Changes in body melanisation and desiccation resistance in highland vs. lowland populations of D. melanogaster

Wild caught samples of Drosophila melanogaster from five highland localities showed parallel changes in melanisation and desiccation resistance in darker versus lighter phenotypes, i.e. darker flies (>45% melanisation) showed significantly higher desiccation resistance than lighter flies (<30% melanisation). In order to find an association between body melanisation and desiccation resistance, highland and lowland populations from tropical and subtropical regions (11.15-31.06 degrees N) of the Indian subcontinent were raised and investigated at 21 degrees C for four physiological traits, i.e. per cent body melanisation, desiccation resistance, rate of water loss and rate of water absorption. On the basis of mother-offspring regression, body melanisation and desiccation resistance showed higher heritability (0.58-0.68) and thus these traits are suitable for laboratory analyses. Significantly higher melanisation as well as desiccation resistance were observed in highland populations as compared with lowland populations. The rates of water loss as well as absorption were negatively correlated with body melanisation, i.e. darker flies from highlands showed a reduced rate of water loss as well as a lower rate of water absorption while the reverse trend was observed in lighter flies from lowlands. On the basis of multiple regressions, significant effects due to combined altitude and latitude were observed for all the four physiological traits. Local climatic conditions (i.e. annual average temperature and relative humidity) helped in explaining parallel changes in body melanisation and desiccation resistance in D. melanogaster.     

Divergence of larval resource acquisition for water conservation and starvation resistance in Drosophila melanogaster

Laboratory selection experiments have evidenced storage of energy metabolites in adult flies of desiccation and starvation resistant strains of D. melanogaster but resource acquisition during larval stages has received lesser attention. For wild populations of D. melanogaster, it is not clear whether larvae acquire similar or different energy metabolites for desiccation and starvation resistance. We tested the hypothesis whether larval acquisition of energy metabolites is consistent with divergence of desiccation and starvation resistance in darker and lighter isofemale lines of D. melanogaster. Our results are interesting in several respects. First, we found contrasting patterns of larval resource acquisition, i.e., accumulation of higher carbohydrates during 3rd instar larval stage of darker flies versus higher levels of triglycerides in 1st and 2nd larval instars of lighter flies. Second, 3rd instar larvae of darker flies showed ~40?h longer duration of development at 21°C; and greater accumulation of carbohydrates (trehalose and glycogen) in fed larvae as compared with larvae non-fed after 150?h of egg laying. Third, darker isofemale lines have shown significant increase in total water content (18%); hemolymph (86%) and dehydration tolerance (11%) as compared to lighter isofemale lines. Loss of hemolymph water under desiccation stress until death was significantly higher in darker as compared to lighter isofemale lines but tissue water loss was similar. Fourth, for larvae of darker flies, about 65% energy content is contributed by carbohydrates for conferring greater desiccation resistance while the larvae of lighter flies acquire 2/3 energy from lipids for sustaining starvation resistance; and such energy differences persist in the newly eclosed flies. Thus, larval stages of wild-caught darker and lighter flies have evolved independent physiological processes for the accumulation of energy metabolites to cope with desiccation or starvation stress.     

Divergence of water balance mechanisms in two melanic Drosophila species from the western Himalayas

Drosophila busckii is more abundant under colder and drier montane habitats in the western Himalayas as compared to Drosophila melanogaster but the mechanistic basis of such climatic adaptations is largely unknown. We tested the hypothesis whether genetic variation or phenotypic plasticity of cuticular traits confer adaptive protection against desiccation stress in two melanic Drosophila species living under drier montane localities. For D. melanogaster, changes in melanisation are known to be associated with reduced water loss but there are no data on D. busckii. We investigated changes in body melanisation, cuticular lipids, desiccation resistance, water loss, extractable hemolymph volume (%), and dehydration tolerance in six sympatric populations of D. busckii and D. melanogaster over an altitudinal range of 640-2236 m. D. busckii is a melanic species but changes in cuticular water loss are negatively correlated with cuticular lipid mass and not with body melanisation. In D. melanogaster, there are no plastic effects (14-28 °C) for cuticular lipid mass but variation in body melanisation is associated with desiccation-related traits. Effects of organic solvents (hexane or chloroform: methanol), developmental plasticity and seasonal variation in cuticular lipids affect body water loss in D. busckii but no such changes occur in D. melanogaster. Thus, sympatric populations of D. busckii and D. melanogaster have evolved different water balance mechanisms under shared environmental conditions in the western Himalayas. Multiple measures of desiccation resistance in these species show clinal variation with altitude, consistent with adaptation to increased desiccation stress.     

