Increased total and regional vascular resistance produced by propranolol

Propranolol when administered acutely causes little change in blood pressure and a decrease in cardiac output. Blood pressure is maintained due to increased vascular resistance. The purpose of this investigation was to determine if increased vascular resistance after propranolol occurs uniformly among various tissues and if increased resistance is due to reflex vasoconstriction. Total and regional vascular resistance were determined with the radioactive microsphere technique in dogs anesthetized with chloralose. Intravenous propranolol, 1 mg/kg, caused little change in blood pressure, cardiac rate, cardiac output and total and regional vascular resistance 30 min after administration. These changes were not different than changes after saline injection. In dogs pretreated with the alpha adrenergic receptor antagonist, dibozane, i.v. propranolol did not affect cardiac rate or blood pressure but reduced cardiac output and increased total peripheral resistance. Vascular resistance in brain, heart, lung, duodenum and skin was increased whereas kidney, spleen and muscle vascular resistance was not significantly changed. It is concluded that increased vascular resistance produced by propranolol does not occur uniformly among tissues. Increased vascular resistance after propranolol is not due to reflex activation of alpha adrenergic receptors but may involve alterations in unidentified vasoconstrictor or vasodilator influences in certain vascular beds.

Evaluation of the absorption from some commercial sustained-release theophylline products

Absorption of theophylline from three commerical products labeled as sustained release was compared to the absorption from a standard uncoated tablet (Searle 200-mg aminophylline tablet) in a single-dose study. Aminodur tablets (Cooper) and Slophyllin Gyrocap capsules (Dooner) had bioavailability (100.2% +/- 19.8% and 98.5% +/- 13.8%) statistically indistinguishable from that of the standard but showed significantly slower absorption (peak times of 10.4 +/- 2.8 and 4.36 +/- 1.35 hr) and lower peak plasma concentrations (13.9 +/- 4.5 and 22.6 +/- 3.5 micrograms/ml/g dose) than the standard (tpeak, 1.52 +/- 0.45 hr; Cpeak, 28.1 +/- 6.2 micrograms/ml/g dose). The time of the plasma concentration peak (2.47 +/- 1.38 hr) after a dose of Tedral S.A. (Warner/Chilcott) was not statistically different from that after the standard, but both the peak concentration (16.0 +/- 3.9 micrograms/ml/g dose) and availability (76.0 +/- 18.4%) were. Multiple-dose projections from single-dose data indicate that of the three test products only Aminodur maintains reasonably constant interdose plasma levels during 12 hoursly dosing. With an 8 hourly dosing schedule Gyrocaps also might be satisfactory. Reasonable predictions of the plasma concentrations arising from Aminodur doses have been made using a single-compartment body model and assuming input from an outer followed by an inner layer of the tablet.

Influence of allopurinol on theophylline disposition in adults

Theophylline kinetics after intravenous aminophylline were determined in 5 nonsmoking healthy males before and after allopurinol for 1 wk. There was no significant alteration in theophylline disposition.

A world-wide survey of genetic variation in the yellow fever mosquito, Aedes aegypti

Thirty-four populations ofAedes aegyptirepresenting the world-wide distribution of the species, were analysed for genetic variation at 19–22 isozyme loci. The species has an average expected heterozygosity of 0·129±0·045 based on 19 loci analysed in every population. Based on this genetic information, two major groups can be defined: the dark, often sylvan, African subspeciesformosusand the light domestic subspeciesaegyptiin Africa and the New World. Asian populations do not fall easily into either group. These results are related to models which have been proposed for the evolution of this species. AlthoughA. aegyptiwas introduced into the New Worldc. 350 years ago and has recently recolonized many areas following eradication programmes, no signs of founder effects are evident in this region. Asian populations, on the other hand, do show a significantly lower level of genetic variation compared to other populations. This may be related to the time of introduction ofA. aegyptiinto Asia and historical absence of yellow fever on the Asian continent.

