Polymorphic Allozyme Research Articles

DNA polymorphism underlying allozyme variation at a malic enzyme locus (mMEP-2*) in Atlantic salmon (Salmo salar L.).

A non-synonymous single nucleotide polymorphism (SNP) underlies a diallelic allozyme polymorphism at the mitochondrial NADP-dependent mMEP-2* locus in Atlantic salmon (Salmo salar L.). The resultant amino acid substitution, which alters the charge of the allelic products, matches the differential mobility of the two allozyme alleles, whereas allozyme and SNP assays revealed genotyping concordance in 257 of 258 individuals. A single mismatch, homozygous allozyme vs. heterozygote SNP, suggests the presence of a second, less common null allele.

An allozyme polymorphism is associated with a large chromosomal inversion in the marine snail Littorina fabalis.

Understanding the genetic targets of natural selection is one of the most challenging goals of population genetics. Some of the earliest candidate genes were identified from associations between allozyme allele frequencies and environmental variation. One such example is the clinal polymorphism in the arginine kinase (Ak) gene in the marine snail Littorina fabalis. While other enzyme loci do not show differences in allozyme frequencies among populations, the Ak alleles are near differential fixation across repeated wave exposure gradients in Europe. Here, we use this case to illustrate how a new sequencing toolbox can be employed to characterize the genomic architecture associated with historical candidate genes. We found that the Ak alleles differ by nine nonsynonymous substitutions, which perfectly explain the different migration patterns of the allozymes during electrophoresis. Moreover, by exploring the genomic context of the Ak gene, we found that the three main Ak alleles are located on different arrangements of a putative chromosomal inversion that reaches near fixation at the opposing ends of two transects covering a wave exposure gradient. This shows Ak is part of a large (3/4 of the chromosome) genomic block of differentiation, in which Ak is unlikely to be the only target of divergent selection. Nevertheless, the nonsynonymous substitutions among Ak alleles and the complete association of one allele with one inversion arrangement suggest that the Ak gene is a strong candidate to contribute to the adaptive significance of the inversion.

Morpho-genetic variability of native and adventitious populations of the <i>Brephulopsis cylindrica </i>(Gastropoda, Pulmonata, Enidae)

The population structure of the terrestrial mollusc Brephulopsis cylindrica (Gastropoda, Pulmonata, Enidae) in the native area (Crimea Peninsula) and out of its borders (two adventive groups in the city of Belgorod) was studied on the basis of conchometric characteristics and analysis of polymorphic allozyme loci. For all the morphometric parameters statistically significant differences were found between the studied groups. In all studied populations a high level of intra-population genetic variability was revealed ( Fit = 0,401). At the same time, the considerable variability of the conchological parameters and the high level of allelic polymorphism at a number of loci identified in adventitious colonies create the prerequisites for successful adaptation to new conditions and further expansion of the species range in urbanized areas.

Genetic Diversity and Population Structure In the Rare, Endemic Baker Cypress (Hesperocyparis bakeri)

Abstract Baker cypress (Hesperocyparis bakeri [Jeps.] Bartel) is one of 10 species of cypress found in western North America. It is restricted to a small number of highly disjunct, isolated populations, making it particularly vulnerable to the influences of genetic drift, inbreeding, and reduced gene flow. Baker cypress is fire adapted and the serotinous cones require heat to open and release seeds. Altered fire regimes have negatively impacted the health and vigor of some populations and lower levels of genetic diversity could make this species more susceptible to the impacts of predicted future climate change. Previously, no information on genetic diversity and population structure of Baker cypress was available. We used 12 polymorphic allozyme loci to assess genetic diversity and population structure for eight of the 11 known populations of Baker cypress. Overall mean observed heterozygosity (Ho) was 0.178 and expected heterozygosity (He) was 0.204, values higher than for other cypress species and othe...

Polymorphism of Got2 DNA sequences sheds light on Aegilops tauschii Coss. intraspecies divergence and origin of Triticum aestivum L.

