Longitudinal Clines Research Articles

A Population Bottleneck Did Not Affect Polymorphism Rates in California Swainson's Hawks

ABSTRACT Raptor polymorphisms have played an important role in understanding how evolutionary forces within and between populations operate. However, within a population little is known about the history of the polymorphism, the effects of any population bottlenecks, and the overall stability of the polymorphism. We investigated the stability of a melanin-based color polymorphism in Swainson's Hawks (Buteo swainsoni) in California over a 100-year period. In the mid-20th century Swainson's Hawks in California declined by 90%. Therefore, we examined the morphs of breeding individuals collected before 1950 and compared them to images from eBird taken between 2008–2019 and from a Google Images search, because a disproportionate survival of rare alleles after a population bottleneck could lead to changes in current clines. Between the two periods, we did not find differences in plumage morphs, nor did we find evidence of latitude or longitudinal clines over this relatively small spatial scale. Thus, despite a large population decline, this polymorphism has remained consistent over time. Our results suggest that the relatively high occurrence of dark morphs in this population is not simply a result of a bottleneck.

Precipitation and local environment shape the geographic variation of seed size across natural populations of sand rice (Agriophyllum squarrosum).

Sand rice (Agriophyllum squarrosum) is widely distributed on dunes in the Asian interior arid zone, and its large intraspecific trait variation makes it a very good model for investigating the ecological processes underlying its adaptation to the desert environment. In this study, seed size variation across 68 natural populations was used to establish geographic patterns and to quantify the effects of the climate, soil, and collection-year weather variables. The length of the seed major axis and thousand seed weight (TSW) both showed significant longitudinal patterns. Long-term climate variables accounted for most of the explained variances for seed major axis (57.20%) and TSW (91.54%). Specifically, annual precipitation and minimum monthly precipitation had the most significantly positive and negative effects, indicating that longitudinal clines are driven by a precipitation gradient across the species' distribution range. A substantial unique effect of soil variables (27.27%) was found for seed major axis variation, but only 3.64% of TSW variation was explained by soil variables. Two extreme groups were selected to evaluate the genetic and plastic effects on seed size in a common garden experiment. Large-seeded individuals were more competitive in semi-arid regions, and had stronger adaptive plasticity as well as better performance in early seedling establishment, and hence they have potential for use in future domestication projects.

Amplitude of circadian rhythms becomes weaken in the north, but there is no cline in the period of rhythm in a beetle.

Many species show rhythmicity in activity, from the timing of flowering in plants to that of foraging behavior in animals. The free-running periods and amplitude (sometimes called strength or power) of circadian rhythms are often used as indicators of biological clocks. Many reports have shown that these traits are highly geographically variable, and interestingly, they often show latitudinal or longitudinal clines. In many cases, the higher the latitude is, the longer the free-running circadian period (i.e., period of rhythm) in insects and plants. However, reports of positive correlations between latitude or longitude and circadian rhythm traits, including free-running periods, the power of the rhythm and locomotor activity, are limited to certain taxonomic groups. Therefore, we collected a cosmopolitan stored-product pest species, the red flour beetle Tribolium castaneum, in various parts of Japan and examined its rhythm traits, including the power and period of the rhythm, which were calculated from locomotor activity. The analysis revealed that the power was significantly lower for beetles collected in northern areas than southern areas in Japan. However, it is worth noting that the period of circadian rhythm did not show any clines; specifically, it did not vary among the sampling sites, despite the very large sample size (n = 1585). We discuss why these cline trends were observed in T. castaneum.

Biostratigraphy and Palaeoecology of European Equus

We present an inventory of the progress of recent research on the biostratigraphy and palaeoecology of the genus Equus sensu lato in Europe. Our discussion starts with the new hypotheses concerning the dispersal and evolution of non-caballine equids of the Early and the beginning of the Middle Pleistocene, focusing on recent discoveries, description of taxa and revised diagnosis. In particular, we deal with the major debate surrounding the number of lineages, “stenonid horses”, related species and the new subgenus “Sussemionus”. Possible phylogenetic scenarios and relationships with extant species are also taken into consideration. There is consensus that the lineage of true horses emerged in Europe at the beginning of the Middle Pleistocene. Their extensive skeletal plasticity enabled them to survive under a wide range of climatic conditions and environments, from interglacial forests to grass-steppes during glacial episodes. They exhibit homogeneous overall morphology but variability in terms of dental and skeletal proportions. Patterns of general body-size, muzzle shape, macro- and microdonty, proportions of the limbs, robustness of the metapodials and breadth of the third phalanx are influenced by global climate, the characteristics of the vegetation (in particular the degree of openness) and substrate, and are governed by Bergman’s and Allen’s rules or other environmental pressures. In addition to palaeoecological information, these ecomorphological adaptations paradoxically provide real biochronological details in a given geographical province. Throughout the Upper Pleistocene, horses underwent a size diminution initiated at the end of the Middle Pleistocene. After the Last Glacial Maximum, investigation of body-size in different regions of Europe demonstrates the existence of latitudinal and longitudinal clines, and the fragmentation of the horse population. The so-called European wild ass, Equus hydruntinus, has a wide geographical distribution but seems to be less ecologically flexible, or, alternatively, more specialized than true horses, with which it is often found in sympatry. The latest palaeogenetic studies place the species into phylogenetic context within the Asiatic wild asses, however, palaeontological evidence points to Equus hydruntinus as a separate species. Its tooth morphology varies between biogeographical areas.

