Greater Gene Diversity Research Articles

Relevance of iron metabolic genes in biofilm and infection in uropathogenic Proteus mirabilis.

The microorganisms are found in the environment, forming sessile communities embedded in an extracellular matrix of their own production, called biofilm. These communities have a great relevance in the clinical context, since they are associated with infections caused by biofilm in medical implants, such as urinary catheters. The development of biofilms is a complex process where a great diversity of genes participate. The present work is based on the study of genes related to iron metabolism and its implication in the development of P. mirabilis biofilms and pathogenicity. For this study, two mutant strains defective in biofilm formation were selected, generated by the interruption of genes that encoded non-heme ferritin and TonB-dependent receptor. The mutations influence on the development of the biofilm was evaluated by different approaches. The complexity of the biofilm was analyzed using Confocal Laser Microscopy and image analysis. The mutants infectivity potential was assessed in two experimental mice models of urinary tract infection. The results obtained in the present work show us the role of the ferritin and a TonB-associated porin protein over the initial and later stages of biofilm development. Moreover, in the ascending UTI mouse model, both mutants failed to colonize the urinary tract. In CAUTI models, ferritin mutant damaged the bladder similarly to wild type but the Ton-B mutant was unable to generate infection in the urinary tract. The results obtained in the present work confirm the relevant role that iron metabolism genes have in P. mirabilis biofilm development and for infection in the urinary tract.

Relationships between Some Biodiversity Indicators and Crown Damage of Pinus sylvestris L. in Natural Old Growth Pine Forests

Biodiversity at the species and individual levels is one of the fundamental elements characterizing an ecosystem. It is assumed that the greater the level of biodiversity, the more tolerant the environment is to changes in external conditions. In recent years, dynamic climate change has negatively impacted the health of many forest trees across Europe, in particular Scots pine. Tree health is commonly characterized by crown defoliation. The study presented here describes and correlates crown defoliation with biodiversity indicators at the species and individual tree levels. Research was conducted in two national parks in Poland (Kampinoski and Bory Tucholskie). Since stands have been under legal protection for many years and forest management is not practiced there, stand development processes taking place there are similar to natural ones. This study provided empirical data on ecosystem response to external stresses based on species and genetic structure. The results confirm differing health of the populations, which results from, among other factors, stand age and the environmental conditions in which they grow. Pine stands in both national parks are genetically diverse but with low genetic variability. Differences in stand health are related to the number of alleles forming the genetic pool. This conclusion is supported by a high correlation coefficient for interactions between defoliation, the number of alleles, and the Shannon index for genotypes. This suggests that greater gene diversity is likely to provide a wider range of phenotypic responses to environmental change.

Extreme seascape drives local recruitment and genetic divergence in brooding and spawning corals in remote north-west Australia.

Management strategies designed to conserve coral reefs threatened by climate change need to incorporate knowledge of the spatial distribution of inter‐ and intra‐specific genetic diversity. We characterized patterns of genetic diversity and connectivity using single nucleotide polymorphisms (SNPs) in two reef‐building corals to explore the eco‐evolutionary processes that sustain populations in north‐west Australia. Our sampling focused on the unique reefs of the Kimberley; we collected the broadcast spawning coral Acropora aspera (n = 534) and the brooding coral Isopora brueggemanni (n = 612) across inter‐archipelago (tens to hundreds of kilometres), inter‐reef (kilometres to tens of kilometres) and within‐reef (tens of metres to a few kilometres) scales. Initial analysis of A. aspera identified four highly divergent lineages that were co‐occurring but morphologically similar. Subsequent population analyses focused on the most abundant and widespread lineage, Acropora asp‐c. Although the overall level of geographic subdivision was greater in the brooder than in the spawner, fundamental similarities in patterns of genetic structure were evident. Most notably, limits to gene flow were observed at scales <35 kilometres. Further, we observed four discrete clusters and a semi‐permeable barrier to dispersal that were geographically consistent between species. Finally, sites experiencing bigger tides were more connected to the metapopulation and had greater gene diversity than those experiencing smaller tides. Our data indicate that the inshore reefs of the Kimberley are genetically isolated from neighbouring oceanic bioregions, but occasional dispersal between inshore archipelagos is important for the redistribution of evolutionarily important genetic diversity. Additionally, these results suggest that networks of marine reserves that effectively protect reefs from local pressures should be spaced within a few tens of kilometres to conserve the existing patterns of demographic and genetic connectivity.