DNA sequences of nuclear gene Got2 was studied in 60 accessions of Aegilops tauschii, 29 of subsp. tauschii and 31 of subsp. strangulata. It was found that Got2 allozyme polymorphism in Ae. tauschii is due to a single, unique, mutation which led to replacement of glutamic acid by isoleucine in residue 256 of the enzyme molecule, encoded by Got2. As revealed by Got2 DNA sequences variation, initially in its history Ae. tauschii was presented by subsp. strangulata, and among phylogenetic lineages of subsp. strangulata, the lineage “t-91s” (TauL3) is the most ancient, a relict one. Subspecies tauschii is relatively “young”. Initially it was presented by the lineage marked by combination of allozyme alleles Got2105 and Acph1100. In the past it inhabited the Continental area from Caucasia to Pakistan, but later on it was forced out by newly originated, now—a major lineage of subsp. tauschii, marked by Got2100. This lineage extended the Continental area of the species up to Kirgizstan, but actually failed to penetrate into pre-Caspian area, occupied by subsp. strangulata. These results essentially differ from those obtained previously, using chloroplast DNA (cpDNA) sequences polymorphism. As revealed by cpDNA, the major, “usual”, subsp. strangulata (TauL2) is “younger” than subsp. tauschii, which resided on phylogenetic tree between relict lineage “t-91s”of subsp. strangulata—and major subsp. strangulata. But both cpDNA and Got2 DNA sequences indicate that the level of genetic variation in subsp. tauschii is much lower than in subsp. strangulata. According to Got2 DNA sequences variation, it was Ae. tauschii subsp. strangulata lineage “k-109″ which donated genome D to Triticum aestivum L. This lineage includes accessions: k-109 from South-Eastern Precaspian Azerbaijan; KU-2105, KU-2159 from Western Precaspian Iran; KU-2080 from Eastern Precaspian Iran.

Morphological and genetic characterization of the sharpsnout seabream populations (Diplodus puntazzo, Sparidae) along a boundary area between the two Mediterranean basins

ABSTRACTIn order to test the potential ecological role of the Siculo-Tunisian Strait as a geographic barrier, the morphological and genetic variation of eight Tunisian samples of the sharpsnout seabream, Diplodus puntazzo, were studied, based on 23 truss network elements and 13 polymorphic allozyme loci. Significant morphological differences were observed between studied samples, especially between lagoon ones. Although genetic data did not support the detected morphometric variation, F-statistics indices (FIS and FST) revealed a significant departure from panmixia with heterozygote deficiencies and slight genetic differentiation between samples. Genetic results suggested the existence of moderate and local genetic heterogeneity that can be explained by the chaotic genetic patchiness hypothesis. Morphological and genetic results showed that the Siculo-Tunisian Strait does not seem to act as a barrier limiting the connectivity between the natural populations of D. puntazzo, at least at the scale of the Tunisian coast. Thus, the phenotypic variation identified in this study appears to be environmentally induced through the exploitation of different ecological niches and hydrodynamic constraints.

Genetic structure of Parnassius mnemosyne (Lepidoptera: Papilionidae) populations in the Carpathian Basin

The pattern of genetic variation in a butterfly species depends on the past history of the given species and also on recent evolutionary processes affecting its populations. The aim of the present study was (i) to analyse the enzyme polymorphism in the Clouded Apollo populations of the Carpathian Basin to reveal the contemporary pattern of their genetic differentiation and (ii) to compare it with an expanded mitochondrial DNA (mtDNA) haplotype network of the SE European populations. Allozyme polymorphism was analysed in 22 populations of four geographic regions: Transdanubian (TM) and North Hungarian Mountains (NM), Koros (KOR) and Bereg–Apuseni–East Carpathian regions (BEAC). The results of the Bayesian clustering analyses based on allozymes supported the presence of three main genetic lineages in the Carpathian Basin: One was typical for TM, another was characteristic for NM and the third cluster was predominant in KOR. The populations of BEAC harboured a mixture of two clusters. The mtDNA haplotype network suggested a fairly similar distribution: The peri-Alpine clade together with the West Balkan clade was detected in TM, while the East Balkan clade occurred in NM, partly in TR and in the two eastern regions of the Basin (KOR and BAEC). The incongruities between the results of the mtDNA and allozyme studies can be explained by the different timescales represented by the two markers. The mtDNA haplotype network provided strong evidence concerning the existence of two Balkan lineages, which probably formed a ‘zone of admixture’ in the Transdanubian and North Hungarian Mountains. The possibility of Last Glacial survival of Parnassius mnemosyne in the Carpathian Basin and the conservation implications of these results are discussed.

