外,研究发现,红、绿体色间的遗传分化并不显著,且存在频繁的基因交流。这说明不同区域的不同体色麦长管蚜种群各自之间具有相似的遗传背景。     

Latitudinal Adh allozymic variation and ethanol tolerance in Indian populations of Drosophila melanogaster

Ten Indian geographical populations of D. melanogaster were assayed electrophoretically for Adh genic variation. The Indian geographical populations of D. melanogaster revealed significant clinal variation (3 % for 1 d? latitude) at Adh locus and Adh^F allelic frequency correlated significantly with increase in latitude. It was suggested that the abundance of secondary alcohols in the southern Indian tropical and humid environment might exert selective pressure favouring higher frequency of Adh^S allele. Patterns of ethanol utilization as well as ethanol tolerance were analyzed in larval and adult individuals of six geographical populations of D. melanogaster. Latitudinal variation in ethanol tolerance was observed in D. melanogaster populations from India. The parallel occurrence of latitudinal variation it Adh locus as well as ethanol tolerance in Indian geographical populations of D. melanogaster could be maintained by balancing natural selection varying spatially along the north-south axis of the Indian sub-continent.     

How to overwinter and be a founder: egg-retention phenotypes and mating status in Drosophila melanogaster

In temperate regions, Drosophila melanogaster has perennial overwintering populations. These populations present seasonal variations, under the influence of developmental temperature, for several genetically determined physiological traits. The capacity of virgin females to control ovulation is one of these characteristics. Phenotypes able to postpone egg-laying in the absence of insemination are favored under low temperature development and are numerous in Autumn generations. Moreover, a shift between Autumn and the following Spring has often been observed in favor of these phenotypes. The aim of the present study is to determine the characteristics and situations which confer an advantage on long as compared with short-retention phenotypes, during this non-reproductive period. Several traits were studied: resistance to cold shocks, resistance to long cold periods, developmental duration and viability, longevity and starvation resistance. Long-retention phenotypes (LL) had a longer life expectancy than short-retention phenotypes (ss) under virgin or mated status and greater resistance to starvation, by avoiding waste material (eggs). At 14 °C, flies that had mated once survived for several months on normal substrate with live spermatozoa, and flies on deficient medium (without proteins) survived for more than 3 months varying with phenotype. Flies with the best chance of overwintering are the long-retention phenotypes and some hybrids. The most favorable situation for population restoration is when flies are inseminated once in Autumn rather than when they remain virgin until Spring, because males die sooner than females.     

Variations in body melanisation,ovariole number and fecundity in highland and lowland populations of Drosophila melanogaster from the Indian subcontinent

We investigated geographical variations in three fitness‐related traits (body melanisation, ovariole number and fecundity) in laboratory‐reared offspring of 10 populations of Drosophila melanogaster. The populations were collected from adjacent lowland and highland localities (～80–100 km apart) in the tropical as well as subtropical regions (11.15–31.06 °N) covering a linear distance about 3 000 kilometers from south to north on the Indian subcontinent. Persistence of within‐as well as between‐population differences at 21 °C suggest that observed variations in fitness‐related traits have a genetic basis. Populations from higher altitudes showed consistently higher trait values (1.4‐fold increase) as compared with their corresponding lowland populations. By contrast, latitudinal variations were about two‐fold higher across the entire continent. Along latitude as well as altitude, population means showed higher correlation values (r > 0.98) between all the three fitness traits. However, on the basis of within‐population analysis (assorted darker and lighter flies), changes in body melanisation were significantly correlated with fecundity but not with ovariole number. Thus, analysis of within‐population trait variability should be preferred as compared with data on population means for adaptive significance of fitness‐related traits. In the present study, the role of climatic selection is evident from regression analysis with changes in annual average temperature of the sites of origin of populations along latitude as well as altitude.     

