Allometric exponent
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Several phenomenological descriptions, such as the von Bertalanffy growth model, have been widely used to describe size-at-age and individual growth across a diverse range of organisms. However, for modelling life histories, as opposed to just growth, biologically and mechanistically meaningful growth models, based on allocation decisions, have become increasingly important. This is because fitness is determined by survival and reproduction, which are not addressed directly in phenomenological growth models. To elucidate these considerations, we take as a starting point the biphasic growth model by Quince et al. (2008a, J. Theor. Biol. 254:197) which has the advantage that the underlying allometric scaling of net energy intake can be freely chosen. First, we reformulate this model such that individual size is given in meaningful units of length and weight, facilitating the model׳s interpretation and application. Second, we show that even though different allometric scaling relationships can produce practically identical growth trajectories, the accompanying reproductive investments are highly dependent on the chosen allometric exponent. Third, we demonstrate how this dependence has dramatic consequences for evolutionary predictions, in particular with regard to the age and size at maturation. These findings have considerable practical relevance, because empirically observed allometric exponents are often uncertain and systematically differ from those assumed in current standard growth models.
- Klíčová slova
- Allometric exponent, Fitness, Maturation, Reproductive investment, Size-at-age,
- MeSH
- druhová specificita MeSH
- genetická zdatnost MeSH
- lidé MeSH
- přežití MeSH
- rozmnožování fyziologie MeSH
- růst fyziologie MeSH
- tělesné váhy a míry * MeSH
- teoretické modely * MeSH
- velikost těla * MeSH
- životní prostředí MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
BACKGROUND: Although absolute handgrip strength has been associated with health-related outcomes in older adults, little evidence has been provided regarding its adjustment by a variety of body size dimensions. Therefore, the main purpose of the study was to establish the most appropriate normalization of handgrip strength by different body size parameters in a large sample of noninstitutionalized older adults. METHODS: In this cross-sectional study, we enrolled 643 men and women aged > 60, who were part of the rehabilitation center facility program. Handgrip strength was objectively measured using a Jamar Plus* + Digital Hand Dynamometer. Body size parameters included body weight and height, body mass index, waist circumference, waist-to-height ratio, fat mass and fat-free mass. The most appropriate parameter associated with handgrip strength was identified using allometry. RESULTS: Findings showed that the most appropriate body size parameter for handgrip strength normalization was height (allometric exponent: 0.85), compared to fat-free mass (0.26) and body mass (0.12). Other body size variables were not significantly associated with handgrip strength and were omitted from further analyses. The correlations between normalized handgrip strength were significant when handgrip strength was normalized by body mass and fat-free mass, while no significant correlations were found, when handgrip strength was normalized by body height. CONCLUSION: Based on the study results, body height seems to be the best body size parameter for handgrip strength normalization in older adults, omitting the influence of body size on strength performance. If handgrip strength is measured, body height may help normalize strength for large-scale research.
- Klíčová slova
- Allometric modelling, Body size, Elderly population, Hand strength, Muscle strength dynamometer performance,
- Publikační typ
- časopisecké články MeSH
Rensch's rule predicts an allometric relationship between male and female body size stating that the sexual size dimorphism (SSD) increases with body size in male-larger taxa and decreases in female-larger taxa in groups of related species. It means that the relationship between the male and female body size is hyperallometric, i.e., the allometric exponent of this relationship exceeds the unity. We explored the relationship between the male and female body size in a New World clade of lizards consisting of sister families Teiidae and Gymnophthalmidae, which exhibit a great variation in both their adult body sizes and SSD. All our estimates of the reduced major axis regression slopes ranged from 1.067 to 1.229 and clearly followed a pattern consistent with the Rensch's rule. Despite a clear general trend, giant species from the subfamily Tupinambinae show paradoxically only poor SSD. The cases of extreme male-larger SSD were found in species of moderate body size belonging to the genera Ameiva and Cnemidophorus. The abovementioned deviations from the hyperallometric relationship between the male and female body size are surprising and require further examination.
- MeSH
- fylogeneze MeSH
- ještěři anatomie a histologie klasifikace fyziologie MeSH
- pohlavní dimorfismus * MeSH
- velikost těla fyziologie MeSH
- zvířata MeSH
- Check Tag
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Střední Amerika MeSH
The Metabolic Scaling Theory (MST), hypothesizes limitations of resource-transport networks in organisms and predicts their optimization into fractal-like structures. As a result, the relationship between population growth rate and body size should follow a cross-species universal quarter-power scaling. However, the universality of metabolic scaling has been challenged, particularly across transitions from bacteria to protists to multicellulars. The population growth rate of unicellulars should be constrained by external diffusion, ruling nutrient uptake, and internal diffusion, operating nutrient distribution. Both constraints intensify with increasing size possibly leading to shifting in the scaling exponent. We focused on unicellular algae Micrasterias. Large size and fractal-like morphology make this species a transitional group between unicellular and multicellular organisms in the evolution of allometry. We tested MST predictions using measurements of growth rate, size, and morphology-related traits. We showed that growth scaling of Micrasterias follows MST predictions, reflecting constraints by internal diffusion transport. Cell fractality and density decrease led to a proportional increase in surface area with body mass relaxing external constraints. Complex allometric optimization enables to maintain quarter-power scaling of population growth rate even with a large unicellular plan. Overall, our findings support fractality as a key factor in the evolution of biological scaling.
Egg size has a crucial impact on the reproductive success of a mother and the performance of her offspring. It is therefore reasonable to employ egg size as a proxy for egg content when studying variation in offspring performance. Here, we tested species differences in allometries of several egg content parameters with egg area. We measured individual eggs in five species of annual killifish (Cyprinodontiformes), a group of fish where egg banks permit population survival over dry season. Apart from comparing allometric scaling exponents, amounts and compositions of egg components across the different species, we assessed the explanatory power of egg area for egg wet and dry weight and for hatchling size. We found notable species-specific allometries between egg area and the other egg parameters (egg dry weight and water content, elemental composition and triglyceride content). Across species, egg area predicted egg wet weight with highest power. Within species, coefficients of determination were largest in A. elongatus, a large piscivorous species with large eggs. Our study shows that systematically using egg area as a proxy of egg content between different species can ignore relevant species-specific differences and mask within-species variability in egg content.
- Klíčová slova
- Allocation strategy, Allometry, Austrolebias, Egg composition, Nothobranchius furzeri,
- MeSH
- druhová specificita MeSH
- embryo nesavčí fyziologie MeSH
- energetický metabolismus fyziologie MeSH
- Fundulidae fyziologie MeSH
- roční období MeSH
- rozmnožování fyziologie MeSH
- triglyceridy metabolismus MeSH
- velikost těla MeSH
- žloutkový vak metabolismus MeSH
- zvířata MeSH
- Check Tag
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- triglyceridy MeSH