Molecular profiling in relation to drought tolerance in advance breeding lines of rice using microsatellite markers

Using agro-morphological characters and microsatellite markers, advance breeding lines of rice were discriminated for their ability to tolerate drought stress at reproductive stage. Experimental materials consisting of 17 advance breeding lines and a check were evaluated in randomized block design with three replications under irrigated condition and drought condition created under rainout shelter during three consecutive years. An analysis of variance revealed significant differences among the genotypes for all the ten agro-morphological characters evaluated under both the conditions across the years. Principal component analysis showed the relative importance of root length, number of tillers per plant, number of grains per panicle, harvest index and grain yield per plant among agro-morphological characters and stress tolerance level, stress susceptibility index, stress tolerance index and drought tolerance efficiency among drought tolerance indices as the important classification variables. Relative mean performance in respect of grain yield as well as drought tolerance indices reflected remarkably greater degree of drought tolerance in 11 advance breeding lines and the check, discriminating them from remaining entries under evaluation. Utilizing a panel of 32 microsatellite primers, selective amplification of targeted genomic regions revealed that the primers RM 72, RM 163, RM 212, RM 225, RM 231, RM 302, RM 327, RM 518, RM 521, RM 555, RM 1349, RM 3549 and RM 5443 were highly informative with greater gene diversity and discrimination ability. Hierarchical cluster analysis based on molecular profiles discriminated the entries into five genotypic groups and drought tolerant entries were accommodated into three distinct groups with remarkably greater efficiency (85.7%). Principal coordinate analysis based two dimensional plots of microsatellites dependent genetic profiles displayed a very close correspondence with the genotypic clustering pattern revealed from a perusal of dendrogram. Sequential exclusion of primers in cluster analysis led to identification of RM 212, RM 231, RM 324, RM 431, RM 521, RM 3549 and RM 6374 as the most useful primers for discrimination of drought tolerant and susceptible lines of rice. Molecular profiling based on these markers can be utilized as efficient tools for discrimination and identification of drought tolerant lines.

Systematic Evaluation of Landrace Tea Populations in Northern Sichuan, China, Based on Morphology, DNA Markers, and Biochemistry Analyses

Landrace tea populations are important recourses for germplasm conservation and selection of elite tea clone cultivars. To understand their genetic diversity and use them effectively for breeding, two traditional landrace tea populations, Beichuan Taizicha (BCTZ) and Nanjiang Dayecha (NJDY), localized to northern Sichuan, were evaluated for morphological characters, simple sequence repeat (SSR)–based DNA markers and the contents of biochemical components. A wide range of morphological variation and a moderately high level of DNA polymorphism were observed from both BCTZ and NJDY. NJDY had on average, bigger leaves, larger flowers, higher total catechins (TCs), and greater gene diversity (GD) than BCTZ. Interestingly, samples from BCTZ had a wide range in the ratio of galloylated catechins to nongalloylated catechins (G/NG) (1.83–8.12, cv = 48.8%), whereas samples from NJDY were more variable in total amino acid (TAA) content (25.3–50.8 mg·g−1 dry weight) than those from BCTZ. We concluded that the two Camellia sinensis landrace populations are of great interest for both individual selection breeding and scientific studies.

PCR-Based Analysis of ColE1 Plasmids in Clinical Isolates and Metagenomic Samples Reveals Their Importance as Gene Capture Platforms.

