Divergence in Female Duetting Signals in the Enchenopa binotata Species Complex of Treehoppers (Hemiptera: Membracidae)

Sexual communication often involves signal exchanges between the sexes, or duetting, in which mate choice is expressed through response signals. With both sexes acting as signalers and receivers, variation in the signals of males and females may be important for mate choice, reproductive isolation, and divergence. In the Enchenopa binotata species complex – a case study of sympatric speciation in which vibrational duetting may have an important role – male signals are species‐specific, females choose among males on the basis of signal traits that reflect species and individual differences, and female preferences have exerted divergent selection on male signals. Here, we describe variation in female signals in the E. binotata species complex. We report substantial species differences in the spectral and temporal features of female signals, and in their timing relative to male signals. These differences were similar in range to differences in male signals in the E. binotata complex. We consider processes that might contribute to divergence in female signals, and suggest that signal evolution in the E. binotata complex may be influenced by mate choice in both sexes.     

among-Environment Heteroscedasticity and Genetic Autocorrelation: Implications for the Study of Phenotypic Plasticity

The impact of among-environment heteroscedasticity and genetic autocorrelation on the analysis of phenotypic plasticity is examined. Among-environment heteroscedasticity occurs when genotypic variances differ among environments. Genetic autocorrelation arises whenever the responses of a genotype to different environments are more or less similar than expected for observations randomly associated. In a multivariate analysis-of-variance model, three transformations of genotypic profiles (reaction norms), which apply to the residuals of the model while preserving the mean responses within environments, are derived. The transformations remove either among-environment heteroscedasticity, genetic autocorrelation or both. When both nuisances are not removed, statistical tests are corrected in a modified univariate approach using the sample covariance matrix of the genotypic profiles. Methods are illustrated on a Chlamydomonas reinhardtii data set. When heteroscedasticity was removed, the variance component associated with the genotype-by-environment interaction increased proportionally to the genotype variance component. As a result, the genetic correlation r(g) was altered. Genetic autocorrelation was responsible for statistical significance of the genotype-by-environment interaction and genotype main effects on raw data. When autocorrelation was removed, the ranking of genotypes according to their stability index dramatically changed. Evolutionary implications of our methods and results are discussed.     

Estimates of Gene Flow among Populations, Geographic Races, and Species in the Ipomopsis Aggregata Complex

Interpopulational gene flow within a species can reduce population differentiation due to genetic drift, whereas genetic exchange among taxa can impede speciation. We used allozyme data to estimate gene flow within and among geographic races and species of perennial herbs in the Ipomopsis aggregata complex (Polemoniaceae). Estimates of interpopulational gene flow within taxa from two methods (F statistics and private alleles) were correlated with one another. Gene flow among populations within each geographic race (subspecies) of I. aggregata was relatively high (Nm greater than approximately 1.0). Gene flow was also high among populations of I. arizonica and among four northern populations of I. tenuituba. However, gene flow was low (Nm less than 1.0) for I. tenuituba when a population representing subsp. macrosiphon was included. This is consistent with previous findings that subsp. macrosiphon has had an independent origin and is reproductively, as well as geographically, isolated. A recently developed model, based on hierarchical F statistics, was employed to estimate genetic exchange among taxa. Gene flow estimates were generally high among races of I. aggregata (dNmrace greater than 1.0) but were low among subspecies of I. tenuituba (dNmrace less than 1.0). Consistent with morphological evidence, estimates of interspecific gene flow were moderate between I. aggregata and I. tenuituba, which hybridize in several areas. However, contrary to morphological evidence, we estimated relatively high levels of interspecific gene flow involving I. arizonica. Our results suggest that I. arizonica has hybridized with other species without the transfer of morphological traits.(ABSTRACT TRUNCATED AT 250 WORDS)     

Measuring Gene Flow among Populations Having High Levels of Genetic Fragmentation

