Genetic Variation In Natural Populations Research Articles

Bonobos' saliva remaining on the pith of terrestrial herbaceous vegetation can serve as non-invasive wild genetic resources.

Evaluating the genetic diversity of natural populations of endangered species is important for conservation. Although the genetic analysis of wildlife usually requires collecting DNA non-invasively, the variety of non-invasive DNA sampling methods is limited for each species. We present a method to obtain DNA of an endangered species, the bonobo (Pan paniscus), in which the pith of the terrestrial herbaceous vegetation (THV) that they consumed was newly utilized. We investigated the (1) frequency of encountering remnant saliva on three types of THV pith; (2) concentrations of DNA in the saliva samples by the real-time quantitative PCR; and (3) rates of positive PCR, accurate genotyping, and allelic drop out by analyzing two autosomal microsatellite loci (D7s817 and D9s910). The number of remnant saliva samples was recorded by following the bonobo groups on a daily basis. The frequency of encountering DNA samples was higher in saliva samples than in fecal samples. More than half of the saliva samples remaining on two types of THV pith provided sufficient concentrations of bonobo DNA (> 200pg/μl). Rates of positive PCR and accurate genotyping were high, and allelic drop out rate was low when the amount of template DNA was above 200pg per reaction. Our results suggest that the remnants of bonobo saliva on the pith of THV are a potential resource for obtaining DNA, and better than other kinds of samples from the perspective of the abundant sampling opportunities.

Genetic diversity in natural populations of Hancornia speciosa Gomes: Implications for conservation of genetic resources

ABSTRACT The continuing fragmentation of forests has been a threat to the maintenance of genetic resources. Genetic diversity is fundamental to the survival of species in natural environments in the long term, as well as being the basis for genetic improvement. The objective of this study was to evaluate the genetic diversity in natural populations of Hancornia speciosa and to contribute to the development of conservation strategies. We sampled 105 individuals of H. speciosa, distributed in seven populations. The ISSR (Inter-Simple Sequence Repeat) markers provided 70 loci, of which 81% were polymorphic. The mean genetic diversity of Nei (h) was 0.19, and the Shannon index (I) was 0.27. The h and I diversity indices ranged respectively from 0.16 to 0.24 in the PAD (Parque das Dunas) population and from 0.21 to 0.29 in MAC (Macaíba) population. Resulting from a Bayesian analysis, the genotypes were divided into four groups (K = 4). The allelic diversity patterns observed indicated the occurrence of the genetic bottleneck in all populations, according to the stepwise mutation model (SMM). The infinite allele model (IAM) revealed an imbalance between mutation and genetic drift only in the PAD population. Genetic conservation strategies for H. speciosa should cover each genetic group that was differentially structured. We recommend in situ conservation and the creation of germplasm banks, especially with the PAD population which demonstrated the lower genetic diversity and decreased effective population size according to the two mutational models.

Genetic and phenotypic differentiation of lumpfish (Cyclopterus lumpus) across the North Atlantic: implications for conservation and aquaculture.

Demand for lumpfish (Cyclopterus lumpus) has increased exponentially over the last decade, both for their roe, which is used as a caviar substitute, and increasingly also as cleaner fish to control sea lice in salmon farming. The species is classified as Near Threatened by the IUCN and there are growing concerns that over-exploitation of wild stocks and translocation of hatchery-reared lumpfish may compromise the genetic diversity of native populations. We carried out a comparative analysis of genetic and phenotypic variation across the species’ range to estimate the level of genetic and phenotypic differentiation, and determined patterns of gene flow at spatial scales relevant to management. We found five genetically distinct groups located in the West Atlantic (USA and Canada), Mid Atlantic (Iceland), East Atlantic (Faroe Islands, Ireland, Scotland, Norway and Denmark), English Channel (England) and Baltic Sea (Sweden). Significant phenotypic differences were also found, with Baltic lumpfish growing more slowly, attaining a higher condition factor and maturing at a smaller size than North Atlantic lumpfish. Estimates of effective population size were consistently low across the North East Atlantic (Iceland, Faroe Islands and Norway), the area where most wild lumpfish are fished for their roe, and also for the aquaculture industry. Our study suggests that some lumpfish populations are very small and have low genetic diversity, which makes them particularly vulnerable to over-exploitation and genetic introgression. To protect them we advocate curtailing fishing effort, closing the breeding cycle of the species in captivity to reduce dependence on wild stocks, restricting the translocation of genetically distinct populations, and limiting the risk of farm escapes.

