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The article discusses what the author refers to as the degrammaticalization of the suffix ish in the English language. It examines grammatical change in the English language, the concept of the cline of grammaticality, and ish in the history of Modern English. It also discusses the acceptability of utterances in the English language.

Predicted climate change is heading in many respects into untested environmental conditions for trees and to the reshuffling of species distributions. We explore the consequences that these changes are likely to have on population differentiation of adaptive traits. Superimposed on the spatial redistribution of the species, will there be a redistribution of their genetic variation?, We base our predictions on a conceptual framework, whose elements are the extant differentiation, and the predicted divergent evolution of populations along purposely chosen altitudinal/latitudinal gradients. We consider simultaneously phenotypic and genetic divergence, but emphasize genetically driven population differentiation. We illustrate phenotypic and genetic patterns of variation with examples from well-studied northern and southern hemisphere tree genera Quercus and Eucalyptus., Most phenotypic traits show very large in situ clinal variation with variation in altitude or latitude. Genetic clines detected in common gardens usually follow the observed in situ phenotypic clines, reflecting cogradient variation. Rare counter gradients have also been detected, where phenotypic and genetic clines exhibit opposing signs. These patterns suggest that plasticity and selection contributed in most cases synergistically to the extant differentiation., We anticipate that microevolutionary processes will be different along environmental gradients. At the leading edge, availability of newly suitable habitats will trigger migration favouring genotypes equipped with colonists attributes. At the rear edges of the distribution, populations will be submitted to strong selective pressures favouring genotypes capable of withstanding drought and heat stress. Central populations will benefit from the plastic response of trees that will temporarily compensate for the maladaptation, until genetic adaptive variation will be restored by gene flow, mutation or recombination., We make predictions about future differentiation along environmental gradients, by highlighting traits that are likely to diverge, the rate at which differentiation will take place, and the role of gene flow and hybridization. We envisage that parallel selection may maintain differentiation at extant levels, whereas divergent selection will promote substantial differentiation for traits facilitating adaptation to contrasting conditions along the environmental gradient. We anticipate that genetic divergence may occur very rapidly and will be enhanced by the multilocus architecture of most adaptive traits. [ABSTRACT FROM AUTHOR]

Aim To utilize comprehensive geographical sampling and a new, multilocus dataset to re-examine the biogeography of spotted stream frogs ( Hylarana signata complex) throughout Southeast Asia. To compare patterns of diversification among stream frog populations on land-bridge islands and oceanic islands and to re-evaluate a previous 'dual-invasion' hypothesis for the origins of endemic Philippine taxa. Location Southeast Asia, Sundaland, and the Philippines. Methods We sequenced two mitochondrial and two nuclear gene regions for members of the Hylarana signata complex. We used summary statistics and phylogenetic networks to characterize genetic variation; phylogenetic relationships and ancestral ranges were estimated using Bayesian and likelihood methods. We used the preferred topology and Bayesian methods to evaluate a previous biogeographical 'dual-invasion' hypothesis. Results In contrast to expectations, we found highly divergent, demographically stable and geographically regionalized lineages on the mainland and on land-bridge islands, but minimally divergent, widespread and clinally distributed populations, with evidence of recent demographic expansion, in adjacent oceanic island populations. Novel phylogenetic relationships depart from previous studies and our data strongly reject the previously published 'dual-invasion' hypothesis. Main conclusions Our results join new literature demonstrating that species on mainland and continental shelf islands may harbour high levels of unrecognized diversity, whereas adjacent oceanic island archipelagos can and do support naturally occurring widespread species. Although our data indicate that the individual identities of species previously hypothesized to be involved in the 'dual-invasion' scenario may have been incorrect, this mechanism for faunal exchange between the archipelago and adjacent mainland undoubtedly has contributed substantially to the accumulation of endemic vertebrate diversity in the Philippines. [ABSTRACT FROM AUTHOR]

Hybrid zones act as genomic sieves. Although globally advantageous alleles will spread throughout the zone and neutral alleles can be freely exchanged between species, introgression will be restricted for genes that contribute to reproductive barriers or local adaptation. Seminal fluid proteins (SFPs) are known to contribute to reproductive barriers in insects and have been proposed as candidate barrier genes in the hybridizing field crickets Gryllus pennsylvanicus and Gryllus firmus. Here, we have used 125 single nucleotide polymorphisms to characterize patterns of differential introgression and to identify genes that may contribute to prezygotic barriers between these species. Using a transcriptome scan of the male cricket accessory gland (the site of SFP synthesis), we identified genes with major allele frequency differences between the species. We then compared patterns of introgression for genes encoding SFPs with patterns for genes expressed in the same tissue that do not encode SFPs. We find no evidence that SFPs have reduced gene exchange across the cricket hybrid zone. However, a number of genes exhibit dramatically reduced introgression, and many of these genes encode proteins with functional roles consistent with known barriers. [ABSTRACT FROM AUTHOR]

Spatio-temporal studies of hybrid zones provide an opportunity to test evolutionary hypotheses of hybrid zone maintenance and movement. We conducted a landscape genetics study on a classic hybrid zone of the south-eastern Australian frogs, Litoria ewingii and Litoria paraewingi. This hybrid zone has been comprehensively studied since the 1960s, providing the unique opportunity to directly assess changes in hybrid zone structure across time. We compared both mtDNA and male advertisement call data from two time periods (present and 1960s). Clinal analysis of the coincidence (same center) and concordance (same width) of these traits indicated that the center of the hybrid zone has shifted 1 km south over the last 40 years, although the width of the zone and the rate of introgression remained unchanged. The low frequency of hybrids, the strong concordance of clines within a time period, and the small but significant movement across the study period despite significant anthropogenic changes through the region, suggest the hybrid zone is a tension zone located within a low-density trough. Hybrid zone movement has not been considered common in the past but our findings highlight that it should be considered a crucial component to our understanding of evolution. [ABSTRACT FROM AUTHOR]

Comparative phylogeography of deep-sea hydrothermal vent species has uncovered several genetic breaks between populations inhabiting northern and southern latitudes of the East Pacific Rise. However, the geographic width and position of genetic clines are variable among species. In this report, we further characterize the position and strength of barriers to gene flow between populations of the deep-sea vent mussel Bathymodiolus thermophilus. Eight allozyme loci and DNA sequences of four nuclear genes were added to previously published sequences of the cytochrome c oxidase subunit I gene. Our data confirm the presence of two barriers to gene flow, one located at the Easter Microplate (between 21°33′S and 31°S) recently described as a hybrid zone, and the second positioned between 7°25′S and 14°S with each affecting different loci. Coalescence analysis indicates a single vicariant event at the origin of divergence between clades for all nuclear loci, although the clines are now spatially discordant. We thus hypothesize that the Easter Microplate barrier has recently been relaxed after a long period of isolation and that some genetic clines have escaped the barrier and moved northward where they have subsequently been trapped by a reinforcing barrier to gene flow between 7°25′S and 14°S. [ABSTRACT FROM AUTHOR]

