Intraspecific and interspecific genetic variation in Drosophila

Utilizing the technique of DNA-DNA hybridization, we have characterized the degree of genetic variability in single-copy DNA both within and between several species of Drosophila. The results of intraspecific variation studies indicate considerable variation both for levels of nucleotide heterozygosity (estimated to be over 2%) as well as for insertions-deletions. Interspecific studies confirm this great deal of variability and further establish an extreme heterogeneity within Drosophila genomes for rates of divergence. This heterogeneity is much more extreme than that seen between exons and introns. The degree of single-copy DNA divergence generally supports phylogenetic affinities deduced from more traditional methods. However, exceptions occur where single-copy DNA divergence is not correlated with other properties such as degree of chromosomal differentiation, morphology, or ability to form interspecific hybrids. We argue that single-copy DNA divergence as measured by DNA-DNA hybridization is an accurate indicator of phylogenetic relationships and therefore sheds light on the evolution of other biological properties. Many, if not most, evolutionary tests require an accurate phylogeny of the group being studied and DNA, because of the high information content inherent within the molecule, offers the best hope of deriving true phylogenies.     

Intraspecific and interspecific variation of female genitalia in two species of watersnake

The morphological differences in female genitalia within and between species are little studied and poorly understood, yet understanding patterns of variation in female genitalia can provide insights into mechanisms of genital evolution. The present study aimed to explore the patterns of intraspecific and interspecific variation in female genitalia in two sister taxa of watersnake (Nerodia sipedon and Nerodia fasciata) that have similar genital shape. We used a geometric morphometric (GM) approach to study variation in shape of the vagina between and within two sister species. We examined genital shape in female watersnakes ranging from small, sexually immature females to large reproductive females that had recently given birth. We found that shape variation of genitalia is strongly correlated with body size, where larger but not smaller females have a bifurcation in the vagina. However, we also found significant shape variation in the structure of the vagina between the two species, where N. fasciata has narrower genitalia with more prominent bifurcation, whereas N. sipedon has wider genitalia with less marked bifurcation. Using GM allowed us to detect significant differences in genital shape that were not apparent upon visual examination alone, suggesting that shape variation in female genitalia may be greater than previously assumed. Additional study of morphological differences in male reproductive organs for these species would help to determine whether there has been genital co‐evolution, and potentially mechanical reproductive isolation, in these two closely‐related and occasionally sympatric species. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 183–191.     

Intraspecific and interspecific variation in drumming signals in the genus Capnioneura (Plecoptera: Capniidae)

The male drumming calls of four species of the genus Capnioneura, and for the first time, the female answer signal from one species of this genus are described. Only the male call of C. mitis from a southern Iberian Peninsula is known. In the current study, the male calls of three additional C. mitis populations from two different mountain drainages and the male calls of C. gelesae, C. libera and C. petitpierreae are described and analysed. The calls were near-ancestral and percussive signals with variable numbers of beats and approximately constant, monophasic beat intervals. The mean interbeat intervals were species specific, ranging from 250 to 1500 ms. The C. mitis female answer interbeat intervals were similar to the call but composed of 3–4 beats. Intraspecific and interspecific variation is discussed and these results support the hypothesis that stonefly drumming plays an important role as a reproductive isolating mechanism.     

Intraspecific versus interspecific variation in Miocene Great Basin mylagaulids: implications for systematics and evolutionary history

The Mylagaulidae are a family of burrowing rodents abundant in Miocene faunas from western North America. Recent taxonomic revisions of mylagaulids from the Great Plains suggest that their systematics may be best understood on a regional basis. Previous studies addressed the taxonomy and evolutionary history of mylagaulids from the Great Basin, but recent discoveries of specimens, new phylogenetic data, and more detailed stratigraphical information necessitate a thorough reanalysis of their relationships and occurrences. We present a revision of the systematics of the mylagaulids from the Great Basin. In addition to rare large mylagaulids of uncertain taxonomic affinity, we recognize four species of mylagaulids distributed throughout Oregon and Nevada from the late Hemingfordian through to the early late Hemphillian: Alphagaulus vetus, Hesperogaulus gazini, Hesperogaulus wilsoni, and a new species from the genus Hesperogaulus. All species are known from large sample sizes of isolated premolars, allowing consideration of ontogenetic variation in determining the key morphological differences that allow recognition of different species. Although the number of enamel lakes varies within a given taxon, the presence of some of these lakes is taxonomically significant. This result emphasizes the importance of understanding ontogeny in describing species of fossil hypsodont mammals. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 164 , 427–450.     