ColE1 plasmids are important vehicles for the spread of antibiotic resistance in the Enterobacteriaceae and Pasteurellaceae families of bacteria. Their monitoring is essential, as they harbor important resistant determinants in humans, animals and the environment. In this work, we have analyzed ColE1 replicons using bioinformatic and experimental approaches. First, we carried out a computational study examining the structure of different ColE1 plasmids deposited in databases. Bioinformatic analysis of these ColE1 replicons revealed a mosaic genetic structure consisting of a host-adapted conserved region responsible for the housekeeping functions of the plasmid, and a variable region encoding a wide variety of genes, including multiple antibiotic resistance determinants. From this exhaustive computational analysis we developed a new PCR-based technique, targeting a specific sequence in the conserved region, for the screening, capture and sequencing of these small plasmids, either specific for Enterobacteriaceae or specific for Pasteurellaceae. To validate this PCR-based system, we tested various collections of isolates from both bacterial families, finding that ColE1 replicons were not only highly prevalent in antibiotic-resistant isolates, but also present in susceptible bacteria. In Pasteurellaceae, ColE1 plasmids carried almost exclusively antibiotic resistance genes. In Enterobacteriaceae, these plasmids encoded a large range of traits, including not only antibiotic resistance determinants, but also a wide variety of genes, showing the huge genetic plasticity of these small replicons. Finally, we also used a metagenomic approach in order to validate this technique, performing this PCR system using total DNA extractions from fecal samples from poultry, turkeys, pigs and humans. Using Illumina sequencing of the PCR products we identified a great diversity of genes encoded by ColE1 replicons, including different antibiotic resistance determinants, supporting the previous results achieved with the collections of bacterial isolates. In addition, we detected cryptic ColE1 plasmids in both families with no known genes in their variable region, which we have named sentinel plasmids. In conclusion, in this work we present a useful genetic tool for the detection and analysis of ColE1 plasmids, and confirm their important role in the dissemination of antibiotic resistance, especially in the Pasteurellaceae family of bacteria.

Autism is an Acquired Cellular Detoxification Deficiency Syndrome with Heterogeneous Genetic Predisposition

Neurodevelopmental disorders, including Autism Spectrum Disorders, have a complex biological and medical basis involving diverse genetic risk and myriad environmental exposures. Teasing apart the role of specific stressors is made challenging due to the large number of apparently contributing associations, gene X environment interactions and phenomimicry [1]. Historically, these conditions have been rare, making causality assessment at the population level infeasible. Only a few vaccines have been tested for association with autism, and it has been shown that improved diagnosis only explains a percentage of the increase in diagnosis. Now, the rates are so high in some countries that public school programs cannot handle the large numbers of special needs students, and professionals are quitting their jobs due to security concerns. Here, I review evidence of the pathophysiology of that reconciles the apparent paradox between the high degree of causal heterogeneity in environmental toxins, the absence of common autism gene, and the high degree of genetic concordance (heritability) of ASD and ASD-like traits. In brief, the sampling of environmental toxins, and thus the environmental toxin sampling liability for ASD varies among families involving different local exposures following injury to normal cellular endoplasmic detoxification and mitochondrial processes from toxic metals. The literature strongly supports that is most accurately seen as an acquired cellular detoxification deficiency syndrome with heterogeneous genetic predisposition that manifests pathophysiologic consequences of accumulated, run-away cellular toxicity. At a more general level, it is a form of a toxicant-induced loss of tolerance of toxins, and of chronic and sustained ER overload (ER hyper stress), contributing to neuronal and glial apoptosis via the unfolded-protein response (UPR). Inherited risk of impaired cellular detoxification and circulating metal retoxification in neurons and glial cells accompanied by chronic UPR is key. This model explains the aberrant protein disorder observed in ASD; the great diversity of genes that are found to have low, but real contributions to ASD risk and the sensitivity of individuals with ASD to environmental toxins. The hindrance of detoxification and loss of cellular energetics leads to apoptosis, release of cytokines and chronic neuroinflammation and microglial activation, all observed hallmarks of ASD. Interference with the development of normal complex (redundant) synapses leads to a pathological variation in neuronal differentiation, axon and dendrite outgrowth, and synaptic protein expression. The most general outcomes are overall simplification of gross synaptic anatomy and, neurofunctionally, a loss of inhibitory feedback and aberrations in long-term connections between distant regions of the brain. Failed resolution of the ER stress response leads to re-distribution of neurotoxic metals, and the impaired neurocellular processes lead to subsequent accumulation of a variety of additional types of toxins with secondary, sometime life-threatening comorbidities such as seizures, with overlapping (not mutually exclusive) causality. Reduction of exposure to toxins known to cause mitopathy (mercury) and endoplasmic reticulum dysfunction (mercury and aluminum) during pregnancy and during the early years of development will reduce the risk of ER overload and ER hyper stress, and of ASD diagnosis. This knowledge has immediate clinical translational relevance: post-vaccination symptoms should be heeded as a sign of susceptibility to toxin; Vitamin D can be increased to drive the healthy early phases of the UPR, and mutations in ASD genes encoding proteins with high intrinsic disorder may contraindicate the use of aluminum and mercury for carriers of risk alleles. Clinicians should be alert to a patient’s Vitamin D receptor (BSM) mutational status prior to recommending increased doses. Approaches to improving overall brain health in autistics must be de-stigmatized and given high priority. Reduction of lifetime exposures of industrial and agricultural toxins will improve brain health for the entire human population. Purely genetic studies of ASD, and studies that do not include vaccination as an environmental exposure with potential liability and interactions with genes, are unethical. To qualify as science, studies must test plausible hypotheses, and the absence of association from poorly designed, unethically executed, and underpowered and unsound whole-population association studies have been harmful distractions in the quest for understanding. Skilled paediatricians and ob/gyns will seek evidence of genetic predisposition to environmental susceptibility in the form of non-synonymous substitutions in brain proteins that require ER-folding, and they will provide informed cautions on exposures (from all sources) to environmental toxins to patients and parents of patients with signs of metal and chemical sensitivity. To aid in this, a list of ASD environmental susceptibility protein-encoded genes is presented. A clinical Exome sequence test, followed by loss of function prediction analysis, would point to individuals most susceptible to vaccine metal-induced ER hyper stress leading to failed cellular detoxification.