The unprecedented rate of global warming requires a better understanding of how ecosystems will respond. Organisms often have smaller body sizes under warmer climates (Bergmann's rule and the temperature-size rule), and body size is a major determinant of life histories, demography, population size, nutrient turnover rate, and food-web structure. Therefore, by altering body sizes in whole communities, current warming can potentially disrupt ecosystem function and services. However, the underlying drivers of warming-induced body downsizing remain far from clear. Here, we show that thermal clines in body size are predicted from universal laws of ecology and metabolism, so that size-dependent selection from competition (both intra and interspecific) and predation favors smaller individuals under warmer conditions. We validate this prediction using 4.1 × 106 individual body size measurements from French river fish spanning 29 years and 52 species. Our results suggest that warming-induced body downsizing is an emergent property of size-structured food webs, and highlight the need to consider trophic interactions when predicting biosphere reorganizations under global warming. [ABSTRACT FROM AUTHOR]

The climate is often evoked to explain broad-scale clines of body size, yet its involvement in the processes that generate size inequality in the two sexes (sexual size dimorphism) remains elusive. Here, we analyse climatic clines of sexual size dimorphism along a wide elevation gradient (i) among grasshopper species in a phylogenetically controlled scenario and (ii) within species differing in distribution and cold tolerance, to highlight patterns generated at different time scales, mainly evolutionary (among species or higher taxa) and ontogenetic or microevolutionary (within species). At the interspecific level, grasshoppers were slightly smaller and less dimorphic at high elevations. These clines were associated with gradients of precipitation and sun exposure, which are likely indicators of other factors that directly exert selective pressures, such as resource availability and conditions for effective thermoregulation. Within species, we found a positive effect of temperature and a negative effect of elevation on body size, especially on condition-dependent measures of body size (total body length rather than hind femur length) and in species inhabiting the highest elevations. In spite of a certain degree of species-specific variation, females tended to adjust their body size more often than males, suggesting that body size in females can evolve faster among species and can be more plastic or dependent on nutritional conditions within species living in adverse climates. Natural selection on female body size may therefore prevail over sexual selection on male body size in alpine environments, and abiotic factors may trigger consistent phenotypic patterns across taxonomic scales. [ABSTRACT FROM AUTHOR]

All species demonstrate intraspecific anatomical variation. While generalisations such as Bergman's and Allen's rules have attempted to explain the geographic structuring of variation with some success, recent work has demonstrated limited support for these in certain Old World monkeys. This study extends this research to the baboon: a species that is widely distributed across sub- Saharan Africa and exhibits clinal variation across an environmentally disparate range. This study uses trend surface analysis to map the pattern of skull variation in size and shape in order to visualise the main axes of morphological variation. Patterns of shape and size-controlled shape are compared to highlight morphological variation that is underpinned by allometry alone. Partial regression is used to dissociate the effects of environmental terms, such as rainfall, temperature and spatial position. The diminutive Kinda baboon is outlying in size, so analyses were carried out with and without this taxon. Skull size variation demonstrates an east-west pattern, with small animals at the two extremes and large animals in Central and Southern Africa. Shape variation demonstrates the same geographical pattern as skull size, with small-sized animals exhibiting classic paedomorphic morphology. However, an additional north-south axis of variation emerges. After controlling for skull size, the diminutive Kinda baboon is no longer an outlier for size and shape. Also, the east-west component is no longer evident and discriminant function analysis shows an increased misclassification of adjacent taxa previously differentiated by size. This demonstrates the east-west component of shape variation is underpinned by skull size, while the north-south axis is not. The latter axis is explicable in phylogenetic terms: baboons arose in Southern Africa and colonised East and West Africa to the north, diverging in the process, aided by climate-mediated isolating mechanisms. Environmental terms appear poorly correlated with shape variation compared with geography. This might indicate that there is no simple environment-morphology association, but certainly demonstrates that phylogenetic history is an overbearing factor in baboon morphological variation. [ABSTRACT FROM AUTHOR]

Abstract: The strong dependence of metabolic rates on body mass has attracted the interest of ecological physiologists, as it has important implications to many aspects of biology including species variations in body size, the evolution of life history, and the structure and function of biological communities. The great diversity of observed scaling exponents has led some authors to conclude that there is no single universal scaling exponent, but instead it ranges from 2/3 to 1. Most of the telling evidence against the universality of power scaling exponents comes from ontogenetic changes. Nevertheless, there could be other sources of phenotypic variation that influence this allometric relationship at least at the intraspecific level. In order to explore the general concept of the metabolic scaling in terrestrial molluscs we tested the role of several biological and methodological sources of variation on the empirically estimated scaling exponent. Specifically, we measured a proxy of metabolic rate (CO2 production) in 421 individuals, during three generations, in three different populations. Additionally, we measured this scaling relationship in 208 individuals at five developmental stages. Our results suggest that the metabolic scaling exponent at the intraspecific level does not have a single stationary value, but instead it shows some degree of variation across geographic distribution, transgenerational change and ontogenetic stages. The major differences in the metabolic scaling exponent that we found were at different developmental stages of snails, because ontogeny involves increases in size at different rates, which in turn, generate differential energy demands. [Copyright &y& Elsevier]

Dispersal is a key parameter of adaptation, invasion and persistence. Yet standard population genetics inference methods hardly distinguish it from drift and many species cannot be studied by direct mark-recapture methods. Here, we introduce a method using rates of change in cline shapes for neutral markers to estimate contemporary dispersal. We apply it to the devastating banana pest Mycosphaerella fijiensis, a wind-dispersed fungus for which a secondary contact zone had previously been detected using landscape genetics tools. By tracking the spatio-temporal frequency change of 15 microsatellite markers, we find that σ, the standard deviation of parent-offspring dispersal distances, is 1.2 km/generation1/2. The analysis is further shown robust to a large range of dispersal kernels. We conclude that combining landscape genetics approaches to detect breaks in allelic frequencies with analyses of changes in neutral genetic clines offers a powerful way to obtain ecologically relevant estimates of dispersal in many species. [ABSTRACT FROM AUTHOR]

