Genetic structure within and among populations of the endangered razorback sucker (Xyrauchen texanus) as determined by analysis of microsatellites

Razorback sucker (Xyrauchen texanus) was once common and widely distributed throughout the Colorado River drainage of western North America. Water development and predation by non-native species led to significant decrease in the species’ range, and dramatic reduction in size of remaining populations. Previous analyses of mtDNA variation determined that most variation was found within locations and that haplotypes were randomly distributed relative to geography, indicating these samples represent remnants of a single, basin-wide population. In addition, both diversity and number of haplotypes declined progressively down- to upstream, consistent with geologically-recent expansion into the northern portions of the basin. Analyses of variation at 13 microsatellite loci also identified a decrease in genetic variation from down- to upstream, also consistent with the hypothesis of recent expansion. Analyses of population structure identified three distinct groups, but the majority of microsatellite variation was found within populations. Most individuals from the upper Colorado River were identified as a discrete unit. These individuals exhibited high levels of relatedness, indicating this represented an isolated group of closely related individuals. There also were significant differences between populations above and below the Grand Canyon; however, estimates of Θ were relatively low. Given nothing is known of local adaptation in this species, populations above and below the canyon should be managed as independent units; however, if numbers become too low it will be possible to translocate individuals from southern populations northward to increase levels of genetic variability and decrease relatedness within units. These results also illustrate the need for careful consideration of all available information when using molecular data in identifying units for management.     

An assessment of the spatial scale of local adaptation in brown trout (Salmo trutta L.): footprints of selection at microsatellite DNA loci

Local adaptation is considered a paradigm in studies of salmonid fish populations. Yet, little is known about the geographical scale of local adaptation. Is adaptive divergence primarily evident at the scale of regions or individual populations? Also, many salmonid populations are subject to spawning intrusion by farmed conspecifics that experience selection regimes fundamentally different from wild populations. This prompts the question if adaptive differences between wild populations and hatchery strains are more pronounced than between different wild populations? We addressed these issues by analyzing variation at 74 microsatellite loci (including anonymous and expressed sequence tag- and quantitative trait locus-linked markers) in 15 anadromous wild brown trout (Salmo trutta L.) populations, representing five geographical regions, along with two lake populations and two hatchery strains used for stocking some of the populations. F_ST-based outlier tests revealed more outlier loci between different geographical regions separated by 522±228 km (mean±s.d.) than between populations within regions separated by 117±79 km (mean±s.d.). A significant association between geographical distance and number of outliers between regions was evident. There was no evidence for more outliers in comparisons involving hatchery trout, but the loci under putative selection generally were not the same as those found to be outliers between wild populations. Our study supports the notion of local adaption being increasingly important at the scale of regions as compared with individual populations, and suggests that loci involved in adaptation to captive environments are not necessarily the same as those involved in adaptive divergence among wild populations.     

Environmental factors predict adaptive phenotypic differentiation within and between two wild Andean tomatoes

Environmental variation is widely viewed as a major force driving morphological change and speciation. Although many environmental attributes are potentially critical for adaptive responses within and between species, the individual and relative importance of these diverse attributes remain poorly understood. Here we combine a geographical information systems (GIS)-based analysis of environmental variation with a multipopulation analysis of phenotypic, physiological, and genetic variation, to generate and test hypotheses of environmental factors likely driving adaptive divergence within and between two wild Andean plant species. First, we document large environmental differences between population locations of the two species, and among regions within species. Second, we show evidence for inter- and intraspecific differences in genetically based phenotypic and physiological variation. Third, combining these data, we report evidence for trait-environment associations both among populations within species, and between species, that are strongly indicative of recent and rapid adaptive responses. Finally, we show that these trait-environment associations cannot be simply explained by genetic relatedness within species, reinforcing our inference that local, regional, and species-wide environmental conditions are responsible for phenotypic and physiological diversification. The strongest trait-environment associations involve temperature and precipitation gradients, suggesting these climatic factors are predominant drivers of adaptive diversification in these species.     

