Climatic adaptations of body melanisation in Drosophila melanogaster from Western Himalayas

We investigated population divergence in body melanisation in wild samples of Drosophila melanogaster across an elevational gradient (512 - 2202m) in the Western Himalayas. Wild populations are characterized by higher phenotypic variability as compared with laboratory populations. Significant differences in elevational slope values for three posterior abdominal segments (5th, 6th and 7th) in wild versus laboratory populations suggest plastic effects. However, elevational slope values do not differ for the three anterior abdominal segments (2nd, 3rd and 4th). Thus, elevational changes in melanisation include genetic as well as plastic effects. Fitness consequences of within population variability were analyzed on the basis of assorted darker and lighter flies from two highland as well as from two lowland localities. There is lack of correlation of melanisation with body size as well as ovariole number in assorted darker and lighter flies. For each population, darker flies showed higher desiccation resistance, lower rate of water loss, longer copulation duration and greater fecundity as compared with lighter flies. Phenotypic variations in body melanisation can be interpreted in relation with seasonal changes in temperature as well as humidity (Tcv and RHcv) of the sites of origin of populations. Thus, elevational changes in body melanisation may represent genetic response to selection pressures imposed by colder and drier climatic conditions in the Western Himalayas.     

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.     

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.     

Impact of body melanisation on desiccation resistance in montane populations of D. melanogaster: Analysis of seasonal variation

In the montane localities of subtropical regions, winter is the dry season and ectothermic drosophilids are expected to evolve desiccation resistance to cope with drier climatic conditions. An analysis of six montane populations (600–2226 m) of D. melanogaster showed variations for body melanisation (i.e. pigmentation) and desiccation resistance across seasons as well as along altitude. During winter season, plastic changes for melanisation of three posterior abdominal segments (5th + 6th + 7th) correspond with higher desiccation resistance. Thus, we analyzed genetic and plastic effects for these ecophysiological traits by comparing wild-caught and laboratory reared individuals of D. melanogaster for autumn as well as winter season. A ratio of slope values in wild vs. laboratory populations has shown a 1.64-fold plastic effect during autumn; and a two-fold effect during winter. For body melanisation and desiccation resistance, evolutionary response to altitudinal environmental gradient is similar to the phenotypic response across seasons. Thus, our observations are in agreement with the co-gradient hypothesis. Further, we tested the hypothesis whether a thicker cuticle (either due to melanisation or cuticular lipids) leads to lesser cuticular water loss and higher desiccation resistance across seasons as well as according to altitude. Based on within and between population analyses, body melanisation was found to be positively correlated with desiccation resistance but negatively with cuticular water loss. Interestingly, there were no changes in the amount of cuticular lipids per fly across seasons as well as along altitude; and therefore cuticular lipids did not account for desiccation resistance. Cuticular water loss exhibited negative correlation with body melanisation but not with cuticular lipids as well as with changes in body size across seasons. Thus, our data suggest that seasonal changes in body melanisation confer desiccation resistance in montane populations of D. melanogaster.     

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.     

Shifting clinal patterns of stress resistance traits in Drosophila ananassae

Drosophila ananassae, a desiccation and cold sensitive species, is abundant along the latitudinal gradient of the Indian subcontinent. Analysis of seasonally varying wild-caught flies showed two independent patterns of melanisation: (1) narrow to broad melanic stripes on three anterior abdominal segments only; (2) a novel body color pattern (dark vs. light background). We investigated the degree to which these two melanisation systems vary; first with latitude and secondly among seasons. There is a shallow latitudinal cline for percent striped melanisation as well as for frequency of body color alleles during the rainy season. The frequencies of body color alleles vary significantly across seasons in the northern populations i.e. the light allele occur abundantly (>0.94) during the rainy season while the frequency of the dark allele increases (0.22–0.35) during the dry season causing steeper clines during the dry season. By contrast, the low variations in abdominal stripes showed non-significant changes and the cline was similar across seasons. Furthermore, both types of melanisation patterns showed no plasticity with respect to temperature. The present study also investigated clines related to desiccation, heat and cold stress in D. ananassae females across seasons (rainy and dry) from nine latitudinal populations. The clines for stress related traits changes to steeper and non-linear during the dry season. Thus, latitudinal populations of D. ananassae differ in slope values of clines for stress related traits across seasons. This study reports seasonal changes in latitudinal clines of stress resistance traits as seen in a changing frequency of body color alleles of D. ananassae in northern locality, while in southern localities it remains constant. This is presumably the result of only minor seasonal changes in humidity and temperature in the South, whereas in the North seasonal climatic variability is much higher.     

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.     