We present an analysis of the genetic structures of 22 species of salamanders, with regard to levels of gene flow among populations. We estimate the gene flow parameter, Nm (the product of the effective population number and rate of migration among populations) using two alternative methods described by Wright and Slatkin. For most species, these two methods give approximately congruent estimates of Nm; when estimates differ, the method of Wright produces values slightly larger than those derived by the method of Slatkin. We analyze these results in light of independently derived historical inferences of the fragmentation of populations. This analysis suggests that the Nm values calculated from protein polymorphisms may contain information more relevant to historical patterns of gene exchange than to the current population dynamics; moderately large values of Nm may be calculated for species containing populations known to be no longer exchanging genes. Application of a method for estimating the maximum possible rate of gene exchange among populations indicates that, for most species studied here, gene flow among populations probably is no greater than the mutation rate. We suggest that most plethodontid species cannot be viewed as units whose cohesion is maintained by continuing gene exchange. Furthermore, we suggest that phenotypic uniformity among populations is not easily explained by hypotheses of continual stabilizing selection and propose that future work concentrate upon clarification of the genetic and epigenetic factors conferring self-maintenance or autopoietic properties on living systems.     

两种濒危水韭植物迁地保护居群的基因流动态及回归重建保育遗传管理策略

采用微卫星分子标记对中华水韭（Isoetessinensis）安徽休宁、浙江建德和东方水韭（I.orientalis）浙江松阳三个孑遗居群的迁地保护居群开展了遗传多样性检测与遗传结构分析。7对多态性微卫星引物在36个迁地保护亚居群的720个样本中共检测到59个等位基因,每位点平均等位基因数（A）为8·43。迁地保护亚居群均维持很高的遗传多样性,多态信息含量（PIC）平均为0·707。迁地保护亚居群间遗传分化较低,遗传分化系数GST仅为0·070,居群间具有较大基因流（Nm=3·59）。单因素方差分析发现水韭孢子或孢子体在沿主要水流方向上的长距离传播能力要强于弱水流方向上的短距离传播能力,水流动态对水韭植物的基因流有重要影响。这与UPGMA聚类分析中迁地保护亚居群按邻近位置或水流相通程度优先聚类的结果相一致,水流所带动的强大基因流导致了不同孑遗居群来源的迁地保护亚居群间的遗传混杂。建议在开展水韭植物的迁地保护或回归自然重建时,对具有地方适应分化或者显著性进化的水韭植物居群应相互隔离而不宜配置在一起,以避免远交衰退的遗传风险。     

Seed-Mediated Gene Flow Promotes Genetic Diversity of Weedy Rice within Populations: Implications for Weed Management

Increased infestation of weedy rice—a noxious agricultural pest has caused significant reduction of grain yield of cultivated rice (Oryza sativa) worldwide. Knowledge on genetic diversity and structure of weedy rice populations will facilitate the design of effective methods to control this weed by tracing its origins and dispersal patterns in a given region. To generate such knowledge, we studied genetic diversity and structure of 21 weedy rice populations from Sri Lanka based on 23 selected microsatellite (SSR) loci. Results indicated an exceptionally high level of within-population genetic diversity (H_e = 0.62) and limited among-population differentiation (F_st = 0.17) for this predominantly self-pollinating weed. UPGMA analysis showed a loose genetic affinity of the weedy rice populations in relation to their geographical locations, and no obvious genetic structure among populations across the country. This phenomenon was associated with the considerable amount of gene flow between populations. Limited admixture from STRUCTURE analyses suggested a very low level of hybridization (pollen-mediated gene flow) between populations. The abundant within-population genetic diversity coupled with limited population genetic structure and differentiation is likely caused by the considerable seed-mediated gene flow of weedy rice along with the long-distance exchange of farmer-saved rice seeds between weedy-rice contaminated regions in Sri Lanka. In addition to other effective weed management strategies, promoting the application of certified rice seeds with no weedy rice contamination should be the immediate action to significantly reduce the proliferation and infestation of this weed in rice ecosystems in countries with similar rice farming styles as in Sri Lanka.     

