Interspecific Genetic Differences Research Articles

Effect of water stress on growth and dry matter distribution of four dryland species used in tree planting in the Sahel

AbstractWater stress is the most important factor limiting early survival and growth of seedlings in arid and semi-arid zones. Many woody species develop adaptive mechanisms in response to water stress. This study assesses survival rate, growth and dry matter distribution in response to water stress in four dryland species (Senegalia dudgeonii, Senegalia gourmaensis, Vachellia nilotica and Vachellia tortilis). A total of 240 seedlings (60 per species) were grown using a completely randomized block design with three replicates in each of three water treatments (control = 100 percent of field capacity; moderate water stress = 50 percent of field capacity; severe water stress = 25 percent of field capacity) with a 7 day watering frequency. Data were collected on seedling survival, height, collar diameter, leaf production and dry matter distribution. Survival rate of the four species was not affected by water stress. However, the morphological responses to water stress were significantly different between species. Water stress resulted in significant reductions in height and collar diameter, higher below-ground biomass and significant increase in shedding of leaves. Under water stress, S. dudgeonii, S. gourmaensis and V. tortilis invested more in root growth. The allocation pattern from above-ground to below-ground parts was found to be the main adaption to drought. In contrast, V. nilotica gave preference to above-ground development, which could be an indication that the seedlings are adapted to grow under severe water stress. The results confirm the interspecific genetic differences in growth and dry matter distribution among species. These variations in water stress response may be used as criteria for species selection for degraded land reforestation.

The bougainvillea mealybug, Phenacoccus peruvianus Granara de Willink, in Granara de Willink & Szumik, 2007 (Hemiptera: Pseudococcidae), an invasive species new to North America, with a description of the adult male and new host records

Phenacoccus peruvianus Granara de Willink, in Granara de Willink & Szumik, 2007, the bougainvillea mealybug (Hemiptera: Coccomorpha: Pseudococcidae), is recorded from California and North America for the first time. Comparison of the morphology of the adult females from California with those described from South America, found a closer match with specimens from Argentina than with those from Peru. The adult male is described for the first time and compared with that of Phenacoccus solenopsis Tinsley, 1898. A table listing all 36 known host plant families in California is appended, 28 of which are new. DNA sequences from the COI and 18S portions of the genome were analyzed and compared with those available for specimens of P. peruvianus introduced to Europe and those of other congeners, confirming conspecificity between the Californian and European specimens and displaying interspecific genetic differences from other known Phenacoccus species within the range of values so far known to occur within the genus.

First molecular characterization of the facultative myiasis agent Eristalis tenax in Turkey using mitochondrial cytochrome c oxidase subunit I DNA barcoding sequences

This report is the first molecular characterization of the facultative myiasis agent Eristalis tenax collected from cattle barns in Kayseri province of Central Anatolia, Turkey. A total of 10 adult fly specimens were included in the study. All flies were identified as female adults of E. tenax by morphologic characteristics under a stereomicroscope. The barcode region of the mitochondrial cytochrome oxidase 1 (CO1) gene was amplified with PCR from the genomic DNA extracts of E. tenax specimens for molecular identification and phylogenetic analyses. There was no polymorphism among the CO1 sequences of all isolates leading to the detection of a single haplotype for E. tenax. Haplotype and nucleotide diversities in the CO1 data set comprised of the sequence of the detected haplotype and the published sequences of E. tenax from different countries in GenBank were determined as 0.775 and 0.002, respectively. The newly characterized haplotype in this study clustered with the haplotypes from Australia and Canada in a monophyletic clade and exhibited a 100.0% identity to the Australian E. tenax isolate (JN991985). Interspecific genetic differences between E. tenax and other Eristalis species were in the range of 5.7% to 7.9%.

An Extension of the Kimura Two-Parameter Model to the Natural Evolutionary Process

Accurate estimates of genetic difference are required for research in evolutionary biology. Here we extend the Kimura two-parameter (K2P) model by considering gaps (insertions and/or deletions) and introduce a new measure for estimating genetic difference between two nucleotide sequences in terms of nucleotide changes that have occurred during the evolutionary process. Using the nuclear ribosomal DNA internal transcribed spacer 2 region from the genus Physalis, we demonstrate that species identification and phylogenetic studies strongly depend on evolutionary models. It is especially noteworthy that the use of different models affects the degree of overlap between intraspecific and interspecific genetic differences. We observe that the percentage of interspecific sequence pairs with values less than the maximum intraspecific genetic difference is 43.2% for the K2P model which is calculated by removing gap sites across all sequences, 22.7% for the K2P model which is calculated by removing gap sites for sequence pairs, and 16.9% for our model which is calculated without removing gap sites. Additionally, the numbers of sequence pairs with interspecific genetic differences of zero are 50 for the K2P model and 29 for our model. The genetic difference measure based on the K2P model, compared to our model, overestimates 21 sequence pairs that are not originally identical. These results indicate the importance of estimating genetic differences under the model of sequence evolution that includes insertions and deletions in addition to substitutions.

