Significant Clinal Variation Research Articles

Expression-environment associations in transcriptomic heat stress responses for a global plant lineage.

The increasing frequency and severity of heatwaves will intensify stress on plants. Given regional variation in heatwave exposure and expected differences in thermal tolerance between species it is unlikely that all plant species will be affected equally by climate change. However, little is currently known about variation in the responses of plants to heat stress, or how those responses differ among closely related species adapted to different environments. Here we quantify the response of 17 Acacia species (175 RNA-seq libraries), from across Australia's diverse biomes, to a multi-day experimental heatwave treatment to identify variation in transcriptomic and physiological responses to heat stress. Genes with known heat response functions showed consistent responses across Acacia species. Up to 10% of all genes and over 100 gene families showed significant clinal variation in the magnitude of their expression plasticity across species. Specifically, gene families linked to the temperature stress response were overrepresented among significant relationships with home range temperature conditions. Gene expression responses seen on the first day of the heatwave were more frequently associated with home range climates, while expression responses by day four were more commonly related to photosystem II acclimation. Comparative transcriptomics on non-model species has the potential to provide key information on stress response plasticity, especially when linked with our understanding of model species. Our study indicates that the pressing challenge to identifying potentially vulnerable species to climate change could be benefited by the further exploration of clinal variation in transcriptome plasticity.

Clinal variation in PHY (PAS domain) and CRY (CCT domain)-Signs of local adaptation to light quality in Norway spruce.

Detection of the genomic basis of local adaptation to environmental conditions is challenging in forest trees. Phytochromes (PHY) and cryptochromes (CRY) perceive the red (R)/far-red (FR)and blue lightrespectively, thus playing a fundamental role in regulating plant growth and development. PHYO and PHYP from conifers are the equivalents of PHYA/PHYCand PHYB in angiosperms, respectively. Norway spruce shows an adaptive latitudinal cline for shade (low R:FR or FR-enriched light) tolerance and requirement of FR light for its growth. We analyzed the exome capture data that included a uniquely large data set of 1654 Norway spruce trees sampled across many latitudes in Sweden to capture the natural clines for photoperiod and FR light exposure during the growth season. Statistically significant clinal variation was detected in allele and genotype frequencies of missense mutations in coding regions belonging to well-defined functional domains of PHYO (PAS-B),PHYP2 (PASfold-2), CRY1 (CCT1)and CRY2 (CCT2)that strongly correlates with the latitudinal gradient in response to variable light quality in Norway spruce. The missense SNP in PHYO resulting in Asn835Ser, displayed the steepest cline among all other polymorphisms. We propose that these variations in the photoreceptors represent signs of local adaptation to light quality.

Relative contributions of neutral and non-neutral processes to clinal variation in calyx lobe length in the series Sakawanum (Asarum: Aristolochiaceae).

Clines, the gradual variation in measurable traits along a geographical axis, play a major role in evolution and can contribute to our understanding of the relative roles of selective and neutral process in trait variation. Using genetic and morphological analyses, the relative contributions of neutral and non-neutral processes were explored to infer the evolutionary history of species of the series Sakawanum (genus Asarum), which shows significant clinal variation in calyx lobe length. A total of 27 populations covering the natural geographical distribution of the series Sakawanum were sampled. Six nuclear microsatellite markers were used to investigate genetic structure and genetic diversity. The lengths of calyx lobes of multiple populations were measured to quantify their geographical and taxonomic differentiation. To detect the potential impact of selective pressure, morphological differentiation was compared with genetic differentiation (QCT-FST comparison). Average calyx lobe length of A. minamitanianum was 124.11 mm, while that of A. costatum was 13.80 mm. Though gradually changing along the geographical axis within series, calyx lobe lengths were significantly differentiated among the taxa. Genetic differentiation between taxa was low (FST = 0.099), but a significant geographical structure along the morphological cline was detected. Except for one taxon pair, pairwise QCT values were significantly higher than the neutral genetic measures of FST and G'ST. Divergent selection may have driven the calyx lobe length variation in series Sakawanum taxa, although the underlying mechanism is still not clear. The low genetic differentiation indicates recent divergence and/or gene flows between geographically close taxa. These neutral processes would also affect the clinal variation in calyx lobe lengths. Overall, this study implies the roles of population history and divergent selection in shaping the current cline of a flower trait in the series Sakawanum.