Exploring Phenotypic Plasticity in the LichenRamalina capitata: Morphology, Water Relations and Chlorophyll Content in North- and South-facing Populations

The present work analyses the morphology, anatomy, water relationsand chlorophyll content of thalli of the lichenRamalina capitatavar.protectafromtwo different populations exposed to contrasting microclimaticconditions due to differences in the orientation of the rocksurface. The population on the north-facing rock surface (NFS)was exposed to lower photosynthetic photon flux densities (PPFD),remained at high relative humidities for longer periods of timeand was exposed to lower temperatures than the population onthe south-facing surface (SFS). We proposed the hypothesis thatthe shadier the habitat the greater the ecological advantagefor enhanced light harvesting. Thalli from the SFS had shorterand wider lacinia, thicker thalli, mostly due to increased medullathickness, a higher water-retention capacity, a higher percentageof thallus volume occupied by the algal cells and a higher chlorophyllcontent than thalli from NFS. The phenotypic plastic responseof the traits studied inR. capitatavar.protectawas not directlyrelated to differences in the light availability, at least forthe range of PPFD experienced by the two populations studied,since the population exposed to higher PPFD exhibited largeramounts of light harvesting pigments. Both populations exhibitedthe same intrathalline distribution of algal cells and chlorophylls,which were more abundant in the apical than in the basal zonesof all thalli studied. Periods of water-induced metabolic activitywere shorter in the SFS than in the NFS, and structural andchlorophyll data indicated that thalli from the SFS were betterprepared for the photosynthetic exploitation of these brieferperiods and for maintaining thallus hydration into dry periods.These results suggest that differences in selective pressurebetween the two populations ofR. capitatavar.protectastudiedinvolved maximization of the photosynthetic exploitation ofthe periods of metabolic activity when they are brief, as hasbeen described for certain vascular plants from xeric environments. Ramalina capitatavar.protecta; algal cells; chlorophylls; water relations; microclimate; morphology; intrathalline variation; lichen; phenotypic plasticity     

Gene Flow among Populations of Two Rare Co-Occurring Fern Species Differing in Ploidy Level

Differences in ploidy levels among different fern species have a vast influence on their mating system, their colonization ability and on the gene flow among populations. Differences in the colonization abilities of species with different ploidy levels are well known: tetraploids, in contrast to diploids, are able to undergo intra-gametophytic selfing. Because fertilization is a post-dispersal process in ferns, selfing results in better colonization abilities in tetraploids because of single spore colonization. Considerably less is known about the gene flow among populations of different ploidy levels. The present study examines two rare fern species that differ in ploidy. While it has already been confirmed that tetraploid species are better at colonizing, the present study focuses on the gene flow among existing populations. We analyzed the genetic structure of a set of populations in a 10×10 km study region using isoenzymes. Genetic variation in tetraploid species is distributed mainly among populations; the genetic distance between populations is correlated with the geographical distance, and larger populations host more genetic diversity than smaller populations. In the diploid species, most variability is partitioned within populations; the genetic distance is not related to geographic distance, and the genetic diversity of populations is not related to the population size. This suggests that in tetraploid species, which undergo selfing, gene flow is limited. In contrast, in the diploid species, which experience outcrossing, gene flow is extensive and the whole system behaves as one large population. Our results suggest that in ferns, the ability to colonize new habitats and the gene flow among existing populations are affected by the mating system.     

