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V Grant

Publications and source records attributed to V Grant.

12 recordsLinked to original sources
PubMed1994

Historical development of ornithophily in the western North American flora.

The 129 ornithophilous plant species in western North America have floristic affinities with one or the other of four geofloras: the Arcto-Tertiary flora (101 species), Madro-Tertiary flora (19 species), Madrean-Tethyan flora (8 species), and Neotropical flora (1 species). The last three floras have been in continuous contact with hummingbirds since some time early in the Tertiary, and ornithophily is old in this subset of western ornithophilous plants. The Arcto-Tertiary flora had no contact with hummingbirds in Eurasia or in its early history in North America. Ornithophily is a new condition in Arcto-Tertiary plant groups, dating from the first significant contact of these plants with hummingbirds in the Eocene. Buildup of the hummingbird pollination system in the Arcto-Tertiary flora is expected to be gradual and stepwise for several reasons. Ornithophilous plant groups with Arcto-Tertiary affinities in the modern western flora form a graded series with respect to taxonomic rank, taxonomic size, and ecological diversity. The series consists of one large genus (Castilleja), three small genera (Zauschneria, etc.), species groups in several genera (Penstemon, Aquilegia, etc.), single ornithophilous species in otherwise nonornithophilous genera (seven genera--e.g., Pedicularis, Monardella), and ornithophilous races in otherwise nonornithophilous species (known in two species). It is suggested that the gradations in size of the groups approximately reflect stages in their development, with the largest ornithophilous genus being oldest, with single ornithophilous species being relatively recent, and with ornithophilous races being most recent. The observed distribution of numbers of ornithophilous species among genera is in agreement with the expectation of a gradual and stepwise development of ornithophily.

Animals↗
PubMed1980

Infarct distribution in subhuman primates after acute coronary occlusion.

The extent of epicardial, endocardial and septal infarct was determined in 24 monkeys and five baboons 1 week after acute left anterior descending or diagonal branch coronary artery ligation. All 24 Macaca cynmologous monkeys had non-dominant left anterior descending coronary arteries. A snare ligature was placed just distal to the first diagonal branch for varying time periods (1, 2, 4, and 6 h followed by reperfusion or left in place permanently). In five baboons a chronic ligature was placed around a diagonal branch. All animals lived and were killed a week later. Histological mapping and planimetry of serial cross-sections were employed to quantify the extent and distribution of the infarct. All infarcts were transmural. The extent of epicardial infarct was significantly greater than the extent of endocardial infarct for 2 h ligations (3.5 +/- 0.87% of the left ventricle versus 2.4 +/- 0.58% of the left ventricle, P less than 0.05), the chronic left anterior descending coronary artery ligations (5.4 +/- 1.06% of the left ventricle versus 4.5 +/- 0.92% of the left ventricle, P less than 0.05 and for the chronic diagonal branch ligations (4.06 +/- 0.66% of the right ventricle + left ventricle versus 2.64 +/- 0.51+ of the right ventricle + left ventricle, P less than 0.02). It is evident, however, that the magnitude of this epicardial preponderance was not great and that, in general, the infarcts were transmural and rectangular in configuration.

Animals↗
PubMed1974

Solutions to the cost-of-selection dilemma.

There are various biologically realistic ways around the cost-of-selection restriction on rapid multiple-gene substitution. Some of these ways depend upon particular forms of interaction or linkage in the genes undergoing substitution; other ways depend on particular conditions of population size and structure. The special genotypic and populational conditions required for rapid evolutionary change in genetically complex characters are not unusual in higher organisms.

Alleles↗
PubMed1974

Population structure in relation to cost of selection.

The opposing requirements in an evolving population for a rapid rate of multiple gene substitution and for the maintenance of normal population size can be reconciled in a variety of ways. The ways out of the impasse suggested here invoke deviations from the usual assumption of a large continuous population with constant numbers. In a colonial population system there may be significant random fluctuations in the accidental mortality rate between different colonies; and those colonies with reduced numbers of accidental deaths could tolerate the larger number of selective deaths that go hand in hand with rapid evolution. In new daughter colonies founded by one or a few colonizing individuals from a large polymorphic ancestral population, some genes may reach complete fixation in one or a few generations, without the usual concomitant selective cost. Or, in the same setup, the favored alleles may change by chance from rare to moderately common, but not to complete fixation, during the founding of some daughter colonies; and this raises the allele frequencies above the low range, where the cost of selection is greatest, so that the cost of further selective changes is bearable.

Alleles↗
PubMed1974

An analysis of the cost-of-selection concept.

It is shown for a continuous haploid model that the common standard assumptions used in calculating the cost of gene substitution, namely, large constant population size and small constant selective value, are unnecessary. Population size may fluctuate during the course of substitution without affecting the calculated total cost. The selective intensity does not need to be small and constant to give the standard result for substitution cost. Diploid models with multiple alleles are analyzed and contrasted with standard two-allele models in respect to calculation of substitution cost. The influence of population structure on the probability of occurrence of complete gene substitution is discussed on the basis of a numerical example. The robust nature of the cost-of-selection concept is examined in the light of a conservation principle.

Alleles↗
PubMedDate not supplied

Tuberous sclerosis (Bourneville's disease).

1. Tuberous sclerosis is a hereditary disorder characterized by mental retardation, epilepsy, skin papules, and multiple developmental tumors, which involve every organ of the body including the eye. 2. Treatment is directed to control seizures and eliminate surface and systemic lesions by dermabrasion and surgery. 3. Genetic counseling is important for patients, their parents, and their siblings.

Adolescent↗