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Melanism seems to have evolved independently through diverse mechanisms in various taxa and different ecological factors could be responsible for selective responses. Increased body melanization at higher altitudes as well as latitudes is generally considered to be adaptive for thermoregulation. Physiological traits such as body melanization and desiccation resistance have been investigated independently in diverse insect taxa at three levels: within populations, between populations and among species. A substantial number of Drosophila studies have reported clinal variations in both these traits along latitude. A possible link between these traits had remained unexplored in wild and laboratory populations of ectothermic insect taxa, including drosophilids, to date. Simultaneous analysis of these traits in assorted darker and lighter phenotypes in each population in the present study showed parallel changes for body melanization and desiccation resistance. The mechanistic basis of evolving desiccation resistance was explained on the basis of differential rates of water loss per hour in darker versus lighter phenotypes in six populations of Drosophila melanogaster from adjacent localities differing substantially in altitude all along the Indian subcontinent. Data on cuticular impermeability suggest a possible role of melanization in desiccation tolerance. However, substantial gaps remain in extending these results to other insect taxa and further exploring the physiological and molecular changes involved in melanization for conferring desiccation resistance.

SUMMARY

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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.

A possible link between melanization and desiccation resistance can be inferred if within population differences in melanization find significant correlations with desiccation resistance and its mechanistic basis i.e. rate of water loss/hr. Accordingly, darker, intermediate and lighter phenotypes of body melanization were analyzed in wild and laboratory reared Drosophila melanogaster L. (Diptera: Clyclorrapha) populations from highland and lowland sites located in close proximity at five different latitudinal locations (11.15 °N to 31.06°N) within the Indian subcontinent. In large population samples, occurrence of significant within population variability made it possible to assort non-overlapping phenotypes of body coloration (i.e. lighter (< 25%), intermediate (30 to 40%) and darker (> 45%)) for all the populations which were further investigated for desiccation resistance and rate of water loss/hr. Significantly, higher desiccation resistance but much reduced rate of water loss/hr were observed in darker and intermediate phenotypes in all the populations. By contrast, lighter phenotypes exhibited lower desiccation tolerance but higher rate of water loss/hr. A regression analysis between traits provided similar slope values for wild and laboratory populations. For all three physiological traits, predicted trait values from multiple regression analysis as a simultaneous function of annual average temperature and relative humidity, matched the observed values. We infer that parallel changes in melanization and desiccation resistance may result from decreasing annual average temperature and relative humidity along increasing latitude as well as altitude on the Indian subcontinent.

Ectothermic species face problems of water balance under colder and drier climatic conditions in montane localities. We investigated five ecophysiological traits (body melanization, desiccation resistance, rate of water loss or gain and body size) in eight populations of Drosophila immigrans from an altitudinal gradient (600-2226 m) in the Western Himalayas. The traits showed bell-shaped variability patterns characteristic of quantitative traits. For body melanization, we observed high heritability (0.65) on the basis of parent-offspring regression. A comparison of highland versus foothill populations showed significant divergence for all the traits except body size. Darker flies from the highlands exhibited higher desiccation resistance but reduced rate of water loss or gain as compared with lighter flies from the foothills, which showed lower desiccation resistance and higher rates of water loss as well as gain. Lack of differences in the amount of epicuticular lipids cannot account for differential reduction in cuticular water loss in altitudinal populations. However, within-as well as between-population differences in body melanization can account for changes in desiccation resistance and reduction in cuticular water loss. Analyses of highland versus lowland populations as well as in assorted darker and lighter flies from a highland population have shown differences in haemolymph and dehydration tolerance. For the mechanistic basis of desiccation resistance, our results on wild populations of Drosophila immigrans are not in agreement with those reported for laboratory-selected desiccation-resistant strains in Drosophila melanogaster. Thus, ecophysiological mechanisms could be different under laboratory versus field selection.

Due to rising incidence rates of liver cancer and worries about the toxicity of current chemotherapeutic medicines, the hunt for further alternative methods to treat this malignancy has escalated. Compared to chemotherapy, quercetin, a flavonoid, is relatively less harmful to normal cells and is regarded as an excellent free-radical scavenger. Apoptotic cell death of cancer cells caused by quercetin has been demonstrated by many prior studies. It is present in many fruits, vegetables, and herbs. Quercetin targets apoptosis, by upregulating Bax, caspase-3, and p21 while downregulating Akt, PLK-1, cyclin-B1, cyclin-A, CDC-2, CDK-2, and Bcl-2. Additionally, it has been reported to increase STAT3 protein degradation in liver cancer cells while decreasing STAT3 activation. Quercetin has a potential future in chemoprevention, based on substantial research on its anticancer effects. The current review discusses quercetin’s mechanisms of action, nanodelivery strategies, and other potential cellular effects in liver cancer.