Desiccation resistance in tropical insects: causes and mechanisms underlying variability in a Panama ant community

Desiccation resistance, the ability of an organism to reduce water loss, is an essential trait in arid habitats. Drought frequency in tropical regions is predicted to increase with climate change, and small ectotherms are often under a strong desiccation risk. We tested hypotheses regarding the underexplored desiccation potential of tropical insects. We measured desiccation resistance in 82 ant species from a Panama rainforest by recording the time ants can survive desiccation stress. Species' desiccation resistance ranged from 0.7 h to 97.9 h. We tested the desiccation adaptation hypothesis, which predicts higher desiccation resistance in habitats with higher vapor pressure deficit (VPD) – the drying power of the air. In a Panama rainforest, canopy microclimates averaged a VPD of 0.43 kPa, compared to a VPD of 0.05 kPa in the understory. Canopy ants averaged desiccation resistances 2.8 times higher than the understory ants. We tested a number of mechanisms to account for desiccation resistance. Smaller insects should desiccate faster given their higher surface area to volume ratio. Desiccation resistance increased with ant mass, and canopy ants averaged 16% heavier than the understory ants. A second way to increase desiccation resistance is to carry more water. Water content was on average 2.5% higher in canopy ants, but total water content was not a good predictor of ant desiccation resistance or critical thermal maximum (CT_max), a measure of an ant's thermal tolerance. In canopy ants, desiccation resistance and CT_max were inversely related, suggesting a tradeoff, while the two were positively correlated in understory ants. This is the first community level test of desiccation adaptation hypothesis in tropical insects. Tropical forests do contain desiccation‐resistant species, and while we cannot predict those simply based on their body size, high levels of desiccation resistance are always associated with the tropical canopy.     

Changes in cuticular lipids, water loss and desiccation resistance in a tropical drosophilid: analysis of variation between and within populations

We investigated within as well as between population variability in desiccation resistance, cuticular lipid mass per fly and cuticular water loss in nine geographical populations of a tropical drosophilid, Zaprionus indianus. Interestingly, the amount of cuticular lipids and desiccation resistance in this non-melanic species are significantly higher as compared with melanic Drosophila melanogaster. On the basis of isofemale line analysis, within population trait variability in cuticular lipid mass per fly is positively correlated with desiccation resistance and negatively correlated with cuticular water loss but show lack of correlation with body size. We observed geographical variation in the amount of cuticular lipid mass per fly in Zaprionus indianus but no such divergence was found in D.melanogaster. In both the species, geographical variations in desiccation resistance are negatively correlated with cuticular water loss but the underlying mechanisms for changes in cuticular permeability are quite different. Thus, we may suggest that body melanisation and cuticular lipids may represent alternative strategies for coping with dehydration stress in melanic versus non-melanic drosophilids. For both the species, desiccation resistance and cuticular water loss are correlated with regular increase in aridity in the northern subtropical localities as compared with southern peninsular humid tropical localities. The role of climatic selection is evident from multiple regression analysis with seasonal changes in temperature and humidity (Tcv and RHcv) of the sites of origin of populations of Zaprionus indianus along latitude.     