Intrinsic factors drive spatial genetic variation in a highly vagile species, the wedge‐tailed eagle Aquila audax, in Tasmania

Knowledge of dispersal in a species, both its quantity and the factors influencing it, are crucial for our understanding of ecology and evolution, and for species conservation. Here we quantified and formally assessed the potential contribution of extrinsic factors on individual dispersal in the threatened Tasmanian population of wedge‐tailed eagle Aquila audax. As successful breeding by these individuals appears strongly related to habitat, we tested the effect of landscape around sampling sites on genetic diversity and spatial genetic variation, as these are influenced by patterns of dispersal. Similarly, we also tested whether habitat intervening sampling sites could explain spatial genetic variation. Twenty microsatellites were scored, but only a small proportion of spatial genetic variation (4.6%) could be explained by extrinsic factors, namely habitat suitability and elevation between sites. However, significant clinal genetic variation was evident across Tasmania, which we explain by intrinsic factors, likely high natal philopatry and occasional long‐distance dispersal. This study demonstrates that spatial genetic variation can be detected in highly vagile species at spatial scales that are small relative to putative dispersal ability, although here there was no substantial relationship with landscape factors tested.

Opsin clines in butterflies suggest novel roles for insect photopigments.

Opsins are ancient molecules that enable animal vision by coupling to a vitamin-derived chromophore to form light-sensitive photopigments. The primary drivers of evolutionary diversification in opsins are thought to be visual tasks related to spectral sensitivity and color vision. Typically, only a few opsin amino acid sites affect photopigment spectral sensitivity. We show that opsin genes of the North American butterfly Limenitis arthemis have diversified along a latitudinal cline, consistent with natural selection due to environmental factors. We sequenced single nucleotide (SNP) polymorphisms in the coding regions of the ultraviolet (UVRh), blue (BRh), and long-wavelength (LWRh) opsin genes from ten butterfly populations along the eastern United States and found that a majority of opsin SNPs showed significant clinal variation. Outlier detection and analysis of molecular variance indicated that many SNPs are under balancing selection and show significant population structure. This contrasts with what we found by analysing SNPs in the wingless and EF-1 alpha loci, and from neutral amplified fragment length polymorphisms, which show no evidence of significant locus-specific or genome-wide structure among populations. Using a combination of functional genetic and physiological approaches, including expression in cell culture, transgenic Drosophila, UV-visible spectroscopy, and optophysiology, we show that key BRh opsin SNPs that vary clinally have almost no effect on spectral sensitivity. Our results suggest that opsin diversification in this butterfly is more consistent with natural selection unrelated to spectral tuning. Some of the clinally varying SNPs may instead play a role in regulating opsin gene expression levels or the thermostability of the opsin protein. Lastly, we discuss the possibility that insect opsins might have important, yet-to-be elucidated, adaptive functions in mediating animal responses to abiotic factors, such as temperature or photoperiod.

Clinal variation at phenology-related genes in spruce: parallel evolution in FTL2 and Gigantea?

Parallel clines in different species, or in different geographical regions of the same species, are an important source of information on the genetic basis of local adaptation. We recently detected latitudinal clines in SNPs frequencies and gene expression of candidate genes for growth cessation in Scandinavian populations of Norway spruce (Picea abies). Here we test whether the same clines are also present in Siberian spruce (P. obovata), a close relative of Norway spruce with a different Quaternary history. We sequenced nine candidate genes and 27 control loci and genotyped 14 SSR loci in six populations of P. obovata located along the Yenisei river from latitude 56°N to latitude 67°N. In contrast to Scandinavian Norway spruce that both departs from the standard neutral model (SNM) and shows a clear population structure, Siberian spruce populations along the Yenisei do not depart from the SNM and are genetically unstructured. Nonetheless, as in Norway spruce, growth cessation is significantly clinal. Polymorphisms in photoperiodic (FTL2) and circadian clock (Gigantea, GI, PRR3) genes also show significant clinal variation and/or evidence of local selection. In GI, one of the variants is the same as in Norway spruce. Finally, a strong cline in gene expression is observed for FTL2, but not for GI. These results, together with recent physiological studies, confirm the key role played by FTL2 and circadian clock genes in the control of growth cessation in spruce species and suggest the presence of parallel adaptation in these two species.