Choice of microsatellite markers for isolation of fertility restorers of wild abortive (WA) type cytoplasmic male sterility in rice

Simple sequence length polymorphism was examined in a set of eight effective restorers, four partial restorers, two weak maintainers and four complete maintainers of WA type CMS system in rice using a set of thirty-two microsatellite primer pairs in order to assess the nature and extent of genetic variation among them at molecular level. Altogether 248 allelic variants were detected with an average of 7.75 alleles per primer pairs. Polymorphic information content ranged from 0.508 for RM 6737 to 0.882 for RM 1 with an average value of 0.740 per primer pair. Amongst the primer pairs used, RM 1, RM 206, RM 591 RM 3873 and RM 8146 had remarkably higher number of allelic variants with greater gene diversity and genotype discrimination ability. Using similarity coefficient in numerical taxonomic approach of classification, the entries were differentiated and classified into different groups. Analysis based on molecular profiles allowed discrimination of effective fertility restorers from rest of the entries including partial fertility restorers, weak sterility maintainers and complete sterility maintainers. Principal coordinate analysis based two dimensional plotting of genetic profiles completely supported the results obtained from hierarchical classification of entries and effective fertility restorers were distinctly discriminated from the remaining entries. Four microsatellite primer pairs namely, RM 171, RM 315, RM 3873 and RM 6100, which allowed unambiguous discrimination of the eight effective fertility restorers from rest of the entries. These microsatellite primer pairs, may be further utilized in identification of effective fertility restorers of WA based CMS system in rice.

Genetic diversity and genetic structure of Corydalis tomentella Franch. (Papaveraceae), an endangered herb species from Central China

Corydalis tomentella Franch. (Papaveraceae), a species endemic to Central China, occurs within specialized habitats of limestone cliffs. To date, extensive harvesting by local people for medical use has led to a sharp decline in wild populations of this plant. To investigate the genetic diversity and genetic structure of the species, differences in the composition of one nuclear DNA (nDNA) locus (NADPH) and two chloroplast DNA (cpDNA) fragments (trnH-psbA and trnG introns) from wild populations of this plant were analysed. Six chlorotypes and 17 nuclear genotypes were identified in a survey of 8 populations distributed in the current geographic regions of C. tomentella. Two cpDNA haplotypes were shared in two present distribution regions, Shennongjia and Nanchuan in Central China, while there were no similar nDNA genotypes in these regions. As a whole, Shennongjia's populations had greater gene diversity than found in Nanchuan's population of C. tomentella. Greater population differentiation was also detected along with low gene flow in the distribution regions. This may result from the plants predominantly self-mating system, the short-distance dispersal system associated with the plant, and the specific habitat requirements for growth. These data suggest that Shennongjia region should be regarded as the priority area for conservation of C. tomentella due to its greater diversity of this plant found there.