Rapid evolutionary responses in a translocated population of intertidal snail (<Emphasis Type="Italic">Bembicium vittatum</Emphasis>) utilise variation from different source populations

The artificial movement of individuals between populations (translocation) can be an effective way to increase genetic diversity within populations, but few studies have undertaken long term genetic monitoring to determine if variation introduced by translocation is maintained over many generations or whether it can be used to adapt to local conditions. Here, we report on the changes in morphological and molecular variation over a 12-year period in a population of an intertidal littorine snail (Bembicium vittatum) that was created by mixing individuals from three geographically disjunct populations. These source populations differ genetically in shell shape and in allele frequency at several allozyme loci. We found that the translocated population had higher allozyme diversity than any of the source populations and that this pattern was maintained over multiple generations. Variation in shell shape also increased, but this declined over time as shells became taller. Some allozyme loci also showed significant changes in frequency over time. These changes were not consistently towards the genetic makeup of a single source population, and in the case of shell shape, were towards a phenotype that was most suited to the local environment. Our results suggest that genetic variation introduced into a population by translocation can be rapidly incorporated and used to adapt to local conditions without domination by a single source population’s genome. However, more studies are needed before generalisations on the benefits of mixing individuals from disjunct populations can be made.     

Phenotypic Plasticity and Population Differentiation in an Ongoing Species Invasion

The ability to succeed in diverse conditions is a key factor allowing introduced species to successfully invade and spread across new areas. Two non-exclusive factors have been suggested to promote this ability: adaptive phenotypic plasticity of individuals, and the evolution of locally adapted populations in the new range. We investigated these individual and population-level factors in Polygonum cespitosum, an Asian annual that has recently become invasive in northeastern North America. We characterized individual fitness, life-history, and functional plasticity in response to two contrasting glasshouse habitat treatments (full sun/dry soil and understory shade/moist soil) in 165 genotypes sampled from nine geographically separate populations representing the range of light and soil moisture conditions the species inhabits in this region. Polygonum cespitosum genotypes from these introduced-range populations expressed broadly similar plasticity patterns. In response to full sun, dry conditions, genotypes from all populations increased photosynthetic rate, water use efficiency, and allocation to root tissues, dramatically increasing reproductive fitness compared to phenotypes expressed in simulated understory shade. Although there were subtle among-population differences in mean trait values as well as in the slope of plastic responses, these population differences did not reflect local adaptation to environmental conditions measured at the population sites of origin. Instead, certain populations expressed higher fitness in both glasshouse habitat treatments. We also compared the introduced-range populations to a single population from the native Asian range, and found that the native population had delayed phenology, limited functional plasticity, and lower fitness in both experimental environments compared with the introduced-range populations. Our results indicate that the future spread of P. cespitosum in its introduced range will likely be fueled by populations consisting of individuals able to express high fitness across diverse light and moisture conditions, rather than by the evolution of locally specialized populations.     

Parasitic mites influence intra‐ and interpopulational variation in sperm length in a simultaneous hermaphrodite land snail (Gastropoda: Helicidae)

Sperm morphology can be highly variable among species, but less is known about patterns of population differentiation within species. Sperm morphology is under strong sexual selection, may evolve rapidly, and often co‐varies with other reproductive traits that differ between populations. We investigated variation in sperm morphology in the simultaneous hermaphrodite land snail Arianta arbustorum in relation to parasitic mite infection. Variation in total sperm length and sperm head length was assessed in 23 populations sampled across the distributional range of the species in Central and Northern Europe. We found a pronounced variation in total sperm length among the populations studied, with a difference of 11.0% of total sperm length between the shortest and longest population means. Differences among populations explained 62.9% of the variance in total sperm length, differences among individual snails within population 23.4% and differences within individual snail 13.7%. Mantel tests showed that interpopulation differences in total sperm length increased significantly with geographical distance between populations. A minimal adequate model revealed that parasitic infection had a positive effect and longitude a negative effect on total sperm length. Thus, independent of the population examined, mite‐infected individuals of A. arbustorum produced larger sperm than uninfected snails and total sperm length decreased from west to east. Sperm head length also varied among populations, but it was not influenced by any of the factors examined. In a subsample of 12 populations restricted to the mountains of Switzerland (elevational range 440–2485 m a.s.l.), total sperm length decreased with increasing elevation. Our results suggest that selection pressures acting among populations may differ from those acting within. Stabilizing selection might be a possible mechanism for producing the reduced variation observed in sperm length within a population. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 1036–1046.     