Sequence Analysis of Ribosomal and Mitochondrial Genes of the Giant Liver Fluke Fascioloides magna (Trematoda: Fasciolidae): Intraspecific Variation and Differentiation from Fasciola hepatica

Complete sequences of ribosomal and mitochondrial genes of the giant liver fluke Fascioloides magna are presented. In particular, small subunit (18S) and internal transcribed spacers (ITS1 and ITS2) of the ribosomal gene (rDNA), as well as cytochrome c oxidase subunit I (cox1) and nicotinamide dehydrogenase subunit I (nad1) of the mitochondrial DNA (mtDNA), were analyzed. The 18S and ITS sequences were compared with previously published sequences of the liver fluke Fasciola hepatica. Fixed interspecific genetic differences were determined that allow molecular differentiation of F. magna and F. hepatica using either the PCR-RFLP method or PCR amplification of species-specific DNA regions. Additionally, intraspecific sequence polymorphism of the complete cox1 and nad1 mitochondrial genes in geographically distinct F. magna populations was determined. Based on the sequence divergences, short (< 500 bp) variable regions suitable for broader biogeographical studies of giant liver fluke were designed.

Early growth, dry matter allocation and water use efficiency of two sympatric Populus species as affected by water stress

We exposed cuttings of two sympatric species of Sect. Tacamahaca Spach, Populus cathayana Rehder and Populus przewalskii Maximowicz, to two watering regimes in a greenhouse. In the semi-controlled environmental study, two watering treatments which were watered to 100 and 25% of field capacity were used, respectively. The effects of water deficit on early growth, biomass allocation and water use efficiency (WUE) were investigated. We found that there were significant interspecific differences in early growth, dry matter allocation and water use efficiency between two sympatric Populus species. Compared with P. cathayana, P. przewalskii showed higher shoot height, dry matter accumulation, number of leaves, total leaf area, fine root mass, fine root/total root ratio and water use efficiency under both well-watered and water-stressed treatments. On the other hand, P. przewalskii also showed higher root mass/foliage area ratio, root/shoot ratio and carbon isotope composition than P. cathayana under water-stressed treatment. The results suggested that there were different water-use strategies between two sympatric Populus species, P. przewalskii with higher drought tolerance may employ a conservative water-use strategy, whereas P. cathayana with lower drought tolerance may employ a prodigal water-use strategy. The findings confirm the existence of interspecific genetic differences in early growth, dry matter allocation and water use efficiency as affected by water stress, these variations in drought responses may be used as criteria for species selection and tree improvement.

Molecular cloning of Taenia solium genomic DNA and characterization of taeniid cestodes by DNA analysis.

Total DNAs, isolated from a range of taeniid cestodes (Taenia solium, T. saginata, T. pisiformis, T. crassiceps, T. hydatigena, T. ovis, T. multiceps and T. taeniaeformis), have been subjected to restriction enzyme digestion, Southern transfer and hybridization analysis using cloned fragments of the ribosomal RNA gene of Schistosoma mansoni. Substantial inter-specific genetic differences have been revealed on the basis of characteristic hybridization patterns for each of the taeniid cestode species. Furthermore, a random genomic DNA library has been constructed in the vector plasmid pAT153 using DNA extracted from a pig isolate (Indian origin) of T. solium. A panel of taeniid cestode DNAs including DNA from Echinococcus granulosus, has been used in conjunction with hybridization and restriction enzyme analysis to identify in the library a single recombinant plasmid with a T. solium-specific insert (coded pTS10) and two recombinant plasmids with T. solium inserts having selective specificities for T. solium and T. ovis (coded pTS17) and T. solium, T. saginata, T. ovis and T. multiceps (coded pTS28). These recombinant plasmids and the cloned fragments of the ribosomal RNA gene of S. mansoni have been used in restriction endonuclease, Southern transfer and hybridization analysis to detect intra-specific genetic variation in cysticerci of T. solium from India, Mexico and Zimbabwe. In addition, pTS10 and pTS17 have been used in a simple dot-blot assay to distinguish T. solium from T. saginata.

Genotypic relationships between strains ofAnabaena(Cyanophyceae) and their correlation with morphological affinities

Genotypic relationships between a number of Anabaena strains, belonging to different species, were determined by means of comparison of their DNA base composition, DNA-DNA reassociation rates, thermal stability values of DNA-DNA hybrids, and electrophoretic behaviour of five different enzymes. In order to compare these relationships with morphological relationships between the strains tested, a numerical analysis of morphological traits was performed. DNA base compositions appeared to be almost identical. Intraspecific DNA DNA hybridizations showed high renaturation rates and high thermal stability values of hybrids, indicating a high degree of similarity of genomes of strains belonging to one species. Interspecific DNA-DNA hybridizations showed considerably lower renaturation rates and thermal stabilities, indicating considerable interspecific genetic differences. Electrophoretic patterns of enzymes more or less confirmed these findings, but also showed intraspecific differences. In general the results d...

Isozyme expression in F1 hybrids between carp and goldfish.

Interspecific genetic differences in malate dehydrogenase (MDH), lactate dehydrogenase (LDH), superoxide dismutase (SOD), and esterase (EST) isozymes in carp (Cyprinus carpio) and goldfish (Carassius auratus) were used to examine the allelic expressions in the hybrid between these species. A unique liver SOD and muscle LDH phenotype unambiguously identifies all presumed hybrid individuals. There was no evidence of F2 or backcross phenotypes in hybrid individuals. Liver MDH and EST phenotypes in hybrids show a preferential expression of goldfish isozymes. Variation in the levels of carp liver MDH isozymes may result from the polymorphism of a regulatory mutation effecting isozyme expression, leading to gene silencing after duplication.

Purification of cytochrome oxidase from mitochondria of higher plants

A simple procedure for the purification of cytochrome oxidase from mitochondria of higher plants is described. The enzyme from wheat, beans, cauliflower and sweet potato was purified 20-, 15-, 20- and 11-fold respectively. Differences in specific activity and Km were observed for the different species. The qualitative differences in cytochrome oxidase activity may be due to the interspecific genetic differences.