Understanding Molecular Mechanisms of Durable and Non-durable Resistance to Stripe Rust in Wheat Using a Transcriptomics Approach

Stripe rust of wheat, caused by Puccinia striiformis f. sp. tritici, continues to cause severe damage worldwide. Durable resistance is necessary for sustainable control of the disease. High-temperature adult-plant (HTAP) resistance, which expresses when the weather becomes warm and plants grow older, has been demonstrated to be durable. We conducted numerous studies to understand the molecular mechanisms of different types of stripe rust resistance using a transcriptomics approach. Through comparing gene expression patterns with race-specific, all-stage resistance controlled by various genes, we found that a greater diversity of genes is involved in HTAP resistance than in all-stage resistance. The genes involved in HTAP resistance are induced more slowly and their expression induction is less dramatic than genes involved in all-stage resistance. The high diversity of genes and less dramatic induction may explain durability and the incomplete expression level of HTAP resistance. Identification of transcripts may be helpful in identifying resistance controlled by different genes and in selecting better combinations of genes to combine for achieving adequate and durable resistance.

Identification, analysis, and linkage mapping of expressed sequence tags from the Australian sheep blowfly

BackgroundThe Australian sheep blowfly Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae) is a destructive pest of the sheep, a model organism for insecticide resistance research, and a valuable tool for medical and forensic professionals. However, genomic information on L. cuprina is still sparse.ResultsWe report here the construction of an embryonic and 2 larval cDNA libraries for L. cuprina. A total of 29,816 expressed sequence tags (ESTs) were obtained and assembled into 7,464 unique clusters. The sequence collection captures a great diversity of genes, including those related to insecticide resistance (e.g., 12 cytochrome P450s, 2 glutathione S transferases, and 6 esterases). Compared to Drosophila melanogaster, codon preference is different in 13 of the 18 amino acids encoded by redundant codons, reflecting the lower overall GC content in L. cuprina. In addition, we demonstrated that the ESTs could be converted into informative gene markers by capitalizing on the known gene structures in the model organism D. melanogaster. We successfully assigned 41 genes to their respective chromosomes in L. cuprina. The relative locations of these loci revealed high but incomplete chromosomal synteny between L. cuprina and D. melanogaster.ConclusionsOur results represent the first major transcriptomic undertaking in L. cuprina. These new genetic resources could be useful for the blowfly and insect research community.

Structure of Allozymatic Diversity of Ten Temperate and Adapted Exotic Breeding Populations of Maize ( Zea mays L.)

Ten temperate and adapted exotic breeding populations of maize were studied with electrophoretic techniques. Three isozyme systems coded by nine allozyme loci were used for evaluating the genetic variability within and among populations. The results revealed that 78.57% of allozyme loci were polymorphic. Low allelic variation with a mean number of 1.84 alleles per locus per population was detected. But, these populations still maintained higher level of heterozygosity; moreover, the exotic populations had greater gene diversity than the temperate populations. All the populations were non-panmictic with negative Wright's fixation indexes (−0.091–−0.424). The tropical BS16 was typified by maximum allelic richness, percent of polymorphic loci and heterozygosity. More than 93% of the gene diversity maintained within populations, and the genetic differentiation among populations was low (0.002–0.191). Multivariate analysis demonstrated that the tropical BS29 diverged from other populations in the reverse direction. The temperate BS9 and tropical BS16 were divergent each other, and highly differentiated from other temperate and tropical populations, consequently, these two populations would be analogically postulated as potential germplasms to establish new heterotic groups for temperate maize breeding programs.

Genome-wide SNP typing reveals signatures of population history

Single-nucleotide polymorphism (SNP) arrays have become a popular technology for disease-association studies, but they also have potential for studying the genetic differentiation of human populations. Application of the Affymetrix GeneChip Human Mapping 500K Array Set to a population of 102 individuals representing the major ethnic groups in the United States (African, Asian, European, and Hispanic) revealed patterns of gene diversity and genetic distance that reflected population history. We analyzed allelic frequencies at 388,654 autosomal SNP sites that showed some variation in our study population and 10% or fewer missing values. Despite the small size (23–31 individuals) of each subpopulation, there were no fixed differences at any site between any two subpopulations. As expected from the African origin of modern humans, greater gene diversity was seen in Africans than in either Asians or Europeans, and the genetic distance between the Asian and the European populations was significantly lower than that between either of these two populations and Africans. Principal components analysis applied to a correlation matrix among individuals was able to separate completely the major continental groups of humans (Africans, Asians, and Europeans), while Hispanics overlapped all three of these groups. Genes containing two or more markers with extraordinarily high genetic distance between subpopulations were identified as candidate genes for health differences between subpopulations. The results show that, even with modest sample sizes, genome-wide SNP genotyping technologies have great promise for capturing signatures of gene frequency difference between human subpopulations, with applications in areas as diverse as forensics and the study of ethnic health disparities.