高山垫状植物团状福禄草开花面积与方位随海拔的变化及其适应性

作为高山生态系统中的奠基种(foundation species), 垫状植物自身种群的繁殖与扩张, 对高山生态系统功能稳定性起着关键作用。但是, 垫状植物如何在极端环境条件下实现资源的有效利用与分配, 达到繁殖最优化, 至今鲜为人知。该研究在滇西北白马雪山沿海拔梯度选择具有不同坡度及坡向的5个团状福禄草(Arenaria polytrichoides)种群, 调查、比较种群内、种群间以及具有不同性系统的植株个体之间的开花面积比、开花方位, 并分析不同生态因子对其开花特性的影响。结果表明: 随着海拔的升高, 团状福禄草个体变小, 其分配到开花的资源比例总体上随海拔上升呈现下降的趋势, 说明团状福禄草的繁殖分配受到由海拔所引起的生态因子的调控。但是, 部分低海拔种群内植物个体的繁殖分配显著低于部分高海拔种群, 说明海拔并非控制植物繁殖分配的唯一因素。此外, 植株开花总面积随植株个体增大而增加, 但开花面积比却随个体增大而变小, 说明植株分配到开花的资源增长速率可能低于植株个体的增长速率。在性别差异方面, 两性植株对开花的资源分配比例要显著高于雌性植株, 但是, 其差异程度受到海拔因素的影响。最后, 在同一种群内, 团状福禄草在冠层表面不同方位上的开花面积比存在显著差异性, 这种差异性在不同种群之间又具有不同的表现形式。     

Altitudinal variation in flowering area and position and their ecological significances of an alpine cushion Arenaria polytrichoides,a gynodioecious herb

Aims As foundation species in the alpine ecosystems, the reproduction and recruitment of alpine cushion plants are very important for sustaining the alpine ecosystem functions. However, it still remains unclear that how cushion plants effectively allocate resources to optimize reproductive fitness.Methods Here we selected five populations of a gynodioecious herb Arenaria polytrichoides with different exposures and slopes along an altitudinal gradient on the Baima snow mountain in northwest Yunnan, southwest China, to investigate and compare flowering area and positions, within and among populations and between female and hermaphroditic morphs. By doing so, we further discuss how the environmental stresses affect the cushion’s flowering attributes thus the population-level reproduction.Important findings The results showed that, individual plant size and resources allocated to flowering (flowering area %) both decreased with increasing elevation, indicating that the reproductive allocation strategy was significantly affected by elevation. However, a population at lower elevation showed lower reproductive investment than higher populations, suggesting that elevation was not the only factor affecting the cushion’s reproductive allocation. In addition, absolute flowering area increased with increasing individual size, but the flowering area ratio decreased, indicating that the increases in reproductive allocation are fewer than that in vegetative allocation. Hermaphroditic individuals invested more resources to flowering than females did, but again, such effect was affected by elevation. Moreover, within a single population, the flowering areas were significantly different among the four directions (east, south, west and north) within one single individual canopy, but such differences varied in different populations.     

Morphological Consequences of Developmental Plasticity in <Emphasis Type="Italic">Rana temporaria</Emphasis> are not Accommodated into Among-Population or Among-Species Variation

Environmental induced developmental plasticity occurs in many organisms and it has been suggested to facilitate biological diversification. Here we use ranid frogs to examine whether morphological changes derived from adaptive developmental acceleration in response to pool drying within a species are mirrored by differences among populations and across species. Accelerated development in larval anurans under pool drying conditions is adaptive and often results in allometric changes in limb length and head shape. We examine the association between developmental rate and morphology within population, among populations in divergent environments, and among species inside the Ranidae frog family, combining experimental approaches with phylogenetic comparative analyses. We found that frogs reared under decreasing water conditions that simulated fast pool drying had a faster development rate compared to tadpoles reared on constant water conditions. This faster developmental rate resulted in different juvenile morphologies between the two pool drying conditions. The association between developmental rate and morphology found as a result of plasticity was not mirrored by differences among populations that differed in development, neither was it mirrored among species that differed in development rate. We conclude that morphological differences among populations and species were not driven by variation in developmental time per se. Instead, selective factors, presumably operating on locomotion and prey choice, seem to have had a stronger evolutionary effect on frog morphology than evolutionary divergences in developmental rate in the ranid populations and species studied.     

Wrong place,wrong time: climate change‐induced range shift across fragmented habitat causes maladaptation and declined population size in a modelled bird species

