Gene Frequency Clines Research Articles

"The Environment is Everything That Isn't Me": Molecular Mechanisms and Evolutionary Dynamics of Insect Clocks in Variable Surroundings.

Circadian rhythms are oscillations in behavior, metabolism and physiology that have a period close to 24 h. These rhythms are controlled by an internal pacemaker that evolved under strong selective pressures imposed by environmental cyclical changes, mainly of light and temperature. The molecular nature of the circadian pacemaker was extensively studied in a number of organisms under controlled laboratory conditions. But although these studies were fundamental to our understanding of the circadian clock, most of the environmental conditions used resembled rather crudely the relatively constant situation at lower latitudes. At higher latitudes light-dark and temperature cycles vary considerably across different seasons, with summers having long and hot days and winters short and cold ones. Considering these differences and other external cues, such as moonlight, recent studies in more natural and semi-natural situations revealed unexpected features at both molecular and behavioral levels, highlighting the dramatic influence of multiple environmental variables in the molecular clockwork. This emphasizes the importance of studying the circadian clock in the wild, where seasonal environmental changes fine-tune the underlying circadian mechanism, affecting population dynamics and impacting the geographical variation in clock genes. Indeed, latitudinal clines in clock gene frequencies suggest that natural selection and demography shape the circadian clock over wide geographical ranges. In this review we will discuss the recent advances in understanding the molecular underpinnings of the circadian clock, how it resonates with the surrounding variables (both in the laboratory and in semi-natural conditions) and its impact on population dynamics and evolution. In addition, we will elaborate on how next-generation sequencing technologies will complement classical reductionist approaches by identifying causal variants in natural populations that will link genetic variation to circadian phenotypes, illuminating how the circadian clock functions in the real world.

Polymorphism in the couch potato gene clines in eastern Australia but is not associated with ovarian dormancy in Drosophila melanogaster

Natural selection can generate parallel latitudinal clines in traits and gene frequencies across continents, but these have rarely been linked. An amino acid (isoleucine to lysine, or I462K) polymorphism of the couch potato (cpo) gene in Drosophila melanogaster is thought to control female reproductive diapause cline in North America (Schmidt et al. 2008, Proc Natl Acad Sci USA, 105, 16207-16211). Here, we show that under standard diapause-inducing conditions (12 °C and short photoperiod) (Saunders et al. 1989, Proc Natl Acad Sci USA, 86, 3748-3752), egg maturation in Australian flies is delayed, but not arrested at previtellogenic stages. At 12 °C, the phenotypic distribution in egg development was bimodal at stages 8 and 14 and showed a strong nonlinear pattern on the east coast of Australia, with incidence of egg maturation delay (ovarian dormancy) increasing both toward tropical and temperate climates. Furthermore, we found no evidence for an association between the cpo I462K polymorphism and ovarian dormancy at either 12 or 10 °C (when egg maturation was often delayed at stage 7). Owing to strong linkage disequilibrium, the latitudinal cline in cpo allele frequencies was no longer evident once variation in the In(3R)P inversion polymorphism was taken into account. Our results suggest that the standard diapause-inducing conditions (12 °C and short photoperiod) were not sufficient to cause the typical previtellogenic developmental arrest in Australian flies and that the cpo I462K polymorphism does not explain the observed delay in egg development. In conclusion, ovarian dormancy does not show a simple latitudinal cline, and the lack of cpo-dormancy association suggests a different genetic basis to reproductive dormancy in North America and Australia.

Genetic and Morphometric Evidence for the Conspecific Status of the Bumble Bees,Bombus melanopygusandBombus edwardsii

The taxonomic status of closely related bumble bee species is often unclear. The relationship between the two nominate taxa, Bombus melanopygus Nylander (Hymenoptera: Apidae) and Bombus edwardsii Cresson (Hymenoptera: Apidae), was investigated using genetic (enzyme electrophoretic) and morphometric analyses. The taxa differ in the color of the abdominal terga two and three, being ferruginous in B. melanopygus and black in B. edwardsii. B. edwardsii occurs throughout California, while B. melanopygus extends north through Oregon, to Alaska and Canada. They are sympatric only in southern Oregon and northern California. The taxonomic status of these taxa was questioned when Owen and Plowright (1980) reared colonies from queens collected in the area of sympatry, and discovered that pile coloration was due to a single, biallelic Mendelian gene, with the red (R) allele dominant to the black (r). Here it is shown that all the taxa, whether from California, Oregon, or Alberta, have the same electrophoretic profile and cannot be reliably distinguished by wing morphometrics. This strongly supports the conclusion that B. melanopygus and B. edwardsii are conspecific and should be synonymized under the name B. melanopygus. Hence, there is a gene frequency cline running from north to south, where the red allele is completely replaced by the black allele over a distance of about 600 km.