Divergent strategies for adaptation to desiccation stress in two Drosophila species of immigrans group

Water balance mechanisms have been investigated in desert Drosophila species of the subgenus Drosophila from North America, but changes in mesic species of subgenus Drosophila from other continents have received lesser attention. We found divergent strategies for coping with desiccation stress in two species of immigrans group--D. immigrans and D. nasuta. In contrast to clinal variation for body melanization in D. immigrans, cuticular lipid mass showed a positive cline in D. nasuta across a latitudinal transect (10°46'-31°43'N). Based on isofemale lines variability, body melanization showed positive correlation with desiccation resistance in D. immigrans but not in D. nasuta. The use of organic solvents has supported water proofing role of cuticular lipids in D. nasuta but not in D. immigrans. A comparative analysis of water budget of these two species showed that higher water content, reduced rate of water loss and greater dehydration tolerance confer higher desiccation resistance in D. immigrans while the reduced rate of water loss is the only possible mechanism to enhance desiccation tolerance in D. nasuta. We found that carbohydrates act as metabolic fuel during desiccation stress in both the species, whereas their rates of utilization differ significantly between these two species. Further, acclimation to dehydration stress improved desiccation resistance due to increase in the level of carbohydrates in D. immigrans but not in D. nasuta. Thus, populations of D. immigrans and D. nasuta have evolved different water balance mechanisms under shared environmental conditions. Multiple measures of desiccation resistance in D. immigrans but reduction in water loss in D. nasuta are consistent with their different levels of adaptive responses to wet and dry conditions on the Indian subcontinent.     

Evidence for a robust sex-specific trade-off between cold resistance and starvation resistance in Drosophila melanogaster

In insects changes in lipid metabolism may underlie a trade-off between cold resistance and starvation resistance. To test this we examined correlated responses in independent sets of Drosophila melanogaster lines selected for increased cold resistance and increased starvation resistance. The starvation lines showed correlated patterns found in other D. melanogaster populations selected for this trait, including higher lipid levels and increased resistance to desiccation, although the selected lines did not show a longer development time as found in some other studies. Consistent with the trade-off hypothesis, selected lines with increased starvation resistance showed decreased resistance to a cold stress as measured by mortality, whereas selected lines with increased cold resistance showed a decrease in starvation resistance. To counter the possibility of inadvertent selection accounting for these patterns, selected and control lines from both selection regimes were crossed to form mass bred populations, which were left for four generations prior to establishing isofemale lines. By scoring starvation and cold resistance in these lines derived from both sets of selection regimes, we confirmed the negative association between resistance to these stresses in females but not in males. Potential implications of this trade-off for surviving cold conditions when food resources are limiting are discussed.     

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.     

Desiccation resistance and water balance in southern African keratin beetles (Coleoptera, Trogidae): the influence of body size and habitat

Desiccation resistance and water balance were examined in the adults of seven trogid species, which differed both in body size and in the habitats from which they were collected. Body water contents (51–58% fresh mass) and desiccation rates at 27 °C (0.00026–0.00093 g h⁻¹) in these species were very similar to those of unrelated, similar-sized beetles from arid habitats. The keratin beetles differed markedly from many other adult Coleoptera by virtue of their very high haemolymph osmolality and inability to regulate haemolymph osmolality, and to catabolise lipids for water production, during desiccation. Like most other insects, the xeric trogid species had lower rates of water loss and longer survival times than trogids from mesic areas. This was due both to lower rates of water loss and to the larger body size of species from the more arid areas. Because absolute body water content was higher in large beetles than in small ones, larger body size conferred higher desiccation resistance on the very large Kalahari desert species. This suggests that there may be strong selection for large body size in such insects from arid areas. Most ecological and ecophysiological investigations of geographical variation in body size, and the species-body size distribution, have focused on temperature and metabolic rate as explanatory variables. This study suggests that attention should also be given to desiccation resistance. Accepted: 29 September 1997     

Using experimental evolution to study the physiological mechanisms of desiccation resistance in Drosophila melanogaster

Data from populations undergoing experimental evolution can be used to make comparisons between physiologically differentiated populations and to determine evolutionary trajectories. Comparisons of long-established laboratory populations of Drosophila melanogaster that are strongly differentiated with respect to desiccation resistance are used to test alternative hypotheses concerning the mechanisms that fruit flies use to survive bouts of extreme desiccation. This comparative study supports the hypothesis that, in at least one case, D. melanogaster can evolve increased resistance to desiccation by decreasing water loss rates and by increasing bulk water content but not by increasing metabolic water content or dehydration tolerance. While glycogen was involved in water storage, its primary role was in water binding, not the production of metabolic water. Measurement of the trajectories of these component mechanisms during selection for desiccation resistance is used to demonstrate that water loss rate quickly plateaus in response to selection, while water content continues to improve. This disparity reveals the value of studying evolutionary trajectories and the need for longer-term selection studies in evolutionary physiology.     