Many species are locally adapted to decreased habitat quality at their range margins, and therefore show genetic differences throughout their ranges. Under contemporary climate change, range shifts may affect evolutionary processes at the expanding range margin due to founder events. In addition, populations that are affected by such founder events will, in the course of time, become located in the range centre. Recent studies investigated evolutionary changes at the expanding range margin, but have not assessed eventual effects across the species' range. We explored the possible influence of range shift on the level of adaptation throughout the species' total range. For this we used a spatially explicit, individual‐based simulation model of a woodland bird, parameterized after the middle spotted woodpecker ( Dendrocopos medius) in fragmented habitat. We simulated its range under climate change, and incorporated genetic differences at a single locus that determined the individual's degree of adaptation to optimal temperature conditions. Generalist individuals had a large thermal tolerance, but relatively low overall fitness, whereas climate specialists had high fitness combined with a small thermal tolerance. In equilibrium, the populations in the range centre were comprised of the specialists, whereas the generalists dominated the margins. In contrast, under temperature increase, the generalist numbers increased at the expanding margin and eventually also occupied the centre of the shifting range, whereas the specialists were located in the retracting margins. This was caused by founder events and led to overall maladaptation of the species, which resulted in a reduced metapopulation size and thus impeded the species' persistence. We therefore found no evidence for a complementary effect of local adaptation and range shifts on species' survival. Instead, we showed that founder events can cause local maladaptation which can amplify throughout the species' range, and, as such, hamper the species' persistence under climate change.     

RAPD variation within and among natural populations of outcrossing buffalograss [Buchloë dactyloides (Nutt.) Engelm.]

RAPD markers provide a powerful tool for the investigation of genetic variation in natural and domesticated populations. Recent studies of strain/cultivar identification have shown extensive RAPD divergence among, but little variation within, inbred species or cultivars. In contrast, little is known about the pattern and extent of RAPD variation in heterogeneous, outcrossing species. We describe the population genetic variation of RAPD markers in natural, diploid sources of dioecious buffalograss [Buchloë dactyloides (Nutt.) Engelm.]. Buffalograss is native to the semi-arid regions of the Great Plains of North America, where it is important for rangeland forage, soil conservation, and as turfgrass. Most sources of buffalograss germplasm are polyploid; diploid populations are previously known only from semi-arid Central Mexico. This is the first report of diploids from humid Gulf Coastal Texas. These two diploid sources represent divergent adaptive ecotypes. Seven 10-mer primers produced 98 polymorphic banding sites. Based on the presence/ absence of bands, a genetic distance matrix was calculated. The new Analysis of Molecular Variance (AMOVA) technique was used to apportion the variation among individuals within populations, among populations within adaptive regions, and among regions. There was considerable variation within each of the four populations, and every individual was genetically distinct. Even so, genetic divergence was found among local populations. Within-population variation was larger and among-population variation smaller in Mexico than in Texas. The largest observed genetic differences were those between the two regional ecotypes. These patterns of genetic variation were very different from those reported for inbred species and provide important baseline data for cultivar identification and continuing studies of the evolution of polyploid races in this species.     

The cuticular hydrocarbons of the giant soil-burrowing cockroach Macropanesthia rhinoceros saussure (Blattodea: Blaberidae: Geoscapheinae): analysis with respect to age, sex and location

The cuticular hydrocarbons of a widespread species of soil-burrowing cockroach, Macropanesthia rhinoceros, have been sampled from most of its known geographical locations. Analysis of extracts from individual insects has enabled a study of differences within a population as well as among geographical locations. In the case of M. rhinoceros, except for newly hatched first-instar nymphs, variations in hydrocarbon composition among individuals of different cohorts of M. rhinoceros, based on age and sex, are no greater than those among individuals of a single cohort. Geographical populations of this species are variable in hydrocarbon composition unless they occur within a few kilometres of each other. A few populations showed very different hydrocarbon patterns but, in the absence of any correlating biological differences, it is uncertain whether this signifies the presence of otherwise unrecognizable sibling species or just extreme examples of the geographical variation characteristic of this group of insects.     

Repertoire Sharing and Song Similarity between Great Tit Males Decline with Distance between Forest Fragments

Birdsong can play a critical role in establishing a territory and finding a mate among individuals from local and foreign populations. Variation in birdsong among populations can be influenced by habitat fragmentation and might affect successful dispersal among habitat fragments. We studied variation in great tit song in a long‐term study population distributed over nine forest fragments. All individual males recorded had a known dispersal history within the fragmented forest habitat. We found spatial structure of declining song‐type sharing with distance, with a marked drop from an individual’s own forest fragment to another across a habitat gap. We also found decreasing song similarity among increasingly distant fragments in terms of temporal and spectral characteristics of shared song types. The change in acoustic structure was more gradual and seemed less affected by habitat discontinuity but also showed a tight correlation with dispersal index among forest fragments. Immigrant birds shared fewer song types with neighbouring birds that were born within the same forest fragment, but not less compared to birds born in another forest fragment within the study area. Our data provide detailed insight into the relationship between song differentiation and male dispersal and contribute to our understanding of the potential role of song in reproductive exchange and avian speciation. The fact that birds in small forest fragments shared more songs than birds in larger forest fragments confirms that song analysis has potential as a tool for conservation in rare species.     

