Almost 50 years ago Neel proposed a hypothesis to explain the prevalence of obesity and diabetes in modern societyFthe ‘thrifty gene’ hypothesis. The fundamental basis of the hypothesis was that, in our early evolutionary history, genes, that promoted efficient fat deposition would have been advantageous because they allowed their holders to survive at periods of famine. In modern society, such genes are disadvantageous because they promote fat deposition in preparation for a famine that never comes, and the result is widespread obesity and diabetes. In recent years I, and others, have questioned some of the fundamental assumptions of this hypothesisFparticularly focusing on whether differential survival of lean against obese in famines provides sufficient selective pressure for the spread of so-called ‘thrifty genes’. These arguments have been criticized because famines not only affect survival but also fecundity, and obese people would be expected to sustain fecundity longer in the face of food shortages. In this paper, I show that the reduced fecundity argument is flawed because famines are almost universally followed by periods of enhanced fecundity, which offsets the decline observed during the famine itself. The net effect of famines on fecundity is consequently insufficient to rescue the thrifty gene idea. Elsewhere, I have suggested an alternative scenario that subsections of the population have a genetic predisposition to obesity due to an absence of selection, combined with genetic drift. The scenario presented earlier was based on evidence from prehistory concerning the release of our ancestors from heavy predation pressure around 2 million years ago. I suggest here that this is one of a number of potential scenarios based on random genetic drift that may explain the specific aetiology of the obesity epidemic. Together, these alternatives, based on central notion that genetic drift rather than positive selection was a dominant factor, may be called the ‘drifty gene’ hypothesis.

/pdf/thrifty-genes-for-obesity-an-attractive-but-flawed-idea-and-2q60vd2plv.pdf

Thrifty genes for obesity, an attractive but flawed idea, and an alternative perspective: the 'drifty gene' hypothesis.

Obesity is considered one of the most common forms of malnutrition occurring in dogs Laboratory methods of evaluation of body composition in live dogs have included dual-energy X-ray absorptiometry (DEXA) and deuterium oxide (D2O) dilution Clinical methods of evaluation include assigning a body condition score (BCS) based on visual observation, palpation, and morphometric measurements This study used these four methods to evaluate 23 healthy, adult, client-owned dogs Good correlation (coefficient of determination [r2]=078) was found between measurements of percent body fat (%BF) determined by the D2O dilution method and the DEXA scan Percent body fat can also be estimated using BCS (r2=092 comparison with DEXA) or by using morphometric measurements with simple calculations (r2=092 comparison with DEXA)

Comparison of various methods for estimating body fat in dogs

Objective: to evaluate the applicability, precision, and accuracy of the new EchoMRI quantitative magnetic resonance (QMR) method for in-vitro bovine bone analysis and in-vivo whole-body-composition analysis of conscious live mice. Research methods and procedures: bovine tibia bone samples were measured by QMR and dual-energy X-ray adsorptiometry (DEXA). Repeated measures of whole-body composition were made using live and dead mice with different levels of fat by QMR and DEXA and by classic chemical analysis of the mouse carcass. Results: bone-mineral density (BMD) and bone-mineral content (BMC) measured in bovine tibia by QMR and DEXA were highly correlated. Precision of fat and lean measurement in mice was found to be better for QMR than for DEXA. The coefficient of variation (CV) for fat was 0.34–0.71% for QMR compared with 3.06–12.60% for DEXA. Discussion: QMR offers more specific parameters of bone structure than does DEXA. QMR and DEXA did not differ in the total amount of fat detected in live mice but QMR had improved precision. QMR was superior to DEXA in measuring fat in very small mice. Conclusions: in bone tissue there is a strong correlation between hydrogen NMR signal and bone-mineral density as measured by X-ray. QMR provides a very precise, accurate, fast, and easy to use method for determining fat and lean mass of mice without the need for anesthesia. Its ability to detect differences and monitor changes in body composition in mice with great precision should be of great value in characterizing phenotypes and studying drugs affecting obesity.