Species radiation in the Alps: multiple range shifts caused diversification in Ringlet butterflies in the European high mountains

The distributions of European high mountain species are often characterised by small and geographically isolated populations and, in many cases, have highly complex biogeographic histories. The butterfly genus Erebia represents one of the best examples for small-scale diversification in the European high mountain systems and therefore to understand speciation processes and associated range dynamics of high mountain species. In this study, we analysed 17 polymorphic allozyme loci of 1731 individuals from 49 populations representing four species, one of which has three subspecies: Erebia nivalis; Erebia tyndarus; Erebia ottomana; and Erebia cassioides cassioides, Erebia cassioides arvernensis, and Erebia cassioides neleus. Samples were collected in the high mountain systems of Europe (i.e. Pyrenees, Massif Central, Alps, Apennines, Carpathians, Balkan high mountains). Genetic analyses supported all previously accepted species. However, the genetic differentiation within E. cassioides sensu lato into three geographically delimited groups is justifying species rank: E. arvernensis distributed in the Pyrenees, Massif Central and western Alps; E. cassioides sensu stricto in the eastern Alps and Apennines; and E. neleus in the Balkan mountains and the south-western Carpathians. While the differentiation between western Alps and Massif Central as well as eastern Alps and Apennines was low, the Pyrenees as well as the south-western Carpathians were significantly differentiated from the other regions within the respective taxon. In general, the differentiation among the populations of E. neleus was stronger than between populations of the other taxa. Within E. cassioides, we found a west-east gradient of genetic similarity over the eastern Alps. Based on the obtained genetic structures, we are able to delineate glacial refugia and interglacial range modifications. Based on the genetic structures and genetic diversity patterns, we conclude that, triggered by the glacial-interglacial cycles, repeated range modifications have taken place with subsequent differentiation and speciation in the region of the Alps and Balkans. Colonisations to Pyrenees (E. arvernensis pseudomurina, E. arvernensis pseudocarmenta), Massif Central (E. ottomana tardenota, E. a. arvernensis) and Apennines (E. cassioides majellana) appear to be recent and most probably not older than the last interglacial period.

Genetic and spatial structuring of the California vole (Microtus californicus) through a multiannual density peak and decline

Arvicoline rodents serve as model organisms for investigating the intricacies of ecological/evolutionary feedbacks that characterize multiannual fluctuations in abundance. A population of California voles (Microtus californicus) in central California was followed for 3.5 years using 4 small grids located 50 m apart. Blood samples were scored for 4 polymorphic allozyme loci by starch gel electrophoresis. These were carefully chosen for their potential to reveal details of genetic structuring among demes. A low density of voles developed into a peak followed by a rapid decline to low density. Heterozygosity averaged 20.2% (n = 709) with loci-specific shifts associated with density, season, and cyclic phase. Statistically significant heterogeneity in genotypic and allelic frequencies among the grids was found for 3 of the loci. Pairwise comparisons among the grids for each locus separately (n = 24) yielded 11 significantly disparate pairs for genotypic frequencies and 10 for alleles. Significant correlations...

Heterogeneity of clonal patterns among patches of kudzu, Pueraria montana var. lobata, an invasive plant.

Viny species are among the most serious invasive plants, and better knowledge of how vines grow to dominate landscapes is needed. Patches may contain a single genotype (i.e. genet), a competitively dominant genet or many independent but interacting genets, yet the clonal structure of vining species is often not apparent. Molecular markers can discriminate among the genetic identities of entwined vines to reveal the number and spatial distribution of genets. This study investigated how genets are spatially distributed within and among discrete patches of the invasive vine kudzu, Pueraria montana var. lobata, in the United States. It was expected that ramets of genets would be spatially clustered within patches, and that an increase in the number of genets within a patch would be associated with a decrease in the average size of each genet. Six discrete kudzu patches were sampled across 2 years, and 1257 samples were genotyped at 21 polymorphic allozyme loci. Variation in genotypic and genetic diversity among patches was quantified and patterns of genet interdigitation were analysed. Substantial genotypic and genetic variation occurred within and among patches. As few as ten overlapping genets spanned up to 68 m(2) in one patch, while >90% of samples were genetically unique in another patch. Genotypic diversity within patches increased as mean clone size decreased, although spatially widespread genets did not preclude interdigitation. Eight genets were shared across ≥2 patches, suggesting that vegetative dispersal can occur among patches. Genetically unique kudzu vines are highly interdigitated. Multiple vegetative propagules have become established in spatially discrete patches, probably through the movement of highway construction or maintenance machinery. The results suggest that common methods for controlling invasive vines (e.g. mowing) may inadvertently increase genotypic diversity. Thus, understanding vine architecture and growth has practical implications.