Intraspecific heritable variation in life-history traits can alter the outcome of interspecific competition among insect herbivores

Competition is one of the most important biotic factors determining the structure of ecological communities. In this study, we show that there is variation in competitive ability between two clones of the pea aphid, Acyrthosiphon pisum, both of which out-compete a clone of the vetch aphid, Megoura viciae, in the laboratory. We tested whether this variation in competitive ability would alter the outcome of interspecific competition in the field. While one pea aphid clone followed the pattern set in the laboratory, out-competing the Megoura viciae clone, another showed the reverse effect with Megoura viciae dominating. These differences appear to be the result of variation in early population growth rate between the pea aphid clones, rather than predation, although predation did lead to the eventual extinction of colonies. We also questioned whether intra- and interspecific differences in predator escape behaviour could affect the outcome of competition in the field. All three clones responded similarly to the presence of foraging hoverfly larvae (Episyrphus balteatus), but the Megoura viciae clone dropped from the plant significantly less often in response to the presence of a foraging two-spot ladybird (Adalia bipunctata). This work provides evidence that intraspecific variation in competitive ability can alter the outcome of interspecific competitive interactions in nature and suggests that species–specific behavioural traits may have the potential to modify the outcome of these interactions.     

Intraspecific flavonoid variation

This review is concerned with variation of flavonoid patterns within species. Many examples of species with invariant flavonoid patterns are known; there are at least as many examples where complex arrays of pigments are known. Eight categories of variation are discussed: 1) qualitatively invariant pigment profiles, 2) quantitative variation, 3) flavonoid races that do not correspond to recognized taxonomic groups, 4) flavonoid races that do correspond to recognized taxonomic groups, 5) flavonoid profile differences between different ploidy levels, 6) differences between organs or between tissues, 7) differences between developmental stages, and 8) environmentally influenced flavonoid profiles. These types of variation seem to occur randomly in the plant kingdom. Members of the same family, or in some cases, the same genus, can display different types of variation. Careful attention to these sources of variation is necessary before flavonoid characters can be used in taxonomic studies.     

Intraspecific variation in production of astringent phenolics over a vegetation-resource availability gradient

Summary The chemical constituency of flowering dogwood (Cornus florida L.) and red maple (Acer rubrum L.) foliage was analyzed over a species compositional gradient to test the hypothesis that over subtle gradients of moisture and nutrient availability production of phenolic compounds will be increased on sites of greatest stress. Calcium and nitrogen concentrations declined along the gradient in both species, while phosphorus showed a significant decline only in red maple. Lignin concentrations in both species were unrelated to the vegetation gradient, but astringent phenolics increased by 156% and 159% in dogwood and red maple, respectively. The correlation between production of polyphenolds and site quality supports previous observations that under conditions of environmental stress production of many secondary compounds is increased, and suggests that this relationship is significant over subtle environmental gradients.This investigation (No. 86-8-104) is connected with a project of the Kentucky Agricultural Experiment Station and is published with the approval of the director. This is publication no. 10 of Lilley Cornett Woods: Appalachian Research Station of Eastern Kentucky University, Richmond, Kentucky     

Intraspecific variability modulates interspecific variability in animal organismal stoichiometry