Phenotypic Variation across Chromosomal Hybrid Zones of the Common Shrew (Sorex araneus) Indicates Reduced Gene Flow

Sorex araneus, the Common shrew, is a species with more than 70 karyotypic races, many of which form parapatric hybrid zones, making it a model for studying chromosomal speciation. Hybrids between races have reduced fitness, but microsatellite markers have demonstrated considerable gene flow between them, calling into question whether the chromosomal barriers actually do contribute to genetic divergence. We studied phenotypic clines across two hybrid zones with especially complex heterozygotes. Hybrids between the Novosibirsk and Tomsk races produce chains of nine and three chromosomes at meiosis, and hybrids between the Moscow and Seliger races produce chains of eleven. Our goal was to determine whether phenotypes show evidence of reduced gene flow at hybrid zones. We used maximum likelihood to fit tanh cline models to geometric shape data and found that phenotypic clines in skulls and mandibles across these zones had similar centers and widths as chromosomal clines. The amount of phenotypic differentiation across the zones is greater than expected if it were dissipating due to unrestricted gene flow given the amount of time since contact, but it is less than expected to have accumulated from drift during allopatric separation in glacial refugia. Only if heritability is very low, N_e very high, and the time spent in allopatry very short, will the differences we observe be large enough to match the expectation of drift. Our results therefore suggest that phenotypic differentiation has been lost through gene flow since post-glacial secondary contact, but not as quickly as would be expected if there was free gene flow across the hybrid zones. The chromosomal tension zones are confirmed to be partial barriers that prevent differentiated races from becoming phenotypically homogenous.     

Quantitative Assessment of the Importance of Phenotypic Plasticity in Adaptation to Climate Change in Wild Bird Populations

Predictions about the fate of species or populations under climate change scenarios typically neglect adaptive evolution and phenotypic plasticity, the two major mechanisms by which organisms can adapt to changing local conditions. As a consequence, we have little understanding of the scope for organisms to track changing environments by in situ adaptation. Here, we use a detailed individual-specific long-term population study of great tits (Parus major) breeding in Wytham Woods, Oxford, UK to parameterise a mechanistic model and thus directly estimate the rate of environmental change to which in situ adaptation is possible. Using the effect of changes in early spring temperature on temporal synchrony between birds and a critical food resource, we focus in particular on the contribution of phenotypic plasticity to population persistence. Despite using conservative estimates for evolutionary and reproductive potential, our results suggest little risk of population extinction under projected local temperature change; however, this conclusion relies heavily on the extent to which phenotypic plasticity tracks the changing environment. Extrapolating the model to a broad range of life histories in birds suggests that the importance of phenotypic plasticity for adjustment to projected rates of temperature change increases with slower life histories, owing to lower evolutionary potential. Understanding the determinants and constraints on phenotypic plasticity in natural populations is thus crucial for characterising the risks that rapidly changing environments pose for the persistence of such populations.     

Phenotypic Plasticity in Response to the Social Environment: Effects of Density and Sex Ratio on Mating Behaviour Following Ecotype Divergence

The ability to express phenotypically plastic responses to environmental cues might be adaptive in changing environments. We studied phenotypic plasticity in mating behaviour as a response to population density and adult sex ratio in a freshwater isopod (Asellus aquaticus). A. aquaticus has recently diverged into two distinct ecotypes, inhabiting different lake habitats (reed Phragmites australis and stonewort Chara tomentosa, respectively). In field surveys, we found that these habitats differ markedly in isopod population densities and adult sex ratios. These spatially and temporally demographic differences are likely to affect mating behaviour. We performed behavioural experiments using animals from both the ancestral ecotype (“reed” isopods) and from the novel ecotype (“stonewort” isopods) population. We found that neither ecotype adjusted their behaviour in response to population density. However, the reed ecotype had a higher intrinsic mating propensity across densities. In contrast to the effects of density, we found ecotype differences in plasticity in response to sex ratio. The stonewort ecotype show pronounced phenotypic plasticity in mating propensity to adult sex ratio, whereas the reed ecotype showed a more canalised behaviour with respect to this demographic factor. We suggest that the lower overall mating propensity and the phenotypic plasticity in response to sex ratio have evolved in the novel stonewort ecotype following invasion of the novel habitat. Plasticity in mating behaviour may in turn have effects on the direction and intensity of sexual selection in the stonewort habitat, which may fuel further ecotype divergence.     

