Simulations of human colonization history.
Explore the source record for details and available documents.
Computer Simulation↗
Biomedical subjects
K M Ibrahim
Publications and source records attributed to K M Ibrahim.
Testing for recombination in a short nuclear DNA sequence of the European meadow grasshopper, Chorthippus parallelus.
Single-copy nuclear DNA sequences have high potential as a source of genetic markers for population analyses. However, the difficulties that arise when haplotypes that are the product of recombinational rearrangements are present require additional consideration. Two statistical methods for identifying potential recombinants by detecting anomalies in the distribution of variable sites along sequences were used to screen sequences from a single-copy nuclear DNA fragment, cpnl-1, of the European meadow grasshopper (Chorthippus parallelus). Five of the 71 haplotypes in the cpnl-1 data set showed nonrandom distribution of polymorphic sites using both methods. The second method pinpointed an additional four haplotypes. Estimates of the rate of recombination in the entire data set were obtained using standard methods. It is concluded that cpnl-1 haplotypes have been involved in recombination or gene conversion events at a rate more than twice the mutation rate. This confirms that recombination and gene conversion are significant factors in the generation of haplotype variation in nuclear gene sequences. The cpnl-1 haplotypes identified by the tests were present only in populations that have had recent contact; the Balkan and Turkish refugial populations and their post-glacial colonies to the north. This is discussed in relation to the phylogenetic inferences drawn from the same data in a previous report.
Animals↗
Plague dynamics and population genetics of the desert locust: can turnover during recession maintain population genetic structure?
The desert locust (Schistocerca gregaria) undergoes crowding-induced phase transformation from solitary form to gregarious form. The transformations involves changes in behaviour, colour, development, morphometry, fecundity and endocrine physiology. Recession populations of the desert locust exist primarily in the solitary phase as small populations in patchy environments and are prone to extinction because of climatic events. Significant genetic differentiation among recession populations along the Red Sea coast of Eritrea was previously reported. It was hypothesized that despite the mixing effect of recurrent swarms, metapopulation dynamics could have produced genetic divergence among these highly scattered recession populations. A Monte Carlo simulation of the population dynamics of the desert locust in a metapopulation setting, with a realistic range of parameter values clearly demonstrated that this is possible. Population growth was represented by a discrete-time logistic equation. The duration of recessions and swarms was sampled from normal distributions whose means and standard deviations were varied based on reported estimates. An average recession duration of 10 +/- 3 generations and swarm periods half as long but almost twice as variable produced a partitioning of the total genetic variance most similar to that in the empirical study. In conventional metapopulation analysis, whether turnover leads to increased or reduced divergence is dependent on the number of colonists relative to the number of recurrent migrants, and on whether the colonists arise from a single patch or many patches. In the case of locusts, the stochastic boom and bust cycle is the overriding factor. Divergence between patches during recession due to founder effect and recurrent drift is balanced by the high rate of mixing during plagues.
Alleles↗
Are recession populations of the desert locust (Schistocerca gregaria) remnants of past swarms?
The desert locust (Schistocerca gregaria) undergoes crowding-induced phase transformation from solitary to gregarious, which involves changes in behaviour, colour, development, morphometry, fecundity and endocrine physiology. During recession, solitary locusts persist in the central, drier part of the species' range in small pocket populations that are prone to extinction. During the intermittent upsurges and the subsequent plagues, gregarious swarms attain huge population size and invade a vast area causing major damage to agriculture. A highly variable nuclear DNA marker, a noncoding 3' end fragment of an antennapedia-class homeobox gene, was screened in locust samples from Eritrea. Despite the homogenizing potential of plague swarms, the last of which was in 1986-89 and originated in this region, the population genetic structure of solitary phase locusts along the Red Sea coast of Eritrea revealed significant divergence. The pattern of divergence indicated that the invasion of the western and northern plains in the summer of 1995 may not, as reported then, have originated in eastern Chad or western Sudan. A number of interrelated hypotheses have been presented to explain the observed genetic heterogeneity between the sampled populations. We conclude, with caution due to the limited sample sizes, that: (i) geographical isolation between breeding sites during plagues and recession; (ii) the marked differences in the flight behaviour of plague swarms and recession populations; (iii) possible failure of gregarious locusts to solitarize and re-establish in recession areas; and (iv) the effect of repeated extinction and recolonization in the meta-population contribute to the maintenance of the genetic structure of recession populations. Potentially productive future research has been identified.
Animals↗
Fine-scale genetic structuring in a natural population of European wild rabbits (Oryctolagus cuniculus).