A comparison of AFLPs and microsatellites to identify the population structure of brown trout (Salmo trutta L.) populations from Hardangervidda, Norway

A total of 495 fish from 11 Hardangervidda lakes were genotyped in order to compare amplified fragment length polymorphisms (AFLP) and microsatellites in terms of their capacity to infer population genetic structure. The 11 microsatellites used in this study gave a greater polymorphism information content and greater gene diversity, with an average of 14.8 alleles per locus, than the six AFLP primer combinations used. However, the AFLPs resulted in 178 polymorphic loci and a 3.1 times larger marker index (effective multiplex ratio multiplied with the gene diversity). Comparable population structuring, for example in terms of distinguishing fish from the different river systems, was obtained with both marker systems. An AFLP and microsatellite multilocus Bayesian assignment test with the structure program divided the fish into six groups largely concurrent with main branches on a population neighbour-joining tree. Yet, the admixture status of individuals is mostly contradictory in the AFLP and the microsatellite analyses. The results are discussed concerning migration between lake populations.

KIR Gene in Ethnic and Mestizo Populations from Mexico

Killer cell immunoglobulin-like receptors are characterized by their great diversity of genes and alleles. Population studies have identified the presence of a broad variety of genotypes. In Mexico, there are diverse ethnic groups representing 9% of the total population and the rest is composed of Mestizos with a more varied biology. For the purpose of this study, genotyping was performed in Mestizos, in Mexico City inhabitants, and in three ethnic groups. The frequencies of genes KIR2DL2, 2DL5, 2DS1-3, 2DS5, and 3DS1 showed a greater variability in the groups studied. A total of 12 different genotypes were identified, the higher number for the Mestizos and the lower number for the Tarahumaras. Genotype 1 was found at a greater frequency in all the groups, except for the Tarahumaras, in which genotype 4 was more frequent. The frequency of genotypes 4 and 8 in Mexicans was higher than that for other populations analyzed. By subtyping of KIR3DL1, 3DL2, 2DL1, and 2DL3, two B haplotypes were identified in families; both were absent in Caucasian families. Our results indicated a greater diversity of genes in the Mestizos group than in the ethnic groups.

Genetic structure and diversity among maize inbred lines as inferred from DNA microsatellites.

Two hundred and sixty maize inbred lines, representative of the genetic diversity among essentially all public lines of importance to temperate breeding and many important tropical and subtropical lines, were assayed for polymorphism at 94 microsatellite loci. The 2039 alleles identified served as raw data for estimating genetic structure and diversity. A model-based clustering analysis placed the inbred lines in five clusters that correspond to major breeding groups plus a set of lines showing evidence of mixed origins. A "phylogenetic" tree was constructed to further assess the genetic structure of maize inbreds, showing good agreement with the pedigree information and the cluster analysis. Tropical and subtropical inbreds possess a greater number of alleles and greater gene diversity than their temperate counterparts. The temperate Stiff Stalk lines are on average the most divergent from all other inbred groups. Comparison of diversity in equivalent samples of inbreds and open-pollinated landraces revealed that maize inbreds capture <80% of the alleles in the landraces, suggesting that landraces can provide additional genetic diversity for maize breeding. The contributions of four different segments of the landrace gene pool to each inbred group's gene pool were estimated using a novel likelihood-based model. The estimates are largely consistent with known histories of the inbreds and indicate that tropical highland germplasm is poorly represented in maize inbreds. Core sets of inbreds that capture maximal allelic richness were defined. These or similar core sets can be used for a variety of genetic applications in maize.