Latitudinal and longitudinal clines of phenotypic plasticity in the invasive herb Solidago canadensis in China.

Phenotypic plasticity is thought to be important for plants in variable environments. The climatic variability hypothesis poses that populations at higher latitudes, due to the stronger variation in temperature, there should be more plastic in response to temperature than populations at lower latitudes. Similarly, populations at locations with stronger precipitation fluctuations should be more plastic in response to water availability than populations at locations with less variable precipitation. We sampled seven and nine populations of Solidago canadensis, a North American native that is invasive in China, along a latitudinal (temperature variability) and a longitudinal (precipitation variability) gradient, respectively, in China, and grew them under two temperature treatments and two water-availability treatments, respectively. Among the four traits with significant variation in plasticity among populations in response to temperature, plasticity of leaf length-to-width ratio was significantly positively correlated with latitude and temperature seasonality of the populations. In addition, root/shoot ratio and water-use efficiency showed significant variation in plasticity among populations in response to water availability, and plasticities of these two traits were significantly negatively correlated with longitude and positively correlated with precipitation seasonality. The observed geographic clines in plasticity suggest that phenotypic plasticity of S. canadensis may have evolved rapidly in regions with different climatic conditions, and this may have contributed to the spread of this invasive species.

Longitudinal clines in the frequency distribution of 'super-clones' in an aphid crop pest.

Parthenogenesis is the main mode of reproduction of aphids. Their populations are therefore composed of clones whose frequency distribution varies in space and time. Previous population genetic studies on aphids have highlighted the existence of highly abundant clones ('super-clones'), distributed over large geographic areas and persisting over time. Whether the abundance of 'super-clones' results from their ecological success or from stochastic forces, such as drift and migration, is an open question. Here, we looked for the existence of clines in clonal frequency along a climatic gradient in the cereal aphid Rhopalosiphum padi (Linnaeus, 1758) and examined the possible influence of geographical distance and environmental variables in the buildup and maintenance of such clonal clines. We investigated the spatial distribution of the commonest genotypes of R. padi by sampling populations along an east-west transect in maize fields in the northern half of France in both spring and late summer. Individual aphids were genotyped at several polymorphic loci, allowing the assessment of frequency distributions of multilocus genotypes (MLGs) across the cropping season. We found several MLGs showing longitudinal clines in their frequency distribution in both spring and summer. In particular, two dominant asexual genotypes of R. padi showed inverted geographical clines, which could suggest divergent adaptations to environmental conditions. We concluded that while the distribution of some 'super-clones' of R. padi seems most likely driven by the action of migration and genetic drift, selection could be also involved in the establishment of longitudinal clines of others.

Diversity of Fusarium head blight populations and trichothecene toxin types reveals regional differences in pathogen composition and temporal dynamics