The genetic structure of a free-living tagged population of European wild rabbits (Oryctolagus cuniculus) was investigated for two consecutive years (1990 and 1991) using 10 polymorphic microsatellite loci. A specific social behaviour, the formation of stable breeding groups, influenced the genetic structure of the population. These breeding groups were shown to constitute genetically differentiated units with low levels of gene flow between them. The average relatedness among members of a social group was higher than within the population as a whole. As a result of female philopatry coupled with male-biased natal dispersal, the relatedness of females was higher than that of males, both within social groups and in the whole population. Furthermore, the average relatedness of females within groups was twice the relatedness of females between groups. This study reveals marked fine-scale, intrapopulation genetic structure, which is attributable to the social behaviour of the European wild rabbit.
Age Factors↗
The phylogeography of the darkling beetle, Hegeter politus, in the eastern Canary Islands.
We investigated the phylogeography of Hegeter politus, a saprophagous, flightless darkling beetle endemic to the eastern Canary Islands, using a fragment of the mitochondrial COI gene. Distance and parsimony based gene trees of the mitotypes identified revealed a striking association between mitotype clades and sampling locations. The branching order of the clades suggested that the colonization of the islands by Hegeter politus proceeded from the southern part of Fuerteventura in a north-northeast direction to Lanzarote and the smaller islands. Based on this, a colonization scenario compatible with the reported geological ages and volcanisms of the various parts of the islands has been proposed. The high divergence of the beetles collected from the extreme south of Fuerteventura (the Jandía peninsula) from all other samples has led us to propose that they may be from a new species that has not been described previously. The ecological isolation of Jandía from the rest of Fuerteventura by the sand dunes that cover its narrow isthmus in the north, and the existence of many plant and animal endemisms unique to Jandía, lend supportive evidence to our proposal. The similarities between the evolution of island endemics in the Hawaiian and Canary archipelagos have been discussed. We conclude that many endemics in the Canary archipelago, like the Hawaiian Islands, are most likely to have originated from post-colonization differentiation and divergence.
Animals↗
mtDNA phylogeography and postglacial patterns of subdivision in the meadow grasshopper Chorthippus parallelus.
A 300 bp portion of the mitochondrial cytochrome oxidase subunit I (COI) gene was used to investigate the intraspecific genetic structure of the European meadow grasshopper Chorthippus parallelus. Levels of genetic subdivision between geographical regions in Europe were assessed using the KST statistic and revealed patterns indicative of the postglacial history of this organism. Northern European populations are shown to share a very recent common ancestor with, and hence originate from, a Balkan expansion. Genetic distances between these areas and both southern Italy and central Spain are shown to be approximately equal, even though only the Spanish form is recognized as a distinct subspecies. Distance estimates indicate that the common ancestor of the two subspecies lived more than one glacial cycle ago, and the refugial populations have probably been diverging in isolation for five or six glacial cycles (approximately equal to 550,000 years). Comparisons are made to the analysis of a similar data set using an anonymous nuclear DNA marker (Cooper et al., 1995). Although the structure revealed is generally very similar, differences in the location of transition zones between different genetic forms of C. parallelus may reflect the different historical assortment of these molecules.
Animals↗
Mitochondrial DNA sequence variation and phylogeography of Pimelia darkling beetles on the island of Tenerife (Canary Islands).
Four morphological taxa of the beetle genus Pimelia (Coleoptera, Tenebrionidae) are known to exist on the Atlantic island of Tenerife. We have obtained DNA sequences for 61 individuals from these taxa across the island for a 200 bp long fragment of the mitochondrial COI gene. In addition, a restriction site polymorphism in the nuclear rRNA ITS-1 sequence was identified and screened in a sample of these individuals using the enzyme Kpn2I. The results were analysed using approaches which allow inferences to be made about the population genetic structure and the mitochondrial genealogy of these closely related beetles. The mtDNA haplotype distribution and the estimates of sequence divergence revealed the presence of two ancient mtDNA lineages which coincide with the disjunct volcanic evolution of the island. The ITS-1 polymorphism was found to be diagnostic of these two lineages. However, the morphological and mitochondrial phylogenies were found to be discordant. We argue that this is possibly the result of rapid morphological change, produced by selection in different habitats, which has been recently superimposed on an older mitochondrial DNA divergence.
Animals↗
Role of the hypoglycemic plant extract cleome droserifolia in improving glucose and lipid metabolism and its relation to insulin resistance in fatty liver.
In this work the mechanism of the hypoglycemic effect of the plant Cleome-Droserifolia (C.d.) was studied in a group of albino rats rendered glucose intolerant by tetracycline (T.) induced fatty liver, and compared with a normal control (C.) rats. The plant extract significantly suppressed the rise in peripheral blood glucose concentrations, both in the basal (fasting) state and after glucose intake. Suppression of basal blood glucose indicated a lowering effect of the plant extract on hepatic glucose output (HGO). The postprandial hypoglycemic effect of the plant extract without increasing insulin secretion was explained by; First: Potentiation of peripheral and hepatic insulin sensitivity. Second: by diminishing intestinal glucose absorption, which was evident by blunting plasma glucose levels throughout the oral glucose challenge. This plant might prove to have a promising therapeutic value in the treatment of diabetes mellitus, for besides its postprandial hypoglycemic effect, its suppression to hepatic glucose output in the fasting state is a beneficial therapeutic finding in favour of the plant as insulin is the most important drug that brings about this effect. The plant has also got a hypocholesterolemic effect more specifically on low density lipoprotein cholesterol (LDL-C) which consequently raised the high density lipoprotein cholesterol/low density lipoprotein cholesterol (HDL-C/LDL-C) ratio. This adds to its value as a protective and antiatherogenic agent.