Lake Cadagno is characterized by a compact chemocline that harbors high concentrations of various phototrophic sulfur bacteria. Four strains representing the numerically most abundant populations in the chemocline were tested in dialysis bags in situ for their ability to fix CO2. The purple sulfur bacterium Candidatus 'Thiodictyon syntrophicum' strain Cad16T had the highest CO2 assimilation rate in the light of the four strains tested and had a high CO2 assimilation rate even in the dark. The CO2 assimilation of the population represented by strain Cad16T was estimated to be up to 25% of the total primary production in the chemocline. Pure cultures of strain Cad16T exposed to cycles of 12 h of light and 12 h of darkness exhibited the highest CO2 assimilation during the first 4 h of light. The draft genome sequence of Cad16T showed the presence of cbbL and cbbM genes, which encode form I and form II of RuBis CO, respectively. Transcription analyses confirmed that, whereas cbbM remained poorly expressed throughout light and dark exposure, cbbL expression varied during the light-dark cycle and was affected by the available carbon sources. Interestingly, the peaks in cbbL expression did not correlate with the peaks in CO2 assimilation. [ABSTRACT FROM AUTHOR]

Stress resistance characters are valuable tools for the study of acclimation potential, adaptive strategies and biogeographic patterns in species exposed to environmental variability. Water stress is a challenge to terrestrial arthropods because of their small size and relatively high area: volume ratio. Fruit flies have been investigated to record adaptive morphological and physiological traits, as well as to test their responses to stressful factors. In this study, we investigate the ability to cope with water stress, by examining variation in desiccation resistance in a species that lives mainly in desert lands. Specifically, we explored the genetic and ecological basis of desiccation resistance in populations of Drosophila buzzatii from Northern Argentina. We used a common garden experiment with desiccation treatments on a number of isofemale lines from four populations along an aridity gradient. Our results revealed significant among-population differentiation and substantial amounts of genetic variation for desiccation resistance. We also detected significant genotype-by-environment and genotype-by-sex interactions indicative that desiccation resistance responses of the lines assayed were environment- and sex-specific. In addition, we observed clinal variation in female desiccation resistance along gradients of altitude, temperature and humidity; that desiccation resistance is a sexually dimorphic trait, and that sexual dimorphism increased along the aridity and altitudinal gradients. Based on current evidence, we propose that the observed sex-specific responses may reflect different life history traits, and survival and reproductive strategies in different ecological scenarios. [ABSTRACT FROM AUTHOR]

Hybrid zones provide excellent opportunities to study processes and mechanisms underlying reproductive isolation and speciation. Here we investigated sex-specific clines of molecular markers in hybrid zones of morphologically cryptic yet genetically highly-diverged evolutionary lineages of the European common vole (Microtus arvalis). We analyzed the position and width of four secondary contact zones along three independent transects in the region of the Alps using maternally (mitochondrial DNA) and paternally (Y-chromosome) inherited genetic markers. Given male-biased dispersal in the common vole, a selectively neutral secondary contact would show broader paternal marker clines than maternal ones. In a selective case, for example, involving a form of Haldane's rule, Y-chromosomal clines would not be expected to be broader than maternal markers because they are transmitted by the heterogametic sex and thus gene flow would be restricted. Consistent with the selective case, paternal clines were significantly narrower or at most equal in width to maternal clines in all contact zones. In addition, analyses using maximum likelihood cline-fitting detected a shift of paternal relative to maternal clines in three of four contact zones. These patterns suggest that processes at the contact zones in the common vole are not selectively neutral, and that partial reproductive isolation is already established between these evolutionary lineages. We conclude that hybrid zone movement, sexual selection and/or genetic incompatibilities are likely associated with an unusual unidirectional manifestation of Haldane's rule in this common European mammal. [ABSTRACT FROM AUTHOR]

Populations of the polymorphic land snail Cepaea nemoralis ( L.) from Deepdale, Derbyshire, UK, sampled in 1965-67, showed a pattern of area effects, with steep clines among groups of populations differing in shell colour and banding morph frequencies. In 2010, most of these populations were resampled. In particular, a continuous transect made in 1967 of 42 quadrats (18.34 × 18.34 m) across a steep cline in several morph frequencies was completely resampled. In the dale as a whole, yellow shells had increased in frequency. In the transect, the frequencies of banding morphs showed no significant changes, although colour morphs showed some changes. Pink shells had increased in frequency in a section in which scrub had developed, and brown shells had increased in frequency in the area in which they had originally been at the highest frequency. In each case, the selection coefficients were of the order of 4%. Yellow had increased elsewhere. Nevertheless, both in the dale as a whole and in the transect, the pattern of geographical change in morph frequencies had remained essentially the same. Estimates of migration based on previous studies of marked snails and on modelling of the effect of drift and migration suggest that, regardless of whether the cline is a product of differential selection or of the gradual merging of previously separate founding populations, it has been in existence for a long time, and that migration occurs over greater distances than estimated from direct observation on marked snails. Although we can demonstrate that selection has occurred, the origin and maintenance of the cline and others similar to it remain in doubt; the development and maintenance of polymorphism in this species may require consideration of several processes operating on different time scales. © 2012 The Linnean Society of London [ABSTRACT FROM AUTHOR]

Introgressive hybridization between genetically divergent populations is an important evolutionary process. The degree to which repeated hybridization events between the same parental taxa lead to similar genomic outcomes is unknown. This study addressed this question by following genomic trajectories of replicate hybrid swarms of the copepod Tigriopus californicus over many generations of free mating. Swarm composition was determined both by differential reproductive success of founder individuals and subsequent selection on hybrid genotypes. For one cross, between two populations showing differential fitness in the laboratory and no hybrid breakdown, the genetic trajectory was highly repeatable: replicates rapidly became dominated by alleles from the fitter parent. In a second cross, between two populations showing similar fitness and significant F2 hybrid breakdown, alleles from alternative populations dominated different replicates. Swarms exhibited a general temporal trend of decreasing cytonuclear mismatch. Some patterns of differential introgression across the genome were strikingly congruent amongst swarm replicates, both within and between cross types, and reflected patterns of segregation distortion previously observed within controlled crosses between the same parental populations. Differences in heterozygosity between the sexes, and evidence for a previously suspected sex-distortion locus, suggest that complex interactions between sex and genotype influence hybrid swarm outcome. [ABSTRACT FROM AUTHOR]