Impact of body melanisation on contrasting levels of desiccation resistance in a circumtropical and a generalist <Emphasis Type="Italic">Drosophila</Emphasis> species

We investigated the role of cuticular lipids, body melanisation and body size in conferring contrasting levels of desiccation resistance in latitudinal populations of Drosophila melanogaster and Drosophila ananassae on the Indian subcontinent. Contrary to the well known role of cuticular lipids in water proofing in diverse insect taxa, there is lack of geographical variations in the amount of cuticular lipids per fly in both the species. In D. ananassae, quite low levels of body melanisation are correlated with lower desiccation resistance. By contrast, increased levels of desiccation resistance are correlated with quite high melanisation in D. melanogaster. Thus, species specific cuticular melanisation patterns are significantly correlated with varying levels of desiccation resistance within as well as between populations and across species. Role of body melanisation in desiccation resistance is further supported by the fact that assorted dark and light flies differ significantly in cuticular water loss, hemolymph and dehydration tolerance. However, similar patterns of body size variation do not account for contrasting levels of desiccation resistance in these two Drosophila species. Climatic selection is evidenced by multiple regression analysis with seasonal amplitude of thermal and humidity changes (Tcv and RHcv) along latitude on the Indian subcontinent. Finally, the contrasting levels of species specific distribution patterns are negatively correlated with RHcv of sites of origin of populations i.e. a steeper negative slope for D. ananassae corresponds with its desiccation sensitivity as compared with D. melanogaster. Thus, evolutionary changes in body melanisation impact desiccation resistance potential as well as distribution patterns of these two Drosophila species on the Indian subcontinent.     

Body melanization and its adaptive role in thermoregulation and tolerance against desiccating conditions in drosophilids

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.     

Correlated Changes in Body Melanisation and Mating Traits of Drosophila melanogaster: A Seasonal Analysis

Altitudinal localities of the northern India are associated with high seasonal changes. Drosophila melanogaster flies are darker during the winter season as compared to the autumn season. We tested the hypothesis whether there are altitudinal clines for mating related traits. We observed negative cline for mating latency and positive for copulation period along altitude in D. melanogaster. We further tested if seasonally varying body melanisation is correlated with mating propensity in D. melanogaster. Thus, we examined the D. melanogaster flies collected during autumn and winter season for changes in body melanisation and mating-related traits. Flies from the winter season show high melanisation, copulation duration and fecundity/day as compared to the autumn season flies. By contrast mating latency is longer during autumn as compared to winter season. Based on within- and between-population analysis, body melanisation shows positive correlation with copulation duration and fecundity/day, while negative correlation with mating latency. Within-population analyses show no correlation between body size and ovariole number with body melanisation. Thus, our data suggest that seasonal changes in body melanisation are correlated with mating latency, copulation duration and fecundity/day, but no correlation with body size and ovariole numbers. Further, we observed that seasonal changes in these clines, although have some component of plasticity, have strong genetic basis as the seasonal and population differences were maintained for various traits after 8 generations in the laboratory.     

Correlated changes in thermotolerance traits and body color phenotypes in montane populations of Drosophila melanogaster: analysis of within- and between-population variations

Thermotolerance traits vary across geographical gradients but there is a lack of clinal variation in some Drosophila species. Thus, it is not clear whether thermotolerance or other correlated traits are the target of natural selection. In order to test selection responses, we investigated body melanization and thermotolerance traits in six altitudinal populations of Drosophila melanogaster . Based on rearing different geographical populations under uniform growth conditions at 21 °C (common garden experiments), clinal variations for cold resistance are in the direction opposite to heat resistance along an altitudinal gradient, that is darker flies from highland populations evidenced higher levels of cold resistance while lowland populations showed higher heat resistance. Phenotypic plastic responses for body melanization at 17–28 °C showed significant correlations with thermotolerance traits. At 17 °C, regression coefficients as a function of altitude are highly significant and positive for cold resistance but negative for heat knockdown. However, for flies reared at 28 °C, there is no elevational change in melanization as well as thermotolerance traits. Thus, both genetic and plastic changes of body melanization and thermotolerance traits suggest a correlated selection response. Further, within-population analyses of body melanization (based on dark, intermediate and light color phenotypes) showed significant associations with thermotolerance traits. Correlated variations in body melanization and thermal tolerances are associated with climatic thermal variability ( T _cv) but not with T _min. or T _max. along an altitudinal gradient.     

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.     

GROWTH TEMPERATURE AND ADULT PIGMENTATION IN TWO DROSOPHILA SIBLING SPECIES: AN ADAPTIVE CONVERGENCE OF REACTION NORMS IN SYMPATRIC POPULATIONS?

Phenotypic plasticity of abdomen pigmentation was investigated in populations of the sibling species Drosophila melanogaster and D. simulans, living in sympatry in two French localities. Ten isofemale lines of each population and species were grown at different constant temperatures spanning their complete thermal range from 12 to 31°C. Genetic variability between isofemale lines was not affected by growth temperature, but was consistently less in D. simulans. For all traits, the dark pigmentation of the abdominal segments decreased according to growth temperature, in agreement with the thermal budget adaptive hypothesis. The shapes of the response curves were different between the abdominal segments, but for a given segment, quite similar in the two species. On average D. simulans was lighter than D. melanogaster, but the difference was mainly expressed at higher temperatures. An interesting result was the difference observed between the two localities: flies from the colder locality (Villeurbanne) were found to be darker than flies from the warmer locality (Bordeaux). Interestingly, this difference was expressed only at low temperatures, 21°C and below, that is, at temperatures encountered in natural conditions. This suggests an adaptive response resulting in a change of the shape of reaction norm and involving genotype-environment interactions. When comparing the genetic structure of geographic populations for quantitative traits, several laboratory environments should be preferred to a single one.     