Analyses of genetic diversity, trichothecene genotype composition, and population structure were conducted using 4086 Fusarium graminearum isolates collected from wheat in eight Canadian provinces over a three year period between 2005 and 2007. The results revealed substantial regional differences in Fusarium head blight pathogen composition and temporal population dynamics. The 3ADON trichothecene type consistently predominated in Maritime provinces (91%) over the sampled years, and increased significantly (P<0.05) between 2005 and 2007 in western Canada, accounting for 66% of the isolates in Manitoba by the end of the sampling period. In contrast, 3ADON frequency was lower (22%, P<0.001) in the eastern Canadian provinces of Ontario and Québec and did not change significantly between 2005 and 2007, resulting in two distinct longitudinal clines in 3ADON frequency across Canada. Overall, genetic structure was correlated with toxin type, as the endemic population (NA1) was dominated by 15ADON isolates (86%), whereas a second population (NA2) consisted largely of 3ADON isolates (88%). However, the percentage of isolates with trichothecene genotypes that were not predictive of their genetic population assignment (recombinant genotypes) increased from 10% in 2005 to 17% in 2007, indicating that trichothecene type became an increasingly unreliable marker of population identity over time. In addition, there were substantial regional differences in the composition of recombinant genotypes. In western and maritime provinces, NA2 isolates with 15ADON genotypes were significantly more common than NA1 isolates with 3ADON genotypes (P<0.001), and the reverse was true in the eastern provinces of Québec and Ontario. Temporal trends in recombinant genotype composition also varied regionally, as the percentage of 15ADON isolates with NA2 genetic backgrounds increased approximately three fold in western and Maritime provinces, while the opposite trends were observed in Québec and Ontario. The results indicate that F. graminearum population dynamics in Canada have been influenced by a complex adaptive landscape comprising different regional selective pressures, and do not reflect a simple model of dispersal and integration following the introduction of a novel pathogen population. In addition, we identified F. graminearum strains that produce the recently discovered A-trichothecene mycotoxin (NX-2) for the first time in Canada, representing a significant expansion of the known range of NX-2 producing strains in North America.

Variability in height growth, survival and nursery carryover effect of Betula papyrifera provenances

Eleven paper birch (Betula papyrifera Marsh.) provenances from a single geographic region in northern Idaho and four geographic regions in British Columbia (BC) were studied to determine whether morphometric variability was due to species' genetics, growing environment, or their interaction. Seedlings were grown at three nurseries in BC and Idaho and planted in a randomised single-tree interlocking block design at Skimikin (50°47′) and Red Rock (53°45′) common gardens in BC. Geographic variation in birch height growth was regulated by genetics and a complex interaction with environmental factors. Growth does not follow latitudinal, longitudinal or elevational clines although provenances at the southern garden showed better height growth compared to the northern garden. Greater percentages of seedling mortality were observed at the northern garden compared to provenances planted at the southern garden. Birch height growth was significantly influenced by nursery displacement effects up to four years after establishment. The safe range of southward seed-transfer distance may be as much as 5°, and beyond this limit a detrimental effect likely occurs. Collectively, these results suggest that a provenance best suited to one environment might not be the best for another environment. However, these findings will be useful in understanding the genecology of paper birch when establishing operational seed-transfer guidelines in BC.

Longitudinal differentiation among pelagic populations in a planktic foraminifer

Evolutionary processes in marine plankton have been assumed to be dependent on the oceanic circulation system, which transports plankton between populations in marine surface waters. Gene flow facilitated by oceanic currents along longitudinal gradients may efficiently impede genetic differentiation of pelagic populations in the absence of confounding marine environmental effects. However, how responsible oceanic currents are for the geographic distribution and dispersal of plankton is poorly understood. We examined the phylogeography of the planktic foraminifer Pulleniatina obliquiloculata in the Indo-Pacific Warm Pool (IPWP) by using partial small subunit ribosomal DNA (SSU rDNA) sequences. We found longitudinal clines in the frequencies of three distinct genetic types in the IPWP area. These frequencies were correlated with environmental factors that are characteristic of three water masses in the IPWP. Noteworthy, populations inhabiting longitudinally distant water masses at the Pacific and Indian sides of the IPWP were genetically different, despite transportation of individuals via oceanic currents. These results demonstrate that populations of pelagic plankton have diverged genetically among different water masses within a single climate zone. Changes of the oceanic circulation system could have impacted the geographic patterns of dispersal and divergence of pelagic plankton.

Geographical structure and adaptive population differentiation in herbivore defence genes in European aspen (Populus tremula L., Salicaceae)

When a phenotypic trait is subjected to spatially variable selection and local adaptation, the underlying genes controlling the trait are also expected to show strong patterns of genetic differentiation because alternative alleles are favoured in different geographical locations. Here, we study 71 single nucleotide polymorphisms (SNPs) from seven genes associated with inducible defence responses in a sample of Populus tremula collected from across Sweden. Four of these genes (PPO2, TI2, TI4 and TI5) show substantial population differentiation, and a principal component analyses conducted on the defence SNPs divides the Swedish population into three distinct clusters. Several defence SNPs show latitudinal clines, although these were not robust to multiple testing. However, five SNPs (located within TI4 and TI5) show strong longitudinal clines that remain significant after multiple test correction. Genetic geographical variation, supporting local adaptation, has earlier been confirmed in genes involved in the photoperiod pathway in P.tremula, but this is, to our knowledge, one of the first times that geographical variation has been found in genes involved in plant defence against antagonists.