Interaction of imidazoline alpha-adrenergic receptor antagonists with histamine receptors

Because the alpha-adrenergic receptor antagonists phentolamine and tolazoline are similar in structure to histamine, it is possible that the vasodilatation caused by these drugs may be due in part to stimulation of histamine receptors. The vascular effects of these agents were studied in the hindquarters of rats and the gracilis muscle of dogs. To eliminate interruption of sympathetic vasoconstrictor tone as a mechanism of vasodilatation, all animals were treated with the alpha-adrenergic receptor antagonist, dibozane. After dibozane, histamine caused vasodilatation in the rat, whereas both tolazoline and phentolamine caused vasoconstriction. It is concluded that phentolamine and tolazoline do not stimulate vascular histamine receptors in the rat. In the dog, after alpha-receptor blockade, phentolamine and tolazoline caused vasodilatation, as did histamine. Responses to histamine were partially attenuated by mepyramine and greatly attenuated by the combination of mepyramine and metiamide, indicating the participation of both H1- and H2-histamine receptors. Vasodilatation caused by phentolamine was not reduced by antihistamines and does not appear to involve histamine receptors. Vasodilatation following tolazoline was blocked by metiamide but not mepyramine. It is concluded that in addition to blockade of alpha-adrenergic receptors, tolazoline can cause vasodilatation by stimulation of histamine H2-receptors.

Characterization of vascular histamine receptors in the rat

1 In the rat the decrease in blood pressure caused by histamine involves activation of both H1- and H2-receptors. Since arterial pressure measurements alone do not permit the separation of responses into cardiac and vascular components, the following experiments were undertaken to study vascular histamine receptors. 2 Vascular responses were studied in the autoperfused hindquarters of anaesthetized rats. Intra-arterial histamine caused vasodilatation which was only partially attenuated by treatment with mepyramine, an H1-receptor antagonist. Treatment with metiamide, the H2-receptor antagonist, did not affect vasodilatation caused by histamine but did attenuate vasodilatation which persisted after mepyramine. 3 Intra-arterial 4-methylhistamine, an H2-receptor agonist, caused vasodilatation which was reduced by metiamide. The H1-receptor agonist, 2-(2-pyridyl)ethylamine also caused vasodilatation which was blocked by mepyramine. 4 It is concluded that in the rat, histamine causes vasodilatation mediated by both H1- and H2-receptors.

Population genetics of Drosophila amylase. I. Genetic control of tissue-specific expression in D. pseudoobscura

Drosophila pseudoobscura is polymorphic for tissue-specific expression of alpha-amylase in adult midguts. This enzyme is encoded by a single locus, Amy, on the third chromosome. In this paper we show: (1) Up to about 12 days post-eclosion, the midgut activity patterns remain stable; after 12 days areas not showing activity previously begin to show activity. Thus, the genes controlling the expression of Amy are temporally acting. (2) Diet affects the quantitative, but not the qualitative, expression of Amy. (3) The expression of Amy in adult midguts is under genetic control. Selection for different frequencies of patterns is possible; realized heritabilities are 0.20 to 0.50. Partial linkage with third chromosome inversions has been demonstrated; the genes or elements controlling Amy expression are not, however, confined to the third chromosome. (4) The genetic elements controlling tissue-specific expression of amylase do not coordinately control the expression of five other "digestive-type" enzymes that were studied.--This polymorphism appears to be analogous to that studied by Abraham and Doane (1978) in D. melanogaster, wherein they have mapped regulatory genes.

Population genetics of Drosophila amylase. II. Geographic patterns in D. pseudoobscura

Morph frequencies of three related polymorphisms were determined in ten natural populations of Drosophila pseudoobscura. They are the well-known inversion polymorphism of the third chromosome and the polymorphism for alpha-amylase produced by the structural gene Amy (which resides on the third chromosome). The third polymorphism was for tissue-specific expression of Amy in adult midguts; a total of 13 different patterns of activity have been observed. The preceding paper (Powell and Lichtenfels 1979) reports evidence that the variation in Amy expression is under polygenic control. Here we show that the polymorphism for midgut patterns occurs in natural populations and is not an artifact of laboratory rearing.--From population to population, Amy allele frequencies and frequencies of inversions belonging to different phylads vary coordinately. The geographic variation in alpha-amylase midgut activity patterns is uncorrelated with that for the other two types of polymorphisms. Furthermore, no correlation was detected between activity pattern(s) and Amy genotype(s) when both were assayed in the same individual.--These results imply that whatever the evolutionary-ecological forces are that control frequencies of the structural gene variants, they are not the same factors that control the frequencies of polymorphic genetic factors responsible for the tissue-specific expression of the enzyme.

