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Males of Drosophila nepalensis show dimorphism in wing melanization, but how do they evolve and coordinate during evolution is unknown. Heterogeneity in the environment helps individuals to adapt accordingly either through genetic polymorphism or through phenotypic plasticity. In this study, we tried to untangle the genetic architecture underlying differences in wing melanization in males because in nature the frequency of spotted and spotless males is different. We investigated the genetic basis of the inheritance of the sexually dimorphic characteristic of wing spot area (WSA) in D . nepalensis males with the aid of genetic crosses. We found spot formation on wings in male is directly correlated to female body melanization. In addition to this, we studied the phenotypic plasticity in the degree of wing spot melanization in males with respect to changes in temperature. We observed that increased WSA is negatively correlated with higher temperature. We found dark and light females only at 21°C. Dark females always produced males with spotted wing, whereas lighter females always produced males without wing spots. Finally, we found wing spot is highly correlated in reciprocal progeny due to linkage or pleiotropy which could help in evolution.

Beneficial acclimation hypothesis (BAH) is the phenotypic plasticity in response to changing environments which enables organisms to enhance their fitness. In recent years, however, BAH has received vigorous criticism and is still debatable. In this study, we tested thermal hardiness phenotypes (melanization, chill coma recovery, heat knockdown and percentage survival) on adult and pre-adult stages of Drosophila nepalensis, reared in different thermal environments (14, 17, 21 and 25 °C) to check whether increasing natural surrounding temperature and acclimation limit towards environmental change is detrimental or beneficial. Results showed that rearing D. nepalensis at higher temperatures (21 and 25 °C) reduces its melanization and cold hardiness but improves heat knockdown times. When temperature was raised to 26.2 °C (0.6 °C above the upper thermal maxima), to determine the short-term acclimation effects, survival and fitness of adults diminished approximately 1.5 to 2 folds. These results suggest that D. nepalensis has long-term developmental acclimation to both heat and cold which would be extremely beneficial as temperatures and climates alter in the region due to global warming. However, a lack of short-term heat acclimation suggests that rapid shifts in thermal extreme could be detrimental to D. nepalensis.

Drosophila leontia (warm adapted) has been considered as a sister species of Drosophila kikkawai (sub-cosmopolitan) with a very similar morphology. We found divergent strategies for coping with desiccation stress in these two species of montium subgroup. Interestingly, in contrast to clinal variation for body melanization in D. kikkawai, cuticular lipid mass showed a positive cline in D. leontia across a latitudinal transect. 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 in D. leontia. A comparative analysis of water budget of these two species showed that higher abdominal melanization, reduced rate of water loss and greater dehydration tolerance confer higher desiccation resistance in D. kikkawai while the reduced rate of water loss is the only possible mechanism to enhance desiccation tolerance in D. leontia. The use of organic solvents has supported water proofing role of cuticular lipids in D. leontia but not in D. kikkawai. Thus, we may suggest that body melanization and cuticular lipids may represent alternative strategies for coping with dehydration stress in melanic versus non-melanic drosophilids. In both these species, carbohydrates were utilized under desiccation stress but a higher level of stored carbohydrates was evident in D. kikkawai. Further, we found increase desiccation resistance in D. kikkawai through acclimation while D. leontia lacks such a response. Thus, species specific divergence in water balance related traits in these species are consistent with their adaptations to wet and dry habitats., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Drosophila nepalensis is more abundant under colder and drier montane habitats in the western Himalayas compared with Drosophila takahashii, but the mechanistic basis of such a climatic adaptation is largely unknown. We tested the hypothesis that divergence in the physiological basis of desiccation-related traits is consistent with species-specific adaptations to climatic conditions. Drosophila nepalensis showed approximately twofold higher desiccation resistance, hemolymph content as well as carbohydrate content than D. takahashii despite a modest difference in rate of water loss (0.3% h(-1)). Water loss before succumbing to death (dehydration tolerance) was much higher in D. nepalensis (82.32%) than in D. takahashii (∼50%). A greater loss of hemolymph water under desiccation stress until death is associated with higher desiccation resistance in D. nepalensis. In both species, carbohydrates were utilized under desiccation stress, but a higher level of stored carbohydrates was evident in D. nepalensis. Further, we found increased desiccation resistance in D. nepalensis through acclimation whereas D. takahashii lacked such a response. Thus, species-specific divergence in water-balance-related traits in these species is consistent with their adaptations to wet and dry habitats.

Drosophila jambulina exhibits color dimorphism controlled by a single locus but its ecological significance is not clear. Dark and light morphs differ significantly in body melanisation, desiccation resistance, rate of water loss, mating activity and fecundity. Interestingly, this species lacks clinal variation for body size, desiccation resistance and life history traits. For body melanisation, lack of geographical variation as well as plastic effects is not in agreement with a thermal melanism hypothesis. However, based on field data, there are seasonal changes in phenotypic frequencies of dark and light body color morphs which correlate significantly with variation in humidity levels. Under short-term (8h) desiccation stress, we observed higher number of assortative matings, longer copulation period and increased fecundity for dark strains as compared with light strains. By contrast, both the morphs when exposed to high humid conditions exhibited higher assortative matings and fecundity for light strains as compared with dark strains. In tropical populations of D. jambulina, body color polymorphism seems to be maintained through humidity changes as opposed to thermal melanism. Thus, seasonal changes in the frequency of body color morphs in this tropical species supports melanism-desiccation hypothesis.