Interspecific differences in organismal stoichiometry (OS) have been documented in a wide range of animal taxa and are of significant interest for understanding evolutionary patterns in OS. In contrast, intraspecific variation in animal OS has generally been treated as analytical noise or random variation, even though available data suggest intraspecific variability in OS is widespread. Here, we assess how intraspecific variation in OS affects inferences about interspecific OS differences using two co‐occurring Neotropical fishes: Poecilia reticulata and Rivulus hartii. A wide range of OS has been observed within both species and has been attributed to environmental differences among stream systems. We assess the contributions of species identity, stream system, and the interactions between stream and species to variability in N:P, C:P, and C:N. Because predation pressure can impact the foraging ecology and life‐history traits of fishes, we compare predictors of OS between communities that include predators, and communities where predators are absent. We find that species identity is the strongest predictor of N:P, while stream or the interaction of stream and species contribute more to the overall variation in C:P and C:N. Interspecific differences in N:P, C:P, and C:N are therefore not consistent among streams. The relative contribution of stream or species to OS qualitatively changes between the two predation communities, but these differences do not have appreciable effects in interspecific patterns. We conclude that although species identity is a significant predictor of OS, intraspecific OS is sometimes sufficient to overwhelm or obfuscate interspecific differences in OS.     

大别山五针松种内和种间竞争强度

通过对安徽省岳西县大别山五针松群落内的53株对象木及2079株竞争木的调查,运用Hegyi单木竞争模型分析了大别山五针松的种内和种间竞争强度。结果表明,大别山五针松的种内和种间竞争强度分别为17.11%和82.89%,说明竞争主要来自种间。大别山五针松的伴生种较多,种内与主要伴生种间的竞争关系为短柄枹大别山五针松种内黄山松满山红茅栗金缕梅紫茎四照花灯台树鹅耳枥。竞争强度随对象木胸径的增大而减小,当对象木的胸径小于25cm时,所受到的竞争强度较大;当胸径在25cm以上时,竞争强度变化很小,二者符合幂函数关系(CI=AD-B),所得的预测模型能很好的预测大别山五针松种内和种间竞争强度。     

Intraspecific variation and species coexistence

We use a two-species model of plant competition to explore the effect of intraspecific variation on community dynamics. The competitive ability ("performance") of each individual is assigned by an independent random draw from a species-specific probability distribution. If the density of individuals competing for open space is high (e.g., because fecundity is high), species with high maximum (or large variance in) performance are favored, while if density is low, species with high typical (e.g., mean) performance are favored. If there is an interspecific mean-variance performance trade-off, stable coexistence can occur across a limited range of intermediate densities, but the stabilizing effect of this trade-off appears to be weak. In the absence of this trade-off, one species is superior. In this case, intraspecific variation can blur interspecific differences (i.e., shift the dynamics toward what would be expected in the neutral case), but the strength of this effect diminishes as competitor density increases. If density is sufficiently high, the inferior species is driven to extinction just as rapidly as in the case where there is no overlap in performance between species. Intraspecific variation can facilitate coexistence, but this may be relatively unimportant in maintaining diversity in most real communities.     

Intraspecific and interspecific adaptive latitudinal cline in Brassicaceae seed oil traits

Premise of the Study

Nearly all seed plants rely on stored seed reserves before photosynthesis can commence. Natural selection for seed oil traits must have occurred over 319 million years of evolution since the first seed plant ancestor. Accounting for the biogeographic distribution of seed oil traits is fundamental to understanding the mechanisms of adaptive evolution in seed plants. However, the evolution of seed oils is poorly understood. We provide evidence of the adaptive nature of seed oil traits at the intraspecific and interspecific levels in Brassicaceae—an oilseed‐rich and economically important plant family.

Methods

Univariate statistics, Pearson's correlation, multiple regression, generalized linear mixed model analysis, and phylogenetic autocorrelation tests on seed oil traits of 360 accessions of Arabidopsis thaliana and 216 Brassicaceae species helped provide evidence of the adaptive nature of seed oil traits.

Key Results

At higher latitudes, both seed oil content and unsaturated fatty acids have selective advantages in Arabidopsis thaliana (intraspecific‐level), while only unsaturated fatty acids have selective advantages across 216 Brassicaceae species (interspecific‐level). The seed oil patterns fit within the theoretical framework of the gradient model. Seed oil content increases significantly from temperate to subtropical to tropical regions in Brassicaceae herbs. Absence of phylogenetic signals for seed oil traits and high seed oil content in four tribes of Brassicaceae were observed.