Genetic, evolutionary and phylogenetic aspects of the plastome of annatto (Bixa orellana L.), the Amazonian commercial species of natural dyes.

The plastome of B. orellana reveals specific evolutionary features, unique RNA editing sites, molecular markers and the position of Bixaceae within Malvales. Annatto (Bixa orellana L.) is a native species of tropical Americas with center of origin in Brazilian Amazonia. Its seeds accumulate the apocarotenoids, bixin and norbixin, which are only found in high content in this species. The seeds of B. orellana are commercially valued by the food industry because its dyes replace synthetic ones from the market due to potential carcinogenic risks. The increasing consumption of B. orellana seeds for dye extraction makes necessary the increase of productivity, which is possible accessing the genetic basis and searching for elite genotypes. The identification and characterization of molecular markers are essential to analyse the genetic diversity of natural populations and to establish suitable strategies for conservation, domestication, germplasm characterization and genetic breeding. Therefore, we sequenced and characterized in detail the plastome of B. orellana. The plastome of B. orellana is a circular DNA molecule of 159,708bp with a typical quadripartite structure and 112 unique genes. Additionally, a total of 312 SSR loci were identified in the plastome of B. orellana. Moreover, we predicted in 23 genes a total of 57 RNA-editing sites of which 11 are unique for B. orellana. Furthermore, our plastid phylogenomic analyses, using the plastome sequences available in the plastid database belonging to species of order Malvales, indicate a closed relationship between Bixaceae and Malvaceae, which formed a sister group to Thymelaeaceae. Finally, our study provided useful data to be employed in several genetic and biotechnological approaches in B. orellana and related species of the family Bixaceae.

Relationship between Genetic Variability and Land Use and Land Cover in Populations of Campomanesia adamantium (Myrtaceae)

Campomanesia adamantium is an endemic plant of Cerrado biome that has potential for cultivation because its fruits have culinary and medicinal uses. However, genetic diversity studies using molecular markers with Cerrado species are scarce, and the inadequate extractive exploitation of fruits and the expansion of agricultural frontiers may also affect genetic variability. Therefore, studies in this field are of interest as they can provide sources for conservation and breeding programs. In this context, we investigated the genetic diversity of native populations of C. adamantium from different sites and the relationship between genetic variability and the land use and land cover of each site. A total of 207 plants were sampled in seven sites and characterized with seven polymorphic microsatellite markers. The use and coverage of land were mapped based on aerial images, and the land was classified into different categories. The genetic diversity was high in all populations, with low levels of differentiation due to allele sharing, mainly in Mato Grosso do Sul and Paraguay populations. The geographically closest populations were more genetically similar. The use and coverage of land indicated that intense agriculture promotes a significant decrease in genetic variability.

Female-biased dispersal and non-random gene flow of MC1R variants do not result in a migration load in barn owls.

