Genetic variation and climatic selection in the lizard Agama stellio in Israel and Sinai

Summary Allozymic variation in proteins encoded by 25 loci was analyzed electrophoretically in 242 adult specimens representing nine populations of the Levantine lizard, Agama stellio, comprising two subspecies: the Mediterranean A. stellio subsp., and the desert-inhabiting A. stellio brachydactyla from the Negev and Sinai. Likewise, four body traits were measured in the same populations. The nine populations were sampled along a general southward transect of increasing aridity. Agama stellio is above average in both polymorphism, P, and heterozygosity, H, as compared to other reptiles and vertebrates in general, displaying levels of genetic variation characterizing habitat generalist vertebrates. In the populations studied no fixation of alternative alleles was found in any of the 25 loci: rather the commonest allele was either fixed or predominated in 23 of 25 loci examined. Eleven loci (44%) were monomorphic in all nine populations. However, of the remaining 14 polymorphic loci, eight were strongly polymorphic displaying distinct genetic differentiation between populations. Genetic diversity (indexed by P and H) displayed geographic variation and was slightly higher in A.s. brachydactyla than in A. stellio subsp. Nevertheless, genic similarity between populations was high. A statistically significant amount of morphological variation between localities was found for all body characters. In general, body size increased southwards and eastwards with aridity.Selection at some loci is suggested by significant deviation from Hardy-Weinberg expectations and possibly by excess heterogeneity of effective inbreeding coefficients, F_e. Furthermore, allozymic variation at seven loci (Ldh-1, Idh-1, 6-Pgd-1, Aat-1, Pgm-2, Pept-1, and Trf) and geographic variation in body size and weight were significantly correlated with, and predictable by, climatic variables, primarily by water availability and secondarily by temperature. Finally, allozymic and morphological variations were partly correlated.The spatial patterns and ecological correlates of genic and morphological variations in Agama stellio in Israel and Sinai suggest that at least some proteins and body size differentiate geographically and appear to be adaptive, presumably with respect to factors affecting the availability of water.     

Genetic diversity and climatic determinants of tree frogs in Israel

Summary Allozymic variation in proteins encoded by 27 loci was analyzed electrophoretically in 218 adult specimens, mostly males, representing 8 populations, 5 central and 3 marginal, of lemon yellow treefrogs, Hyla arborea savignyi, in Israel along two transects of increasing aridity: (a) north to south and (b) west to east. The results indicate that (a) Of the 27 loci examined, 5 are monomorphic in all 8 populations; 9 are locally and weakly polymorphic; 6 are regionally and weakly polymorphic; and 7 are regionally and strongly polymorphic; (b) In the populations studied, no alternative fixations were found in any of the 27 loci, except in the Wasit population. The commonest allele predominates across all populations, except Wasit, central as well as marginal; (c) Clinal patterns associated with increasing aridity southwards and eastwards occur in polymorphism, P, heterozygosity, H, and in allele frequencies of Ldh-1, Fum, Got-1, and Sdh; (d) For habitat generalists, treefrogs have above average number of alleles per locus, A, and polymorphism, P, while the heterozygosity, H, is average. All three estimates A, P, and H exhibit wide geographic variation decreasing progressively southwards and eastwards; (e) Central populations harbor more genic variation then marginal populations; (f) Genic similarity between populations is high; (g) Significant gametic phase disequilibria were found in several tests in 2 populations; (h) P, H, and allozymic variation in several gene loci are significantly correlated and predictable by environmental variables, primarily those related to water; (i) Morphological and allozymic variations are uncorrelated.The spatial patterns and environmental correlates and predictors of genic variation in Hyla arborea savignyi in Israel suggest that (i) protein polymorphisms are largely adaptive and are molded primarily by climatic selection rather than by stochastic processes or neutrality, and (ii) the environmental variation model seems to be the best predictor of genic variation in treefrogs.     