Selection and gene flow on a diminishing cline of melanic peppered moths

Historical datasets documenting changes to gene frequency clines are extremely rare but provide a powerful means of assessing the strength and relative roles of natural selection and gene flow. In 19th century Britain, blackening of the environment by the coal-fired manufacturing industry gave rise to a steep cline in the frequency of the black (carbonaria) morph of the peppered moth (Biston betularia) across northwest England and north Wales. The carbonaria morph has declined across the region following 1960s legislation to improve air quality, but the cline had not been comprehensively described since the early 1970s. We have quantified changes to the cline as of 2002, equivalent to an interval of 30 generations, and find that a cline still exists but that it is much shallower and shifted eastward. Joint estimation of the dominant fitness cost of carbonaria and dispersal parameters consistent with the observed cline change indicate that selection against carbonaria is very strong across the landscape (s approximately 0.2), and that dispersal is much greater than previously assumed. The high dispersal estimate is further supported by the weak pattern of genetic isolation by distance at microsatellite loci, and it implies that in addition to adult dispersal, wind-dispersed first instar larvae also contribute to lifetime dispersal. The historical perspective afforded by this study of cline reversal provides new insight into the factors contributing to gene frequency change in this species, and it serves to illustrate that, even under conditions of high dispersal and strong reverse selection acting against it, complete erosion of an established cline requires many generations.

Genetic studies of Gammarus

The marine amphipods Gammarus salinus and G. oceanicus are both polymorphic at the enzyme loci glucosephosphate isomerase (Gpi), glutamic-pyruvic transaminase (Gpi), and mannosephosphate transaminase (Mpi). In addition, G. solinus is polymorphic at the glutamic-oxaloacetic transaminase locus Gotl. The variation at these loci is described for populations ranging from the Limfjord, Denmark, to the Baltic Sea at Askô, Sweden. In both species the Baltic populations and the Kattegat populations have diverged from each other. The populations are connected through gene frequency clines that can be smooth (at the Gpi locus in both species) or more irregular (at the Mpi locus in both species).

Tension versus ecological zones in a two-locus system

Previous theories show that tension and ecological zones are indistinguishable in terms of gene frequency clines. Here I analytically show that these two types of zones can be distinguished in terms of genetic statistics other than gene frequency. A two-locus cline model is examined with the assumptions of random mating, weak selection, no drift, no mutation, and multiplicative viabilities. The genetic statistics for distinguishing the two types of zones are the deviations of one- or two-locus genotypic frequencies from Hardy–Weinberg equilibrium (HWE) or from random association of gametes (RAG), and the deviations of additive and dominance variances from the values at HWE. These deviations have a discontinuous distribution in space and different extents of interruptions in the ecological zone with a sharp boundary, but exhibit a continuous distribution in the tension zone. Linkage disequilibrium enhances the difference between the deviations from HWE and from RAG for any two-locus genotypic frequency.

Genetic polymorphism and linkage disequilibrium of the HLA-DP region in Basques from Navarre (Spain).

In this work, a sample of 116 individuals from an autochthonous Basque population (northern Navarre, Spain) was typed at the DNA level for HLA-DPA1 and HLA-DPB1 loci, with the aim of analysing the genetic polymorphism and the linkage disequilibrium (LD) of the HLA-DP region. In this Basque subpopulation, the most frequent alleles were *0103 (0.767) and *0201 (0.185) for DPA1 locus, whereas for DPB1 locus the *0401 allele was predominant (0.307). Accordingly, the most frequent haplotype was DPA1*0103-DPB1*0401 (0.300), which showed a significant LD. However, the haplotypes that most differentiated the sample of Navarre from other worldwide populations already analysed were DPA1*0105-DPB1*1901 (0.011) and DPA1*0201-DPB1*7601 (0.021), both of which showed a strong LD. Analysis of the relationships between populations based on data provided by HLA-DPA1 and HLA-DPB1 loci revealed a high genetic affinity between the Basque samples (North Navarre and Guipúzcoa), which, in turn, tend to plot separately from the remaining European populations. Gene frequency clines for DPB1*01, DPB1*04 and DPB1*11 alleles among European populations are reported for the first time. These alleles showed maximum values of F(ST) (0.033, 0.034 and 0.025, respectively). Various evolutionary forces were considered in discussing the origin of the spatial structuring of the gene frequencies: (i) gene flow, argued from the hypotheses of Post-glacial recolonization from southern Europe or the demic diffusion of farmers from the Near East into Europe, and (ii) the existence of selective pressures that could have generated genetic microdifferentiation.