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.     

Fitness consequences of body melanization in Drosophila immigrans from montane habitats

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 .     

Impact of body melanization on mating success in Drosophila melanogaster

Mating speed and copulation duration respond rapidly to laboratory selection in Drosophila melanogaster Meigen (Diptera: Drosophilidae), but there is a lack of data on the evolutionary response to natural selection in the wild. Further, it is not clear whether body melanization and mating behavior are correlated traits. Accordingly, we tested whether variation in body color impacts on mating latency, copulation duration, and fecundity in latitudinal populations of D. melanogaster. We observed geographical variation (cline) for mating propensity, i.e., mating speed as well as copulation duration increased along latitude. Phenotypic plastic responses for body melanization at 17 and 25 °C also showed significant correlations with mating latency and copulation duration. Within‐population analysis based on assorted dark and light flies of five geographical populations showed significant positive correlations of copulation duration and fecundity with body melanization. To assess the role of males and/or females on mating speed and copulation duration, we used atypical body color strains (i.e., dark and light males of D. melanogaster) for no‐choice mating tests. Our data showed a major influence of males for copulation duration and of females for mating speed. Furthermore, a difference in impact of body melanization on mating speed and copulation duration was demonstrated between species, i.e., low melanization in Drosophila ananassae Doleschall is correlated with lower mating speed and shorter copulation duration than in D. melanogaster. Geographical changes in mating propensity were significantly correlated with body melanization at three levels, i.e., within and between populations and between species. Thus, we have shown that a relationship exists between body melanization and mating success. Further, we found seasonal changes in temperature and humidity to confer selection pressures on mating‐related traits.     

Seasonal changes in humidity level in the tropics impact body color polymorphism and desiccation resistance in Drosophila jambulina—Evidence for melanism-desiccation hypothesis

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 (8 h) 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.     

Trade-offs between melanisation and life-history traits in Helicoverpa armigera

Abstract.  1. Previously we established a homozygous melanic strain (JBM) with 16 black pupae spontaneously occurring within a laboratory population (JBW) of Helicoverpa armigera and demonstrated that the melanisation is controlled by a single recessive autosomal gene.
2. Data obtained indicate that the melanisation is globally expressed in the pupal and adult stages (except for the body hairs of adults) but not in the egg and larval stages. No differences in body colour can be found between the melanic JBM and the wild-type JBW strains before the metamorphic pupation moult. After pupation, the JBM pupae gradually blacken, whereas the wild-type JBW pupae gradually turn brown, indicating that the biosynthetic steps leading to brown pigments are shut off in the JBM strain. In the adult stage, wings are darker and hairs on the abdomen and tergum are lighter in the melanic moths than in the wild-type individuals.
3. Life-table experiments reveal that the melanism is associated with slower development in all life stages, smaller body weight, lower mating rate and fecundity, less mating time, and accordingly, lower net reproduction rate and population trend index.
4. Single pair inbreeding and reciprocal crosses show that the mating rate is much lower in the inter-strain crosses than in the intra-strain crosses, indicating the presence of mating preference for its own colour morph and the presence to some degree of reproductive isolation between the two colour morphs.     

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.     

Adaptive plasticity in wing melanisation of a montane butterfly across a Himalayan elevational gradient

1. Traits that are significant to the thermal ecology of temperate or montane species are expected to prominently co-vary with the thermal environment experienced by an organism. The Himalayan Pieris canidia butterfly exhibits considerable variation in wing melanisation. We investigated: (i) whether variation in wing melanisation and (ii) activity period of this montane butterfly was influenced by the seasonally and elevationally changing thermal landscape.
2. We discovered that wing melanisation varied across elevation, seasons, sex, and wing surfaces, with the variation strongly structured in space and time: colder seasons and higher elevations produced more melanic individuals. Notably, melanisation did not vary uniformly across all wing surfaces: (i) melanisation of the ventral hindwing co-varied much more prominently with elevation, but (ii) melanisation on all other surfaces varied with seasonal changes in the thermal environment.
3. Observed wing surface-specific patterns indicated thermoregulatory function for this variation in melanisation. Such wing surface-specific responses to seasonal and elevational variation in temperature have rarely been reported in montane insects.
4. Moreover, daily and seasonal thermal cycles were found to strongly influence activity periods of this species, suggesting the potential limits to wing melanisation plasticity.
5. Overall, these results showed that the seasonal and elevational gradients in temperature influence the thermal phenotype as well as activity periods of this Himalayan butterfly. It will be critical to study the phenotypic evolution of such montane insects in response to the ongoing climate change, which is already showing significant signs in this iconic mountain range.