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J Prothero

Publications and source records attributed to J Prothero.

32 records · Page 2Linked to original sources
PubMed1987

Scaling of maximal lifespan in bats.

1. Values for maximal lifespan in heterothermic and homeothermic bats as a function of body weight, brain weight and lifetime basal energy consumption were submitted to linear (log-log) and multiple regression analysis. 2. The results of the regression analyses of maximal lifespan in bats were compared with those reported for non-flying mammals based on both narrow and wide weight ranges. 3. It was found that the regression lines (linear or multiple) for maximal lifespan in bats (heterothermic or homeothermic) lie well above the regression lines for non-flying mammals. 4. Predictions of maximal lifespan in heterothermic bats based on estimated lifetime basal energy consumption and body weight are in reasonable agreement with observed values when torpor and hibernation behaviour are taken into account. 5. But observed values of maximal lifespan in homeothermic bats were found to lie substantially above the regression lines derived for non-flying mammals. 6. It was concluded that existing hypotheses do not account for the long lifespan observed in bats generally.

Animals↗
PubMed1986

Methodological aspects of scaling in biology.

Interest in the scaling approach to problems of biological design has increased dramatically in the past few years. But thus far no systematic attempt has been made to review the possible pitfalls attendant upon this approach. As a beginning, the problems which can arise from rounding exponents, or taking standard errors at face value, or expressing dependent variables in ratio form are discussed. There follows a discussion of fitting specific functions to scaling data, of the special needs for documentation and of the potential value to be derived from suitable computer programs in scaling studies. Finally, the possible difficulties of demonstrating global optimization in biological systems, the risks of dimensional analysis and the value and nature of scaling models are discussed.

Animals↗
PubMed1986

Scaling of energy metabolism in unicellular organisms: a re-analysis.

The database used by Hemmingsen (1960) to compute energy metabolism in unicellular organisms was reassembled and submitted to linear (log-log) analysis. As Hemmingsen noted, this data set includes marine zygotes, which are not unicellular organisms. If no temperature correction factors are applied to the data the best-fit regression line has a slope of 0.698 +/- 0.024. Application of the temperature correction factors assumed to have been used by Hemmingsen gave a slope of 0.756 +/- 0.021, identical to the value he reported. The correlation coefficient is 0.97. The mean scatter about the regression line exceeds 100%. A revised set of temperature correction factors gave a slope of 0.730 +/- 0.021, suggesting that the value of almost exactly three-quarters obtained by Hemmingsen was probably fortuitous. The slope of the best-fit regression line is very sensitive to the inclusion of bacteria and flagellates. When the data points for these organisms are omitted from the calculation the slope decreases to 0.645 +/- 0.045. When the data points for bacteria, flagellates and marine zygotes are omitted, the slope drops to 0.608 +/- 0.025. The correlation coefficient (0.97), compared to the best-fit line reported by Hemmingsen, is unaffected; the mean deviation about the regression line drops to 40% and the points are evenly distributed about the regression line. Because of the small number of species for which measurements have been made, the existing database relating energy metabolism to cell size is not representative of unicellular organisms generally. It is concluded that the case for a three-quarters power rule expressing energy metabolism as a function of size in unicellular organisms generally is not at all persuasive.

Animals↗
PubMed1984

Scaling of standard energy metabolism in mammals: I. Neglect of circadian rhythms.

The original data employed to derive the three-quarters power rule relating standard or basal energy metabolism in mammals to adult body weight are examined. It is shown that the data may contain a systematic bias due to an (apparent) neglect of circadian rhythms. Correction for this bias would tend to decrease the slope of the regression line, bringing it into better conformity with the value of about two-thirds obtained in a recent study of a larger sample by Bartels (1982).

Animals↗
PubMed1984

Organ scaling in mammals: the kidneys.