Influence of Gene Flow and Breeding Tactics on Gene Diversity within Populations

Expressions describing the accumulation of gene correlations within and among lineages and individuals of a population are derived. The model permits different migration rates by males and females and accounts for various breeding tactics within lineages. The resultant equations enable calculation of the probabilistic quantities for the fixation indices, rates of loss of genetic variation, accumulation of inbreeding, and coefficients of relationship for the population at any generation. All fixation indices were found to attain asymptotic values rapidly despite the consistent loss of genetic variation and accumulation of inbreeding within the population. The time required to attain asymptotic values, however, was prolonged when gene flow among lineages was relatively low (less than 20%). The degree of genetic differentiation among breeding groups, inbreeding coefficients, and gene correlations within lineages were found to be primarily functions of breeding tactics within groups rather than gene flow among groups. Thus, the asymptotic value of S. Wright's island model is not appropriate for describing genetic differences among groups within populations. An alternative solution is provided that under limited conditions will reduce to the original island model. The evolution of polygynous breeding tactics appears to be more favorable for promoting intragroup gene correlations than modification of migration rates. Inbreeding and variance effective sizes are derived for populations that are structured by different migration and breeding tactics. Processes that reduce the inbreeding effective population size result in a concomitant increase in variance effective population size.     

Implications of Genotypic Diversity and Phenotypic Plasticity in the Ecophysiological Success of CAM Plants,Examined by Studies on the Vegetation of Madagascar1

Abstract: On the basis of δ¹³C‐values, genotypic diversity and phenotypic plasticity of CAM behaviour in plants of the Malagasy vegetation is surveyed. The study compares CAM patterns performed in the wild on the levels of genera (Kalanchoë [Crassulaceae], Angraecum [Orchidaceae], Lissochilus [Orchidaceae] and Rhipsalis [Cactaceae]), on the level of a family (Didiereaceae) and finally on the level of a common growth form, namely in leafless orchids. For Rhipsalis, also non‐Malagasy species were included in the comparison. The genus Kalanchoë was found to be dominated by species representing the CAM‐physiotype with CO₂ fixation taking place only during the night, whereas the CAM/C3‐ and the C3‐physiotypes (with limited intrinsic CAM potential) were less frequent. The opposite holds true for Angraecum. In the genus Rhipsalis, in the Didiereacean family and in the leafless orchids only the CAM‐physiotype is represented. The photosynthetic physiotypes of CAM plants were found to be related to the environmental conditions of the habitat. That is, strong CAM performers are typically abundant in the dry climatic zones or at otherwise dry niches, species of the C3‐physiotype (possibly with weak intrinsic capability of CAM performance) are distributed at humid sites and those of the CAM/C3‐physiotype occupy sites with medium and changing exposure to stress. Phenotypic plasticity of CAM, as indicated by the intraspecific variability of the δ¹³C‐values, was lower in the CAM‐physiotype compared with the CAM/C3‐physiotype. Our data support the view that strong stress leads to the dominance of highly adapted specialists among the CAM plants, with low phenotypic plasticity of the photosynthetic behaviour, whereas medium stress advances the unfolding of plastic CAM behaviour. Moreover, the data suggest that genera comprising all three physiotypes (Kalanchoë, Angraecum) are dispersed all over Madagascar, whilst groups comprising only strong CAM performers are restricted to limited areas or special types of habitats. This suggests that both genotypic diversity and phenotypic plasticity are important factors for the ecophysiological success of CAM.     