Genetic diversity, climatic selection and speciation of Sphincterochila landsnails in Israel

Allozymic variation in proteins encoded by 29 loci was analysed electrophoretically in 364 adult specimens representing 12 populations and five species of the landsnail Sphincterochila in Israel along a north-south general transect of increasing aridity. In addition, geographic variation in three morphological body variables of these snails was also studied. The results indicate that: (i) most loci (86%) are strongly polymorphic; (ii) most loci (65%) display fixation of alternative alleles either within or between species; (iii) most of the variant alleles (51%) are not widespread, and genie differentiation is very high (66%) between populations and species, indicating sharp local and regional geographic differentiation; (iv) clinal patterns are rare or nonexistent; (v) populations of Sphincterochila display average estimates of mean alleles per locus,A=1.53; polymorphism, P (5% criterion) = 0.31; heterozygosity, H=0.07; and genie diversity, He= 0.11; (vi) wide geographic variation within and between species is displayed in A= 1.18-2.07; P=0.11–0.61; H=0.02-0.15, and He = 0.042-0.22. Wright's fixation index, F, ranges from 0.03 to 0.65. (vii) Genie diversity, He, increases southwards with aridity from 0.051 to 0.145. (viii) A differential amount of variation in different functional classes of enzymes follows the Gillespie-Kojima hypothesis, (ix) Coefficients of genetic distance, D, between populations are high, D= 0.34, range 0.09-0.58, and between species, D= 0.27, range 0.12-0.40. D's within species may be higher than between species. Likewise, D's increase clinally southwards, (x) Deviations from Hardy-Weinberg equilibria were found in several loci in some populations and species, (xi) A statistically significant (P< 0.001) amount of morphological variation of body variables exists within and between species. Size between three species increases eastwards and southwards with aridity, (xii) P, H, He, and allozymic variation in several gene loci are significantly correlated with, and predictable by, climatic variables, primarily those related to the moisture index, (xiii) Allozymic and morphological variations are partly correlated, (xiv) Significant microgeographical climatic differentiation was found in three critical tests. The pattern of genetic variation within and between species suggests that: (a) climatic selection plays a conspicuous role in allozymic morphological differentiation into ecologically adaptive patterns; (b) the environmental variation model seems to be a good predictor of genetic variation in Sphincterochila; (c) adaptive radiation of the five species of Sphincterochila in Israel occurred during Pleistocene times in accord with climatic differentiation and apparently involved few changes of structural genes.     

The water frogs of Greece: Bioacoustic evidence for a new species

The structure of the mating call of lake frogs (referred to as R. ridibunda) from 16 populations in Greece was analyzed for local variation using multivariate statistics. The populations of Thrace and of the island of Samothraki form a group giving the same type of mating call, whereas the mating call of the other populations differs in the degree of temperature dependence of four parameters, and specifically in the number of pulses/pulse group and pulse groups/call. Discriminant functions distinguish even single call series with a probability of 97%, intermediate mating calls are absent, and there is a significant, but slight differentiation of external morphological characters. These results have strong taxonomic implications. We conclude that the lake frogs of Greece comprise two species. The mating call of the lake frogs from Thrace resembles in all parameters that of the Rana ridibunda in the terra typica restricta (Guryev, CIS). Accordingly, the lake frogs of eastern Greece belong to R. ridibunda. The mating call of these lake frogs consists of 20 pulses/pulse group and of 7 pulse groups/call on the average. Most of Greece is inhabited by the second taxon, Rana balcanica sp. n. Its mating call is characterized by 27 pulses/pulse group and 4 pulse groups/call on the average. The two species in Greece do not differ with respect to coloration and size, but several standardized indices vary significantly: body length/digitus primus length; body length/callus internus length; body length/snout-eye distance; body length/tympanum diameter; tibia length/callus internus length; maximal head width/snout-eye distance.     

Allozyme variation among Rana balcanica,R. levantina,and R. ridibunda (Amphibia: Anura)1

The allozyme variation among water frogs of the species R. balcanica, R. levantina and R. ridibunda, all formerly considered as one species (R. ridibunda Pallas, 1771), was studied using horizontal starch gel electrophoresis. Blood samples (N # 63) of frogs were collected from five populations in Greece and Israel. Samples (N = 9) of the hybrid frog R. esculenta collected from a locality in Germany were used as an outgroup for phylogenetic analyses. Fifteen enzymes controlled by twenty presumptive loci were identified. Thirteen loci were polymorphic within or among the studied populations. Genetic differentiation among the species was considerably greater than among populations of the same species. Even at Nestos River where R. ridibunda and R. balcanica occur in the same habitats, individuals could be assigned to either species due to characteristic differences of the genotypes (GPI1). This indicates reproductive isolation among these species. The reconstruction of phylogenetic relationships among the three species based on the allozyme data corroborated the model presented on the basis of bioacoustic data: R. ridibunda and R. balcanica (Nei's genetic distance D = 0.0820) are sibling species pertaining to an Eurasian lineage, whereas R. levantina (distance to the European species D = 0.1780 - 0.1955) together with R. perezi represent an independent afroasian lineage.     