Kin-structured migration: causes and consequences.

Migration among local populations classically has been seen as the principal process retarding genetic microdifferentiation. However, as Sewall Wright pointed out long ago, migration may also act as a random differentiating force. In fact, when migrants comprise a biological kin group, migration may be considered a component of genetic drift. The causes of kin-structured migration (KSM) lie in the common, if not universal, tendency for kin to associate and cooperate. However, similar to genetic drift, KSM has its greatest effect in smaller populations and is most apparent in low-density fission-fusion societies such as the Yanomamo of South America and the Semai of Malaysia, and less salient in higher density, low-mobility populations such as those of the New Guinea Highlands. The evolutionary consequences of KSM begin with increased genetic variation among populations. Such intergroup variation provides a basis for group selection. The origin of larger-scale geographic differentiation can arise from kin-structured migrant groups colonizing new regions. Waves of colonizing kin-structured founder groups may produce gene frequency clines, mimicking demic diffusion and natural selection. Finally, because kin structuring reduces the effective size of a population, it may be speculated that the extremely small effective size inferred for ancestral populations of Homo sapiens may be an artifact of kin-structured demographically larger populations.

Gene Frequency Clines in Europe: Demic Diffusion or Natural Selection?

According to the demic diffusion model ofCavalli-Sforza and colleagues, agriculture was spread through Europe by a rapid population expansion of early farmers from the Near East. These scholars use the presence of gene frequency clines paralleling this direction of spread to support their model. However, genetic clines may also be caused by natural selection. This article shows that the archaeological and demographic evidence for demic diffusion is questionable, and proposes an alternative selective clinal model. The model posits that genetic fitnesses changed through time as functions of increasing disease intensities brought on by the diffusion of agriculture and, especially, by the association between humans and newly domesticated animals. Since agriculture required several thousand years to spread across Europe, a gradient in duration of selection was generated. A computer simulation shows that clinal patterns similar to those observed in European populations can be produced by temporal gradients in natural selection. Thus gene frequency clines in Europe may indeed be due to domestication (specifically, to animal husbandry) but not necessarily to the mechanism of demic diffusion.

Genetic evidence on origin and dispersal of human populations speaking languages of the Nostratic macrofamily.

Contemporary patterns of allele frequencies allow inferences on past evolutionary processes. L.L. CavalliSforza [(1988) Munibe 6, 129-137] and C. Renfrew [(1991) Cambridge Archaeol. J. 1, 3-23] proposed that neolithic farmers from the Near East propagated a group of related ancestral languages, from which three or four linguistic families developed. Here we show that genetic variation among Indo-European, Elamo-Dravidian, and Altaic speakers (grouped by some linguists in the Nostratic macrofamily) supports this hypothesis, whereas the evidence on Afro-Asiatic speakers is ambiguous. Gene-frequency clines within these linguistic families suggest that language diffusion was largely associated with population movements rather than with purely cultural transmission. Archeological, linguistic, and genetic evidence can be reconciled by envisaging a process of population growth and multidirectional dispersal from the Near East as the main factor shaping genetic and linguistic diversity in Eurasia and perhaps in North Africa.

Alpha-2-HS-glycoprotein gene frequencies in Galicia: further evidence for a cline in European populations.

alpha 2-HS-glycoprotein (AHSG) phenotypes were determined in 506 unrelated autochthonous individuals from the Galician population (NW Spain) by means of isoelectric focusing followed by silver stain immunofixation. The phenotype frequency distribution fitted with the Hardy-Weinberg law. No evidence of intrapopulation heterogeneity was observed. The allele frequencies obtained were: AHSG*1 = 0.7559 +/- 0.013 and AHSG*2 = 0.2441 +/- 0.013. Our findings lend support to the hypothesis of an AHSG gene frequency cline in European populations. Other population genetics' considerations have also been discussed.