Low Interannual Variation of Mating System and Gene Flow of Symphonia globulifera in the Brazilian Amazon

Six microsatellite loci were used to compare the mating system and gene flow in two consecutive years of a natural, unlogged population of Symphonia globulifera in a 500 ha experimental plot in the Brazilian Amazon (Flona Tapajós). The species had a low density of reproductive trees per hectare (   d = 0.46  trees/ha). We analyzed 205 trees and 261 and 487 open-pollinated seeds from 26 and 30 mother-trees in the years 2002 and 2003, respectively. A significant spatial genetic structure was detected for the adult trees for distances up to 100 m. We observed only small interannual differences in multilocus outcrossing rate (     ,     ), biparental inbreeding (     ,     ), and paternity correlation (     ,     ). The number of pollen donors contributing to mating of each tree in both years was estimated to be low (     ). Using TwoGener analysis to calculate the density of reproductive trees and the distance of pollen dispersal for normal and exponential models, the lowest error was detected for exponential model. For this model, the estimated density of reproductive trees was lower in 2002 (     trees/ha) than 2003 (     trees/ha), resulting in a higher distance of pollen dispersal in 2002 (     m) than 2003 (     m), although these changes did not affect the outcrossing and correlated mating rates.     

Phenotypic Plasticity in the Reproductive Behavior of Female Sand Tilefish, Malacanthus plumieri

Female sand tilefish (Malacanthus plumieri) inhabiting a deep channel in the fringing reef at Glover's Atoll, Belize (channel females) spawned planktonic eggs more frequently than those occupying the shallow sand‐rubble slopes adjacent to patch coral reefs inside the atoll lagoon (reef‐slope females). We tested five non‐exclusive hypotheses to explain habitat differences in female spawning frequency. We found no evidence that spawning frequency variation was a consequence of differences in food availability, variation in male fertility, or the intensity of predation on spawned eggs. On reef slopes, barracuda stalked tilefish near their benthic burrows, whereas these piscivores attacked channel tilefish by diving suddenly from higher in the water column. Differences in the hunting behavior of barracuda suggested that the behavior of tilefish females might be influenced by temporal variation in predation risk (risk allocation hypothesis). Consistent with this hypothesis, reef‐slope females had a much higher frequency of retreats to burrows in response to barracuda, spent more time burrowing and ventured less far from these refugia in response to a simulated predatory threat. As predicted by the risk allocation hypothesis, reef‐slope females also had lower and more variable frequencies of foraging bites, and shorter and more variable travel distances to forage than channel females. Estimated mortality from predation was over nine times higher in channel tilefish. Consistent with the hypothesis that investment in current vs. future reproduction is influenced by rates of adult mortality (mortality risk hypothesis), channel females invested more supplemental energy in egg production whereas reef‐slope females invested more in growth. Our results indicate that behavioral and life‐history traits of female tilefish show phenotypic plasticity depending upon the nature and intensity of localized predation risk.     

Phenotypic Integration and the Plasticity of Integration in an Amphicarpic Annual

In annual plants, including amphicarpic annuals, variation in light availability can evoke phenotypic plasticity in multiple traits. We examined plasticity to light availability of vegetative and reproductive performance traits in Amphicarpaea bracteata (Fabaceae) by developing and evaluating three path-analysis models using data from a greenhouse study. To assess whether light availability altered the phenotypic integration of these performance traits, we examined the models' fit to data collected within a high- or a low-light treatment. We also examined whether a single model or alternate models were required to fit data from the two contrasting light treatments. Using our path-analysis approach, we also made comparisons among three population types: shade- and sun-native populations of the widespread variety A. bracteata var. bracteata and sun-native populations of the variety A. bracteata var. comosa. Although each type of population was somewhat distinctive in patterns of integration and in the plasticity of integration, patterns did not correspond to contrasting ecological affinity, i.e., shade- and sun-native population types or to genetic relatedness of the two varieties. Counter to the prediction that selection regimes involving variation in one or more environmental factor favor intermediate levels of integration, phenotypic integration in A. bracteata was very flexible, with plasticity occurring in a trait-by-trait manner. In particular, there was an inverse relationship between aerial and subterranean reproductive modes in low but not high light. Previous studies of amphicarpic annuals have not observed this type of environment-specific life history trade-off.