Natural selection maintains a single‐locus leaf shape cline in Ivyleaf morning glory, Ipomoea hederacea

Clines in phenotypic traits with an underlying genetic basis potentially implicate natural selection. However, neutral evolutionary processes such as random colonization, spatially restricted gene flow, and genetic drift could also result in similar spatial patterns, especially for single-locus traits because of their susceptibility to stochastic events. One way to distinguish between adaptive and neutral mechanisms is to compare the focal trait to neutral genetic loci to determine whether neutral loci demonstrate clinal variation (consistent with a neutral cline), or not. Ivyleaf morning glory, Ipomoea hederacea, exhibits a latitudinal cline for a Mendelian leaf shape polymorphism in eastern North America, such that lobed genotypes dominate northern populations and heart-shaped genotypes are restricted to southern populations. Here, we evaluate potential evolutionary mechanisms for this cline by first determining the allele frequencies at the leaf shape locus for 77 populations distributed throughout I.hederacea's range and then comparing the geographical pattern at this locus to neutral amplified fragment length polymorphism (AFLP) loci. We detected both significant clinal variation and high genetic differentiation at the leaf shape locus across all populations. In contrast, 99% of the putatively neutral loci do not display clinal variation, and I.hederacea populations show very little overall genetic differentiation, suggesting that there is a moderate level of gene flow. In addition, the leaf shape locus was identified as a major F(ST) outlier experiencing divergent selection, relative to all the AFLP loci. Together, these data strongly suggest that the cline in leaf shape is being maintained by spatially varying natural selection.

Evolution of dispersal traits along an invasion route in the wind-dispersed Senecio inaequidens (Asteraceae)

In introduced organisms, dispersal propensity is expected to increase during range expansion. This prediction is based on the assumption that phenotypic plasticity is low compared to genetic diversity, and an increase in dispersal can be counteracted by the Allee effect. Empirical evidence in support of these hypotheses is however lacking. The present study tested for evidence of differentiation in dispersal-related traits and the Allee effect in the wind-dispersed invasive Senecio inaequidens (Asteraceae). We collected capitula from individuals in ten field populations, along an invasion route including the original introduction site in southern France. In addition, we conducted a common garden experiment from field-collected seeds and obtained capitula from individuals representing the same ten field populations. We analysed phenotypic variation in dispersal traits between field and common garden environments as a function of the distance between populations and the introduction site. Our results revealed low levels of phenotypic differentiation among populations. However, significant clinal variation in dispersal traits was demonstrated in common garden plants representing the invasion route. In field populations, similar trends in dispersal-related traits and evidence of an Allee effect were not detected. In part, our results supported expectations of increased dispersal capacity with range expansion, and emphasized the contribution of phenotypic plasticity under natural conditions.

Estimation of population structure in coastal Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco var. menziesii] using allozyme and microsatellite markers

Characterizing population structure using neutral markers is an important first step in association genetic studies in order to avoid false associations between phenotypes and genotypes that may arise from non-selective demographic factors. Population structure was studied in a wide sample of ∼1,300 coastal Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco var. menziesii] trees from Washington and Oregon. This sample is being used for association mapping between cold hardiness and phenology phenotypes and single-nucleotide polymorphisms in adaptive-trait candidate genes. All trees were genotyped for 25 allozyme and six simple sequence repeat (SSR) markers using individual megagametophytes. Population structure analysis was done separately for allozyme and SSR markers, as well as for both datasets combined. The parameter of genetic differentiation (θ or F ST) was standardized to take into account high within-population variation in the SSR loci and to allow comparison with allozyme loci. Genetic distance between populations was positively and significantly correlated with geographic distance, and weak but significant clinal variation was found for a few alleles. Although the STRUCTURE simulation analysis inferred the same number of populations as used in this study and as based on previous analysis of quantitative adaptive trait variation, clustering among populations was not significant. In general, results indicated weak differentiation among populations for both allozyme and SSR loci (θ s = 0.006–0.059). The lack of pronounced population subdivision in the studied area should facilitate association mapping in this experimental population, but we recommend taking the STRUCTURE analysis and population assignments for individual trees (Q-matrix) into account in association mapping.