Conclusions

Multiple seed oil traits are adaptive in nature and follow a gradient model. Consistent evolutionary patterns of seed oil traits were observed at the intraspecific and interspecific levels in Brassicaceae. Seed oil traits change with latitude and across biomes, suggesting selection. The absence of a phylogenetic signal for seed oil traits and the occurrence of high seed oil content in four Brassicaceae tribes provides evidence of the adaptive nature of seed oil traits in Brassicaceae.     

Intraspecific trait variation can weaken interspecific trait correlations when assessing the whole‐plant economic spectrum

The worldwide plant economic spectrum hypothesis predicts that leaf, stem, and root traits are correlated across vascular plant species because carbon gain depends on leaves being adequately supplied with water and nutrients, and because construction of each organ involves a trade‐off between performance and persistence. Despite its logical and intuitive appeal, this hypothesis has received mixed empirical support. If traits within species diverge in their responses to an environmental gradient, then interspecific trait correlations could be weakened when measured in natural ecosystems. To test this prediction, we measured relative growth rates (RGR) and seven functional traits that have been shown to be related to fluxes of water, nutrients, and carbon across 56 functionally diverse tree species on (1) juveniles in a controlled environment, (2) juveniles in forest understories, and (3) mature trees in forests. Leaf, stem, and fine root traits of juveniles grown in a controlled environment were closely correlated with each other, and with RGR. Remarkably, the seven leaf, stem, and fine root tissue traits spanned a single dimension of variation when measured in the controlled environment. Forest‐grown juveniles expressed lower leaf mass per area, but higher wood and fine root tissue density, than greenhouse‐grown juveniles. Traits and growth rates were decoupled in forest‐grown juveniles and mature trees. Our results indicate that constraints exist on the covariation, not just the variation, among vegetative plant organs; however, divergent responses of traits within species to environmental gradients can mask interspecific trait correlations in natural environments. Correlations among organs and relationships between traits and RGR were strong when plants were compared in a standardized environment. Our results may reconcile the discrepancies seen among studies, by showing that if traits and growth rates of species are compared across varied environments, then the interorgan trait correlations observed in controlled conditions can weaken or disappear.     

Intraspecific genotypic variability determines concentrations of key truffle volatiles

? Aroma variability in truffles has been attributed to maturation (Tuber borchii), linked to environmental factors (Tuber magnatum), but the involvement of genetic factors has been ignored. We investigated aroma variability in Tuber uncinatum, a species with wide distribution. Our aim was to assess aroma variability at different spatial scales (i.e. trees, countries) and to quantify how aroma was affected by genotype, fruiting body maturity, and geographical origin. ? A volatile fingerprinting method was used to analyze the aroma of 223 T. uncinatum fruiting bodies from seven European countries. Maturity was estimated from spore melanization. Genotypic fingerprinting was performed by amplified fragment length polymorphism (AFLP). ? Discriminant analysis revealed that, regardless of the geographical origin of the truffles, most of the aroma variability was caused by eight-carbon-containing volatiles (C8-VOCs). In an orchard of T. uncinatum, truffles producing different concentrations of C8-VOCs clustered around distinct host trees. This clustering was not associated with maturity, but was associated with fungal genotype. ? These results indicate that the variation in C8-VOCs in truffles is most likely under genetic control. They exemplify that understanding the factors behind aroma variability requires a holistic approach. Furthermore, they also raise new questions regarding the ecological role of 1-octen-3-ol in truffles.     

Intraspecific variation in herbivore‐induced plant volatiles influences the spatial range of plant–parasitoid interactions