Variations in body melanisation,ovariole number and fecundity in highland and lowland populations of Drosophila melanogaster from the Indian subcontinent

We investigated geographical variations in three fitness-related traits （body melanisation, ovariole number and fecundity） in laboratory-reared offspring of 10 populations of Drosophila melanogaster. The populations were collected from adjacent lowland and highland localities （-80-100 km apart） in the tropical as well as subtropical regions （11.15-31.06°N） covering a linear distance about 3 000 kilometers from south to north on the Indian subcontinent. Persistence of within- as well as between-population differences at 21 ℃ suggest that observed variations in fitness-related traits have a genetic basis. Populations from higher altitudes showed consistently higher trait values （1.4-fold increase） as compared with their corresponding lowland populations. By contrast, latitudinal variations were about two-fold higher across the entire continent. Along latitude as well as altitude, population means showed higher correlation values （r 〉 0.98） between all the three fitness traits. However, on the basis of within-population analysis （assorted darker and lighter flies）, changes in body melanisation were significantly correlated with fecundity but not with ovariole number. Thus, analysis of within-population trait variability should be preferred as compared with data on population means for adaptive significance of fitness-related traits. In the present study, the role of climatic selection is evident from regression analysis with changes in annual average temperature of the sites of origin of populations along latitude as well as altitude.     

A comprehensive assessment of geographic variation in heat tolerance and hardening capacity in populations of Drosophila melanogaster from eastern Australia

We examined latitudinal variation in adult and larval heat tolerance in Drosophila melanogaster from eastern Australia. Adults were assessed using static and ramping assays. Basal and hardened static heat knockdown time showed significant linear clines; heat tolerance increased towards the tropics, particularly for hardened flies, suggesting that tropical populations have a greater hardening response. A similar pattern was evident for ramping heat knockdown time at 0.06 °C min^?1 increase. There was no cline for ramping heat knockdown temperature (CT_max) at 0.1 °C min^?1 increase. Acute (static) heat knockdown temperature increased towards temperate latitudes, probably reflecting a greater capacity of temperate flies to withstand sudden temperature increases during summer in temperate Australia. Larval viability showed a quadratic association with latitude under heat stress. Thus, patterns of heat resistance depend on assay methods. Genetic correlations in thermotolerance across life stages and evolutionary potential for critical thermal limits should be the focus of future studies.     

Horn polyphenism in the beetle Onthophagus taurus: larval diet quality and plasticity in parental investment determine adult body size and male horn morphology

In a wide range of taxa, individuals are able to express strikinglydifferent morphologies in response to environmental conditionsencountered during development. Such polyphenisms have receivedparticular attention from evolutionary biologists because thecondition-dependent expression of alternative morphologies isbelieved to reflect the existence of discrete sets of adaptationsto heterogeneous ecological or social conditions, which precludethe evolution of a single, optimal phenotype. Correct interpretationof the adaptive significance, if any, of facultative trait developmentrequires a solid understanding of the determinative regime governingmorph expression. Here I explore the environmental variablesdetermining male morphology in the horn-dimorphic beetle Onthophagustaurus. I demonstrate that natural variation in both the quantityand quality of food that larvae receive from their parents determinesbody size in males and females, and, by means of a thresholdresponse, the presence or absence of horns in males. In addition,results suggest that parent beetles adjust the amount of foodthey provision for their offspring according to diet quality,which may help to compensate for environmental variation inducedby differential resource quality in the wild. I use these resultsto further characterize the selective regime responsible forthe evolution of male polyphenism in onthophagine beetles anddiscuss its significance for understanding the origin and maintenanceof morphological variation in the genus Onthophagus.     