Population genetic analyses of Plasmodium falciparum chloroquine receptor transporter gene haplotypes reveal the evolutionary history of chloroquine-resistant malaria in India

Inferring the origin and dispersal of the chloroquine-resistant (CQR) malaria parasite, Plasmodium falciparum, is of academic and public health importance. The Pfcrt gene of P. falciparum is widely known as the CQR gene and two major haplotypes of this gene (CVIET and SVMNT) occur widely across CQR-endemic regions of the globe. In India, studies to date of the Pfcrt gene have indicated the widespread prevalence of the SVMNT haplotype (prevalent in the South America and Papua New Guinea), whereas the CVIET haplotype, primarily found in southeast Asia, was not detected at a high frequency in India. This distribution pattern of the two most common CQR- Pfcrt haplotypes in India is quite surprising. Thus, in order to understand probable evolutionary and migration patterns of the CQR- Pfcrt haplotypes into India, we generated new sequence data of exon 2 of the Pfcrt gene and collected published information on the CQR- Pfcrt haplotype data from India, Papua New Guinea, southeast Asia and South America, and performed several population and evolutionary genetic analyses. Among several interesting findings, statistically significant longitudinal clines for the CVIET and SVMNT haplotypes (in opposite directions) in India, and the clustering of India and Papua New Guinea under the SVMNT-specific clade in the phylogenetic tree, are the two most remarkable aspects of the data. It also appears that both the SVMNT and CVIET haplotypes in India have migrated from southeast Asia. In particular, whereas the Indian CVIET haplotype has a southeast Asian origin, the SVMNT haplotype, prevalent in India, seems to have originated in Papua New Guinea and entered India through southeast Asia.

Natural variation of morphological traits in wild wheat progenitor Aegilops tauschii Coss.

Aegilops tauschii Coss. (syn Ae. squarrosa L.) is a wild diploid wheat species. It has a wide natural species range in central Eurasia, spreading from northern Syria and Turkey to western China. Ae. tauschii is known as the D genome progenitor of hexaploid bread wheat. The genealogical and geographical structure of variation of morphological traits was analyzed using a diverse array of 205 sample accessions that represented the entire species range. In total, 27 traits, including anther and pistil shape and internode length, were examined in this study. Large-scale natural variation was found for all examined traits. Geographically, significant longitudinal clines were detected for anther size, internode length and spike size and shape. Anthers tended to be small in accessions from the eastern region. Internodes also tended to be short, whereas spikes tended to be long in accessions from the eastern region. Spikelet density per spike tended to be high in the eastern habitats. In the process of west-to-east dispersal, Ae. tauschii underwent extensive morphological, genetic and ecological diversification that produced the variation seen among today’s natural populations.

DISCORDANT LONGITUDINAL CLINES IN FLOWERING TIME ANDPHYTOCHROME CINARABIDOPSIS THALIANA

Using seasonal cues to time reproduction appropriately is crucial for many organisms. Plants in particular often use photoperiod to signal the time to transition to flowering. Because seasonality varies latitudinally, adaptation to local climate is expected to result in corresponding clines in photoperiod-related traits. By experimentally manipulating photoperiod cues and measuring the flowering responses and photoperiod plasticity of 138 Eurasian accessions of Arabidopsis thaliana, we detected strong longitudinal but not latitudinal clines in flowering responses. The presence of longitudinal clines suggests that critical photoperiod cues vary among populations occurring at similar latitudes. Haplotypes at PHYC, a locus hypothesized to play a role in adaptation to light cues, were also longitudinally differentiated. Controlling for neutral population structure revealed that PHYC haplotype influenced flowering time; however, the distribution of PHYC haplotypes occurred in the opposite direction to the phenotypic cline, suggesting that loci other than PHYC are responsible for the longitudinal pattern in photoperiod response. Our results provide previously missing empirical support for the importance of PHYC in mediating photoperiod sensitivity in natural populations of A. thaliana. However, they also suggest that other loci and epistatic interactions likely play a role in the determination of flowering time and that the environmental factors influencing photoperiod in plants vary longitudinally as well as latitudinally.

B chromosome polymorphism in maize landraces: adaptive vs. demographic hypothesis of clinal variation.