Geographic variation for climatic stress resistance traits in the springtail Orchesella cincta

Multiple traits of stress resistance were investigated in the epedaphic springtail Orchesella cincta. Second generation adults from five laboratory populations were compared with respect to resistance to extreme temperatures and desiccation, and traits relevant to climatic adaptation. Populations were collected along a 2000-km latitudinal gradient ranging from Denmark to southern Italy and reared under the same standard laboratory conditions. Traits investigated were resistance to high and low temperature, desiccation resistance, body size and water loss rate (WLR). Results showed genetically based differences in resistance to high and low temperature, desiccation, WLR, water pool and body size between populations. Individuals from the most northern population had the highest desiccation-and cold shock resistance, and the lowest heat shock resistance. Females were significantly more desiccation resistant than males. The results of cold shock resistance showed a positive increase with lowest environmental temperature recorded at the sites of population origin, whereas heat shock resistance showed a positive increase with highest recorded temperature at the sites of population origin. Desiccation resistance increased towards the most southern and northern population, suggesting that both low and high temperature extremes affect desiccation resistance. Body mass, water pool and WLR showed interpopulation as well as sex specific variation. This provides evidence for geographical variation in stress resistance of springtails related to climatic conditions.     

Effects of age on water balance in Drosophila species.

Age-related declines in physiological performance have been documented in a wide variety of organisms. However, it is unknown whether related species age in a similar manner or whether physiological differences associated with aging differ widely among species. Previous work has shown that the desiccation resistance of Drosophila melanogaster decreases rapidly with age. Other Drosophila species may have delayed reproductive maturity or may inhabit arid habitats, so that age-related changes in water balance may be a significant physiological constraint on their ecological success. We may, therefore, predict that physiological systems involved in water balance will deteriorate with age at a reduced rate in these species. We quantified several components of water budgets for 14 species of Drosophila, including both desert and mesic representatives differing in their age of maturity. Desiccation resistance decreased with age in all but one species studied, primarily because of increased rates of water loss. However, there was no significant relationship between the rate of aging, as indicated by the rate of increase in water-loss rates as flies aged, and either habitat or age of maturity.     

High resolution mapping of candidate alleles for desiccation resistance in Drosophila melanogaster under selection

The ability to counter periods of low humidity is an important determinant of distribution range in Drosophila. Climate specialists with low physiological tolerance to desiccation stress are restricted to the tropics and may lack the ability to further increase resistance through evolution. Although the physiological adaptations to desiccation stress are well studied in Drosophila and other ectotherms, factors underlying evolutionary responses remain unknown because of a paucity of genetic data. We address this issue by mapping evolutionary shifts in D. melanogaster under selection for desiccation resistance. Genomic DNA from five independent replicate selected, and control lines were hybridized to high density Affymetrix Drosophila tiling arrays resulting in the detection of 691 single feature polymorphisms (SFPs) differing between the treatments. While randomly distributed throughout the genome, the SFPs formed specific clusters according to gene ontology. These included genes involved in ion transport and respiratory system development that provide candidates for evolutionary changes involving excretory and respiratory water balance. Changes to genes related to neuronal control of cell signaling, development, and gene regulation provide candidates to explore novel biological processes in stress resistance. Sequencing revealed the nucleotide shifts in a subset of the SFPs and highlighted larger regions of genomic diversity surrounding SFPs. The association between natural desiccation resistance and a 463-bp region of the 5' promoter region of the Dys gene undergoing allele frequency changes in response to selection in the experimental evolution lines was tested in an independent population from Coffs Harbour, Australia. The allele frequencies of 23 SNPs common to the two populations were inferred from the parents of the 10% most and 10% least resistant Coffs Harbour flies. The frequencies of the selected alleles were higher at all sites, with three sites significantly associated with the resistant Coffs Harbour flies. This study illustrates how rapid mapping can be used for discovering natural molecular variants associated with survival to low humidity and provides a wealth of candidate alleles to explore the genetic basis of physiological differences among resistant and susceptible Drosophila populations and species.     