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

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

Geographical and taxonomic influences on cranial variation in red colobus monkeys (Primates, Colobinae): introducing a new approach to ‘morph’ monkeys

ABSTRACTAim To provide accurate but parsimonious quantitative descriptions of clines in cranial form of red colobus, to partition morphological variance into geographical, taxonomic and structured taxonomic components, and to visually summarize clines in multivariate shape data using a method which produces results directly comparable to both univariate studies of geographical variation and standard geometric morphometric visualization of shape differences along vectors.Location Equatorial Africa.Methods Sixty‐four three‐dimensional cranial landmarks were measured on 276 adult red colobus monkeys sampled over their entire distribution. Geometric morphometric methods were applied, and size and shape variables regressed onto geographical coordinates using linear and curvilinear models. Model selection was done using the second‐order Akaike information criterion. Components of variation related to geography, taxon or their combined effect were partitioned using partial regresssion. Multivariate trends in clinal shape were summarized using principal components of predictions from regressions, plotting vector scores on maps as for univariate size, and visualizing differences along main axes of clinal shape variation using surface rendering.Results Significant clinal variation was found in size and shape. Clines were similar in females and males. Trend surface analysis tended to be more accurate and parsimonious than alternative models in predicting morphology based on geography. Cranial form was relatively paedomorphic in East Africa and peramorphic in central Africa. Most taxonomic variation was geographically structured. However, taxonomic differences alone accounted for a larger proportion of total explained variance in shape (up to 40%) than in size (≤ 20%).Main conclusions A strong cline explained most of the observed size variation and a significant part of the shape differences of red colobus crania. The pattern of geographical variation was largely similar to that previously reported in vervets, despite different habitat preferences (arboreal versus terrestrial) and a long period since divergence (c. 14–15 Myr). This suggests that some aspects of morphological divergence in both groups may have been influenced by similar environmental, geographical and historical factors. Cranial size is likely to be evolutionarily more labile and thus better reflects the influence of recent environmental changes. Cranial shape could be more resilient to change and thus better reflects phylogenetically informative differences.

Parallel patterns of clinal variation inSolidago altissimain its native range in central USA and its invasive range in Japan

The ability of exotic species to proliferate and expand their range may hinge critically upon their potential for adaptive evolution. The finding of parallel patterns of genetically based clinal variation in native and non-native ranges across similar environmental gradients supports the hypothesis that adaptive evolution has played a role in establishment and spread. In this common garden study, we compared patterns of phenotypic variation among 12 populations of Solidago altissima L. that were sampled across similar latitudes in the native range in central USA (25°N–43°N) and across its invasive range in Japan (26°N–43°N). Significant clinal variation in phenotype corresponding to latitude was found among US and Japanese populations for height, leaf number, leaf length, leaf width, stem diameter, and stomatal guard-cell size. Only the slope of leaf width differed significantly between the native and invasive range, and the slope was significantly steeper in Japan. These results indicate that patterns of selection across latitude are similar in these two countries. We suggest that populations of S. altissima have rapidly differentiated in response to the cline in selection in Japan, possibly by the sorting of lineages from multiple introductions, and this has contributed to their success as an exotic invader.

Clinal Variation in phyB2, a Candidate Gene for Day-Length-Induced Growth Cessation and Bud Set, Across a Latitudinal Gradient in European Aspen (Populus tremula)

The initiation of growth cessation and dormancy represents a critical ecological and evolutionary trade-off between survival and growth in most forest trees. The most important environmental cue regulating the initiation of dormancy is a shortening of the photoperiod and phytochrome genes have been implicated in short-day-induced bud set and growth cessation in Populus. We characterized patterns of DNA sequence variation at the putative candidate gene phyB2 in 4 populations of European aspen (Populus tremula) and scored single-nucleotide polymorphisms in an additional 12 populations collected along a latitudinal gradient in Sweden. We also measured bud set from a subset of these trees in a growth chamber experiment. Buds set showed significant clinal variation with latitude, explaining approximately 90% of the population variation in bud set. A sliding-window scan of phyB2 identified six putative regions with enhanced population differentiation and four SNPs showed significant clinal variation. The clinal variation at individual SNPs is suggestive of an adaptive response in phyB2 to local photoperiodic conditions. Three of four SNPs showing clinal variation were located in regions with excessive genetic differentiation, demonstrating that searching for regions of high genetic differentiation can be useful for identifying sites putatively involved in local adaptation.