Values of kidney weight in adult male and female mammals, both terrestrial and aquatic, as well as values for renal blood flow and glomerular number and diameter, were submitted to linear (log-log) regression analysis. The slope of the regression line for kidney weight in 63 species of adult terrestrial mammals was 0.85 %/- 0.01. No statistically significant difference was found between the slopes of the regression lines for male and female terrestrial mammals. The slope of regression line for kidney weight in eight species of adult aquatic mammals was 0.92 +/- 0.01. Again, no statistically significant difference was found between the slopes for males and females. However, the slope (0.92) of the regression line for aquatic mammals was significantly different from the slope (0.85) for terrestrial mammals (P much less than 0.001). The slope of the regression of renal blood flow on body weight was 0.82 +/- 0.01. This value is consistent with the hypothesis that renal blood flow represents a constant fraction of cardiac output (over about 3.4 orders of magnitude in body weight). The slopes of the regression lines for glomerular number (per kidney) and mean glomerular diameter were 0.59 +/- 0.02 and 0.11 +/- 0.01, respectively. A schematic model representing the scaling of energy-partitioning in mammals is introduced.

Animals↗
PubMed1981

A model of clonal attenuation.

Two formal models of clonal attenuation [Kirkwood, T. B. L. & Holliday, R. (1975) J. Theor. Biol. 53, 481-496; Shall, S. & Stein, W. D. (1979) J. Theor. Biol. 76, 219-231] are considered in the light of recent data on the changing distribution of replicative potential among individual cultured fibroblasts on subcloning. The experimental data [Smith, J. R., Pereira-Smith, O. & Good, P. I. (1977) Mech. Ageing Dev. 6, 283-286] are shown to contradict both models. A new model, compatible with the subcloning data, is proposed. This model involves a gradual increase in the probability of commitment during cell growth in culture and a small number (about seven) of divisions following commitment. The gradual increase in commitment probability is shown to be compatible with the gradual accumulation of a gene product subject to autogenous regulation.

Cell Differentiation↗
PubMed1979

Heart weight as a function of body weight in mammals.

Linear regression analysis was carried out on logarithmically transformed heart weight and body weight data in 104 mammalian species. It was shown that heart weight varies as the 0.98 power of body weight over essentially the whole mammalian weight range. The coefficient of correlation between heart weight and body weight is 0.99. Student's test was employed to compare the slopes of the several regression lines as between male and female animals, and as between terrestrial and aquatic mammals. In neither case were the differences in slope found to be statistically significant (df greater than 177, p less than 0.5).

Animals↗
PubMed1978

Cell kinetics in the erythroid compartment of guinea pig bone marrow: a model based on 3H-TdR studies.

A model of steady-state erythropoiesis in the guinea pig is described. The model incorporates an unidentified progenitor compartment, as well as compartments representing proerythroblasts, basophilic, polychromatic and orthochromatic cells. A computer representation of the model permits a simulation of the labeling curves obtained in pulse and intermittent labeling regimes. It was found that a reasonable fit to the data can be achieved when the parameters for the various compartments are essentially identical. The results of a preliminary sensitivity analysis, carried out by perturbing the duration of S phase from the best fit value, are reported. The fit achieved to the data supports the hypothesis underlying the model that each compartment corresponds to one generation and that the flux within and between compartments is sequential.

Animals↗
PubMedDate not supplied

Adult life span as a function of age at maturity.

A regression analysis was made of age at first reproduction in female mammals, as a function of body weight, using the data of Wootton. Data on maximal life span, also expressed as a function of body weight, were used to calculate "adult" life span, wherever possible, by subtracting the cognate value for age at first reproduction. Then a regression analysis of adult life span as a function of age at first reproduction was made. In both cases global regression lines (i.e., for whole data sets) were computed by standard least squares and by a robust method, as well as local regression lines for subgroups classified by taxonomic and ecological criteria. The slopes of the various regression lines were found to vary widely as a function of the method of classification. This result argues against the notion that the ratio of life history variables is a constant, or that one life history variable is likely to be a simple function of another. The results for bats are anomalous, in that age at first reproduction appears to be independent of body weight (over about two orders of magnitude). It is concluded that a full understanding of life history variables, such as maximal life span and age at maturity, is likely to depend on combined physiological, ecological, and evolutionary insights.

Age Factors↗