Circadian rhythmicity of tyrosine aminotransferase activity in larval and prepupal fat body of Drosophila melanogaster

Abstract

Drosophila melanogaster was reared under LD 12:12. Fat body was isolated in form of cells and cell groups from dissected larvae or prepupae by treatment with collagenase and hyaluronidase and subsequent centrifugation. Tyrosine aminotransferase of the fat body showed an extremely sharp pH dependence, with two narrow, well separable maxima at pH 5.6 and 6.0, possibly caused by different isoenzymes. Enzyme activity at pH 5.6 exhibited biphasic circadian rhythms in both wild‐type 3rd instar larvae and early prepupae. At pH 6.0, the rhythmicity was much weaker, perhaps even absent. In larvae from an ebony strain, at either pH the basal tyrosine aminotransferase activity was enhanced, and the rhythmicity was altered.     

Population genetics of Drosophila ananassae: inversion polymorphism and body size in Indian geographical populations

Twelve Indian natural populations of Drosophila ananassae, a cosmopolitan and domestic species, were sampled and laboratory populations (mass cultures) were established from naturally impregnated females. These populations were maintained in the laboratory for some generations and were analysed chromosomally to know the frequency of different inversions. The chromosomal analysis revealed the presence of three cosmopolitan inversions. The data on the whole show that there are significant differences in the frequencies of different chromosome arrangements in these populations. Body size (wing length and thorax length) was measured in both sexes (50 females and 50 males), in all the 12 geographical populations of D. ananassae. There are statistically significant differences in wing length as well as in thorax length of both sexes among different geographical populations. Five geographical strains were crossed reciprocally and body size (wing length and thorax length) was measured in F₁ and F₂ progeny. The comparison of body size (both traits) between mid‐parent, F₁ and F₂ shows that there is an increase in body size in F₁ and F₂ progeny as compared with parents. Thus, there is no break down of heterosis in F₂, which suggests absence of coadaptation in geographical populations of D. ananassae. Scaling test statistical analysis showed additive, dominance and epistatic effects in certain crosses involving geographical strains of D. ananassae. Correlation between chromosome arrangement frequency and body size has also been tested and significant negative correlation has been found between 2L – ST chromosome arrangement and male thorax.     

Overwintering in Drosophila melanogaster: outdoor field cage experiments on clinal and laboratory selected populations help to elucidate traits under selection

Insects can adapt to temperate environments by increasing levels of resistance to cold conditions over winter and/or altering reproductive patterns to focus reproduction in favourable conditions. In temperate areas, Drosophila melanogaster persists over winter at the adult stage. A previous experiment, conducted with flies kept in outdoor population cages in the temperate winter, indicated that temperate populations produced more eggs than did tropical populations following an abrupt increase in reproduction in late winter. In contrast, the tropical populations produced more eggs prior to the increase. Both patterns resulted in a higher net number of surviving offspring for temperate populations. Here we again examine the clinal pattern in reproduction using outdoor cages, this time held under tropical winter conditions. In this environment, surprisingly, egg production was higher and on average earlier in populations originating from temperate areas. However, mortality rates also increased with latitude of origin, and the relationship of lifetime egg production to latitude should therefore be measured. To test the role of altered pattern of egg production per se in the reproductive advantage of temperate populations in the temperate winter, we tested the performance of laboratory lines selected for altered reproductive patterns, under temperate winter conditions. Lines selected for high early fecundity exhibited this characteristic in the field cages and lines selected for late reproduction exhibited a relatively high fecundity in spring. The timing of the abrupt increase in egg production was identical in these sets of lines and occurred at the same time in recently collected populations, suggesting evolutionary conservation of the switch. These findings suggest that changes in early and late reproduction per se determine adaptation to temperate winter conditions, and illustrate how laboratory selection lines can be used to understand traits underlying adaptive shifts in field performance.     