Linking ecology, behaviour and conservation: does habitat saturation change the mating system of bearded vultures?

The social organization of a population is the consequence of the decisions made by individuals to maximize their fitness, so differences in social systems may arise from differences in ecological conditions. Here, we show how a long-lived species that used to breed monogamously, and at low densities, can change its mating system in response to habitat saturation. We found that a significant proportion of unpaired birds become potential breeders by entering high-quality territories, or by forming polyandrous trios as a strategy to increase their individual performance. However, productivity of territories was reduced when those occupied by breeding pairs changed to trios, suggesting that the third individual was costly. The decision of some individuals to enter into breeding trios as subordinates also had clear negative consequences to population demography. This unusual mating behaviour is thus compromising the conservation effort directed to this endangered species; management to encourage floaters to settle in other suitable but unoccupied areas may be beneficial.     

The single-copy DNA sequence polymorphism of the sea urchin strongylocentrotus purpuratus

The single-copy DNA sequence difference between individual sea urchins of the species Strongylocentrotus purpuratus has been estimated by comparing the thermal stability of reassociated DNA duplexes from two individuals with that for DNA from an individual. Thermal stability was measured by hydroxyapatite thermal chromatography, S1 nuclease resistance after heating in a solvent which neutralizes the effect of DNA base composition, and spectrophotometric melting. One pair of individuals appear to differ from each other in about 4% of the nucleotide pairs of their single-copy DNA sequence. The differences in DNA sequence among individuals in local populations are not distinguishably smaller than those among populations as far apart as 2000 kilometers along the Pacific coast of North America.     

Aging and chiasma frequency in Eyprepocnemis plorans (Orthoptera: Acrididae)

The mean frequency of chiasmata was analysed in 29 males of the grasshopper Eyprepocnemis plorans at three different ages considered representative of the whole adult life in this species. In the factors which could potentially affect the parameter studied—namely age, family, individual and the presence or absence of B chromosomes—significant differences were only observed at the individual level. Aging produces no general effect but interacts strongly with the individuals though the age-induced variations in chiasma frequency are not directional. The fact that the range of chiasma frequency variation found within individuals at different ages is comparable to that existing among individuals indicates that the adaptive role of such variations in natural populations must be taken with caution.     

Ribosomal DNA variation within and among individuals ofLisianthius (Gentianaceae) populations

Restriction endonuclease fragment analysis of nuclear ribosomal DNA (rDNA) was completed on 25 individuals each from seven populations of theLisianthius skinneri (Gentianaceae) species complex in Panama. Seven restriction enzymes were used to determine the amount and type of rDNA variation within and among individuals of the populations. No restriction site variation was seen within populations or individuals although site differences were seen among populations. Spacer length variation within and among individuals of populations was mapped to the internal transcribed spacer (ITS) region between the 18S and 5.8S rRNA genes, a region inLisianthius rDNA that previously was shown to exhibit length differences among populations. This is the first reported case of such variation within and among individuals of populations for the ITS region. Presence or absence of ITS spacer length variation is not correlated with levels of isozymic heterozygosity within populations. No detectable length variation within individuals or populations was seen in the larger intergenic spacer (IGS). Although populations varied with respect to IGS length, all individuals of a given population had a single and equivalent IGS length.     

Life-history variation and adaptation in the historically mobile plant Arabidopsis thaliana (Brassicaceae) in North America

We used field-collected seeds of Arabidopsis thaliana (Brassicaceae) to simulate a colonization event of plants from diverse locations into a common environment to compare regionally "local" and "foreign" populations of this historically mobile species. Life history varied among regional groups, but most variation was found among populations within regions. While we found significant differences among populations and regional groups for important life-history characters, we did not find significant differences in performance of plants from different populations or regional groups. Rather, we found evidence that differences in life history contributed to the ability of plants from foreign regions to perform comparably to local Kentucky plants. Had plants from different regions not differed in the timing and size of reproduction, we would have seen that Kentucky (local) plants had higher total fitness via greater reproductive success of individuals that survived to reproduce and that Michigan plants would have had the lowest fitness. The populations are comparably adapted to the environment in Kentucky but through different combinations of life-history characters. Therefore, the life-history variation in this mobile species appears to contribute not to fitness differences among populations but rather to success in colonizing new locations.