Genetic variation in relation to demography of peripheral pool frog populations (Rana lessonae)

Summary Genetic variation in an isolated northern metapopulation of the pool frog (Rana lessonae) in Sweden was compared to that of Central European populations using enzyme electrophoresis and literature data. Of the 31 loci scored, two (EST-2 andIDH-2) were polymorphic while no variation occurred in seven of the eight loci which are polymorphic in Central European populations.The heterozygosity level of the Swedish pool frogs is very low compared to that of other anuran populations, but their mean proportion of fertilized eggs within egg masses (97.5%) was not lower than in more heterozygous species, and their body size-specific fecundity did not differ from that of Polish conspecifics. The low genetic variability of the Swedish pool frogs is discussed in relation to features of the local populations such as size (N), calculated effective size (N _e ) reproductive success and probable history. It is concluded that long-term strong fluctuations in population size caused by reporductive failure in cold years have contributed more to the low genetic variability than could a single founder event due to a recent introduction by man.     

High genetic variability in an ecologically variable vertebrate,Bufo viridis

Allozymic variation in proteins encoded by 26 loci was analyzed electrophoretically in 517 specimens of green toads from 11 populations from Israel and one population from Vis Island in the Adriatic Sea. Genetic variation in this toad is the highest yet reported in any vertebrate. All three genetic parameters, mean number of alleles per locus (A), mean proportion of loci polymorphic per population (P), and mean number of heterozygous loci per individual (H), are very high (A = 1.65, range 1.38-2.04; P = 0.423, range 0.346-0.615; H = 0.133, range 0.108-0.159). Central and marginal mainland populations are only slightly more variable than desert isolates, but much more variable than the Vis Island population. Genetic similarity is very high between mainland populations (S = 0.951, range 0.93-0.97). Frequencies of two alleles (Icd-lc and Tfa) are correlated with an ecological gradient of increasing aridity. Regulatory enzymes appeared to contribute more to overall polymorphism than non-regulatory enzymes. The genetic variation observed suggests that selection for heterozygosity as an adaptive strategy is operating in the ecologically variable environment in which green toads live.     

Genetic structure and climatic correlates of desert landsnails

Summary Allozymic variation in proteins encoded by 20 loci was analyzed electrophoretically in 126 adult specimens representing 4 populations and 2 species of the desert landsnail Trochoidea, subgenus Xerocrassa, in a variable desert climatic back-ground of temperature and water factors. In addition, geographic variation in 3 morphological body variables of these snails was also studied. The results indicate that: (i) Most loci (55%) were strongly polymorphic; (ii) A large proportion of the polymorphic loci (55%) displayed fixation of alternative alleles either within or between species; (iii) Most of the variant alleles (75%) were not widespread, indicating sharp local and regional geographic differentiation; (iv) Southward progressive trends were found in genic diversity, some allele frequencies, shell banding and body characters. (v) The mean estimates of genetic indices are: not of alleles per locus, A=1.69; proportion of polymorphism per population P=0.41, and proportion of heterozygosity per individual, H=0.07; (vi) The level of P increases and that of H decreases southward; (vii) The amount of variation in different functional elasses of enzymes follows the Gillespie-Kojima and partly the Johnson hypotheses; (viii) Coefficients of genetic disfance, D, between populations are high, , range 0.05–0.26. D's within species may be higher than between species. Likewise, D's from the northernmost population increase progressively southwards; (ix) Significant gametic phase disequilibria occur in several populations in both species; (x) Deviations from Hardy-Weinberg equilibria were found in several loci in some populations in both species; (xi) A statistically significant (P<0.001) amount of morphological variation of all 3 body variables occurs within and between species. Body diameter decreases with evaporation. (xii) P, H, and allozymic variation in several gene loci are significantly correlated with climatic variable, primarily related to some water factors and secondarily to temperature; (xiii) Shell banding was negatively correlated with solar radiation; and (xiv) Few correlations between allozymic and morphological variations were revealed.The pattern of genetic variation of Trochoidea (Xerocrassa) vetzenii and T. (X) erkelii suggests that (a) climatic selection plays a major role in allozymic (and morphological) population structure and differentiation; (b) variation in allozyme and visual polymorphisms may provide the genetic basis for the complex physiological adaptations of landsnails enabling them to survive in hostile, hot and dry deserts, and is therefore partly adaptive rather than neutral.     