Estimates of selection and gene flow from measures of cline width and linkage disequilibrium in heliconius hybrid zones.

Hybrid zones can yield estimates of natural selection and gene flow. The width of a cline in gene frequency is approximately proportional to gene flow (sigma) divided by the square root of per-locus selection (square root of s). Gene flow also causes gametic correlations (linkage disequilibria) between genes that differ across hybrid zones. Correlations are stronger when the hybrid zone is narrow, and rise to a maximum roughly equal to s. Thus cline width and gametic correlations combine to give estimates of gene flow and selection. These indirect measures of sigma and s are especially useful because they can be made from collections, and require no field experiments. The method was applied to hybrid zones between color pattern races in a pair of Peruvian Heliconius butterfly species. The species are Müllerian mimics of one another, and both show the same changes in warning color pattern across their respective hybrid zones. The expectations of cline width and gametic correlation were generated using simulations of clines stabilized by strong frequency-dependent selection. In the hybrid zone in Heliconius erato, clines at three major color pattern loci were between 8.5 and 10.2 km wide, and the pairwise gametic correlations peaked at R approximately 0.35. These measures suggest that s approximately 0.23 per locus, and that sigma approximately 2.6 km. In erato, the shapes of the clines agreed with that expected on the basis of dominance. Heliconius melpomene has a nearly coincident hybrid zone. In this species, cline widths at four major color pattern loci varied between 11.7 and 13.4 km. Pairwise gametic correlations peaked near R approximately 1.00 for tightly linked genes, and at R approximately 0.40 for unlinked genes, giving s approximately 0.25 per locus and sigma approximately 3.7 km. In melpomene, cline shapes did not perfectly fit theoretical shapes based on dominance; this deviation might be explained by long-distance migration and/or strong epistasis. Compared with erato, sample sizes in melpomene are lower and the genetics of its color patterns are less well understood. In spite of these problems, selection and gene flow are clearly of the same order of magnitude in the two species. The relatively high per locus selection coefficients agree with "major gene" theories for the evolution of Müllerian mimicry, but the genetic architecture of the color patterns does not. These results show that the genetics and evolution of mimicry are still only sketchily understood.

Gene frequency clines for host races of Rhagoletis pomonella in the Midwestern United States

Speciation in many host specific parasites may be initiated in sympatry when populations shift and adapt to new hosts. The recent shift of the apple maggot fly, Rhagoletis pomonella (Diptera: Tephritidae) from its native host plant hawthorn (Crataegus spp.) to introduced, domesticated apple (Malus pumila), provides a direct test of the “sympatric speciation” hypothesis by indicating whether partially reproductively isolated “host races” can evolve in the absence of geographic isolation. We report finding significant allele frequency differences for six allozymes between paired apple and hawthorn infesting populations of R. pomonella from across the midwestern United States. Latitudinal allele frequency clines exist among both apple and hawthorn populations, however, for a majority of the loci displaying racial differences. Inter-host genetic differentiation is therefore superimposed on clinal patterns of variation within the races such that the magnitude of host associated divergence is a function of latitude. The results indicate that host associated races can form in sympatry and implicate differences in host plant recognition and developmental timing (related to ambient temperature) as key factors restricting gene flow between apple and hawthorn populations. However, some of the same processes differentiating apple and hawthorn populations at sympatric sites also appear to be occurring within the two host races across their respective ranges. R. pomonella populations are therefore diverging with respect to both their host plant affiliations and local environmental conditions.

Gene frequency clines at X-linked or haplodiploid loci.

The equations governing gene frequency clines at X-linked or haplodiploid loci are derived. Clines at X-linked loci will be identical to corresponding clines at autosomal loci only under three restrictive conditions (a) no dominance, (b) dispersal distance the same in each sex, (c) average effect of alleles same in each sex. If any of these conditions are not met then the males and females will have different gene frequencies. Clinal variation in colour morph frequency in the bumble bee Bombus melanopygusis analysed. It is concluded that a minimum selection intensity acting on the queens on the order of 1 per cent or less is sufficient to maintain the cline.