Chemical information influences the behaviour of many animals, thus affecting species interactions. Many animals forage for resources that are heterogeneously distributed in space and time, and have evolved foraging behaviour that utilizes information related to these resources. Herbivore‐induced plant volatiles (HIPVs), emitted by plants upon herbivore attack, provide information on herbivory to various animal species, including parasitoids. Little is known about the spatial scale at which plants attract parasitoids via HIPVs under field conditions and how intraspecific variation in HIPV emission affects this spatial scale. Here, we investigated the spatial scale of parasitoid attraction to two cabbage accessions that differ in relative preference of the parasitoid Cotesia glomerata when plants were damaged by Pieris brassicae caterpillars. Parasitoids were released in a field experiment with plants at distances of up to 60 m from the release site using intervals between plants of 10 or 20 m to assess parasitism rates over time and distance. Additionally, we observed host‐location behaviour of parasitoids in detail in a semi‐field tent experiment with plant spacing up to 8 m. Plant accession strongly affected successful host location in field set‐ups with 10 or 20 m intervals between plants. In the semi‐field set‐up, plant finding success by parasitoids decreased with increasing plant spacing, differed between plant accessions, and was higher for host‐infested plants than for uninfested plants. We demonstrate that parasitoids can be attracted to herbivore‐infested plants over large distances (10 m or 20 m) in the field, and that stronger plant attractiveness via HIPVs increases this distance (up to at least 20 m). Our study indicates that variation in plant traits can affect attraction distance, movement patterns of parasitoids, and ultimately spatial patterns of plant–insect interactions. It is therefore important to consider plant‐trait variation in HIPVs when studying animal foraging behaviour and multi‐trophic interactions in a spatial context.     

濒危植物峨眉含笑的种内、种间竞争

研究植物种内、种间竞争关系是探究植物濒危原因的重要方式之一, 根据竞争来源和竞争预测模型可以制定具有针对性的保护策略。本文以雅安周公山峨眉含笑(Michelia wilsonii)野生种群为研究对象, 使用逐步扩大范围法确定峨眉含笑的竞争范围半径, 运用Hegyi单木竞争模型计算竞争指数(competition index, CI), 分析其种内、种间竞争关系。结果表明: 峨眉含笑的最适竞争范围半径是10 m, 能较好地反映其种内竞争强度; 峨眉含笑的竞争压力主要来自种内, 种内竞争指数(348.72, 62.52%)远大于种间竞争指数(209.03, 37.48%); 小树、中树阶段个体的竞争强度较大, 平均竞争指数(3.97、3.14)远高于总体平均竞争指数(2.68); 内有21种竞争木, 其中杉木(Cunninghamia lanceolata)、华中樱桃(Prunus conradinae)、细刺枸骨(Ilex hylonoma)是峨眉含笑的主要竞争树种; 胸径与竞争指数间服从指数函数关系(CI = 3.8907e^-0.048x, R² = 0.1087, P < 0.01), 随着对象木胸径的增大, 竞争指数不断降低, 当胸径达到30 cm后, 竞争强度基本稳定。综上, 小树、中树阶段的峨眉含笑个体受到极强的种内竞争, 初入老树阶段的个体受到较强的种间竞争。为更好地保护峨眉含笑的天然种群, 降低竞争对种群更替的影响, 在林分管理中需要促进小树、中树的个体更新, 减轻植株间的竞争消耗, 加速峨眉含笑的生长和维持种群稳定。     

Drought and leaf herbivory influence floral volatiles and pollinator attraction

The effects of climate change on species interactions are poorly understood. Investigating the mechanisms by which species interactions may shift under altered environmental conditions will help form a more predictive understanding of such shifts. In particular, components of climate change have the potential to strongly influence floral volatile organic compounds (VOCs) and, in turn, plant–pollinator interactions. In this study, we experimentally manipulated drought and herbivory for four forb species to determine effects of these treatments and their interactions on (1) visual plant traits traditionally associated with pollinator attraction, (2) floral VOCs, and (3) the visitation rates and community composition of pollinators. For all forbs tested, experimental drought universally reduced flower size and floral display, but there were species‐specific effects of drought on volatile emissions per flower, the composition of compounds produced, and subsequent pollinator visitation rates. Moreover, the community of pollinating visitors was influenced by drought across forb species (i.e. some pollinator species were deterred by drought while others were attracted). Together, these results indicate that VOCs may provide more nuanced information to potential floral visitors and may be relatively more important than visual traits for pollinator attraction, particularly under shifting environmental conditions.     