Drosophila ananassae, a desiccation and cold sensitive species, is abundant along the latitudinal gradient of the Indian subcontinent. Analysis of seasonally varying wild-caught flies showed two independent patterns of melanisation: (1) narrow to broad melanic stripes on three anterior abdominal segments only; (2) a novel body color pattern (dark vs. light background). We investigated the degree to which these two melanisation systems vary; first with latitude and secondly among seasons. There is a shallow latitudinal cline for percent striped melanisation as well as for frequency of body color alleles during the rainy season. The frequencies of body color alleles vary significantly across seasons in the northern populations i.e. the light allele occur abundantly (>0.94) during the rainy season while the frequency of the dark allele increases (0.22-0.35) during the dry season causing steeper clines during the dry season. By contrast, the low variations in abdominal stripes showed non-significant changes and the cline was similar across seasons. Furthermore, both types of melanisation patterns showed no plasticity with respect to temperature. The present study also investigated clines related to desiccation, heat and cold stress in D. ananassae females across seasons (rainy and dry) from nine latitudinal populations. The clines for stress related traits changes to steeper and non-linear during the dry season. Thus, latitudinal populations of D. ananassae differ in slope values of clines for stress related traits across seasons. This study reports seasonal changes in latitudinal clines of stress resistance traits as seen in a changing frequency of body color alleles of D. ananassae in northern locality, while in southern localities it remains constant. This is presumably the result of only minor seasonal changes in humidity and temperature in the South, whereas in the North seasonal climatic variability is much higher. [ABSTRACT FROM AUTHOR]

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

Aim We characterize and compare patterns of clinal size variation among diverse widespread sub-Saharan monkeys with the aim of identifying commonalities and differences in biogeographical variation. Thus, we accurately quantify nonlinear clines in representatives of the main lineages of widespread sub-Saharan terrestrial and arboreal monkeys, and provide a crude numerical estimate of the strength of similarities across taxonomic groups. Location Sub-Saharan Africa. Methods Variations of skull centroid size, as a proxy for body mass, were modelled over sub-Saharan Africa within two terrestrial monkey species ( Papio hamadryas and Chlorocebus aethiops) and two arboreal monkey taxa ( Procolobus (Piliocolobus) sp., and the superspecies Cercopithecus nictitans-Cercopithecus mitis) using inverse distance weighting, thin-plate splines and kriging. The model with the highest cross-validated accuracy was used to produce contour plots that visualized clines and predicted size at equally spaced localities across overlapping areas of distribution ranges. Correlations among these predictions were used as a similarity measure among clines. Results Irrespective of phylogenetic distances and ecological differences, all groups showed similarities in clinal size over central Africa: large animals mostly live in and around the tropical forest of the Congo basin; size declines rapidly towards the Horn of Africa and the coasts of Kenya and Tanzania. Size also tends to decrease in western Africa but clinal patterns in this region vary, with vervets ( Chlorocebus aethiops) exceptionally showing a size increase. Main conclusions Similarities in patterns of size across diverse monkey groups were found. Nonetheless, complexity in clines and a degree of heterogeneity across groups were evident, which is unlikely to be compatible with the exclusive effect on size of a single main environmental factor. Primary productivity may be most significant in relation to the consistent observation of large sizes in and adjacent to the central African tropical forest belt. Complex clines, such as those of African monkeys, are difficult to compare visually and data collection from evenly sampled sets of localities, where all species of interest may be found, is often impractical or simply not feasible for primates and other protected animals. The development of improved quantitative methods for the description and comparison of clines in mammals and other organisms is required. [ABSTRACT FROM AUTHOR]

The relative roles of genetic differentiation and developmental plasticity in generating latitudinal gradients in life histories remain insufficiently understood. In particular, this applies to determination of voltinism (annual number of generations) in short-lived ectotherms, and the associated trait values. We studied different components of variation in development of Chiasmia clathrata ( Lepidoptera: Geometridae) larvae that originated from populations expressing univoltine, partially bivoltine or bivoltine phenology along a latitudinal gradient of season length. Indicative of population-level genetic differentiation, larval period became longer while growth rate decreased with increasing season length within a particular phenology, but saw-tooth clines emerged across the phenologies. Indicative of phenotypic plasticity, individuals that developed directly into reproductive adults had shorter development times and higher growth rates than those entering diapause. The most marked differences between the alternative developmental pathways were found in the bivoltine region suggesting that the adaptive correlates of the direct development evolve if exposed to selection. Pupal mass followed a complex cline without clear reference to the shift in voltinism or developmental pathway probably due to varying interplay between the responses in development time and growth rate. The results highlight the multidimensionality of evolutionary trajectories of life-history traits, which either facilitate or constrain the evolution of integrated traits in alternative phenotypes. [ABSTRACT FROM AUTHOR]

The first regional mapping of the averaged turbulent kinetic energy dissipation rate 〈 ɛ 〉 in the upper pycnocline of the northern South China Sea is presented and discussed. At φ = 20°N and to the north of this latitude, 〈 ɛ 〉 appears to be more than two times larger than that to the south of 20°N. It is suggested that this asymmetry is associated with the predominant northwestward propagation and dissipation of the internal waves originated in the Luzon Strait area. An approximately linear relationship between 〈 ɛ 〉 and the available potential energy of the waves P, suggests a characteristic time of the P dissipation of about 6 h. [ABSTRACT FROM AUTHOR]

A common geographical pattern of genetic variation is the one-dimensional cline. Clines may be maintained by diversifying selection across a geographical gradient but can also reflect historical processes such as allopatry followed by secondary contact. To identify loci that may be undergoing diversifying selection, we examined the distribution of geographical variation patterns across the range of the killifish (Fundulus heteroclitus) in 310 loci, including microsatellites, allozymes, and single nucleotide polymorphisms. We employed two approaches to detect loci under strong diversifying selection. First, we developed an automated method to identify clinal variation on a per-locus basis and examined the distribution of clines to detect those that exhibited signifcantly steeper slopes. Second, we employed a classic FST-outlier method as a complementary approach. We also assessed performance of these techniques using simulations. Overall, latitudinal clines were detected in nearly half of all loci genotyped (i.e., all eight microsatellite loci, 12 of 16 allozyme loci and 44% of the 285 SNPs). With the exception of few outlier loci (notably mtDNA and malate dehydrogenase), the positions and slopes of Fundulus clines were statistically indistinguishable. The high frequency of latitudinal clines across the genome indicates that secondary contact plays a central role in the historical demography of this species. Our simulation results indicate that accurately detecting diversifying selection using genome scans is extremely difficult in species with a strong signal of secondary contact; neutral evolution under this history produces clines as steep as those expected under selection. Based on these results, we propose that demographic history can explain all clinal patterns observed in F. heteroclitus without invoking natural selection to either establish or maintain the pattern we observe today. [ABSTRACT FROM AUTHOR]