Non-random gene flow is a widely neglected force in evolution and ecology. This genotype-dependent dispersal is difficult to assess, yet can impact the genetic variation of natural populations and their fitness. In this work, we demonstrate a high immigration rate of barn owls (Tyto alba) inside a Swiss population surveyed during 15 years. Using ten microsatellite loci as an indirect method to characterize dispersal, two-third of the genetic tests failed to detect a female-biased dispersal, and Monte Carlo simulations confirmed a low statistical power to detect sex-biased dispersal in case of high dispersal rate of both sexes. The capture-recapture data revealed a female-biased dispersal associated with an excess of heterozygote for the melanocortin-1 receptor gene (MC1R), which is responsible for their ventral rufous coloration. Thus, female homozygotes for the MC1RWHITE allele might be negatively selected during dispersal. Despite the higher immigration of females that are heterozygote at MC1R, non-random gene flow should not lead to a migration load regarding this gene because we did not detect an effect of MC1R on survival and reproductive success in our local population. The present study highlights the usefulness of using multiple methods to correctly decrypt dispersal and gene flow. Moreover, despite theoretical expectations, we show that non-random dispersal of particular genotypes does not necessarily lead to migration load in recipient populations.

DIVERSIDADE GENÉTICA E ESTRUTURA POPULACIONAL DE JATOBÁ: UMA ESPÉCIE COM POTENCIAL ECONÔMICO PARA A AMAZÔNIA

O jatobá (Hymenaea courbaril L.) é uma espécie que apresenta importância ecológica e ocorre em diferentes regiões geográficas do Brasil. Conhecer e avaliar a existência de locais com maior variabilidade genética pode auxiliar em programas e ações de conservação. Neste contexto, o presente estudo objetivou avaliar a diversidade genética e a estrutura em populações naturais de jatobá com ocorrência na Amazônia mato-grossense por meio de marcadores ISSR. Foram amostrados 54 indivíduos em 3 populações, sendo uma no município de Marcelândia (MA=24) e duas no município de Alta Floresta (Comunidade Central AF=17 e Pista do Cabeça PC=13 indivíduos. DNA genômico total foi extraído de tecido foliar pelo método CTAB. Os 54 indivíduos foram genotipados com 10 primers ISSR. Foram amplificados um total de 110 fragmentos, sendo 78,2% polimórficos. Os maiores índices de diversidade foram encontrados na população de MA (H=0.25; I=0.37 e %P=65.45). A distância genética foi maior entre as populações dos dois municípios (0.17 entre MA e AF; 0.16 entre MA e PC). A análise de variância molecular (AMOVA) indicou que 31.79% da variância total está entre populações e 68.21% dentro de populações. Há diversidade genética nas populações nativas de jatobá na Amazônia mato-grossense. Recomenda-se que sejam preservados indivíduos de ambas as populações, a fim de garantir a manutenção da variabilidade genética e a conservação efetiva da espécie na Amazônia mato-grossense.

Comparing the effectiveness between issr and ssr markers in assessing genetic diversity of natural populations of Dacrydium elatum in Tay Nguyen, Vietnam

The two techniques, ISSR (27 markers) and SSR (20 markers), were used to compare the effectiveness and 
 to assess genetic diversity of 70 Dacrydium elatum samples collected in Lam Dong, Kon Tum, Dak Lak, and Gia Lai. The results showed 38/47 polymorphic markers (23/27 ISSR and 15/20 SSR markers) and 180 amplified DNA fragments, in which 85/127 (66.93%) and 46/53 (86.79%) were polymorphic for ISSR and SSR markers, respectively. Generally, the average values among the genetic diversity parameters of the populations for SSR (Hj = 0.213; Ne = 1.566, I = 0.444; He = 0.301; h = 0.228; and PPB = 72.50%) were higher than those for ISSR (Hj = 0.155; Ne = 1.142, I = 0.125; He = 0.083; h = 0.074 and PPB = 25.07%). The correlation coefficient between genetic distance measured with ISSR and combining ISSR + SSR was higher (r = 0.92) than that measured with SSR and combining ISSR + SSR (r = 0.65). There was not much difference in the total level of molecular variance (AMOVA) among populations and among individuals when analyzing ISSR and SSR data separately or combining both data. The three dendrograms constructed based on similarity matrix generated by ISSR, SSR and ISSR + SSR data were similar and they all divided the 70 D. elatum samples into two main groups with genetic similarity coefficients ranged from 74 to 99%, 78.4 to 100% and 76 to 96.6%, respectively. The obtained results indicated D. elatum species should be protected at the population level.