The Role of Natural Selection in Genetic Differentiation of Worldwide Populations of Drosophila ananassae

The main evolutionary forces leading to genetic differentiation between populations are generally considered to be natural selection, random genetic drift, and limited migration. However, little empirical evidence exists to help explain the extent, mechanism, and relative role of these forces. In this study, we make use of the differential migration behavior of genes located in regions of low and high recombination to infer the role and demographic distribution of natural selection in Drosophila ananassae. Sequence data were obtained from 13 populations, representing almost the entire range of cosmopolitan D. ananassae. The pattern of variation at a 5.1-kb fragment of the furrowed gene, located in a region of very low recombination, appears strikingly different from that of 10 noncoding DNA fragments (introns) in regions of normal to high recombination. Most interestingly, two main haplotypes are present at furrowed, one being fixed in northern populations and the other being fixed or in high frequency in more southern populations. A cline in the frequency of one of these haplotypes occurs in parallel latitudinal transects. Taken together, significant clinal variation and a test against alternative models of natural selection provide evidence of two independent selective sweeps restricted to specific regions of the species range.

Geographical divergence for quantitative traits in colonising populations of Drosophila kikkawai from India.

There are significant geographical variations for four quantitative traits among eight natural populations of Drosophila kikkawai along the Indian latitudinal transect (8.29 to 33 degrees N). Body weight, wing length, thorax length, and ovariole number exhibit significant clinal variation with increase in latitutde. Genetic correlations between all the four traits are significantly higher. Slope values for body weight and wing length are higher (2.32 per degree latitude) while lower for thorax length (0.70) and ovariole number (0.56). South Indian populations are characterised by lower mean values but higher variances as well as CV values as compared with northern populations. Multiple regression analyses (on the basis of temperature related climatic variables) evidence significantly higher association between all the four traits and coefficient of variation of mean annual temperature (seasonal thermal amplitude; TCV). Thus, genetic differentiations for quantitative traits in D. kikkawai are due to selective pressure from variable seasonal environmental conditions occurring on the southern tropical versus northern subtropical regions of the Indian subcontinent.

NESTING ECOLOGY OF RESIDENT LOGGERHEAD SHRIKES IN SOUTHCENTRAL FLORIDA

I studied the reproductive ecology of Loggerhead Shrikes (Lanius ludovicianus) in southcentral Florida from 1991 through 1993. Pairs were sedentary and defended territories year-round. Completed nests were found from late December to mid-May. Nesting peaked during mid-March with second and third nestings attempted from late March to late May. Sixty percent of all nests were built in blackberry bushes (Rubus betulifolius), but cabbage palm (Sabal palmetto) and wax myrtle (Myrica cerifera) also were used frequently. Mean nest height was 1.6 m and mean clutch size was 4.3 eggs. A mean of 17 days was required for incubation and the mean fledging period was 15 days. Nest failure occurred more often during the incubation than the nestling stage. The majority of nest losses were due to predation and inclement weather (49 and 20 nests, respectively). Mean hatching success was 87%, and 81% of chicks fledged successfully. Nesting success (percentage of nests that fledged at least one young) was 55%, and an analysis of other studies that used this measure detected significant clinal variation in Loggerhead Shrike nesting success, with success rate positively correlated with latitude. Unlike conspecifics in northern latitudes where second broods are considered rare, 96% of breeding pairs in Florida attempted second broods.