Quantitative magnetic resonance (QMR) method for bone and whole-body-composition analysis

The domestic dog has undergone extensive artificial se- lection resulting in an extreme diversity in body size, personality, life-history, and metabolic traits among breeds. Here we tested whether proactive personalities (high levels of activity, boldness, and aggression) are related to a fast "pace of life" (high rates of growth, mortality, and energy expenditure). Data from the literature provide preliminary evidence that artificial selection on dogs (through do- mestication) generated variations in personality traits that are cor- related with life histories and metabolism. We found that obedient (or docile, shy) breeds live longer than disobedient (or bold) ones and that aggressive breeds have higher energy needs than unaggressive ones. These correlations could result from either human preference for particular trait combinations or, more likely, correlated responses to artificial selection on personality. Our results suggest the existence of a general pace-of-life syndrome arising from the coevolution of personality, metabolic, and life-history traits.

/pdf/the-pace-of-life-under-artificial-selection-personality-4zje8tyrul.pdf

The pace of life under artificial selection: personality, energy expenditure, and longevity are correlated in domestic dogs.

In most animal taxa, longevity increases with body size across species, as predicted by the oxidative stress theory of aging. In contrast, in within-species comparisons of mammals and especially domestic dogs (e.g. Patronek et al., '97; Michell, '99; Egenvall et al., 2000; Speakman et al., 2003), longevity decreases with body size. We explore two datasets for dogs and find support for a negative relationship between size and longevity if we consider variation across breeds. Within breeds, however, the relationship is not negative and is slightly, but significantly, positive in the larger of the two datasets. The negative across-breed relationship is probably the consequence of short life spans in large breeds. Artificial selection for extremely high growth rates in large breeds appears to have led to developmental diseases that seriously diminish longevity.

Do Large Dogs Die Young

As a species, the dog is unique. Depending on the breed, body weight varies 100-fold from the 1-kg Chihuahua to the 115-kg St. Bernard (1). The time taken for a growing puppy to achieve adult body weight also varies considerably with larger breeds having a longer growth period than smaller breeds. Also the rate of growth during this period is not constant; energy requirements decrease from 3 times maintenance at weaning to1.2 times maintenance as the puppy approaches adulthood (1). The provision of accurate feeding guides is essential if under- and overnutrition are to be prevented. Overnutrition of dogs results in obesity, but in large breeds overnutrition also causes musculoskeletal disorders (2,3). However, present feeding guides are based on "typical" growth data that use only a single equation (4,5). Breed-specific differences in growth patterns might be expected due to huge variations in size, temperament, and coat type, all of which are likely to affect energy requirements. This was evident in a study of six breeds of puppies that demonstrated very different energy requirements despite similar absolute body weights in Great Danes versus Newfoundlands and Briards versus Labrador Retrievers (6). Little information is published on breed-specific variations in puppy growth patterns, and most studies provide only limited data on single breeds, for example, 8-34-mo-old and 6-20-wk-old Labrador Retrievers (7,9) and 0-12-wk-old German Shepherds (8). Other studies are confounded by the use of different groups of dogs to provide data for a variety of age groups (10). Comparisons between these studies are difficult due to differing data presentation and treatment. The aim of this study was to compare the complete growth curves of 12 different-sized dog breeds and to investigate a mathematical basis for the provision of breed-specific feeding guides.

/pdf/body-weight-changes-during-growth-in-puppies-of-different-2rdaiwnm5j.pdf

Body-weight changes during growth in puppies of different breeds.

The repeatability of body composition measurements in dogs and cats using dual energy X-ray absorptiometry.

Isotope-based techniques for the measurement of water turnover, energy expenditure, and milk intake often assume that there is no recycling of isotopes once they have left the labeled animal. In ex...

Isotope recycling in lactating dogs (Canis familiaris)

Body composition of male and female Labrador retriever puppies at 20 wk of age.

Effects of two levels of zinc intake on growth and trace element status in Labrador puppies.

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