Seasonal fluctuations of migratory activity of vertebrate nuclear hemocytes at different incubation temperatures

Agarose migration test has shown that nuclear erythrocytes of Cyprinus carpio, Rana ridibunda, and Gallus domesticus are capable for spontaneous locomotions. The migration of red blood cells from frogs is associated with formations of long pseudopodia, whereas that from carps and hens-with short protrusions. It has been shown that migratory activity of nuclear erythrocytes and leukocytes from Rana ridibunda and Gallus domesticus under effect of temperature in vitro had seasonal nature, while that from Cyprinus carpio did not depend on the year season. In frogs and hens the circadian oscillations of blood cell migration area are coupled with the organism functional activity, whereas no such association is present in carps.     

Genetic variation in a subtropical population of Daphnia

We assayed a subtropical population of Daphnia ambigua for genetic variation using protein electrophoresis (9 loci) and quantitative genetics approaches (life history characters). Our goal was to obtain information about relative levels of variation in a subtropical population, and compare them with extensive previous studies in the temperate and arctic zones. The observed level of allozymic variation (H = 0.11) was consistent with those previously observed in other temperate zone Daphnia populations. However, variation for quantitative traits (heritability) was lower than typically observed in previously-studied temperate populations: estimates were not statistically different from zero. Because allozyme heterozygosity was consistent with previous temperate zone estimates, and the polymorphic allozyme loci did not depart from the expectations of Hardy-Weinberg equilibrium, we concluded that a period of clonal selection was the most likely explanation for the low heritabilities observed. We do not conclude that this study provides evidence to suggest that subtropical populations harbor lower levels of genetic variation because of their location.     

Contrasting Levels of Variation in Neutral and Quantitative Genetic Loci on Island Populations of Moor Frogs (<Emphasis Type="Italic">Rana arvalis</Emphasis>)

Reduced levels of genetic variability and a prominent differentiation in both neutral marker genes and phenotypic traits are typical for many island populations as compared to their mainland conspecifics. However, whether genetic diversity in neutral marker genes reflects genetic variability in quantitative traits, and thus, their evolutionary potential, remains typically unclear. Moreover, the phenotypic differentiation on islands could be attributable to phenotypic plasticity, selection or drift; something which seldom has been tested. Using eight polymorphic microsatellite loci and quantitative genetic breeding experiments we conducted a detailed comparison on genetic variability and differentiation between Nordic islands (viz. Gotland, Öland and Læsø) and neighbouring mainland populations of moor frogs (Rana arvalis). As expected, the neutral variation was generally lower in island than in mainland populations. But as opposed to this, higher levels of additive genetic variation (V _A) in body size and tibia length were found on the island of Gotland as compared to the mainland population. When comparing the differentiation seen in neutral marker genes (F _ST) with the differentiation in genes coding quantitative traits (Q _ST) two different evolutionary scenarios were found: while selection might explain a smaller size of moor frogs on Gotland, the differentiation seen in tibia length could be explained by genetic drift. These results highlight the limited utility of microsatellite loci alone in inferring the causes behind an observed phenotypic differentiation, or in predicting the amount of genetic variation in ecologically important quantitative traits.     

Genetic Structure of Blastocerus dichotomus Populations in the Paraná River Basin (Brazil) Based on Protein Variability

The population structure of 147 marsh deer (Blastocerus dichotomus) from three areas in the Paraná River basin, Brazil, was studied by observing protein polymorphism at 17 loci. Six loci were polymorphic and 11 monomorphic. The proportion of polymorphic loci (P) was 35.29% and the average heterozygosity (H) was 6.31%. Wright's F_ST indicated that only 4.9% of the total variation in allelic frequencies was due to genetic differences between the three groups. The high value of F_IS (0.246) indicated inbreeding in the marsh deer. Genetic distance values (D = 0.014–0.051) showed little divergence between the three areas. We suggest that probable mechanisms accounting for the genetic structure are female phylopatry and polygyny and also that inbreeding has resulted from decreasing areas of wetland leading to isolation, overhunting, and diseases transmitted by cattle.     

Population genetics of a successful invader: the marsh frog Rana ridibunda in Britain

We investigated the genetic outcome of successful invasion by an alien species, the marsh frog Rana ridibunda, in Britain. Twelve adults translocated from Hungary into Kent (Romney) in 1935 resulted rapidly in a large localized population. A further successful translocation in 1973 from Romney to Sussex (Lewes), together with other range extensions, provided an opportunity to test bottleneck effects during colonization events. Romney and Lewes frogs had similar genetic diversities to those in Hungary at 14 random amplified polymorphic DNA marker (RAPD) and five microsatellite loci. The introduced populations were, however, differentiated genetically from each other and from a reference population in Hungary. Fitness assessments (larval growth and survival) revealed no differences between the Lewes and Romney populations. Despite starting with few founders, significant bottleneck effects on R. ridibunda in Britain were therefore undetectable, presumably because population expansions were rapid immediately after the translocations.     