Geographic Patterns of mtDNA Diversity in Europe

Genetic diversity in Europe has been interpreted as a reflection of phenomena occurring during the Paleolithic ( approximately 45,000 years before the present [BP]), Mesolithic ( approximately 18,000 years BP), and Neolithic ( approximately 10,000 years BP) periods. A crucial role of the Neolithic demographic transition is supported by the analysis of most nuclear loci, but the interpretation of mtDNA evidence is controversial. More than 2,600 sequences of the first hypervariable mitochondrial control region were analyzed for geographic patterns in samples from Europe, the Near East, and the Caucasus. Two autocorrelation statistics were used, one based on allele-frequency differences between samples and the other based on both sequence and frequency differences between alleles. In the global analysis, limited geographic patterning was observed, which could largely be attributed to a marked difference between the Saami and all other populations. The distribution of the zones of highest mitochondrial variation (genetic boundaries) confirmed that the Saami are sharply differentiated from an otherwise rather homogeneous set of European samples. However, an area of significant clinal variation was identified around the Mediterranean Sea (and not in the north), even though the differences between northern and southern populations were insignificant. Both a Paleolithic expansion and the Neolithic demic diffusion of farmers could have determined a longitudinal cline of mtDNA diversity. However, additional phenomena must be considered in both models, to account both for the north-south differences and for the greater geographic scope of clinical patterns at nuclear loci. Conversely, two predicted consequences of models of Mesolithic reexpansion from glacial refugia were not observed in the present study.

Phenotypic variability of quantitative traits in Indian populations of Drosophila kikkawai

Drosophila kikkawai, which has colonized the Indian subcontinent in the recent past, exhibits geographical variations for five quantitative traits among eight Indian populations (8.29–32.7?N). Body weight, wing length, thorax length, abdominal bristles and ovariole number exhibit significant clinal variation with increase in latitude, while sternopleural bristles do not demonstrate such a trend. For the female sex, the slope values for body weight (2.25) and wing length (2.40) are higher but they are lower for thorax length (0.64) and ovariole number (0.51 per degree latitude). There is significant sexual dimorphism for the slope values only for body weight and thorax length suggesting simultaneous action of latitudinal selection pressure on these traits. However, the two sexes do not differ statistically in the latitudinal slope values for the wing length. A regression analysis of different traits on body weight implies correlated selection response on wing length and wing/thorax ratio while thorax length corresponds to changes in body size and does not differ in the two sexes. Regression analysis, on the basis of temperature-related climatic variables, evidence significantly higher association between all the five size-related traits and coefficient of variation of mean annual temperature (seasonal thermal amplitude; Tcv), Tmin and relative humidity. Thus, genetic differentiation for quantitative traits in D. kikkawai are due to selective pressure from variable climatic conditions occurring on the Indian subcontinent.

Latitudinal clines for alcohol dehydrogenase allozymic variation and ethanol tolerance in Indian populations of Drosophila ananassae

Summary - Eight Indian geographical populations of D ananassae, collected along a 20°N latitudinal range, revealed significant clinal variation at the Adh (alcohol dehydrogenase) locus and Adh allelic frequency increased by about 1.5% with 1° latitude. Latitudinal increase of ethanol tolerance (1.8-3.7%) was observed in adults. Survival studies with adults showed that, in all cases, ethanol was used as a resource at low concentrations, while becoming a stress at higher concentrations. The resource/stress concentration threshold increased from 1.2 to 4% with latitude. Larval behaviour also exhibited an attraction/avoidance threshold, increasing from 1.6 to 4.4% ethanol with increasing latitude of origin. The parallel occurrence of latitudinal variation at the Adh locus and ethanol tolerance and utilisation in natural populations of D ananassae could be maintained by balancing the natural selection, which varies spatially along the northsouth axis of the Indian sub-continent. Drosophila ananassae / Adh polymorphism / ethanol utilisation / larval behaviour 1

Parallel selection of ethanol and acetic-acid tolerance in Drosophila melanogaster populations from India

Summary - Nine Indian geographical populations of Drosophila melanogaster, collected along the 20°N latitudinal range, revealed a significant clinal variation at the alcohol dehydrogenase (Adh) locus, Adh allelic frequency increasing significantly with latitude (0.036 ! 0.004 for 1° latitude; genetic divergence F = 0.25). Patterns of ethanol and acetic-acid tolerance in adult individuals revealed significant genetic divergence. Parallel patterns of latitudinal ethanol tolerance (10 to 15%) and acetic-acid tolerance (3.7 to 13.2%) were observed in adult individuals from the 9 geographical populations. Thus, the northern and southern populations revealed divergence in the patterns of resource utilisation. The parallel latitudinal genetic divergence at the Adh locus and for ethanol and acetic-acid tolerance in Indian populations of Drosophila melanogaster could be explained by balancing natural selection varying spatially along the north-south axis of the Indian subcontinent. ADH polymorphism / ethanol tolerance / acetic-acid tolerance / latitudinal clines / Indian populations / Drosophila melanogaster