Genetic diversity of populations of the dioecious Myrsine coriacea (Primulaceae) in the Atlantic Forest

ABSTRACT Although a species’ sexual system may influence the genetic diversity of its populations in their natural environment, there have been few such studies involving indigenous species of the Atlantic Forest. Here we study Myrsine coriacea, a dioecious tree widely used in reforestation programs despite a lack of information about its natural interpopulation genetic variation. To address this knowledge gap, intra- and interpopulation genetic diversity were measured for male and female individuals of ten natural populations using ISSR markers. Greater intrapopulation genetic diversity indicated interpopulation gene flow, regardless of isolation and distance between populations. Multivariate analyses detected significant differences in genetic diversity between populations, but not between males and females, which indicates that genetic diversity did not differ between the two sex morphs. Distance between populations was unrelated to genetic diversity. Myrsine coriacea has not experienced a loss of genetic variability despite the characteristic segregated spatial distribution of its populations. These results suggest that obligatory cross-pollination and dispersal by birds may be important mechanisms for the maintenance of genetic diversity in natural populations of M. coriacea.

Genetic resource management for enhancing saffron productivity in Jammu and Kashmir

Lack of high yielding cultivars due to triploid nature of saffron is a major concern of low productivity. To explore and utilize available genetic variability in natural populations of Jammu and Kashmir, about 2500 saffron accessions collected from saffron growing areas of Jammu and Kashmir during 2002-2006 were subjected to variability and divergence studies at genetic and molecular level. Selected lines from natural population exhibited a wide range of variability for economic, morphological and corm attributing traits indicating considerable scope for saffron improvement through clonal selection. Selection scheme for more yield gains have been designed. Stability analysis of 10 elite divergent lines confirmed that behavior of tested lines was predictable over environments for floral and yield attributing characters. Considering the desired population mean coupled with non-significant bi (equal to unity) and deviation from regression (S2di) equal to zero, two lines viz; SMD-45 and SD-3 were observed to be well adapted to all the environments. The results revealed average stability of all lines for these traits except for number of radical leaves and corm yield plot-1 (SD-3). Comparison of different stability models in terms of their relative performance for different traits under study produced uniform information and ranked lines without any major disagreement. Line SMD-45 was observed to be the most stable having high saffron yield.

Genetic diversity assessed by microsatellite markers in the amphicarpic species Trifolium polymorphum Poir.

Trifolium polymorphum Poir. is an amphicarpic forage legume from southern Brazil, Uruguay, Argentina, Paraguay and Chile. Information on the genetic diversity of natural populations in natural grasslands in southern Brazil is limited. In order to increase the knowledge about this species, an analysis of the genetic diversity was carried out in 10 natural populations of T. polymorphum with the use of 20 microsatellite markers. The expected heterozygosity in T. polymorphum populations ranged from 0.40 to 0.43, with a mean of 0.42. A total of 193 alleles were detected with a mean of 9.3 alleles per locus and polymorphic information content (PIC) for these markers of 0.62 to 0.89 with a mean of 0.84.The grouping based on the Jaccard's coefficient of similarity classified populations, regardless of their regions of origin, into two groups with a mean similarity coefficient of 0.32, reflecting the high genetic variability of the populations, especially those located in the Campanha phytogeographic region. This information on diversity can be used to plan future germplasm collection strategies for conservation purposes and also for the breeding of the species.

Genetic and genomic monitoring with minimally invasive sampling methods.