The geographical distribution of selected surnames in Britain. Model gene frequency clines

The distribution of 49 surnames among registration districts in England and Wales is heterogeneous. Intercorrelation between chi values yields significant canonical variates highly correlated with longitude and latitude. Varimax orthogonal factors distinguish Welsh, Indian and Irish groups of surnames. Significant polynomial regressions against longitude and latitude (clines) occur in 34 of the 49 surnames tested.

Aspects of the population genetics of Mytilus (Mytilidae; Mollusca) in the British Isles

Starch gel electrophoresis was used to study variation at 11 loci in mussels sampled mainly from British coastal sites. Two types of mussel were identified, Mytilus edulis, the common mussel and its southern relative Mytilus galloprovincialis. Several partially diagnostic loci were used to map the distribution of the two forms. Mytilus edulis was present at all sites sampled in Britain and Ireland but was at low frequency in SW England; M. galloprovincialis was detected in SW England, the south and west of Ireland. Scotland and NE England, but was absent from south Wales, the Irish sea coasts of Wales and Ireland, and SE England. Apart from the occurrence of M. galloprovincialis in NE England, this distribution conforms with the results of studies using morphological characters and parallels the distribution of many other southern species in Britain. At the microgeographical level, M. edulis was found to prefer more sheltered and estuarine conditions than M. galloprovincialis. Analysis using the best diagnostic loci showed that hybridization is occurring between M. edulis and M. galloprovincialis at all localities where they occur sympatrically but that the extent of hybridization varies considerably between localities. The distribution of localities having high proportions of hybrid individuals is best interpreted by assuming that hybrids have higher fitness than parental types at these localities. A study was made of variation within and between those localities where only M. edulis individuals were observed. Little significant geographic variation in allele frequency was detected, but significant deficits of heterozygotes compared with Hardy-Weinberg expectations were seen for most loci. Analysis suggests that the Wahlund effect is not involved and that the most likely cause of the deficit is low frequencies of null alleles. In M. edulis no differences in phenotypic variance in shell height and width were observed between samples of multiply heterozygous and multiply homozygous individuals and no genetic differences were found between juveniles and adults. Overall little evidence was found that balancing selection is responsible for maintenance of the polymorphisms studied in M. edulis. The pattern of geographic variation in gene frequencies in Mytilus in the British Isles is discussed in relation to variation in the south and north of Europe and North America. It is concluded that steep clines in gene frequencies in M. edulis observed by other workers in the Baltic and in Long Island Sound cannot be attributed to the presence of M. galloprovincialis.

ALCOHOL DEHYDROGENASE AND GLYCEROL-3-PHOSPHATE DEHYDROGENASE CLINES IN DROSOPHILA MELANOGASTER ON DIFFERENT CONTINENTS.

Some of the most persuasive evidence that natural selection can maintain allozymic variation derives from work on polymorphisms for electrophoretically and enzymes of alcohol dehydrogenase (ADH, EC 1.1.1.1.) and glycerol-3-phosphate dehydrogenase (GPDH, EC 1.1.1.8.) in Drosophila melanogaster. The ADH-F and ADH-S variants are encoded by the AdhF and Adhs alleles (11-50. 1; Grell et al., 1965) and the GPDH-F and GPDH-S variants by the GpdhF and Gpdhs alleles (11-20.5; Grell, 1967). Almost every wild population of D. melanogaster which has been investigated has been found to segregate for all four genes (e.g., Voelker et al., 1978). The frequencies of all the genes also show latitudinal clines in eastern United States and Mexico; Adhs and GpdhF decrease, and AdhF and Gpdhs increase in frequency with increasing distance from the equator (Berger, 1971; Johnson and Schaffer, 1973; Pipkin et al., 1973; Vigue and Johnson, 1973). The clines in North America are extensive, covering about 250 of latitude, and it has been suggested that they are maintained by latitude-related selection pressures (e.g., Pipkin et al., 1973; Vigue and Johnson, 1973). However, either stochastic processes or transient stages in the dynamics between migration and latitudinally invariant selection pressures can also produce gene frequency clines (Endler, 1973; Jacquard, 1974). Therefore, we have tested the hypothesis that latitudinally varying selection maintains the Adh and Gpdh clines in North America by testing for the presence of complementary latitudinal clines in Asia, Europe and Australasia. Our rationale is that if the North American clines are simply due to stochastic processes, then they are unlikely to recur in the southern hemisphere or elsewhere in the northern hemisphere. A second hypothesis which we have investigated is based on evidence for thermostability differences between the fast and slow allozymes at the two loci. GPDHF is more thermostable than GPDH-S at 39 C (Alahiotis et al., 1977) and ADH-S is generally more thermostable than ADHF at a variety of temperatures up to 44 C (Gibson, 1970; Vigue and Johnson, 1973; Day et al., 1974; but see also Oakeshott, 1976). Furthermore, in some laboratory tests, flies homozygous for Adhs are more likely to survive heat shock than AdhF homozygotes (Bijlsma-Meeles and van Delden, 1974; Johnson and Powell, 1974; but see Milkman, 1977). These results have led to the hypothesis that positive relationships between maximum temperature and Adhs and GpdhF gene frequencies underlie the latitudinal clines (Johnson and Powell, 1974; Alahiotis et al., 1977). We have tested this hypothesis by examining these relationships on the continents of Asia, Europe, Australasia and North America.