Evidence for selection by male mating success in natural populations of Drosophila pseudoobscura

Gene arrangement frequencies were determined at two stages in the life history of Drosophila pseudoobscura taken from nature. Three populations in the central highlands of Mexico were each sampled twice during 1976. Gene arrangement frequencies were measured in adult males and in larvae that were the offspring of females collected at the same time. The adult males were in all likelihood a representative sample of those who fathered the larvae produced by the wild females. Differences in gene arrangement frequency between these two life stages should indicate the operation of natural selection. One-third of our comparisons of common gene arrangement frequencies in males and in larvae from the next generation were statistically significant, as were one-third of our comparisons of total frequency arrays in the two life stages. We consider the components of selection that could produce such frequency changes and reason that male mating success must be the major one. Gene arrangement frequencies in the Mexican populations fluctuate within wide bounds. Selection must act to retain the polymorphism in the face of this flux in gene arrangement frequencies, and we suggest that male mating success plays an important role.

Carotid sinus reflex coronary vasoconstriction during controlled myocardial oxygen metabolism in the dog

We studied carotid baroreceptor reflex coronary vasoconstriction in closed-chest dogs with controlled aortic blood pressure and myocardial oxygen metabloism. The dogs were anesthetized with morphine and chloralose. Left coronary blood flow was measured by a cannula-tip flowmeter, and myocardial oxygen metabolism was calculated by measuring the arterial-coronary sinus oxygen difference. A bilateral vagotomy was performed in all animals and they were treated with propranolol. Reduction of carotid sinus pressure to 40 mm Hg caused an increase in aortic pressure that was limited to 15 mm Hg by means of a pressure-control reservoir. During carotid hypotension, heart rate and myocardial oxygen metabolism were unchanged but diastolic conronary vascular resistance increased by 21%. Intracoronary artery infusion of norepinephrine had similar effects. After interruption of the reflex are with the alpha-adrenergic receptor antagonist, dibozane, carotid sinus hypotension and the same increase in aortic pressure (15 mm Hg) resulted in only a 5% increase in diastolic coronary resistance. Dibozane also reduced the coronary responses to norepinephrine. It is concluded that carotid sinus hypotension results in reflex sympathetic alpha-receptor coronary vasoconstriction and that this reflex vasoconstriction is independent of changes in myocardial oxygen metabolism or changes in aortic pressure.

Changes in theophylline clearance during acute illness

Three patients demonstrated twofold to threefold changes in total-body theophylline clearance during the course of a single hospitalization for an acute illness. These changes paralleled the changes in the patients' clinical status. Theophylline clearance decreased in one patient with worsening airway obstruction, whereas clearance increased in one patient with resolving pneumonia and in one patient with improving congestive heart failure. Total-body theophylline clearance may be unstable in acute, severe illness. Close monitoring of plasma theophylline concentration in such situations will allow appropriate dose adjustments to be made and is, therefore, indicated.

Theophylline disposition in acutely ill hospitalized patients. The effect of smoking, heart failure, severe airway obstruction, and pneumonia

Theophylline disposition (clearance, volume of distribution, and half-life) was measured in 31 normal volunteers and 26 acutely ill patients with airway obstruction within 24 hours of hospital admission and again when intravenous aminophylline was discontinued 2 to 10 days later. Sex, age, race, the diagnosis of asthma, and the diagnosis of chronic bronchitis were not significantly correlated with clearance. Clearance was significantly increased in smokers and significantly decreased in patients with congestive heart failure, pneumonia, and severe bronchial obstruction. The volume of distribution was not correlated with these variables. Within 24 hours of admission, the mean clearance in our patients without congestive heart failure or pneumonia was 44.5 ml per hour per kg of body weight, 40 per cent less than the value on which the widely used 0.9 mg per kg per hour dosage is based. The unexplained interindividual variability of clearance was significantly higher amont patients than control subjects, but intraindividual variability in clearance was not different in these 2 groups after correction for the effects of smoking, congestive heart failure, and so on. Large variability in clearance among patients makes the plasma theophylline concentration resulting from any dosage relatively uncertain. Based on the the results of this study, recommendations are made concerning theophylline dosage computation, and the clinical circumstances calling for determination of plasma theophylline concentrations.