Abstract: In geographically structured populations, global panmixia can be regarded as the limiting case of long-distance migration. The effect of incorporating partial panmixia into diallelic single-locus clines maintained by migration and selection in an unbounded unidimensional habitat is investigated. Migration and selection are both weak. The former is homogenous and isotropic; the latter has no dominance. The population density is uniform. A simple, explicit formula is derived for the maximum value of the scaled panmictic rate for which a cline exists. The former depends only on the asymptotic values of the scaled selection coefficient. If the two alleles have the same average selection coefficient, there exists a unique, globally asymptotically stable cline for every . Otherwise, if , the allele with the greater average selection coefficient is ultimately fixed. If , there exists a unique, globally asymptotically stable cline, and some polymorphism is retained even infinitely far from its center. The gene frequencies at infinity are determined by a continuous-time, two-deme migration-selection model. An explicit expression is deduced for the monotone cline in a step-environment. These results differ fundamentally from those for the classical cline without panmixia. [Copyright &y& Elsevier]

The role of natural selection in speciation has received increasing attention and support in recent years. Different types of approaches have been developed that can detect genomic regions influenced by selection. Here, we address the question whether two highly different methods- FST outlier analysis and admixture analysis-detect largely the same set of non-neutral genomic elements or, instead, complementary sets. We study genetic architecture in a natural secondary contact zone where extensive admixture occurs. The marine bivalves Macoma balthica rubra and M. b. balthica descend from two independent trans-Arctic invasions of the north Atlantic and hybridize extensively where they meet, for example in the Kattegat-Danish Straits-Baltic Sea region. The Kattegat-Danish Straits region forms a steep salinity cline and is the only entrance to the recently (ca. 8000 years ago) established brackish water basin the Baltic Sea. Salinity along the contact zone drops from 30‰ (Skagerrak, M.b.rubra) to 3‰ (Baltic, M.b.balthica). Both outlier analysis and genomic clines analysis suggest that large parts of the genome are influenced by non-neutral effects. Contrasting samples from well outside the hybrid zone, outlier analysis detects 16 of 84 amplified fragment length polymorphism markers as significant FST outliers. Genomic clines analysis detects 31 of 84 markers as non-neutral inside the hybrid zone. Remarkably, only three markers are detected by both methods. We conclude that the two methods together identify a suite of markers that are under the influence of non-neutral effects. [ABSTRACT FROM AUTHOR]

Ecology Letters (2012) Abstract The geography of adaptive genetic variation is crucial to species conservation yet poorly understood in marine systems. We analyse the spatial scale of genetic variation in traits that broadly display adaptation throughout the range of a highly dispersive marine species. We conducted common garden experiments on the Atlantic silverside, Menidia menidia, from 39 locations along its 3 000 km range thereby mapping genetic variation for growth rate, vertebral number and sex determination. Each trait displayed unique clinal patterns, with significant differences (adaptive or not) occurring over very small distances. Breakpoints in the cline differed among traits, corresponding only partially with presumed eco-geographical boundaries. Because clinal patterns are unique to each selected character, neutral genes or those coding for a single character cannot serve as proxies for the genetic structure as a whole. Conservation plans designed to protect essential genetic subunits of a species will need to account for such complex spatial structures. [ABSTRACT FROM AUTHOR]

Broad-scale geographical gradients in the abiotic environment and interspecific interactions should select for clinal adaptation. How trait clines evolve has recently received increased attention because of anticipated climate change and the importance of rapid evolution in invasive species. This issue is particularly relevant for clines in growth and defense of plants, because both sets of traits are closely tied to fitness and because such sessile organisms experience strong local selection. Yet despite widespread recognition that growth and defense traits are intertwined, the general issue of their joint clinal evolution is not well resolved. To address heritable clinal variation and adaptation of growth and defense traits of common milkweed (Asclepias syriaca), we planted seed from 22 populations encompassing the species' latitudinal range in common gardens near the range center (New York) and toward the range edges (New Brunswick and North Carolina). Populations were differentiated in 13 traits, and six traits showed genetically based latitudinal clines. Higher-latitude populations had earlier phenology, lower shoot biomass, more root buds and clonal growth, higher root-to-shoot ratio, and greater latex production. The cline in shoot biomass was consistent in all three locations. Selection on phenology was reversed in New Brunswick and North Carolina, with early genotypes favored in the north but not the south. We found no clines in foliar trichomes or toxic cardenolides. Annual precipitation of source populations explained variation in phenology, clonal growth, root-to-shoot ratio, and latex. Across four traits measured in New Brunswick and North Carolina, we found garden-by-latitude (and garden-by-precipitation) interactions, indicating plasticity in genetically based trait clines. In the two gardens with substantial herbivory (New York and North Carolina), northern populations showed higher resistance to insects. Resistance to aphids was driven by trichomes and water content, while resistance to monarch caterpillars was driven by latex. However, surveys of natural populations indicated that leaf damage and insect diversity on milkweed are low at the geographical extremes (New Brunswick and North Carolina) and higher toward the range center. We speculate that milkweed plants evolved clines in growth traits in response to climate, and that this set the template for tolerance to herbivory, which subsequently shaped the evolution of defensive traits. [ABSTRACT FROM AUTHOR]

In the marine gastropod Littorina saxatilis differences in relative shell apertural form between two ecotypes from NW Spain have been associated with an environmental cline related to the degree of wave exposure. Such differences have been claimed to have a strong genetic basis, with little influence of phenotypic plasticity. However, dietary changes are expected to affect the growth rate and, potentially, the shell shape, and could thus challenge the adaptive interpretation of the polymorphism. To address this issue we performed a laboratory experiment to grow one of these ecotypes under different food treatments with the aim of testing differences in shell growth. We then investigated the correlation of shell size and shape to quantify the impact of growth on shell aperture. Our results reveal significant dietary effects, an increase in growth rate leading to larger relative apertural size. However, this change occurs in the opposite direction to that expected from the differences between the two ecotypes in nature. This is in line with the low contribution of phenotypic plasticity to the polymorphism observed in previous studies. [ABSTRACT FROM PUBLISHER]

1. Understanding how non-native plants respond to environmental variation, and the limits to these responses, is important for predicting plant invasiveness. Until now, the extent to which species' climatic limits differ on introduction to a new range has not been experimentally tested. Here, we investigate fitness responses to temperature and low-temperature limits to reproduction of native and introduced populations of the widespread forb Plantago lanceolata. 2. We recorded fitness parameters of P. lanceolata accessions collected from nearly complete latitudinal gradients in the species' native and introduced ranges and grown in five common gardens arranged along an elevational gradient in the native range (European Alps). The highest garden was located outside the low-temperature limit of the species. 3. Native populations exhibited clear clinal genetic differentiation along temperature gradients, while any differentiation in introduced populations was much weaker; however, the introduced populations displayed higher average fitness and broad climatic tolerance. Despite these differences, both native and introduced plants failed to set seed beyond the elevational range margin and so shared a similar low-temperature limit to reproduction. 4. Synthesis. Our experimental data support observational studies of niche-limit conservatism in non-native plants, which has important implications for their management. Specifically, it suggests that efforts to predict the extent of an invasion based on knowledge of the native niche are likely to be accurate at the level of the species, even if populations undergo genetic changes or respond differently to climatic gradients in the new range. [ABSTRACT FROM AUTHOR]