The decreasing cost and increasing scope and power of emerging genomic technologies are reshaping the field of molecular ecology. However, many modern genomic approaches (e.g., RAD‐seq) require large amounts of high‐quality template DNA. This poses a problem for an active branch of conservation biology: genetic monitoring using minimally invasive sampling (MIS) methods. Without handling or even observing an animal, MIS methods (e.g., collection of hair, skin, faeces) can provide genetic information on individuals or populations. Such samples typically yield low‐quality and/or quantities of DNA, restricting the type of molecular methods that can be used. Despite this limitation, genetic monitoring using MIS is an effective tool for estimating population demographic parameters and monitoring genetic diversity in natural populations. Genetic monitoring is likely to become more important in the future as many natural populations are undergoing anthropogenically driven declines, which are unlikely to abate without intensive adaptive management efforts that often include MIS approaches. Here, we profile the expanding suite of genomic methods and platforms compatible with producing genotypes from MIS, considering factors such as development costs and error rates. We evaluate how powerful new approaches will enhance our ability to investigate questions typically answered using genetic monitoring, such as estimating abundance, genetic structure and relatedness. As the field is in a period of unusually rapid transition, we also highlight the importance of legacy data sets and recommend how to address the challenges of moving between traditional and next‐generation genetic monitoring platforms. Finally, we consider how genetic monitoring could move beyond genotypes in the future. For example, assessing microbiomes or epigenetic markers could provide a greater understanding of the relationship between individuals and their environment.

Demographic history of the Magellanic Penguin (Spheniscus magellanicus) on the Pacific and Atlantic coasts of South America

Spatial subdivision, local extinction and recolonization influence the genetic variation of natural populations. Different levels of population structure can be identified in nature, from panmictic populations, in which high gene flow homogenizes diversity across localities, to metapopulations, where combinations of moderate to high levels of population differentiation and source-sink population dynamics are expected. Gene flow, dispersal and recolonization can be affected by changes in ecological conditions such as climate and resource distribution. Evaluating demographic history is crucial for understanding current population dynamics. We assessed a mitchondrial DNA (mtDNA) control region and microsatellite data for 210 Magellanic Penguins (Spheniscus magellanicus) from 13 breeding colonies on the coastlines of Chile and Argentina, covering a great portion of the species’ distribution. We found high levels of genetic diversity and detected two genetic-geographic regions, Pacific and Atlantic, probably due to interruption of the connection between the oceans during the Last Glacial Maximum (LGM), when several parts of the Magellanic Channel were connected to the continent. The Atlantic ocean colonies showed a slight differentiation between the northern and southern colonies, and the Falkand/Malvinas one seems to be a mix of northern, southern and Pacific colonies. Magellanic Penguins showed intense gene flown among colonies, and exhibited low levels of genetic differentiation in each region. Furthermore, our findings indicate that the Magellanic Penguin experienced a population expansion around 17,500 years ago, which is in agreement with the timing of a decreased sea level and the exposure of the continental shelf along the coast of Argentina and the Falkland/Malvinas Islands at the end of the LGM. Thus, our results suggest that climate changes that affect the sea level in South America can play important roles in the migration of Magellanic Penguins.

Relationship between chemotypic and genetic diversity of natural populations of Artemisia herba-alba Asso growing wild in Tunisia

A total of 80 individuals collected from eight populations growing wild in different geographic zones were considered to assess the intraspecific variability of essential oil composition, genetic diversity and population structure of Artemisia herba-alba.The essential oil composition varied significantly between populations. Essential oil profiles were classified into four chemotypes (trans-sabinyl acetate, α-thujone/trans-sabinyl acetate, camphor and α-thujone/camphor/β-thujone). Despite significant correlation between the amount of some essential oil compounds and a set of climatic data, the global chemical divergence among populations was not related to their bioclimatic and geographic appurtenances.A high level of genetic diversity within populations was revealed either with RAPD and ISSR markers (Na = 1.67, PPL = 66.5%, H = 0.26, I = 0.38 and Na = 1.7, PPL = 69.8%, H = 0.26, I = 0.38, respectively). The level of genetic diversity varied across populations and chemotypes. Populations from the α-thujone/trans-sabinyl acetate chemotype exhibited the highest genetic diversity as revealed by the RAPD markers. However, populations from α-thujone/camphor/β-thujone chemotype showed the important genetic variation determined by ISSR markers. A significant genetic differentiation among populations and among chemotypes was detected.The combined analysis showed a significant correlation (r = 0.484, p = .032) between the chemical and molecular markers. The PCA, performed on percentages of major oil compounds and the frequencies of polymorphic RAPD and ISSR bands, divided populations according to their chemotypic classification.Taking into consideration the current situation of A. herba-alba populations and their endangered habitats, these results are of value in order to ensure the in-situ and ex-situ conservation of this medicinal species.