The influence of cigarette smoking and sex on theophylline disposition

The effects of cigarette smoking and sex on theophylline clearance, elimination rate constant, and apparent volume of distribution were examined in 28 healthy, young adults given single oral doses of theophylline or aminophylline. Two-way analysis of variance showed no sex effect but a significant effect of smoking habit on theophylline clearance and elimination rate constant. Neither sex nor smoking had an effect on the apparent volume of distribution. The respective mean clearance, elimination rate constant, and volume of distribution were, in nonsmokers, 0.040 +/- 0.008 (SD) liter per hour per kg, 0.084 +/- 0.015 hr-1, 0.47 +/- 0.08 liter per kg; heavy smokers, 0.063 +/- 0.019 liter per hour per kg, 0.129 +/- 0.045 hr-1, 0.50 +/- 0.06 liter per kg; and ex-smokers, 0.051 +/- 0.10 liter per hour per kg, 0.108 +/- 0.025 hr-1, 0.49 +/- 0.08 liter per kg. Cigarette smoking appeared to induce theophylline metabolism as reflected by the mean theophylline half-life in smokers (5.4 hours) versus nonsmokers (8.3 hours). The effect of cigarette smoking on theophylline clearance may be an important consideration in the clinical use of the drug.

Microgeographic differentiation of chromosomal and enzyme polymorphisms in Drosophila persimilis

We studied microgeographic and temporal genetic differentiation in natural populations of Drosophila persimilis with respect to chromosome inversion and enzyme polymorphisms. Both inversion frequencies and allozyme frequencies varied significantly over short distances. Neither differed significantly between morning and evening collections. Because several studies of the dispersal behavior of this species have been performed, we attempt to fit the observed data to mathematical models which relate dispersion to random genetic drift and to spatially varying selection coefficients. We conclude that the observations are due at least partly to behavioral differences among genotypes. i.e., habitat preferences. These results have implications for genetic load theory and models of selection in heterogeneous environments.

Participation of H1 and H2 histamine receptors in physiological vasodilator responses

Histamine causes vasodilation in the dog by activation of H1 and H2 receptors blocked by mepyramine and metiamide, respectively. Experiments were conducted in anesthetized dogs to determine the participation of H1 and H2 receptors in several forms of physiological dilatation. Mepyramine attenuated both histamine-induced and active-reflex dilatation in the hindlimb. Metiamide caused a further reduction in both sets of dilatation. Neither single nor combined antihistamines reduced dilatation due to exercise or after temporary occlusion of the circulation in the hindlimb. Poststimulation dilatation in the gracilis muscle was partially attenuated by metiamide or mepyramine. Neither dilatation caused by sympathetic nerve stimulation in the hindpaw nor dilatation in the gracilis muscle caused by compound 48/80 was reduced by mepyramine. Following combined H1- and H2-receptor blockade, portions of both types of dilatation were reduced. These data provide evidence for the participation of both types of histamine receptor in active reflex dilatation, low-frequency neurogenic dilatation, dilatation caused by compound 48/80, and poststimulation dilatation. Neither type of histamine receptor appears to be involved in reactive hyperemia or dilatation caused by exercise.

A High-Efficiency Power Cycle in Which Hydrogen Is Compressed by Absorption in Metal Hydrides

A high-efficiency power cycle is proposed in which molecular hydrogen gas is used as a working fluid in a regenerative closed Brayton cycle. The hydrogen gas is compressed by an absorption-desorption cycle on metal hydride (FeTiH(x)) beds. Low-temperature solar or geothermal heat (temperature about 100 degrees C) is used for the compression process, and high-temperature fossil fuel or nuclear heat (temperature about 700 degrees C) supplies the expansion work in the turbine. Typically, about 90 percent of the high-temperature heat input is converted to electricity, while about 3 kilowatts of low-temperature heat is required per kilowatt of electrical output.