Assessing spatial population structure and heterogeneity in the dronefly

AbstractIn order to secure pollination services and improve conservation strategies, a better understanding of factors influencing population structure of pollinator species is vital. Here, we aimed to empirically evaluate various individual‐ and population‐based statistical methods for characterization of genetic structure of the widespread dronefly, Eristalis tenax. Thirty‐five European populations, comprising 888 individuals, were genotyped at five polymorphic allozyme loci. Three Bayesian genotypic clustering approaches (STRUCTURE, BAPS and Geneland), pairwise FST estimates, analyses of molecular variance (AMOVA), principle component analysis (PCA) and Mantel tests were applied in a comparative way in attempt to reveal the patterns of gene flow that occurs at various spatial scales in E. tenax. STRUCTURE analysis and PCA results provided no evidence of conspecific differentiation. In contrast, BAPS and Geneland clustering solutions did acknowledge low but significant proportion of among‐populations genetic variation revealed by AMOVA. Similarly, pairwise FST estimates partially argue against genetic homogeneity across Europe. The lack of correlation between genetic distance and both latitude and longitude variation suggests that the flies disperse in multiple directions. Therefore, our results indicate that continued long‐range dispersal tend to homogenize populations over time, resulting in little population structure in E. tenax across the European landmass. On the other hand, significant differentiations between geographically proximate populations indicate that dispersal potential may not be realized and that gene flow patterns in E. tenax might be geographically complex. Using information from our genetic approaches will be useful for identifying patterns of migration and population connectivity across continent, which is an important issue for conservation efforts. Since E. tenax is an important pollinator, our results contribute to understanding the potential extent to which this taxon can facilitate gene flow among plant populations across natural and semi‐natural habitats, agroecosystems and urban environments. Dronefly‐mediated gene flow in plants is likely to occur over large distances and plant–dronefly conservation will require large‐scale action.

Allozyme polymorphism in mono- and dikaryotic cultures of fungus Schizophyllum commune Fr. (Basidiomycetes)

Allozyme polymorphism of a number of enzyme systems in mono- and dikaryotic cultures of the fungus Schizophyllum commune Fr. isolated from basidiocarps, selected in Ivano-Frankivsk, Chernihiv, and Donetsk regions of Ukraine and Crimea was studied. As a result, 16 alleles of seven gene-enzyme loci were detected. Amy-2, Got, Acp, Sod, and Est-1 loci are considered perspective for use in the population genetic studies of the fungus.

Подходы к сохранению генофонда лекарственного растения Oxytropis lanata (Pall.) DC. (Fabaceae)

In order to preserve the gene pool of medicinal plant Oxytropis lanata (Pall.) DC. we analyzed allozyme polymorphism and identified reliable and informative marker enzyme systems of this species; also we studied the response of seeds to deep freezing in liquid nitrogen (–196 ºС). Population has an average level of polymorphism (P95 = 41,2 %, P99 = 52,9 %, A = 1,58, Ho = 0,158, He = 0,171) in general typical for herbaceous legumes, and can serve as a source of material for gene pool conservation of the species. Deep freezing has not led to the death of the seeds; it was marked stimulatory effect of ultralow temperatures, expressed as an acceleration of germination and sharp increase of germinability (98,6 ± 2,3 %) compared to the control (12,0 ± 3,5 %) that is associated with overcoming physical dormancy. There were no abnormalities in the development of seedlings from seeds passed cryopreservation.

Population structure and genetic variation of the endangered species Elaeagnus mollis Diels (Elaeagnaceae)

Elaeagnus mollis Diels is a group of shrubs and dwarf trees endemic to China and are endangered plants. However, the reason why these plants are endangered remains controversial. The current study aimed to explore the endangered status of E. mollis from a genetic perspective and to propose conservation strategies for this species. Using 16 polymorphic allozyme loci, the population genetic structure was investigated for three populations representing the taxa and variants. The variants exhibited relatively high levels of genetic variation compared to other woody shrubs with similar geographic distributions. The overall genetic diversity (HE = 0.352) was elevated compared to long-lived woody angiosperms. The average number of alleles per locus (A), percentage polymorphic loci (P), and observed heterozygosity (HO) were 2.0, 85.2, and 0.371, respectively. Furthermore, gene flow estimates within the population groups were also elevated. The life history and habitats of E. mollis play major roles in the levels of genetic diversity. The results of this study may help to device strategies for preserving the genetic diversity of E. mollis and for promoting planting.