Abstract: The Cariaco Basin is the world''s largest truly marine anoxic basin. We have conducted a comprehensive multidisciplinary investigation of the water column (42–750m) bracketing the redox boundary (a 250-m thick “chemocline”) of the Cariaco Basin to evaluate linkages between lipid biomarkers, distributions of major dissolved chemical species, and the microbial community and associated redox processes. Our multidimensional data set includes: hydrography, water column chemistry, microbial distributions and rates, and lipid biomarkers. Multivariant statistical analysis of this data set partitions the investigated water column into 5 distinct zones, each characterized by different chemistries, microbiologies and biomarker compositions. The core of this chemocline is a 25-m thick suboxic zone where both dissolved oxygen and sulfide were below detection limits, bacterial and archaeal cell numbers and the rate of chemoautotrophic (dark) carbon fixation are elevated, and dissolved chemical species and bacterial and archaeal lipid biomarkers are indicative of tightly coupled cycles of carbon, nitrogen, and sulfur through chemoautotrophy. [Copyright &y& Elsevier]

During the last decades, the Euler scheme was the common 'workhorse' in particle tracking, although it is the lowest-order approximation of the underlying stochastic differential equation. To convince the modelling community of the need for better methods, we have constructed a new test case that will show the shortcomings of the Euler scheme. We use an idealised shallow-water diffusivity profile that mimics the presence of a sharp pycnocline and thus a quasi-impermeable barrier to vertical diffusion. In this context, we study the transport of passive particles with or without negative buoyancy. A semi-analytic solutions is used to assess the performance of various numerical particle-tracking schemes (first- and second-order accuracy), to treat the variations in the diffusivity profile properly. We show that the commonly used Euler scheme exhibits a poor performance and that widely used particle-tracking codes shall be updated to either the Milstein scheme or second-order schemes. It is further seen that the order of convergence is not the only relevant factor, the absolute value of the error also is. [ABSTRACT FROM AUTHOR]

We present a minimal conceptual model for the Atlantic meridional overturning circulation which incorporates the advection of salinity and the basic dynamics of the oceanic pycnocline. Four tracer transport processes following Gnanadesikan in Science 283(5410):2077-2079, () allow for a dynamical adjustment of the oceanic pycnocline which defines the vertical extent of a mid-latitudinal box. At the same time the model captures the salt-advection feedback (Stommel in Tellus 13(2):224-230, ()). Due to its simplicity the model can be solved analytically in the purely wind- and purely mixing-driven cases. We find the possibility of abrupt transition in response to surface freshwater forcing in both cases even though the circulations are very different in physics and geometry. This analytical approach also provides expressions for the critical freshwater input marking the change in the dynamics of the system. Our analysis shows that including the pycnocline dynamics in a salt-advection model causes a decrease in the freshwater sensitivity of its northern sinking up to a threshold at which the circulation breaks down. Compared to previous studies the model is restricted to the essential ingredients. Still, it exhibits a rich behavior which reaches beyond the scope of this study and might be used as a paradigm for the qualitative behaviour of the Atlantic overturning in the discussion of driving mechanisms. [ABSTRACT FROM AUTHOR]

This study reports on the polymorphism of 15 allozyme loci in Ruditapes decussatus clams collected from 11 locations along the Tunisian coasts. We concentrated our sampling effort around the Siculo-Tunisian region to verify if any population structuring exists in this region and to identify the factors that have shaped this structure. Measurements of genetic diversity were quantified both within and between populations, and the geographic variability of gene frequencies was analyzed. Our study shows that the Siculo-Tunisian Strait is an important genetic boundary between eastern and western regions, which agrees with findings for a variety of other species. We suggest that vicariance is a predominant factor shaping the current distribution of genetic diversity of R. decussatus, and the mixing of divergent gene pools from the eastern and western regions still seems to be limited by some physical and/or biological factors. [ABSTRACT FROM AUTHOR]

Age and body size are two important demographic traits that determine the life history strategies of populations and species. We measured these two parameters of Rana amurensis, at a 900 m and a 500 m altitude site in northeastern China. At the two sites, age at first reproduction was 2 years for males and 3 years for females. The maximum age of males and females at the high-altitude site was 6 and 7 years, and 5 and 7 years at the low-altitude population, respectively. Females were significantly larger than males in both populations, due to greater age in both the high- and low-altitude sites. Body size of either males or females did not differ significantly between populations; only males showed increased body size at the high-altitude site when age effect was statistically controlled for. The increased cline of male body size may be attributable to delayed maturation of the sex due to a shorter growing season at high altitudes. [ABSTRACT FROM AUTHOR]

Summary 1. Insect body size is predicted to increase with decreasing latitude because time available for growth increases. In insects with changing voltinism (i.e. number of generations per season), sharp decreases in development time and body size are expected at season lengths where new generations are added to the phenology of a species, giving rise to saw-tooth clines in these traits across latitudes. Growth rate variation may affect the magnitude of variation in body size or even reverse the saw-tooth cline. 2. In this study, we analyse latitudinal body size clines in four geometrid moths with changing voltinism in a common laboratory environment. In addition to body size, we measured larval development time and growth rate and genetic correlations among the three traits. 3. The patterns of clinal variation in body size were diverse, and the theory was not supported even when saw-tooth body size clines were found. Larval development time increased and growth rate decreased consistently with increasing season length, the clines in these traits being uniform. 4. The consistencies of development time and growth rate clines suggest a common mechanism underlying the observations. Such a mechanism is discussed in relation to the complex interdependencies among the traits. [ABSTRACT FROM AUTHOR]

The article presents a study concerning contemporary nuclear and mitochondrial genetic clines in the north temperate estuarine fish, Osmerus mordax or rainbow smelt, taken from coastal Newfoundland in Canada. It is said that present-day spatial genetic structure serves as a reflection of the influences on gene flow. The study also seeks to assess the possible effects of historical isolation, selection and different mutational dynamics among loci on molecular divergence by looking into the variation of mitochondrial DNA (mtDNA) sequence and 11 microsatellite loci in the fish species. Findings show that influences of Pleistocene glaciation and subsequent range expansions are reflected by the broad-scale contemporary genetic differentiation among the fish species.