Identification and blockade of vascular H2 receptors

Experiments were conducted in anesthetized dogs to determine the nature of receptors mediating vascular actions of histamine. In the perfused gracilis muscle histamine caused vasodilatation that was attenuated in part by mepyramine, an H1-receptor blocker. Metiamide, an H2 blocker, given alone had no effect on dilatation. However, the combination of mepyramine and metiamide resulted in a large attenuation of dilatation. Histamine caused constriction of the perfused saphenous vein that was totally blocked by mepyramine suggesting that venoconstriction by histamine involves only H1 receptors. Histamine infusion caused a fall in arterial pressure and a large reduction in peripheral resistance. Mepyramine attenuated the fall in pressure but not the reduction in resistance. Combined H1- and H2-receptor blockade largely eliminated the effects of histamine infusion further documenting the existence of H1 and H2 receptors. The effects of H1 and H2 antihistamines on a variety of physiological vasodilator responses were examined. Evidence was obtained to indicate that H1- and H2-histamine receptors are involved in the active component of baroreceptor-mediated reflex vasodilatation, poststimulation vasodilatation, sympathetic vasodilatation in the guanethidine-treated dog, and vasodilator responses following compound 48/80. No evidence for the participation of either H1- or H2-histamine receptors in reactive hyperemia or the dilatation accompanying exercise was found. It is concluded that in the dog both endogenously-released and exogenous histamine exert vascular effects by activation of both H1 and H2 receptors.

Genetics of natural populations, XLIII. Further studies on rates of dispersal of Drosophila pseudoobscura and its relatives

The amount of gene flow among local populations of a species is determined by the dispersal capacity of that species. Population samples of Drosophila pseudoobscura, D. persimilis, D. azteca, and D. miranda were collected, marked with ultraviolet fluorescent dusts, and released as soon as possible after capture. One and two days after release, recaptures were made on baits placed at 40-meter intervals in straight lines intersecting the release point. On alternative days, the baits were placed in North-South or in East-West directions. The distribution of the recaptured flies about the release point is very nearly normal. No significant differences between the dispersal rates of the four species are observed; however, males disperse slightly further than females. The variances averaged 50,822 m2 on the first day and 80,048 m2 on the second day and the estimated mean distances from the release point averaged 263 m and 361 m respectively. The genetic implications of the results are discussed.

Identification and specific blockade of two receptors for histamine in the cardiovascular system

Histamine caused a fall in blood pressure in anesthetized dogs and cats which was only partially attenuated by mepyramine (pyrilamine), a histamine type H1-receptor antagonist. Further treatment with burimide or metiamide, type H2-receptor antagonists, caused nearly complete attenuation of the response to histamine. Burimamide alone had no effect on vasodilatation produced by histamine in the dog gracilis muscle whereas mepyramine alone caused a partial attenuation. An H2-receptor agonist, 4-methylhistamine and an H1-receptor agonist, 2-(2-pyridyl)ethylamine, both produced vasodilatation which was blocked by metiamide and mepyramine, respectively. Constriction of the saphenous vein produced by histamine was found to involve interaction with H1-receptors only. In the intact dog, histamine increased heart rate and decreased left ventricular dp/dt through direct effects. Mepyramine prevented the increase in heart rate but did not affect the chronotropic actions of isoproterenol and glyceryl trinitrate. H1-receptor blockade did not alter inotropic effects whereas subsequent H2-receptor blockade prevented the negative inotropic effect of histamine. It is concluded that both peripheral vascular and cardiac responses to histamine are mediated through activation of H1- and H2-histamine receptors.

A new sutureless technique for skin closure

A sutureless wound-closure device was used in 150 patients. The average time spent to effect skin closure was reduced; removal was easy; skin apposition was satisfactory; and patient response was favorable. Sutureless tape closures eliminate the disadvantages of invasive skin closures. The device described provides secure tape adhesion to the skin and does not cover the wound. It can be easily applied, adjusted, and removed, in addition to serving as a protective splint to the healing wound. This method can reduce operative time of skin closure with highly satisfactory cosmetic results.