Allozyme polymorphism in Drosophila

Every population possesses genetic variations which are achieved through gene mutation, genetic recombination, hybridization, gene duplication etc. These genetic variations provide raw materials for evolutionary forces to create a better surviving species. Genetic polymorphism is reflected at every level in the populations, for example, at phenotypic, chromosomal, protein and DNA levels. Protein or enzyme polymorphisms have been well studied in various organisms including Drosophila and humans. Drosophila has proven to be a good model organism for carrying out polymorphism studies. Among the different species of Drosophila, there is a wide variation in the levels of allozyme polymorphisms and heterozygosities which depends upon species, geographical regions, number and nature of loci in question etc. In Drosophila, the average polymorphic enzyme loci and average heterozygosity ranges from 35 to 70 percent and 10 to 20 percent respectively. The genetic differentiation as observed through allozyme or isozyme variation affords an important parameter in evaluating the phylogenetic relationships between different species of Drosophila and also for discussing the adaptive significance of allozyme polymorphisms. Therefore, this review attempts to compile all studies on allozyme polymorphism in Drosophila that have been undertaken so far.

Genetic analyses of two spawning stocks of the short-finned squid (Illex argentinus) using nuclear and mitochondrial data

Short-finned squid Illex argentinus (Omastrephidae) is an economically important species which supports a long-term and intensive commercial fishery in the South-West Atlantic Ocean. In this study, the genetic variability of allozymes (40 loci) and mitochondrial regions, COI (556bp) and 16S rDNA (439bp), were addressed in the two most important species’ spawning stocks, the Summer Spawning Stock (SSS) and the South Patagonic Stock (SPS). Five out of 20 polymorphic allozyme loci were polymorphic at 95% criterion and heterozygosity levels were low. The concatenated analysis of mitochondrial molecular markers revealed high to low values of haplotype and nucleotide diversity, respectively. Nuclear and mitochondrial data revealed no significant genetic differences between these two spawning stocks. Our results and the biological characteristics of I. argentinus deal with a no simple genetic structure of populations described as spatial and temporal chaotic patchiness. SSS and SPS spawning stocks of I. argentinus could not be elevated to the status of genetic stocks.

Genetic structure of the continuous and ephemeral populations of the land snail Brephulopsis Cylindrica (Gastropoda; Pulmonata; Enidae)

Background. One may hypothesize that the land snail B. cylindrica distributed in small, isolated, ephemeral populations tends to decrease genetic polymorphism level (e. g., observed heterozygosity for allozyme loci). Thus, the present study aims at estimating the levels of allozyme polymorphism in the land snail B. cylindrica from continuously distributed populations and ephemeral ones. Materials and methods. In the Nikolaev urbanised areas 9 samples were taken and studied electrophoretically for four polymorphic allozyme system. In the Dubki, Neftebasa and Park Pobedy populations (continuously distributed populations - group N 1) the two localities, situated about 50 m apart, were sampled. While only single locality were investigated from the Kosmos, Morechodnaya and Mira populations (ephemeral populations - group N 2). Statistical analysis of electrophoretic data was performed with the program GenAIEx version 6.0. Results. In general, significant differences with respect to the level of genetic polymorphism between the continuous and ephemeral populations of the land snail B. cylindrical have not discovered on the basis of allozymes loci. However, when analyzing the distribution of multilocus allozyme genotypes in the populations studied, we have received fundamentally different results. In general, ephemeral populations differed from the continuous ones with respect to the frequency of studied multilocus allozyme genotypes although one populations has been disrupted this rule (Dubki-2). Conclusion. Based on these results it is concluded that small, isolated (including, urban) populations tend to reduce the level of genetic diversity, due to the manifestation of genetic and stochastic processes (genetic drift or founder effect). In addition, an important consequence of the latter there is a relatively high rate of unpredictable change genotypic profiles of such settlements, which leads to a significant increase in the level of genetic differentiation between them.

