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Biomedical subjects

C C Spencer

Publications and source records attributed to C C Spencer.

6 recordsLinked to original sources
PubMed2005

Age-specific changes in epistatic effects on mortality rate in Drosophila melanogaster.

Models for the evolution of senescence assume that genes with age-specific effects act independently of one another. Although recent empirical data show that longevity is influenced in part by interactions between genes, there are currently few data on whether epistasis influences age-specific components of mortality. To gauge if and how interactions affect age-specific traits, we incorporated the Drosophila visible marker mutations ebony, forked, and purple into seven wild-caught strains of D. melanogaster to examine gene x genetic background interactions. We found significant natural genetic variation for longevity and baseline mortality rates. Gene x genetic background interactions were prevalent not only for longevity but also for baseline mortality rates and age-specific mortality rates. We conclude that gene x genetic background epistasis is prevalent for aging-related traits and could play a significant role in the evolution of aging. These results suggest that future genetic models for the evolution of aging should incorporate the effects of epistasis.

Age Factors↗
PubMed2000

Experimental evaluation of the usefulness of microsatellite DNA for detecting demographic bottlenecks.

Evolutionary and conservation biologists often use molecular markers to evaluate whether populations have experienced demographic bottlenecks that resulted in a loss of genetic variation. We evaluated the utility of microsatellites for detection of recent, severe bottlenecks and compared the amounts of genetic diversity lost in bottlenecks of different sizes. In experimental mesocosms, we established replicate populations by releasing 1, 2, 4 or 8 pairs of the western mosquitofish, Gambusia affinis (Poeciliidae). Using eight polymorphic microsatellite loci, we quantified seven indices of genetic diversity or change that have been used to assess the effects of demographic bottlenecks on populations. We compared indices for the experimentally bottlenecked populations to those for the source population and examined differences between populations established with different numbers of founders. Direct count heterozygosity and the proportion of polymorphic loci were not very sensitive to genetic changes that resulted from the experimental bottlenecks. Heterozygosity excess and expected heterozygosity were useful to varying degrees in the detection of bottlenecks. Allelic diversity and temporal variance in allele frequencies were most sensitive to genetic changes that resulted from the bottlenecks, and the temporal variance method was slightly more correlated with bottleneck size than was allelic diversity. Based on comparisons to a previous study with allozymes, heterozygosity, temporal variance in allele frequencies and allelic diversity, but not proportion of polymorphic loci, appear to be more sensitive to demographic bottlenecks when quantified using microsatellites. We found that analysis of eight highly polymorphic loci was sufficient to detect a recent demographic bottleneck and to obtain an estimate of the magnitude of bottleneck severity.

Animals↗
PubMed1980

Random time sampling with self-observation for library cost studies: unit costs of reference questions.

The working time of reference librarians was sampled using random alarm devices and a structured checklist of mutually exclusive categories of reference questions. An average wage rate was applied to the unit time reciprocals derived from the resulting percentages. Wage costs for directional questions averaged $1.98; extended reference queries, $4.57. Random time sampling with self-observation gives acceptable reliability at low cost, minimal interference with service operations, and minimal distortion of collected data due to the collection process. It can be carried out by library managers themselves.

Costs and Cost Analysis↗
PubMed1970

Unit costs of interlibrary loans and photocopies at a regional medical library. Preliminary report.

UNIT COSTS OF PROVIDING INTERLIBRARY LOANS AND PHOTOCOPIES WERE DETERMINED BY A METHOD NOT PREVIOUSLY USED FOR LIBRARY COST STUDIES: random time sampling with self-observation. The working time of all appropriate personnel was sampled using Random Alarm Mechanisms and a structured checklist of tasks. The total lender's unit cost per request received, including direct labor, materials, fringe benefits, and overhead, was $1.526 for originals mailed postpaid by lender, and $1.534 for photocopies mailed. Corresponding unit costs per request filled were: originals, $1.932, and photocopies, $1.763.

Copying Processes↗
PubMed1968

Development of methodologic tools for planning and managing library services. II. Measuring a library's capability for providing documents.

A method of measuring a library's capability for providing the documents its users need has been developed. The library is tested with a representative sample of such documents to determine how long would be required for users to obtain these documents. Test results are expressed in terms of a Capability Index, which has a maximal value of 100 only if all the sample documents are found "on shelf." Specific tests employing samples of 300 documents have been developed that are appropriate for academic and for "reservoir" biomedical libraries. Realistic field trials have demonstrated that these two tests are practical to administer and that test results are adequately reproducible. When strict comparability is not important, a library can test itself. In assessing a reservoir library, test results are supplemented by data on its typical processing time for interlibrary loan requests. Currently these tests are being used in a national survey. The general method is applicable to other types of libraries, provided appropriate test samples are established. If their limitations are clearly understood, these "Document Delivery Tests" can be valuable tools for planning and managing library services.

Information Services↗