Low genic variation in male-reproductive-tract proteins of Drosophila melanogaster and D. simulans

We report results, using two-dimensional gel electrophoresis (2DE), of natural population surveys of allelic variation in approximately 300 male-reproductive-tract polypeptides in both Drosophila melanogaster and its sibling species, D. simulans. Despite our efforts to maximize operational sensitivity of our 2DE gels to polymorphism, variation estimates in both species were low (proportion of polymorphic loci [P] = 9%, and average heterozygosity [H] = 1%-3%), compared with those by one-dimensional gel electrophoresis (1DE) (P = 29%-55%; H = 8%-19%) in the same populations. However, H of polymorphic loci was very similar for 2DE and 1DE proteins; and for 17 of a total of 54 polymorphic proteins, 2DE detected three or four distinct alleles. The results suggest that the differing levels of variability widely seen with 1DE and 2DE are real and reflect differing intensities of functional constraint between different classes of structural loci. However, the alternative possibility remains that 2DE has a greater between-locus unevenness of variant detection sensitivity than does 1DE.     

Allele frequencies of the human platelet antigen-1 in the Egyptian population

Background

We report the expression pattern of 5S rDNA in the eggs of water frogs Rana lessonae, Rana ridibunda and Rana esculenta using the quantitative real-time PCR. This kind of research had never been performed before.

Results

5S rDNA relative expression of the Rana ridibunda oocytes is approximately six times higher in comparison to the Rana lessonae oocytes. The oocytes of the investigated Rana esculenta frogs, in respect of 5S rDNA relative expression ratio, were very similar to the Rana ridibunda oocytes.

Conclusion

We suggest the possibility of using 5S rDNA as the internal control gene, in the studies of relative mRNA quantitative assays in water frog oocytes, because of its characteristic specific expression pattern in the Rana lessonae, Rana ridibunda and Rana esculenta oocytes.     

Genetic diversity and environmental associations of wild wheat,Triticum dicoccoides,in Israel

Summary Allozyme variation in the tetraploid wild progenitor of wheat, Triticum dicoccoides, was studied for the proteins encoded by about 50 gene loci in 457 individuals representing 12 populations from Israel. Six spikelet morphological traits were measured in the same populations. The results indicate that: (a) 16 loci (= 32%) were monomorphic in all 12 populations, 15 loci (= 30%) were locally polymorphic, and 19 loci (= 38%) were regionally polymorphic. All polymorphic loci (but one) displayed high levels of polymorphism ( 10%). In Israel, the proportion of polymorphic loci per population, P, in wild wheat averaged 0.25 (range, 0.16–0.38), and the genetic diversity index, H_e averaged 0.07, (range, 0.03 – 0.12). (b) Altogether there were 110 alleles at the 50 putative loci tested (c) Genetic differentiation of populations included regional and local patterns: (i) The coefficients of genetic distance between populations were high (mean D = 0.10 range, 0.02 – 0.25), and indicated sharp genetic differentiation over short distances, (ii) Common ( 10%) but sporadic and localized alleles were frequent (76%), and (iii) Rare alleles were few (only 5 alleles). (d) The patterns of allozyme and spikelet variation in the wild gene pool were significantly correlated with, and partly predictable by, water factors, including those of precipitation, evaporation, and relative humidity as well as of soil type, (e) All six spikelet characters showed statistically significant variation among localities and (f) Allozymic variation was correlated with spikelet variation.These results suggest in T. dicoccoides: (i) the operation of natural selection in population genetic structure, (ii) local adaptive genetic differentiation caused by diversifying selection through climate and soil, and (iii) the guidelines for sampling these resources for use in wheat breeding programs.     