Using two sibling species, Drosophila jambulina and D. punjabiensis, interspecific crossabilty were examined in natural as well as laboratory conditions. Collection record showed that hybrids are found only in specific hybrid zone having higher temperature variation suggesting an increased fitness in hybrid zone. In laboratory condition, plastic effects on thermo-tolerance traits (heat knockdown and cold recovery) were investigated by growing parental species [D. jambulina and D. punjabiensis at four growth temperatures (17 to 28 °C)] and their hybrids at six growth temperatures (15 to 31 °C). Hybrids showed higher plasticity for melanization (~ 58%) and thermo-tolerance traits (CV = 39.14 for heat resistance and CV = 43.15 for cold resistance) at different growth temperatures. Acclimation effects were also significant in hybrids (F = 47.89 for heat resistance and F = 56.87 for cold resistance) suggesting an adaptive potential. Results of this study imply that hybridization increases genetic variation which in turn leads to adaptation to new environments. The genetic data obtained in this study would be useful not only for testing basic predictions about evolution but also for understanding the evolutionary significance of hybrids. [ABSTRACT FROM AUTHOR]

Larvae of three latitudinally different populations of Drosophila jambulina belonging to the montium subgroup were tested for pupation site preference in relation to temperature. At 30 °C, larvae preferred to pupate on food whereas at 21 °C pupation occurred on the cotton. Genetic basis of larval pupation behavior was studied by conducting reciprocal crosses for 30 generations on food-selected and on cotton-selected pupae. Results from genetic analysis between food-selected and cotton-selected strains indicated a single gene responsible for the pupation site preference, with F1 progeny pupated on cotton and F2 (F1 × F1) larvae pupated on both food as well as on cotton. Although we found no change in morphological traits in food vs cotton selected populations, significantly different growth rate (body weight) between the two strains was observed. These results suggest that pupation site preferences can affect life-history traits in D. jambulina. [ABSTRACT FROM AUTHOR]

Abstract: The average temperature of the earth has increased from 0.3 to 0.6°C, and warming is facilitating faunal reshuffling. Variable thermal environments warrant mechanisms to adjust the expression of phenotypic values to environmental needs. Ectothermic Drosophilids are profoundly affected by thermal selection (i.e., genetic effects) or through induced effects on phenotypes (i.e., plastic effects). Climatic data for the last fifty years involves a significant change in average temperature (Tave) of Western Himalayas, which has affected the distribution and boundaries of various Drosophilids in this region. There is a significant decline in the number of D. nepalensis from lower ranges; whereas D. ananassae is reported to be introduced to lower to mid mountainous ranges. Further, a comparison of fecundity, hatchability, and viability at different growth temperatures has shown significant decrease in trait values at 17°C in D. ananassae and at 25°C in D. nepalensis. Thus, the recent range changes of these two species involve genetic effects on ecophysiological and plastic effects on life history traits. Our results indicate that thermal plasticity of life history traits can be species-specific; thus climate change may lead to a mismatch of such traits to the changing environment. We suggest that D. nepalensis and D. ananassae could serve as indicator species for analyzing range changes under changing climatic conditions. Evolutionary biologists can provide unique perspective to the examination of how climate change will affect the earth''s biota. [Copyright &y& Elsevier]

We investigated eight populations of Drosophila immigrans from low to high montane localities (600–2202 m) for altitudinal variations in abdominal melanization and fitness-related traits (desiccation resistance, copulation duration, and fecundity). On the basis of common garden experiments, persistence between-population differences at 21°C suggests that observed variations in fitness-related traits have a genetic basis. Parent–offspring regression analyses showed higher heritability (h2= 0.77) for melanization patterns on all the abdominal tergites. All the traits showed significantly higher repeatability across generations. Under colder and drier environments in dispersed montane localities, abdominal melanization and desiccation resistance significantly increased (1.5–1.9 fold) along altitude. Thus, there are correlated effects of abdominal melanization on desiccation resistance. Genetic correlations, based on family means, were significantly high between abdominal melanization and other fitness traits. Furthermore, darker flies along increasing altitude resulted in a 35–40% increase in copulation duration as well as fecundity. There are significantly positive correlations of abdominal melanization with copulation duration as well as fecundity on the basis of within- as well as between-population variations. Such observations are in agreement with the thermal budget hypothesis. Present data suggest that changes in body melanization impact fitness-related traits in montane populations of Drosophila immigrans. [ABSTRACT FROM AUTHOR]

During the past two to three decades, Drosophila ananassae, a warm adapted tropical species, has invaded low to mid altitude localities in the western Himalayas. Due to its cold sensitivity, this species had never been recorded from higher latitudes as well as altitudes in India to the 1960s. A latitudinal cline in this desiccation-sensitive species corresponds with southern humid tropical localities rather than northern drier subtropical localities. An extension of its cline into lowland to midland montane localities has resulted due to global climatic change as well as local thermal effects through anthropogenic impact. However, D. ananassae populations at species borders are characterized by lower genetic variability for body melanization as well as for desiccation resistance. There is a lack of thermal plastic effects for body melanization, and the observed extended cline might represent evolutionary (genetic) response due to selection pressure imposed by drier habitats. A comparison of fecundity, hatchability and viability at three growth temperatures (17, 20 and 25°C) showed significant reduction in trait values at 17°C in D. ananassae. Thus, its recent range expansion into northern montane localities might involve genetic effects on stress-related traits and plastic effects on life history traits. We suggest that D. ananassae could serve as an indicator species for analyzing range expansion under changing climatic conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]