Geographical and altitudinal population genetic structure of two dung fly species with contrasting mobility and temperature preference

Local adaptation of populations requires some degree of spatio-temporal isolation. Previous studies of the two dung fly species Scathophaga stercoraria and Sepsis cynipsea have revealed low levels of geographic and altitudinal genetic differentiation in quantitative life history and morphological traits, but instead high degrees of phenotypic plasticity. These patterns suggest that gene flow is extensive despite considerable geographic barriers and large spatio-temporal variation in selection on body size and related traits. In this study we addressed this hypothesis by investigating genetic differentiation of dung fly populations throughout Switzerland based on the same 10 electrophoretic loci in each species. Overall, we found no significant geographic differentiation of populations for either species. This is inconsistent with the higher rates of gene flow expected due to better flying capacity of the larger S. stercoraria. However, heterozygote deficiencies within populations indicated structuring on a finer scale, seen for several loci in S. cynipsea, and for the locus PGM (Phosphoglucomutase) in S. stercoraria. Additionally, S. cynipsea showed a tendency towards a greater gene diversity at higher altitudes, mediated primarily by the locus MDH (malate dehydrogenase), at which a second allele was only present in populations above 1000 m. This may be caused by increased environmental stress at higher altitudes in this warm-adapted species. MDH might thus be a candidate locus subject to thermal selection in this species, but this remains to be corroborated by direct evidence. In S. stercoraria, no altitudinal variation was found.

Allozyme Divergence and the Mode of Speciation for Coreopsis gigantea and C. maritima (Compositae)

Coreopsis gigantea and C. maritima consist of herbaceous perennial, diploid plants oc- cupying maritime habitats in California and Baja California. They are distinct from all other members of Coreopsis and comprise the only two members of section Tuckermannia. The two species differ by a number of morphological features but their synthetic hybrids are highly fertile, and their allopatric distributions appear to be largely responsible for lack of hybridization under natural conditions. An electrophoretic study of 10 enzymes revealed a lowered mean genetic identity for populations of the two species as compared to conspecific populations. The lowered identity ostensibly results in part from mutations that have accumulated at isozyme genes during the gradual divergence of the two taxa via a geographic mode of speciation. This pattern is contrasted with that found in a number of annual plants where presumed rapid speciation is accompanied by little or no divergence at genes specifying soluble enzymes. Greater gene diversity was found in C. maritima than in C. gigantea, and this suggests possible alternatives within the geographic mode of divergence. Apparent gene duplications for several enzymes are reported and discussed briefly.

The Influence of Multiple Mating On the Reproduction and Genetics of Heterodera Rostochiensis and H. Schachtii

Females of Heterodera rostochiensis Woll. embedded in agar or peat were inseminated more readily than in sand. Females removed from their host plants with small pieces of root attached lived longer and produced more eggs than those taken from roots. The behaviour of males in the presence of females was observed, or was deduced from tracks left on an agar surface or from their behaviour towards attractant substances secreted by the females and absorbed in agar discs. Males of H. rostochiensis attracted each other slightly but were much more strongly attracted to females. When females were in groups, males at a distance responded to the group as a whole, rather than to individuals, but when near to the group they tended to be 'captured' by a single female near the edge of the group. To estimate the proportions of ineffective males and sterile females in matings and the influence of multiple matings on fecundity, females were mated with different numbers of males. Males of H. rostochiensis and H. schachtii Schm. seemed able to inseminate up to ten females. Fecundity depended more on the age of the females when taken from the roots than the number of males that inseminated them. When several males collected around a single female they obstructed each other in attempts to copulate, but several must have succeeded in inseminating the female, counteracting the loss of fecundity caused by sterile or impotent males of which there were many. The genetic effects of multiple matings on inheritance were explored theoretically, using as an example the ability of some larvae of H. rostochiensis to become females in the roots of eelworm resistant potatoes bred from Solanum tuberosum ssp. andigena. Kort's data from single cyst cultures seemed to fit the theory that this ability depended on a recessive gene occurring infrequently. It seems that neither the first nor the last mating was the only effective one and multiple mating would cause a greater diversity of genes in the offspring of one female. Promiscuity and the ability of males to mate several females successfully, are advantageous in species such as H. rostochiensis and H. schachtii, in which the sex ratio ranges greatly and males may be outnumbered nine to one in sparse populations. Because eggs are concentrated in cysts, the progeny from cysts tend to invade roots in groups and clusters of females result. Grouping enhances their attractiveness to males. The males leave the females they have recently mated, move away and so have the opportunity of fertilising others.