A fast likelihood solution to the genetic clustering problem.

The investigation of genetic clusters in natural populations is an ubiquitous problem in a range of fields relying on the analysis of genetic data, such as molecular ecology, conservation biology and microbiology. Typically, genetic clusters are defined as distinct panmictic populations, or parental groups in the context of hybridisation. Two types of methods have been developed for identifying such clusters: model‐based methods, which are usually computer‐intensive but yield results which can be interpreted in the light of an explicit population genetic model, and geometric approaches, which are less interpretable but remarkably faster.Here, we introduce snapclust, a fast maximum‐likelihood solution to the genetic clustering problem, which allies the advantages of both model‐based and geometric approaches. Our method relies on maximising the likelihood of a fixed number of panmictic populations, using a combination of geometric approach and fast likelihood optimisation, using the Expectation‐Maximisation (EM) algorithm. It can be used for assigning genotypes to populations and optionally identify various types of hybrids between two parental populations. Several goodness‐of‐fit statistics can also be used to guide the choice of the retained number of clusters.Using extensive simulations, we show that snapclust performs comparably to current gold standards for genetic clustering as well as hybrid detection, with some advantages for identifying hybrids after several backcrosses, while being orders of magnitude faster than other model‐based methods. We also illustrate how snapclust can be used for identifying the optimal number of clusters, and subsequently assign individuals to various hybrid classes simulated from an empirical microsatellite dataset. snapclust is implemented in the package adegenet for the free software R, and is therefore easily integrated into existing pipelines for genetic data analysis. It can be applied to any kind of co‐dominant markers, and can easily be extended to more complex models including, for instance, varying ploidy levels. Given its flexibility and computer‐efficiency, it provides a useful complement to the existing toolbox for the study of genetic diversity in natural populations.

Genetic and ecological niche modeling of Calydorea crocoides (Iridaceae): an endemic species of Subtropical Highland Grasslands.

Evolutionary analyses have been widely used for evaluation of genetic diversity of natural populations and correlate these data to the fitness of the species, especially in the case of threatened species. Calydorea crocoides occurs in a restricted area at altitudes from 800 to 1500 m in southern Brazil and is considered endangered. A study assessing genetic diversity, cytogenetic features and ecological niche was performed aiming to characterize C. crocoides by multidisciplinary approaches. Molecular data highlighted that most of the total variation (76%; p < 0.001) was found within populations and the parameters of genetic diversity were high at the species level (PPB = 98.97%; I = 0.4319; h = 0.2821). Gene flow (Nm) was estimated in 0.97 individuals per generation. Cytogenetically, C. crocoides presents a bimodal karyotype and low asymmetry. DAPI banding pattern was uniform, but the CMA-signal evidenced a pericentric inversion in the population ESC688. The species presents high pollen viability and two different morphologies of pollen grains. Our data showed high levels of polymorphism maintained in this species that could ensure conservationist practices in which the main goal is to preserve the evolutionary potential of the species through the maintenance of genetic diversity.

Development of microsatellite markers for Myracrodruon urundeuva (F.F. & M.F. Allemão), a highly endangered species from tropical forest based on next-generation sequencing.