Distribution of the genetic diversity of the Siberian stone pine, Pinus sibirica Du Tour, along the latitudinal and longitudinal profiles

The Siberian stone pine (Pinus sibirica Du Tour) is one of the main forest-forming coniferous species of the boreal ecosystems of Western Siberia. We used the isozyme method to analyze 11 ecotypes representing the latitudinal and longitudinal profiles within the species range, including samples from the geographic boundaries of the distribution. The genetic structure of the ecotypes is described on the basis of the variability for 26 isozyme loci encoding for 16 enzyme systems. The greatest genetic diversity was observed in the taiga ecotypes in the central part of the studied area, while the ecotypes along the species range boundaries were shown to be genetically depauperized. Approximately 8.1% of the observed genetic diversity is attributed to differences between the studied ecotypes. We detected high levels of genetic diversity for the Fest_2, Pgm_1, Sod_4, and a few otherloci, as well as a correlation between allele frequencies and geographical locations of the populations. The results of multivariate analysis of allelic frequencies as well as cluster analysis allowed us to discriminate three major groups of ecotypes: north-eastern, central and south-western. In view of our results, we compare two hypotheses: one which attributes the spatial distribution of genetic variations to the selectivity for some of the polymorphic allozyme loci, and the other based in the history of the formation of the range of the Siberian stone pine.

Effects of recent and past climatic shifts on the genetic structure of the high mountain yellow-spotted ringlet butterfly Erebia manto (Lepidoptera, Satyrinae): a conservation problem.

Mountain species have evolved important genetic differentiation due to past climatic fluctuations. The genetic uniqueness of many of these lineages is now at risk due to global warming. Here, we analyse allozyme polymorphisms of 1306 individuals (36 populations) of the mountain butterfly Erebia manto and perform Species Distribution Models (SDMs). As a consensus of analyses, we obtained six most likely genetic clusters: (i) Pyrenees with Massif Central; (ii) Vosges; (iii-v) Alps including the Slovakian Carpathians; (vi) southern Carpathians. The Vosges population showed the strongest genetic split from all other populations, being almost as strong as the split between E. manto and its sister species Erebia eriphyle. The distinctiveness of the Pyrenees-Massif Central group and of the southern Carpathians group from all other groups is also quite high. All three groups are assumed to have survived more than one full glacial-interglacial cycle close to their current distributions with up-hill and down-slope shifts conforming climatic conditions. In contrast with these well-differentiated groups, the three groups present in the Alps and the Slovakian Carpathians show a much shallower genetic structure and thus also should be of a more recent origin. As predicted by our SDM projections, rising temperatures will strongly impact the distribution of E. manto. While the populations in the Alps are predicted to shrink, the survival of the three lineages present here should not be at risk. The situation of the three other lineages is quite different. All models predict the extinction of the Vosges lineage in the wake of global warming, and also the southern Carpathians and Pyrenees-Massif Central lineages might be at high risk to disappear. Thus, albeit global warming will therefore be unlikely to threaten E. manto as a species, an important proportion of the species' intraspecific differentiation and thus uniqueness might be lost.

Fin whale MDH-1 and MPI allozyme variation is not reflected in the corresponding DNA sequences.

The appeal of genetic inference methods to assess population genetic structure and guide management efforts is grounded in the correlation between the genetic similarity and gene flow among populations. Effects of such gene flow are typically genomewide; however, some loci may appear as outliers, displaying above or below average genetic divergence relative to the genomewide level. Above average population, genetic divergence may be due to divergent selection as a result of local adaptation. Consequently, substantial efforts have been directed toward such outlying loci in order to identify traits subject to local adaptation. Here, we report the results of an investigation into the molecular basis of the substantial degree of genetic divergence previously reported at allozyme loci among North Atlantic fin whale (Balaenoptera physalus) populations. We sequenced the exons encoding for the two most divergent allozyme loci (MDH-1 and MPI) and failed to detect any nonsynonymous substitutions. Following extensive error checking and analysis of additional bioinformatic and morphological data, we hypothesize that the observed allozyme polymorphisms may reflect phenotypic plasticity at the cellular level, perhaps as a response to nutritional stress. While such plasticity is intriguing in itself, and of fundamental evolutionary interest, our key finding is that the observed allozyme variation does not appear to be a result of genetic drift, migration, or selection on the MDH-1 and MPI exons themselves, stressing the importance of interpreting allozyme data with caution. As for North Atlantic fin whale population structure, our findings support the low levels of differentiation found in previous analyses of DNA nucleotide loci.