Cytogenetic analysis of maize landraces from northwestern Argentina has revealed an altitudinal cline in the mean number of B chromosomes (B's) per plant, with cultivars growing at higher altitudes exhibiting a higher number of B's. Altitudinal and longitudinal clines are frequently interpreted as evidence of selection, however, they can also be produced by the interplay between drift and spatially restricted gene flow or by admixture between previously isolated populations that have come into secondary contact. Here, we test the adaptive significance of the observed altitudinal gradient by comparing the levels of differentiation in the mean number of B's to those obtained from 18 selectively neutral loci [simple sequence repeats (SSRs)] among seven populations of the cline. The adequacy of alternative genetic-differentiation measures was determined, and associations between cytogenetic, genetic, and altitudinal distances were assessed by means of matrix- correspondence tests. No evidence for association between pairwise F(ST) and altitudinal distance or B-chromosome differentiation was found. The contrasting pattern of altitudinal divergence between the mean number of B's per plant and the genetic differentiation at SSR loci indicates that demographic processes cannot account for the observed levels of divergence in the mean number of B's.

Chromosomal inversion polymorphism in Afrotropical populations of Drosophila melanogaster.

When 41 populations from Africa (south of the Sahara) and Indian Ocean islands were analysed for their chromosomal inversion polymorphism, 34 rearrangements were found, including the four common cosmopolitans (In(2L)t, In(2R)NS, In(3L)P and In(3R)P), four rare cosmopolitans (In(2L)NS, In(3R)C, In(3R)Mo and In(3R)K) and six African polymorphic ('recurrent') endemics. Mean inversion frequencies per major autosome arm were positively and, generally, highly correlated to each other. There was no altitudinal nor latitudinal cline of inversion frequency, except for one African polymorphic endemic. Significant longitudinal clines were detected for In(2L)t, In(3L)P and In(3R)K; in all cases, inversion frequencies decreased eastward. Principal components analysis and ANOVA made it possible to distinguish three groups of populations. A high level of polymorphism was found in populations from west tropical Africa. The other low altitude populations from the mainland were moderately polymorphic, whereas the lowest levels of polymorphism were those of high altitude populations and of Indian Ocean islands. Moreover, some regional and local differentiation was also found. The frequency of unique autosomal inversions was not different from those found in Asia, Australia and America, but was significantly higher than that in Europe and North Africa. A West-East differentiation was also observed for the African polymorphic endemics. The present geographic pattern suggests a long, patchy evolution with restricted gene flow, followed by the modern period with numerous recent migrations linked to human transportation.

Gradients of HLA diversity in South American Indians

SummaryInformation concerning the HLA-A and -B loci was considered in relation to 3796 Amerindians living in 39 places in South America, data related to HLA-C being based on a smaller subset of 2989 persons distributed among 33 localities. Synthetic gene frequency maps were then constructed using principal-components analysis. Clearly significant longitudinal (principal component 1) and latitudinal (principal components 1, 2, and 3) clines were observed, most probably indicating ancient migration routes.

EFFECT OF SEED ORIGIN ON GROWTH OF EUCALYPTUS MICROTHECA F. MUELL. IN ISRAEL

Provenance trials of Eucalyptus microtheca F. Muell. were established in the central Coastal Plain and the northern Negev in 1983, using the seed of 303 trees from 73 provenances in Australia bulked into 21 provenance groups by the CSIRO Division of Forest Research. Survival, height, and diameter development of E. microtheca in the central Coastal Plain were lower than those of Eucalyptus camaldulensis Dehn. In the northern Negev, several progenies of E. microtheca had better growth and survival rates than E. camaldulensis. Variations within provenance groups in growth and survival were very large. Relations between the measured traits and variables describing the seed source of E. microtheca indicate the existence of latitudinal and longitudinal clines. Provenance groups most suitable for use in the northern Negev are Springsure, Qld. (No.14), Rockhampton, Qld. (No. 15), and Walgett, N.S.W. (No. 20).

Comparative morphology of the cottid genus Myoxocephalus based on meristic, morphometric, and other anatomical characters

Specimens representing 15 nominal species of the genus Myoxocephalus were subjected to detailed comparative morphological study to determine some of the more important species characteristics and also those indicating potential for expressing phylogenetic progression.Analysis of seven meristic characters revealed that none of them is consistently sexually dependent. Geographic variation within the species indicated the presence of both latitudinal and longitudinal clines. No evolutionary group affinities were evident.The morphology of the cephalic lateral line system, lateral line ossicles, squamation, and olfactory rosettes were found to exhibit a high degree of specificity, especially the first three systems. With the exception of the lateral line ossicles all evidenced some potential as indicators of phylogeny.Analysis of 23 morphometric characters was accomplished by cluster analysis. The resultant clusters indicated heterogenous unnatural groupings.On the basis of these analyses well-defined species differences exist in most of the major morphological features. The nominal species M. scorpius (Linnaeus) includes three distinct species (Gulf of Alaska, Arctic–East coast, and European). In addition, the data indicate that the genus is probably composed of three basic evolutionary lines: the Holarctic–Atlantic, Bering Sea–Transpacific, and Asiatic.