Zones of contact between divergent biological forms within or between species are critical to the study of speciation. How characters flow across contact zones can be informative of the speciation process. To better understand this phenomenon in a mammal, we investigated cranial shape change in a contact zone between northern and southern phylogeographical groups of California voles ( Microtus californicus). We took 12 linear measurements of skulls, one measurement of the mandible, and coded the presence and absence of two skull foramina for 427 specimens. In multivariate analyses, skulls within parental regions were correctly assigned more than 90% of the time. In the contact zone, 49% were classified as northern and 51% as southern, with a bimodal distribution of posterior probability values. Foraminal patterns in the contact zone were intermediate between northern and southern regions. A cline analysis for coastal populations suggested a similar centre for mitochondrial and nuclear markers, although a centre for the morphological data was offset. Cranial morphology indicates an intermediate area with overlap between the two regions, as suggested by the molecular data, with a pattern distinct from mitochondrial DNA or nuclear DNA markers. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 264-283. [ABSTRACT FROM AUTHOR]

Abstract: The geographical cline of the coevolving traits of weevil rostrum (mouthpart) length and camellia pericarp (fruit coat) thickness provides an opportunity to test the arms race theory of defense (pericarp thickness) and countermeasure (rostrum length) between antagonistically interacting species. By extending the previous model for the coevolution of quantitative traits to introduce nonlinear costs for exaggerated traits, the generation overlap, and density-dependent regulation in the host, we studied the evolutionarily stable (ES) pericarp thickness in the Japanese camellia (Camellia japonica) and the ES rostrum length in the camellia–weevil (Curculio camelliae). The joint monomorphic ES system has a robust outcome with nonlinear costs, and we analyzed how the traits of both species at evolutionary equilibrium depend on demographic parameters. If camellia demographic parameters vary latitudinally, data collected over the geographical scale of rostrum length and pericarp thickness should lie on an approximately linear curve with the slope less than that of the equiprobability line A/B of boring success, where A and B are coefficients for the logistic regression of boring success to pericarp thickness and rostrum length, respectively. This is a robust prediction as long as the cost of rostrum length is nonlinear (accelerating). As a result, boring success should be lower in populations with longer rostrum length, as reported in the weevil–camellia system (Toju, H., and Sota, T., 2006a. Imbalance of predator and prey armament: Geographic clines in phenotypic interface and natural selection. American Naturalist 167, 105–117). The nonlinearity (exponent) for the cost of rostrum length estimated from the geographical cline data for the weevil–camellia system was 2.2, suggesting nonlinearity between quadratic and cubic forms. [Copyright &y& Elsevier]

Random genetic drift shifts clines in space, alters their width, and distorts their shape. Such random fluctuations complicate inferences from cline width and position. Notably, the effect of genetic drift on the expected shape of the cline is opposite to the naive (but quite common) misinterpretation of classic results on the expected cline. While random drift on average broadens the overall cline in expected allele frequency, it narrows the width of any particular cline. The opposing effects arise because locally, drift drives alleles to fixation--but fluctuations in position widen the expected cline. The effect of genetic drift can be predicted from standardized variance in allele frequencies, averaged across the habitat: . A cline maintained by spatially varying selection (step change) is expected to be narrower by a factor of √1- relative to the cline in the absence of drift. The expected cline is broader by the inverse of this factor. In a tension zone maintained by underdominance, the expected cline width is narrower by about 1 - relative to the width in the absence of drift. Individual clines can differ substantially from the expectation, and we give quantitative predictions for the variance in cline position and width. The predictions apply to clines in almost one-dimensional circumstances such as hybrid zones in rivers, deep valleys, or along a coast line and give a guide to what patterns to expect in two dimensions. [ABSTRACT FROM AUTHOR]

The article presents a study which uses satellite tracking locations and fuzzy clustering to quantify subpopulations of caribous in Canada. The study reveals the robustness of barren-ground subpopulations structured by strong annual spatial affiliation in females. Also, the east-west cline reflects the differences in subpopulation size and habitat conditions.

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 (, Proc Natl Acad Sci USA, 105, 16207-16211). Here, we show that under standard diapause-inducing conditions (12 °C and short photoperiod) (, 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. [ABSTRACT FROM AUTHOR]

Competition is thought to be a major influence on community assembly, ecology and evolution; presence of competitors may cause divergence in traits related to resource use (character displacement). Such traits, however, often vary clinally, and this phenomenon may be independent of the presence or absence of competing species. The presence of such clines can either obscure the effects of competition, or create an impression that competition is operating when, in fact, it is not. We corrected for clinal variation while testing for character displacement in two well-studied weasel ( Mustela) guilds, in the Nearctic and the west Palaearctic. Without accounting for clines, our results agreed with previous studies suggesting character displacement in these guilds. However, when we corrected for clines, predictions of competition theory were not met - and often we obtained evidence for character convergence in sympatry. This may suggest that the nature of the resource base may be more important than interspecific competition in shaping morphology and size in these carnivores. Our results highlight the need to account for geographic variation when studying character displacement and cast some doubt on prevailing ideas regarding the effect of competition on morphological evolution. [ABSTRACT FROM AUTHOR]