热带地区相对湿度的季节性变化影响果蝇Drosophila jambulina体色多型性和水分平衡(英文)

在印度次大陆的亚热带地区, 秋天冷而干燥, 春天湿润。变温性果蝇所具有的抗干燥性有助于其度过较为干旱的气候条件。 Drosophila jambulina 具有体色二型性。已有研究表明, 随湿度变化, D. jambulina热带种群始终保持体色多型性, 这与热条件下体色黑化相反, 且该热带物种中体色分化频率随季节性变化, 这符合黑化 干燥假说。但是两种色型的D. jambulina产生这类气候适应的机理尚不明了。为了检验干燥相关性状生理基础的分化与对气候条件的色型特异性适应相关这一假说, 我们利用分别在17℃和25℃、 低湿（40% RH）和高湿（80% RH）条件下饲养获得的两种色型的D. jambulina, 检测了其水分平衡对相对湿度、 温度、 及温湿度相互作用的反应。我们发现, 在低相对湿度下, 两种温度下饲养的深色型果蝇的生理和脱水性状数值显著高于浅色型。对两种色型果蝇的水分收支情况进行的比较分析表明, 在低相对湿度下, 深色型果蝇的含水量较高、 水分损失率较低、 抗脱水能力较强, 使其具有更强的抗干燥性。在干燥胁迫过程中, 两种色型的果蝇均以碳水化合物作为代谢燃料, 但是在低湿条件下, 深色果蝇中贮存碳水化合物的含量明显要高。而且, 在两种湿度条件下, 这两种色型果蝇之间的总能量收支显著不同。据此认为, D. jambulina的水分平衡相关性状表现出的色型特异性分化与其对湿热生境的适应相关。     

Rapid changes in desiccation resistance in Drosophila melanogaster are facilitated by changes in cuticular permeability

Insects can improve their desiccation resistance by one or more of (1) increasing their water content; (2) decreasing water loss rate; or (3) increasing the amount of water able to be lost before death. Female Drosophila melanogaster have previously been reported to increase their resistance to desiccation after a desiccation pre-treatment and recovery, but the mechanism of this increased desiccation resistance has not been explored. We show that female, but not male adult D. melanogaster increased their resistance to desiccation after 1 h of recovery from a 3 to 4.5 h pre-treatment that depletes them of 10% of their water content. The pre-treatment did not result in an increase in water content after recovery, and there is a slight increase in water content at death in pre-treated females (but no change in males), suggesting that the amount of water loss tolerated is not improved. Metabolic rate, measured on individual flies with flow-through respirometry, did not change with pre-treatment. However, a desiccation pre-treatment did result in a reduction in water loss rate, and further investigation indicated that a change in cuticular water loss rate accounted for this decrease. Thus, the observed increase in desiccation resistance appears to be based on a change in cuticular permeability. However, physiological changes in response to the desiccation pre-treatment were similar in male and female, which therefore does not account for the difference in rapid desiccation hardening between the sexes. We speculate that sex differences in fuel use during desiccation may account for the discrepancy.     

Water balance in desert Drosophila: lessons from non-charismatic microfauna

Water stress is a particularly important problem for insects and other small organisms in arid environments. Cactophilic fruit flies in the genus Drosophila have invaded deserts on numerous occasions, including multiple independent invasions of North American deserts. Because the evolutionary history of this genus is so well studied, we can investigate the mechanisms of adaptation in a rigorous phylogenetic context. As expected, desert fruit flies lose water less rapidly than their mesic congeners. They are also able to tolerate the loss of a greater percentage of body water, but this difference is mainly due to phylogenetic history, and does not represent an adaptation specifically to desert habitats. A laboratory analogue of desert Drosophila is provided by populations of D. melanogaster that have been subjected to selection for desiccation resistance. Selected populations resemble desert species in that they lose water slowly, relative to control populations, and are not more tolerant of dehydration stress. They differ, however, in having much higher water contents and different behavioral responses to desiccating conditions. Our comparisons of laboratory and natural populations reveal that not all possible adaptive mechanisms evolve in stressful environments. Different physiological and behavioral strategies may evolve depending upon the particular options available in the environment.     