Development of the cranium and paired fins in Betta splendens (Teleostei: Percomorpha): Intraspecific variation and interspecific comparisons

The development of the chondrocranium and the relative timing of ossification of the osteocranium is described in the teleost fish Betta splendens from a large series of cleared and differentially stained specimens. General trends in ossification patterns are examined from developmental, phylogenetic, and functional contexts. As in many other vertebrates, dermal bones form before cartilage bones. Ossification sequence conforms to functional need in a very general way, but there are many inconsistencies in the details of order. For example, some bones that are directly involved in feeding ossify no earlier than bones more indirectly involved. Comparisons of ossification sequence within specific cranial regions are made among Betta splendens, Oryzias latipes (Atherinomorpha), and Barbus barbus (Ostariophysi) within a phylogenetic framework. Many evolutionary changes in relative sequence of ossification are evident within regions among these taxa, yet many other sequences are conserved. The logistic difficulty of comparing entire cranial ossification sequences (vs. regional sequences) makes evident the need for new methods for identifying and quantifying sequence changes. Intraspecific variation in order of ossification is described for the first time in teleost fishes. To the extent that ossification sequence varies intraspecifically, conclusions drawn from previous interspecific comparisons are compromised. Understanding the importance of changes in ossification order within and among taxa will require experimental, functional, and evolutionary work. © 1996 Wiley-Liss, Inc.     

Intraspecific nuclear DNA variation in Drosophila

We have summarized and analyzed all available nuclear DNA sequence polymorphism studies for three species of Drosophila, D. melanogaster (24 loci), D. simulans (12 loci), and D. pseudoobscura (5 loci). Our major findings are: (1) The average nucleotide heterozygosity ranges from about 0.4% to 2% depending upon species and function of the region, i.e., coding or noncoding. (2) Compared to D. simulans and D. pseudoobscura (which are about equally variable), D. melanogaster displays a low degree of DNA polymorphism. (3) Noncoding introns and 3' and 5' flanking DNA shows less polymorphism than silent sites within coding DNA. (4) X-linked genes are less variable than autosomal genes. (5) Transition (Ts) and transversion (Tv) polymorphisms are about equally frequent in non-coding DNA and at fourfold degenerate sites in coding DNA while Ts polymorphisms outnumber Tv polymorphisms by about 2:1 in total coding DNA. The increased Ts polymorphism in coding regions is likely due to the structure of the genetic code: silent changes are more often Ts's than are replacement substitutions. (6) The proportion of replacement polymorphisms is significantly higher in D. melanogaster than in D. simulans. (7) The level of variation in coding DNA and the adjacent noncoding DNA is significantly correlated indicating regional effects, most notably recombination. (8) Surprisingly, the level of polymorphism at silent coding sites in D. melanogaster is positively correlated with degree of codon usage bias. (9) Three proposed tests of the neutral theory of DNA polymorphisms have been performed on the data: Tajima's test, the HKA test, and the McDonald-Kreitman test. About half of the loci fail to conform to the expectations of neutral theory by one of the tests. We conclude that many variables are affecting levels of DNA polymorphism in Drosophila, from properties of nucleotides to population history and, perhaps, mating structure. No simple, all encompassing explanation satisfactorily accounts for the data.      

Intraspecific variation in the lens proteins

A review of the literature indicates that intraspecific variation among the lens proteins (crystallins) is almost invariably quantitative rather than qualitative. Lens extracts were examined from inbred strains of the laboratory mouse, rat, and guinea pig and from domestic breeds of sheep. Differences in the mobilities of protein bands after electrophoresis in polyacrylamide gels were never found to be greater than the variation observed when a sample was repeatedly subjected to electrophoresis. Differences, however, were observed between widely separated populations of the bank vole (Clethrionomys glareolus). In bank voles and mice, there were variations in the intensities of bands. Electrophoresis of extracts in the presence of 6 m urea indicated that there were no major differences between six mouse strains in the subunits constituting their - and -crystallins. More detailed examination of -crystallins from two mouse strains by isoelectric focusing and amino acid analysis supported this conclusion.This work was carried out while one of the authors (T.H.D.) was supported by a Medical Research Council Research Studentship and a European Molecular Biology Organisation Fellowship. A grant from the Edinburgh University Weir Memorial Fund allowed the collection of some of the Yugoslavian bank voles.