Latitudinal relationships of esterase-6 and phosphoglucomutase gene frequencies in Drosophila melanogaster.

Geographic variation in Esterase-6 (Est-6) and Phosphoglucomutase (Pgm) gene frequencies in Australasian populations of Drosophila melanogaster are compared with analogous data collated from 16 previous reports for North America and Europe/Asia. A large-scale latitudinal cline is found on all three zoogeographic zones for Est-6 and overall, Est-61.00 frequency increases from about 20 per cent around 20 degrees latitude to about 80 per cent approaching 50 degrees latitude. In contrast, there is no consistent evidence for the latitudinal cline in Pgm gene frequencies in any of the three zones with Pgm1.00 frequency generally about 85 per cent and Pgm1.20 and Pgm0.70 frequencies each between 5 per cent and 10 per cent. The consistent Est-6 clines are attributed to latitudinal selection gradients but not consistent correlations are found between Est-6 gene frequencies and maximum or minimum temperature or rainfall which might be associated with these gradients. The directions of the Est-6 clines in fact run counter to expectations based on the in vitro thermostabilities of the respective allozymes.

An Analysis of the ABO Gene Frequency Cline in Japan: A Migration Model

The well known cline in ABO blood group gene frequencies in Japan was analysed based on the working hypothesis of a transient cline formed by the admixture of two heterogeneous populations by diffusion.Mathematically, the model corresponds to solving the diffusion equation with a step function as the initial condition. Using the A allele frequency data, the position of the initial discontinuity in the gene frequency is estimated by simulation as having been in the vicinity of present day Gifu City, and again assuming 20 km per generation of 25 years for a standard deviation of migratory distance the time as approximately 2, 000 years since the commencement of admixture. This and other results of simulation were discussed in the light of possible population movements induced by rice crop farming during the Yayoi era in western Japan.

Overdominance of a Muscle Protein (Mp-1) Locus in the Japanese Oyster, Crassostrea gigas (Ostreidae)

A microgeographical population genetic study of the Japanese oyster, Crassostrea gigas, revealed a case of overdominance for a muscle protein (Mp-1) locus. This locus consists of a two allele polymorphism. A study of the relative "fitness" of the three genotypes (Mp-1105/105, Mp-1105/100, and Mp-1100/100) revealed a heterozygote superiority in the segment of the oyster population at the lowest tidal level (+ 1.2 m). In segments of the population at higher tidal heights (i.e. + 1.8 and + 2.4 m), there appears to be a selective advantage for Mp-1105 allele since the highest "fitness" values belong to the Mp-1105/105 genotype. Since oysters do not appear at the field station lower than 1.2 tidal m, it could not be determined if the Mp-1100 allele had a selective advantage at tidal levels lower than 1.2 m. However, the Mp-1105 allele possibly exhibits a selective advantage in the subtropical marine environment of southern Japan, while the Mp-1100 allele is favored in the temperate marine environment of northern Japan. This suggests perhaps that a micro- and macrogeographical cline in gene frequency exists for the Mp-1 locus due to a thermal gradient. Key words: Japanese oyster, Crassostrea gigas, population genetic study, overdominance, heterozygote superiority, Mp-1 locus, micro- and macrogeographical cline, thermal gradient, tidal height, latitude