Animals↗
Mechanism of insulin resistance and hyper-insulinemia in fatty liver.
Hyperinsulinemia and insulin resistance are common features seen in most liver diseases. The present study was carried out on an experimental model of fatty liver (tetracycline induced) in albino rats. Significantly elevated levels of both peripheral plasma insulin and plasma glucose concentrations were recorded in both the fasting state and after an oral glucose intake in the tetracycline-treated rats. The presence of hyperinsulinemia accompanying hyperglycemia is considered a sign of insulin resistance. Peripheral insulin resistance has been proved in this work by the reduced "A" value which refer to the peripheral insulin activity (sensitivity) in fatty liver rats compared to normal rats. The hyperinsulinemia recorded here was due to pancreatic hypersecretion and not a result of reduced hepatic degradation. Hypersecretion of insulin was clearly determined by measuring the level of immunoreactive insulin (IRI) in pancreatic vein which exhibited a significant rise in tetracycline-treated rats, and there was a positive correlation between the pancreatic venous and peripheral venous insulin in the basal state and after 30 min. of oral glucose administration. Hepatic degradation of insulin was not a cause as evidenced by First: the amount of insulin secreted and insulin consumed were significantly higher in fatty liver rats than normal controls. Second: the whole body extraction ratio or insulin degradation was not significantly different in the tetracycline-treated rats from the normal rats. The present data suggests that insulin resistance and hyperinsulinemia underlie the observed metabolic disturbances that characterize fatty liver disease.
Animals↗
Lupus anticoagulant in the elderly may be associated with both quinine and quinidine usage.
Thirty-one patients aged over 60 yrs and with lupus anticoagulant (LA) were reviewed for their drug intake. Twenty-three (73%) were taking cinchona alkaloids, 10 (32%) quinine for night cramps, 11 (35%) quinidine for cardiac arrhythmia and 2 (6%) were taking both. These frequencies of drugs usage differed significantly from age and sex matched controls (p < 0.001). Five patients had features suggestive of the antiphospholipid syndrome. Repeat testing showed persistent LA activity in all but 2 of 5 patients in whom the relevant drug had been ceased. This is the first description of a possible causal association between LA and quinine therapy.
Aged↗
Postglacial expansion and genome subdivision in the European grasshopper Chorthippus parallelus.
A noncoding nuclear DNA marker sequence (Cpn1-1) was used to investigate subdivision in the grasshopper Chorthippus parallelus and deduce postglacial expansion patterns across its species range in Europe. Investigation of the spatial distribution of 71 Cpn1-1 haplotypes and estimation of levels of genetic differentiation (KST values) between populations and geographic regions provided evidence for subdivision of C. parallelus into at least five major geographic regions and indicated that the French form of C. parallelus originated after range expansion from a Balkan refugium. Further evidence for subdivision of C. parallelus between Italy and northern Europe suggests that the Alps may have formed a significant barrier to gene flow in this grasshopper.
Animals↗
Natal dispersal and genetic structure in a population of the European wild rabbit (Oryctolagus cuniculus).
A combination of behavioural observation, DNA fingerprinting, and allozyme analysis were used to examine natal dispersal in a wild rabbit population. Rabbits lived in territorial, warren based social groups. Over a 6-year period, significantly more male than female rabbits moved to a new social group before the start of their first breeding season. This pattern of female philopatry and male dispersal was reflected in the genetic structure of the population. DNA fingerprint band-sharing coefficients were significantly higher for females within the same group than for females between groups, while this was not the case for males. Wright's inbreeding coefficients were calculated from fingerprint band-sharing values and compared to those obtained from allozyme data. There was little correlation between the relative magnitudes of the F-statistics calculated using the two techniques for comparisons between different social groups. In contrast, two alternative methods for calculating FST from DNA fingerprints gave reasonably concordant values although those based on band-sharing were consistently lower than those calculated by an 'allele' frequency approach. A negative FIS value was obtained from allozyme data. Such excess heterozygosity within social groups is expected even under random mating given the social structure and sex-biased dispersal but it is argued that the possibility of behavioural avoidance of inbreeding should not be discounted in this species. Estimates of genetic differentiation obtained from allozyme and DNA fingerprint data agreed closely with reported estimates for the yellow-bellied marmot, a species with a very similar social structure to the European rabbit.