Electrophoretic variability in island populations of Drosophila simulans and Drosophila immigrans

Genetic structure and variability were investigated in several Hawaiian populations of D. simulans and D. immigrans. Genetic variability is lower in Hawaiian populations of D. simulans than in Texas populations, and allelic differences exist as well. For D. immigrans, Hawaiian and Korean populations are similar in variability, allelic content, and gene frequencies. Several hypothesis are advanced to account for the patterns in gene variation observed between island and continental populations of these two colonizing species.This research was supported by Grant GB-23230 to the Hawaii Subprogram of the International Biology Program, by Grant GB-27586 to Dr. H. L. Carson, and by the Research Board of the School of Life Sciences, University of Illinois, Urbana, Illinois.Technical Report No. 57 of the U.S. IBP, Hawaii Integrated Research Program.     

Coadapted changes in energy metabolites and body color phenotypes for resistance to starvation and desiccation in latitudinal populations of D. melanogaster

In D. melanogaster, resistance to starvation and desiccation vary in opposite directions across a geographical gradient in India but there is lack of such clinal variation on other continents. However, it is not clear whether these resistance traits or other correlated traits are the target of natural selection. For resistance to starvation or desiccation in D. melanogaster, we tested the hypothesis whether body color phenotypes and energy metabolites show correlated selection response. Our results are interesting in several respects. First, based on within population analysis, assorted darker and lighter flies from a given population showed that darker flies store higher amount of trehalose and confer greater desiccation resistance as compared with lighter flies. By contrast, lighter flies store higher lipids content and confer increased starvation tolerance. Thus, there is a trade-off for energy metabolites as well as body color phenotypes for starvation and desiccation stress. Further, trait associations within populations reflect similar patterns in geographical populations. Second, we found opposite clines for trehalose and body lipids. Third, coadapated phenotypes have evolved under contrasting climatic conditions i.e. drier and colder northern localities select darker flies with higher trehalose as well as desiccation resistance while hot and humid localities favor lighter flies with higher lipids level and greater starvation tolerance. Thus, the evolution of coadapated phenotypes associated with starvation and desiccation resistance might have resulted due to specific ecological conditions i.e. humidity changes on the Indian subcontinent.     

Single and multigenerational responses of body mass to atmospheric oxygen concentrations in Drosophila melanogaster : evidence for roles of plasticity and evolution

Greater oxygen availability has been hypothesized to be important in allowing the evolution of larger invertebrates during the Earth’s history, and across aquatic environments. We tested for evolutionary and developmental responses of adult body size of Drosophila melanogaster to hypoxia and hyperoxia. Individually reared flies were smaller in hypoxia, but hyperoxia had no effect. In each of three oxygen treatments (hypoxia, normoxia or hyperoxia) we reared three replicate lines of flies for seven generations, followed by four generations in normoxia. In hypoxia, responses were due primarily to developmental plasticity, as average body size fell in one generation and returned to control values after one to two generations of normoxia. In hyperoxia, flies evolved larger body sizes. Maximal fly mass was reached during the first generation of return from hyperoxia to normoxia. Our results suggest that higher oxygen levels could cause invertebrate species to evolve larger average sizes, rather than simply permitting evolution of giant species.     

Pupal period and adult size in Drosophila melanogaster: a cautionary tale of contrasting correlations between two sexually dimorphic traits

Sexual dimorphism (SD) is widespread, reflecting a resolution of genetic conflicts arising from sex-specific differences in selection. However, genetic correlations among traits may constrain the evolution of SD. Drosophila melanogaster exhibits SD for pupal period (males longer) and adult weight (females heavier). This negative inter-sex covariance between the traits contrasts with a significant intra-sex positive genetic correlation (r(g) = 0.95) estimated using lines selected for fast larval development. Path analysis indicated that within sexes the selection regime indirectly reduced adult weight which in turn reduced pupal period. A hypothesis is proposed for the evolution of SD whereby the trait 'pupal period' is divided into 'intrinsic' (correlated with body size) and 'ecological' (uncorrelated with body size) components, and (the larger) females eclose earlier than males size via a shortening of the ecological component, thus achieving the advantage of provisioning eggs prior to sexual maturity. This hypothesis avoids invoking successful 'incompatible antagonistic selection'.