Here we provide the first detailed description of the hybrid zone between the Cremona chromosomal race of house mouse (ICRE; 2n = 22) and the standard all-telocentric race (40ST; 2n = 40), with full karyotypes of 106 individuals from 17 localities along a transect between the 2 races to the west of Lake Garda in Northern Italy. The ICRE race is characterised by 9 pairs of metacentric chromosomes in a homozygous state and we use the metacentric frequency data along the transect to fit tanh metacentric clines. The clines are narrow (5-8 km, standardised width) suggesting low hybrid fitness. However, the lack of occurrence of ICRE × 40ST F1 hybrids and presence of other hybrid types suggests that the F1 hybrids initially produced in this hybrid zone were at least partially fertile, despite having 9 meiotic trivalent configurations. We apply the same cline-fitting methodology to 3 previously studied hybrid zones between metacentric races and the 40ST race. Taken together with published clinal data on 4 further metacentric-40ST hybrid zones, we are able to make objective generalisations on the characteristics of such zones in the house mouse. Zones involving 22-chromosome races are narrower, on average, than other metacentric-40ST hybrid zones and do not show a tendency towards the generation of new races as found with zones where the metacentric race has a higher 2n. It appears that metacentric-40ST zones are unlikely to be sites of speciation (even when a 22-chromosome race is involved), although a mosaic structure to the hybrid zone may enhance this possibility. We make a comparison between metacentric-40ST zones and contacts between 2 metacentric races, for a comprehensive perspective of chromosomal hybrid zones in the house mouse. Copyright © 2011 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Gene flow among hybridizing species with incomplete reproductive barriers blurs species boundaries, while selection under heterogeneous local ecological conditions or along strong gradients may counteract this tendency. Congeneric, externallyfertilizing fucoid brown algae occur as distinct morphotypes along intertidal exposure gradients despite gene flow. Combining analyses of genetic and phenotypic traits, we investigate the potential for physiological resilience to emersion stressors to act as an isolating mechanism in the face of gene flow. Along vertical exposure gradients in the intertidal zone of Northern Portugal and Northwest France, the mid-low shore species Fucus vesiculosus, the upper shore species Fucus spiralis, and an intermediate distinctive morphotype of F. spiralis var. platycarpus were morphologically characterized. Two diagnostic microsatellite loci recovered 3 genetic clusters consistent with prior morphological assignment. Phylogenetic analysis based on single nucleotide polymorphisms in 14 protein coding regions unambiguously resolved 3 clades; sympatric F. vesiculosus, F. spiralis, and the allopatric (in southern Iberia) population of F. spiralis var. platycarpus. In contrast, the sympatric F. spiralis var. platycarpus (from Northern Portugal) was distributed across the 3 clades, strongly suggesting hybridization/introgression with both other entities. Common garden experiments showed that physiological resilience following exposure to desiccation/heat stress differed significantly between the 3 sympatric genetic taxa; consistent with their respective vertical distribution on steep environmental clines in exposure time. Phylogenetic analyses indicate that F. spiralis var. platycarpus is a distinct entity in allopatry, but that extensive gene flow occurs with both higher and lower shore species in sympatry. Experimental results suggest that strong selection on physiological traits across steep intertidal exposure gradients acts to maintain the 3 distinct genetic and morphological taxa within their preferred vertical distribution ranges. On the strength of distributional, genetic, physiological and morphological differences, we propose elevation of F. spiralis var. platycarpus from variety to species level, as F. guiryi. [ABSTRACT FROM AUTHOR]

We developed a Bayesian genomic cline model to study the genetic architecture of adaptive divergence and reproductive isolation between hybridizing lineages. This model quantifies locus-specific patterns of introgression with two cline parameters that describe the probability of locus-specific ancestry as a function of genome-wide admixture. 'Outlier' loci with extreme patterns of introgression relative to most of the genome can be identified. These loci are potentially associated with adaptive divergence or reproductive isolation. We simulated genetic data for admixed populations that included neutral introgression, as well as loci that were subject to directional, epistatic or underdominant selection, and analysed these data using the Bayesian genomic cline model. Under many demographic conditions, underdominance or directional selection had detectable and predictable effects on cline parameters, and 'outlier' loci were greatly enriched for genetic regions affected by selection. We also analysed previously published genetic data from two transects through a hybrid zone between Mus domesticus and M. musculus. We found considerable variation in rates of introgression across the genome and particularly low rates of introgression for two X-linked markers. There were similarities and differences in patterns of introgression between the two transects, which likely reflects a combination of stochastic variability because of genetic drift and geographic variation in the genetic architecture of reproductive isolation. By providing a robust framework to quantify and compare patterns of introgression among genetic regions and populations, the Bayesian genomic cline model will advance our understanding of the genetics of reproductive isolation and the speciation process. [ABSTRACT FROM AUTHOR]

We explored the transition of 13 X-linked markers across two separate portions of the house mouse hybrid zone, asking whether such a comparison can distinguish the effects of selection from random factors. A heuristic search in the likelihood landscape revealed more complex likelihood profiles for data sampled in two-dimensional (2D) space relative to data sampled along a linear transect. Randomized resampling of localities analyzed for individual loci showed that deletion of sites away from the zone center can decrease cline width estimates whereas deletion of sites close to the center can significantly increase the width estimates. Deleting localities for all loci resulted in wider clines if the number of samples from the center was limited. The results suggest that, given the great variation in width estimates resulting from inclusion/exclusion of sampling sites, the geographic sampling design is important in hybrid zone studies and that our inferences should take into account measures of uncertainty such as support intervals. The comparison of the two transects indicates cline widths are narrower for loci in the central part of the X chromosome, suggesting selection is stronger in this region and genetic incompatibilities may have at least partly common architecture in the house mouse hybrid zone. [ABSTRACT FROM AUTHOR]

Body size and thermal tolerance clines in Drosophila melanogaster occur along the east coast of Australia. However the extent to which temperature affects the genetic architecture underlying the observed clinal divergence remains unknown. Clinal variation in these traits is associated with cosmopolitan chromosome inversions that cline in D. melanogaster. Whether this association influences the genetic architecture for these traits in D. melanogaster is unclear. Drosophila simulans shows linear clines in body size, but nonlinear clines in cold resistance. Clinally varying inversions are absent in D. simulans. Line-cross and clinal analyses were performed between tropical and temperate populations of D. melanogaster and D. simulans from the east coast of Australia to investigate whether clinal patterns and genetic effects contributing to clinal divergence in wing centroid size, thorax length, wing-to-thorax ratio, cold and heat resistance differed under different developmental temperatures (18°C, 25°C, and 29°C). Developmental temperature influenced the genetic architecture in both species. Similarities between D. melanogaster and D. simulans suggest clinally varying inversion polymorphisms have little influence on the genetic architecture underlying clinal divergence in size in D. melanogaster. Differing genetic architectures across different temperatures highlight the need to consider different environments in future evolutionary and molecular studies of phenotypic divergence. [ABSTRACT FROM AUTHOR]

The coastal marine environment of the Northwest Atlantic contains strong environmental gradients that create distinct marine biogeographic provinces by limiting dispersal, recruitment, and survival. This region has also been subjected to numerous Pleistocene glacial cycles, resulting in repeated extirpations and recolonizations in northern populations of marine organisms. In this study, we examined patterns of genetic structure and historical demography in the Atlantic silverside, Menidia menidia, an annual marine fish with high dispersal potential but with well-documented patterns of clinal phenotypic adaptation along the environmental gradients of the Northwest Atlantic. Contrary to previous studies indicating genetic homogeneity that should preclude regional adaptation, results demonstrate subtle but significant ( F = 0.07; P < 0.0001) genetic structure among three phylogeographic regions that partially correspond with biogeographic provinces, suggesting regional limits to gene flow. Tests for non-equilibrium population dynamics and latitudinal patterns in genetic diversity indicate northward population expansion from a single southern refugium following the last glacial maximum, suggesting that phylogeographic and phenotypic patterns have relatively recent origins. The recovery of phylogeographic structure and the partial correspondence of these regions to recognized biogeographic provinces suggest that the environmental gradients that shape biogeographic patterns in the Northwest Atlantic may also limit gene flow in M. menidia, creating phylogeographic structure and contributing to the creation of latitudinal phenotypic clines in this species . [ABSTRACT FROM AUTHOR]