Myracrodruon urundeuva is a tree species of high economic importance due the strength and durability of its wood. Threatened of extinction in Brazil, it is present only in a few forest remnants, mostly in conservation units. Currently, there is little information on the genetic diversity of natural populations in Brazil and even less information about the genome of this species. Here, new species-specific microsatellite loci were developed based on next-generation sequencing (Illumina). More than 100,000 loci were identified in the run, with di- to hexanucleotides motifs. Of these, 20 loci were selected for validation in 30 individuals, with 15 successfully polymorphic loci detected. The number of alleles ranged among loci from 3 to 16, with an average of 7.73, expected (H e ) and observed (H o ) heterozygosity ranged from 0.246 to 0.902 and from 0.103 to 0.867, respectively. These results point out that these new set of markers has a great potential for use in population genetic studies for genetic conservation of the species.

Spatio-temporal ecological and evolutionary dynamics in natural butterfly populations

Long term studies of wild populations indicate that natural selection can cause rapid and dramatic changes in traits, with spatial and temporal variation in the strength of selection a critical driver of genetic variation in natural populations. In 2012, we began a long term study of genome-wide molecular evolution in populations of the butterfly Lycaeides ideas in the Greater Yellowstone Area (GYA). We aimed to quantify the role of environment-dependent selection on evolution in these populations. Building on previous work, in 2017 we collected new samples, incorporated distance sampling, and surveyed the insect community at each site. We also defined the habitat boundary at anew, eleventh site. Our preliminary analyses suggest that both genetic drift and selection are important drivers in this system.&#x0D; &#x0D; Featured photo from Figure 1 in report.

Cost of resistance to trematodes in freshwater snail populations with low clonal diversity

BackgroundThe persistence of high genetic variability in natural populations garners considerable interest among ecologists and evolutionary biologists. One proposed hypothesis for the maintenance of high levels of genetic diversity relies on frequency-dependent selection imposed by parasites on host populations (Red Queen hypothesis). A complementary hypothesis suggests that a trade-off between fitness costs associated with tolerance to stress factors and fitness costs associated with resistance to parasites is responsible for the maintenance of host genetic diversity.ResultsThe present study investigated whether host resistance to parasites is traded off with tolerance to environmental stress factors (high/low temperatures, high salinity), by comparing populations of the freshwater snail Melanoides tuberculata with low vs. high clonal diversity. Since polyclonal populations were found to be more parasitized than populations with low clonal diversity, we expected them to be tolerant to environmental stress factors. We found that clonal diversity explained most of the variation in snail survival under high temperature, thereby suggesting that tolerance to high temperatures of clonally diverse populations is higher than that of populations with low clonal diversity.ConclusionsOur results suggest that resistance to parasites may come at a cost of reduced tolerance to certain environmental stress factors.

The effects of leaf litter and competition from hybrid cattails (Typha × glauca) on the seed germination and seedling performance of its parental species

Invasive species affect native vegetation through combinations of direct interactions (e.g. competition) and indirect interactions (e.g. altered pollination regimes) mediated through the occupation of shared environments. Hybrid cattails (Typha×glauca) are rapidly displacing their parental species, the native broadleaf cattail (T.latifolia) and the introduced narrow-leaf cattail (T. angustifolia), but the mechanisms involved are poorly understood. We evaluated the potential for direct and indirect interactions among cattails using a series of experiments. First, we evaluated whether seed germination was affected by hybrid leaf litter using a factorial experiment in which we tested for indirect effects of leaf-litter leachate and shading. Second we tested whether these indirect effects of hybrid leaf litter affected seedling performance using a factorial common-garden experiment. Finally, we tested for direct competitive interactions between hybrid and native cattail seedlings. One or more components of hybrid leaf-litter leachate strongly reduced the germination of the parental cattail species, but not that of the hybrid. There was no evidence that direct competitive interactions affected seedling performance. Because regular recruitment by seeds appears to be important in shaping patterns of genetic diversity in natural populations, our findings provide a mechanism for explaining the dominance of hybrid cattails in eastern North America.