Population genetics of Mexican Drosophila. I. Chromosomal variation in natural populations of Drosophila pseudoobscura from Central Mexico

Drosophila pseudoobscura populations of Central Mexico are chromosomally highly polymorphic. Five gene arangements in the third chromosome are endemic, including the two newly described in the present article. The phylogenetic tree of the gene arrangements known in the species is shown in Figure 1. The ones found in Central Mexico all belong to the Santa Cruz "phylad", while in the northern part of the species area both Santa Cruz and Standard phylads are widespread. Some inferences concerning the evolutionary history of the species are presented.

Rates of dispersal of Drosophila pseudoobscura and its relatives

The dispersal behaviour of a species determines to a large extent the gene migration rates among its geographic subdivisions. Gene migration is very important in determining the genetic structure of populations which in turn determines the evolution of the species. The purpose of the work reported here was to obtain quantitative measures of the dispersal behaviour of a well studied insectDrosophila, D. pseudoobscura. Population samples ofD. pseudoobscuraand three related species were collected in nature, dusted with powders that fluoresce under ultraviolet light, and released at a certain point in the same locality where they had been collected. One and 2 days after the release, some of the marked flies were recaptured on baits of fermenting banana, spaced at 20 or 40 m intervals in straight lines on both sides of the release point. There were no significant differences among the four species in their dispersal behaviour. The variance of the distances from the release point to the points at which marked flies were recaptured is used as a measure of the active dispersal of the flies. In nine separate experiments, the average variance for all four species 1 day after the release was 21449 ± 1554 m2, and after two days 27844 ± 3414 m2. The estimated average distance travelled was 192 m after one day and 219 m after 2 days. It appears that the flies disperse faster on the first than on the second day after the release. These results differ in several respects from those obtained in the experiments made in 1942 and 1945.

Flounder effects and linkage disequilibria in experimental populations of Drosophila

Six laboratory populations of Drosophila paulistorum were examined for changes in gene frequencies at an enzyme locus, tetrazolium oxidase (To). In some of the populations, the alleles were introduced on over 100 independently derived chromosomes. These populations showed considerable stability in gene frequencies although they were at widely different starting frequencies. Other populations were begun with only a few (about 6) independently derived chromosomes. These populations showed significant and somewhat erratic changes in To gene frequencies. The difference in behavior of the two sets of populations was almost certainly caused by linkage effects due to sample size. The implication of these studies in understanding the role of the founder effect in natural populations is briefly discussed.

Apparent selection of enzyme alleles in laboratory populations of Drosophila

Twelve laboratory populations of recently collected Drosophila willistoni were begun with different frequencies of alleles at three enzyme loci, six populations at 25 degrees and six at 19 degrees . Periodic sampling of the populations allowed monitoring of the frequency changes in allozymes over time.-At Lap-5 (a locus coding for leucine amino peptidase), three alleles converged to the same frequencies in all populations at both temperatures. The apparent equilibrium frequency of the major allele was about.75; this is different from the frequency (.57) found in the natural population from which the experimental populations were begun. Allele frequency changes at the esterase-5 locus (Est-5) were slower but consistent in all cages. It is difficult to determine if an equilibrium has been reached. However, the frequency of the rare allele in all cages is about the same as in wild populations, 5%. Alleles at both Lap-5 and Est-5 are non-randomly associated with inversions in the chromosomes onto which they map. Because of these associations, it is impossible to unambiguously attribute the change in allele frequencies to selection at the loci being observed.-After one year, no significant gene frequency changes were detected at Est-7, the third locus studied.

Enzyme variability in the Drosophila Willistoni group. V. Genic variation in natural populations of Drosophila equinoxialis

We have studied genetic variation at 27 loci in 42 samples from natural populations of a neotropical species,Drosophila equinoxialis, using standard techniques of starch-gel electrophoresis to detect allelic variation in genes coding for enzymes. There is considerarle genetic variability inD. equinoxialis. We have found allelic variation in each of the 27 loci, although not in every population. On the average, 71% of the loci are polymorphic – that is, the most common allele has a frequency no greater than 0·95 – in a given population. An individual is heterozygous on the average at 21·8% of its loci.