The effect of selection for desiccation resistance on cold tolerance of Drosophila melanogaster

Abstract.  Low temperature and desiccation stress are thought to be mechanistically similar in insects, and several studies indicate that there is a degree of cross-tolerance between them, such that increased cold tolerance results in greater desiccation tolerance and vice versa . This assertion is tested at an evolutionary scale by examining basal cold tolerance, rapid cold-hardening (RCH) and chill coma recovery in replicate populations of Drosophila melanogaster selected for desiccation resistance (with controls for both selection and concomitant starvation) for over 50 generations. All of the populations display a RCH response, and there is no effect of selection regime on RCH or basal cold tolerance, although there are differences in basal cold tolerance between sampling dates, apparently related to inter-individual variation in development time. Flies selected for desiccation tolerance recover from chill coma slightly, but significantly, faster than control and starvation-control flies. These findings provide little support for cross-tolerance between survival of near-lethal cold and desiccation stress in D. melanogaster .     

Hygropreference and brood care in the honeybee (Apis mellifera)

Terrestrial organisms need to limit evaporation from their bodies in order to maintain a homeostatic water balance. Owing to a large surface to volume ratio, arthropods are particularly susceptible to desiccation and have evolved behavioural and physiological mechanisms to conserve water. In social insects, water balance is also affected by the interactions between nestmates and by the architecture of the nest. For honeybees, humidity is particularly important for the brood because it affects the hatching success of eggs and because, unlike ants, honeybees cannot relocate their brood to parts of the nest with more favourable humidity. To advance the understanding of the water economy in honeybee nests, we investigated whether workers exhibit a hygropreference when exposed to a gradient of 24-90% relative humidity (RH) and whether the expression of this preference and their behaviour is affected by the presence of brood. The results show that young honeybee workers in the absence of brood exhibit a weak hygropreference for approximately 75% RH. When brood is present the expression of this preference is further weakened, suggesting that workers tend to the brood by distributing evenly in the gradient. In addition, fanning behaviour is shown to be triggered by an increase in humidity above the preferred level but not by a decrease. Our results suggest that humidity in honeybee colonies is actively controlled by workers.     

FAR gene enables the brown planthopper to walk and jump on water in paddy field

Many insects can live on water and survive being caught in the rain. Current research has shown that insect cuticular hydrocarbons(CHC) confer desiccation resistance to maintain water balance. In this study, we identified a fatty acyl-CoA reductase gene(NlFAR) of the rice brown planthopper, Nilaparvata lugens that is essential for the production of CHCs, and found that NlFAR is essential for N. lugens to walk and jump on water when moving from one rice plant to another in paddy fields. NlFAR was mainly expressed in the integument at the beginning of each molt. Cuticular surface analysis by scanning electron microscopy and characterization of CHC extracts indicated that N. lugens with knockdown of NlFAR using RNA inference(RNAi)had a neater epicuticle layer and a significant decrease in CHC contents. Knockdown of NlFAR did not influence the desiccation resistance of N. lugens, but the ds NlFAR-treated insects were easily adhered and moistened by water droplets or their own secreted honeydew and unable to walk or jump on water. These results suggested that NlFAR is a crucial enzyme for CHC biosynthesis and cuticle waterproofing, but not for water retention of N. lugens, which may provide a potential strategy for pest management.     

Desiccation resistance in four Drosophila species: sex and population effects

Desiccation resistance and body mass were measured in multiple populations of each of four species of Drosophila: two desert endemic species (D. nigrospiracula and D. mojavensis), and two with more widespread distributions (D. melanogaster and D. pseudoobscura). While flies from the desert species were more desiccation tolerant, there was, in certain cases, significant variation in desiccation resistance among populations of the same species. A significant difference in desiccation resistance was observed between the sexes, females were more resistant than males, but this relationship was reversed when taking into account body mass differences between the sexes. The degree of observed within-species variability demonstrates that studies focusing upon differences between species can produce different conclusions if they rely on observations for only single populations of a given species. Our data also suggest the existence of multiple mechanisms for desiccation resistance.