Glycolytic adjustments in tissues of frog Rana ridibunda and land snail Helix lucorum during seasonal hibernation

The present work aimed to contribute to the understanding of the adaptation of the glycolytic pathway in tissues of frog Rana ridibunda and land snail species Helix lucorum during seasonal hibernation. Moreover responses of glycolytic enzymes from cold acclimated R. ridibunda and H. lucorum were studied as well. The drop in Po₂ in the blood of hibernated frogs and land snails indicated lower oxygen consumption and a decrease in their metabolic rate. The activities of glycolytic enzymes indicated that hibernation had a differential effect on the glycolyis in the two species studied and also in the tissues of the same species. The activity of l-LDH decreased significantly in the skeletal muscle and heart of hibernated R. ridibunda indicating a low glycolytic potential. Similar biochemical responses were observed in the same tissues during cold acclimation. The continuous increase in the activities of glycolytic enzymes studied, except for HK, might indicate a compensation for the impacts of low temperature on the enzymatic activities. In contrast to R. ridibunda, the activities of the enzymes increased and remained at higher levels than those of the prehibernation controls indicating maintenance of glycolytic potential in the tissues of hibernating land snails.     

A genetic mechanism of species replacement in European waterfrogs?

Introduced Rana ridibunda currentlyreplace the native waterfrogs R. lessonaeand R. esculenta in several areas ofcentral Europe. The unusual reproductive systemin waterfrogs of the Rana esculentacomplex suggests that this replacement may bedriven by a genetic mechanism: Ranaesculenta, a hybrid between R. ridibundaand R. lessonae, eliminates the lessonae genome from the germline and clonallytransmits the ridibunda genome(hybridogenesis). Hybrids form mixedpopulations with R. lessonae (L-E-system)in which they persist by backcrossing with theparental species. Matings between hybrids areunsuccessful, because their ridibundagenomes contain fixed recessive deleteriousmutations. When introduced into a L-E-system,R. ridibunda can mate with both nativetaxa, producing R. ridibunda offspringwith R. esculenta, and R. esculentaoffspring with R. lessonae (primaryhybridizations). If primary hybrids arehybridogenetic, they produce viable R.ridibunda offspring in matings with otherhybrids, because their clonal genomes areunlikely to share the deleterious allelespresent in the ancient clones. Thus, R.ridibunda will increase in the population atthe expense of both native taxa, eventuallyleaving a pure R. ridibunda population.We provide three lines of evidence for thisprocess from a currently invaded population inSwitzerland: (1) Primary hybridizations takeplace, as roughly 10% of hybrids in thepopulation possess ridibunda genomesderived from the introduced frogs. (2)Hybridogenesis occurs in primary hybrids,although at a low frequency. (3) Many hybrid ×hybrid matings in the population indeed produceviable offspring. Hence, the proposed geneticmechanism appears to contribute to the speciesreplacement, although its importance may belimited.     

Development and characterization of polymorphic microsatellite DNA loci for the endangered dusky gopher frog,Rana sevosa,and two closely related species,Rana capito and Rana areolata

A microsatellite library was developed using genomic DNA of the endangered dusky gopher frog, Rana sevosa. Polymerase chain reaction (PCR) primers and conditions are presented for R. sevosa (eight loci) and two sister taxa — other gopher frogs, Rana capito (seven loci) and crawfish frogs, Rana areolata (three loci). Polymorphism of each microsatellite locus was evaluated for each species. All loci have moderate to high genetic variation in terms of allelic richness (four to 10 alleles per locus), observed heterozygosity (0.595–0.946), and expected heterozygosity (0.531–0.856).     

Are there morphological and life‐history traits under climate‐dependent differential selection in S Tunesian Diplotaxis harra (Forssk.) Boiss. (Brassicaceae) populations?

Adaptation of morphological, physiological, or life‐history traits of a plant species to heterogeneous habitats through the process of natural selection is a paramount process in evolutionary biology. We have used a population genomic approach to disentangle selection‐based and demography‐based variation in morphological and life‐history traits in the crucifer Diplotaxis harra (Forssk.) Boiss. (Brassicaceae) encountered in populations along aridity gradients in S Tunisia. We have genotyped 182 individuals from 12 populations of the species ranging from coastal to semidesert habitats using amplified fragment length polymorphism (AFLP) fingerprinting and assessed a range of morphological and life‐history traits from their progeny cultivated under common‐garden conditions. Application of three different statistical approaches for searching AFLP loci under selection allowed us to characterize candidate loci, for which their association with the traits assessed was tested for statistical significance and correlation with climate data. As a key result of this study, we find that only the shape of cauline leaves seems to be under differential selection along the aridity gradient in S Tunisian populations of Diplotaxis harra, while for all other traits studied neutral biogeographical and/or random factors could not be excluded as explanation for the variation observed. The counter‐intuitive finding that plants from populations with more arid habitats produce broader leaves under optimal conditions of cultivation than those from more mesic habitats is interpreted as being ascribable to selection for a higher plasticity in this trait under more unpredictable semidesert conditions compared to the more predictable ones in coastal habitats.