The amount of genetic variation fluctuates widely from locus to locus. At theMdh-2locus arout 1% of the individuals are heterozygotes; at the other extreme more than 56% of the individuals are heterozygous at theEst-3. At any given locus the configuration of allelic frequencies is strikingly similar from locality to locality. At each and every locus the same allele is generally the most common throughout the distribution of the species. Yet differences in gene frequencies occur between localities. The pattern of genetic variation is incompatible with the hypothesis that the variation is adaptively neutral. Genetic variation inD. equinoxialisis maintained by balancing natural selection.

The amount and pattern of genetic variation is similar inD. equinoxialisand its sibling species,D. willistoni. Yet the two species are genetically very different. Different sets of alleles occur at nearly 40% of the loci.

Allozymes as diagnostic characters of sibling species of Drosophila

Considerable enzyme variation that is genetically controlled exists within and between natural populations of Drosophila. Our studies of two groups of sibling species show that allozyme differences can be used as species-diagnostic characters. A locus is defined as diagnostic if an individual can be correctly assigned to one of two species with a probability of 99% or higher. Between 15 and 32% of the loci studied are diagnostic for any two of the sibling species. If several diagnostic loci are used, the species of any individual can be diagnosed with virtual certainty.

Enzyme variability in the Drosophila willistoni group. IV. Genic variation in natural populations of Drosophila willistoni

We describe allelic variation at 28 gene loci in natural populations of D. willistoni. Seventy samples were studied from localities extending from Mexico and Florida, through Central America, the West Indies, and tropical South America, down to South Brazil. At least several hundred, and often several thousand, genomes were sampled for each locus. We have discovered a great deal of genetic variation. On the average, 58% loci are polymorphic in a given population. (A locus is considered polymorphic when the frequency of the most common allele is no greater than 0.95). An individual fly is heterozygous, on the average, at 18.4% loci.-Concerning the pattern of the variation, the most remarkable finding is the similarity of the configuration of allelic frequencies from locality to locality throughout the distribution of the species. Our observations support the conclusion that balancing natural selection is the major factor responsible for the considerable genetic variation observed in D. willistoni.

Genetic polymorphisms in varied environments

Thirteen experimenital populationis of Drosophila willistoni were maintained in cages, in some of which the environments were relatively constant and in others varied. After 45 weeks, the populations were assayed by gel electrophoresis for polymorphisms at 22 protein loci. The average heterozygosity per individual and the average unmber of alleles per locus were higher in populations maintained in heterogeneous environments than in populations in more constant enviroments.

Polymorphisms in continental and island populations of Drosophila willistoni

A comparative study of genic allozyme and chromosomal polymorphisms in four continental (South American) and six oceanic island (West Indies) populations of Drosophila willistoni has been made. The pattern of genic polymorphism is closely similar in all populations. Although regional and local differences in gene frequencies are found, generally the same alleles occur at high, intermediate, and low frequencies in all populations. An average individual is heterozygous at 18.4 and 16.2% of its loci in the continental and island populations, respectively. By contrast, chromosomal polymorphism is sharply reduced on the islands compared to most continental populations, and some chromosomal inversions are more frequent on some islands than on others. The observations are not compatible with the hypothesis that most of the gene variants are adaptively neutral. Balancing natural selection is responsible for most of the genic polymorphism in natural populations of D. willistoni.

Evidence of heterosis associated with an enzyme locus in a natural population of Drosophila

A wild population of Drosophila paulistorum (Andean semispecies) was analyzed by starch gel electrophoresis for a sex-linked enzyme locus, Tetrazolium oxidase. The results of the analysis of F(1) progenies from 106 single female lines from São José do Rio Prêto, Brazil, has allowed us to determine the genotype of 106 wild-collected females and 104 wild-collected males. The population is polymorphic for two alleles with frequencies of 0.56 and 0.44. The observed frequencies among the females of the two homozygotes were 0.23 and 0.13 and of the heterozygote 0.64. The deviation from the frequencies expected according to the Hardy-Weinberg formula is statistically significant (P < 0.005). There is a substantial excess of heterozygotes over the expected number. This observation is interpreted to mean that this polymorphism is maintained by heterosis. This is probably the first reported case of heterosis associated with an enzyme locus in a natural population of Drosophila.