Analysis of Variance↗
Acquired protein S deficiency in a patient with systemic lupus erythematosus causing central retinal vein thrombosis.
A 16 year old girl with systemic lupus erythematosus (SLE) developed the rare complication of central retinal vein occlusion. Although classically a disease of older patients, it has been recognised in association with SLE but only in the presence of the lupus anticoagulant or antiphospholipid antibodies. The thrombosis occurred when free protein S concentrations were transiently reduced and there was no family history or other known causes of reduced protein S concentrations. No other prothrombotic risk factors were present.
Adolescent↗
D-dimer (latex) assay in the diagnosis of deep venous thrombosis.
Explore the source record for details and available documents.
Humans↗
Mild bleeding disorders. A clinical and laboratory study.
OBJECTIVE: To investigate in-vitro haemostasis in subjects with symptoms suggesting a mild bleeding disorder. DESIGN: A prospective study in which an extensive range of in-vitro tests were applied unselectively. SETTING: Patients were referred from community-based practices and hospital outpatient services. PATIENTS: Ninety-three consecutive patients were examined. Hospital patients with severe illness were excluded. CLINICAL FEATURES: Patients presented with easy bruising (68%), epistaxis (12%), excessive operative bleeding (7%), menorrhagia (4%), haematuria (3%), dental bleeding (1%) and bleeding from other sites (5%). In no instance was the bleeding life threatening. OUTCOME MEASURES: Results of laboratory tests for patients presenting with the symptoms of a mild bleeding disorder were compared with the results for a healthy reference group. RESULTS: Abnormal results of in-vitro tests were found in 53% of the subjects. Thirteen per cent had a prolonged bleeding time, of whom the majority had abnormal results of other in-vitro tests. Von Willebrand's disease was diagnosed in 7% of patients, although only half of these had a prolonged bleeding time. CONCLUSIONS: Abnormal results of in-vitro tests were prevalent among subjects with symptoms of mild bleeding disorder. Easy bruising was as powerful a clue as any other bleeding manifestation to the presence of an abnormal in-vitro test result.
Bleeding Time↗
Automation of the Kaolin Clotting Time.
An automated Kaolin Clotting Time (KCT) has been developed to simplify screening for the Lupus Anticoagulant (LA). The assay is performed on the ACL300 Research coagulation analyser, but may be modified for other centrifugal analysers. Automation of the KCT allows up to 17 delta KCT (delta KCT) screens (Gibson J, Starling E, Date L et al. Simplified screening procedure for detecting lupus inhibitor. J Clin Pathol 1988; 44: 226-31) or 2 full Exner curves (Exner T, Rickard KA, Kronenberg H. A sensitive test demonstrating lupus anticoagulant and its behavioural patterns. Br J Haematol 1978; 40: 143-51) to be performed in one test cycle. An automated and manual delta KCT screen was performed on 17 patients with a previously diagnosed LA, 41 hospital patients having routine coagulation studies and 37 blood donors. In addition, 11 patients on full-dose heparin and 12 patients with stable warfarin anticoagulation were tested. The correlation between the automated delta KCT and the manual delta KCT was 0.958 (p less than 0.001). A full Exner curve was performed on 5 of the patients with a LA and 1 blood donor which demonstrated that the automated KCT produced results entirely comparable with the manual method. The automated KCT is a quick, inexpensive approach to screening patients for the presence of LA.
Blood Coagulation Tests↗
The effect of vitamin B12 on tetracycline-induced fatty liver.
The effect of vitamin B12 on the metabolic alterations due to tetracycline toxicity was studied experimentally on laboratory animals. Treatment of Sprague-Dawley rats with 120 or 250 mg tetracycline (i.p.) per kg per day for two or three days caused an accumulation of lipids, mainly triglycerides in the liver of 75% of animals studied, while phospholipid level tend to decrease. These doses are approximately twice and four times the recommended maximum dose for man. In the present work no direct relationship was observed between dose of tetracycline and hepatic accumulation of triglyceride, although livers of rats treated with 250 mg tetracycline/kg appeared uniformly pale yellow. Elevated serum triglyceride was found predominantly in rats treated with 120 mg/kg, while there was no obvious difference between serum triglyceride of rats treated with 250 mg tetracycline and control rats, indicating a block in the release of hepatic triglycerides. Where protection by vitamin B12 was studied, the vitamin was given i.m. (50 microgram/animal) 3 hours before the injection of 120 mg tetracycline per kg. There was a good evidence that lipid abnormalities caused by tetracycline improved by vitamin B12. Thus both hepatic and serum total lipid and triglycerides were significantly lower than those of rats treated with tetracycline, although hepatic total cholesterol was significantly increased as in case of tetracycline only.
Animals↗