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Biomedical subjects

D Raubenheimer

Publications and source records attributed to D Raubenheimer.

14 recordsLinked to original sources
PubMed2006

Flexible diet choice offsets protein costs of pathogen resistance in a caterpillar.

Mounting effective resistance against pathogens is costly in terms of energy and nutrients. However, it remains unexplored whether hosts can offset such costs by adjusting their dietary intake so as to recoup the specific resources involved. We test this possibility by experimentally challenging caterpillars (Spodoptera littoralis) with a highly virulent entomopathogen (nucleopolyhedrovirus), under dietary regimes varying in the content of protein and digestible carbohydrate. We found that dietary protein influenced both resistance to pathogen attack and constitutive immune function to a greater extent than did dietary carbohydrate, indicating higher protein costs of resistance than energy costs. Moreover, when allowed to self-compose their diet, insects surviving viral challenge increased their relative intake of protein compared with controls and those larvae dying of infection, thus demonstrating compensation for protein costs associated with resistance. These results suggest that the change in the host's nutritional demands to fight infection induces a compensatory shift in feeding behaviour.

Animal Feed↗
PubMed2005

Does Bertrand's rule apply to macronutrients?

It has been known for over a century that the dose-response curve for many micronutrients is non-monotonic, having an initial stage of increasing benefits with increased intake, followed by increasing costs as excesses become toxic. This phenomenon, termed Bertrand's rule, is widely assumed not to apply to caloric macronutrients. To date this assumption has been safe, owing to the considerable methodological challenges involved in coaxing animals to over-ingest macronutrients in a way that enables the effects of specific food components to be isolated. Here we report an experiment which overcomes these difficulties, to test whether the second phase (incurring costs with excessive intake) applies to carbohydrate intake by the generalist-feeding caterpillar Spodoptera littoralis. The results showed that excess carbohydrate intake caused increased mortality, thus extending Bertrand's rule to macronutrients.

Animal Feed↗
PubMed2005

Obesity: the protein leverage hypothesis.

The obesity epidemic is among the greatest public health challenges facing the modern world. Regarding dietary causes, most emphasis has been on changing patterns of fat and carbohydrate consumption. In contrast, the role of protein has largely been ignored, because (i) it typically comprises only approximately 15% of dietary energy, and (ii) protein intake has remained near constant within and across populations throughout the development of the obesity epidemic. We show that, paradoxically, these are precisely the two conditions that potentially provide protein with the leverage both to drive the obesity epidemic through its effects on food intake, and perhaps to assuage it. We formalize this hypothesis in a mathematical model. Some supporting epidemiological, experimental and animal data are presented, and predictions are made for future testing.

Animals↗
PubMed2003

Nutrient balancing in grasshoppers: behavioural and physiological correlates of dietary breadth.

We examined correlates of nutrient balancing with dietary range by comparing diet selection and ingestive, post-ingestive and performance-related responses to macronutrient imbalance in two species of grasshopper. One of the two species, Locusta migratoria (the African migratory locust), is a specialist grass-feeder, while the other, Schistocerca gregaria (the desert locust), is a generalist herbivore that includes both grasses and forbs in its diet. In ad libitum conditions, both species composed a balanced intake of the two macronutrients protein and carbohydrate from nutritionally complementary synthetic foods, but the composition of the selected diet differed, with the generalist selecting more protein, but not carbohydrate, than the grass-specialist. The grass-specialist, by contrast, retained ingested nitrogen more efficiently on the ad libitum diets. When confined to nutritionally imbalanced foods, both species regulated ingestion in such a way as to mitigate excesses as well as deficits of the two nutrients. The responses were, however, distinct in the two species, with the generalist feeder ingesting greater excesses of protein than the specialist. The species also differed in their post-ingestive responses to ingested excesses of nutrient, with the generalist but not the specialist using protein-derived carbon as an energy source when fed carbohydrate-deficient foods. The generalist also retained a higher level of body protein when confined to protein-deficient diets. The data suggested one functional reason why the generalist species selected a diet with higher protein content in the ad libitum treatment because, when confined to the nutritionally imbalanced foods, development rate peaked on higher protein foods for the generalist compared with the specialist. Many aspects of these data agree with the prediction that generalist-feeding animals should show greater behavioural and physiological flexibility in their responses to nutrient imbalance than do specialists.

Animal Nutritional Physiological Phenomena↗
PubMed2002

A geometric analysis of nutrient regulation in the generalist caterpillar Spodoptera littoralis (Boisduval).

Nutritional regulatory responses of the generalist caterpillar Spodoptera littoralis (Boisduval) were explored, in choice and no-choice experiments, using the Geometric Framework. In the choice experiment, newly moulted final instar larvae were provided with one of three protein-biased foods (PB-food: p35:c7, p28:c5.6 or p21:c4.2) and one of three equal protein-carbohydrate ratio foods (ER-food: p21:c21, p16.8:c16.8 or p12.6:c12.6). On five of the nine treatments, caterpillars independently regulated protein and carbohydrate intake to a mixture of 57 and 43%, respectively. However, when the concentration of the ER-food decreased and that of the paired PB-food increased, caterpillars progressively abandoned regulation and ate more of the PB-food. Despite these regulatory differences, performance (survivorship, growth and development) was similar across all nine treatments. In the no-choice experiment, caterpillars were given one of five foods (p35:c7, p28:c14, p21:c21, p14:c28 and p7:c35). Results indicated that caterpillars moved to a point in protein-carbohydrate space that was consistent with the Equal Distance Rule of compromise, a pattern previously predicted for generalist feeders. The insects on the two extreme foods, p35:c7 and p7:c35, showed reduced pupal mass and longer development, respectively. There was also strong evidence for post-ingestive regulation of nutrient utilisation, notably for protein.

Journal Article↗
PubMed2002

A comparison of nutritional regulation in solitarious- and gregarious-phase nymphs of the desert locust Schistocerca gregaria.

Nutritional regulatory responses were compared for the cryptic 'solitarious' and the conspicuously coloured, aggregating 'gregarious' phases of the desert locust Schistocerca gregaria. The desert locust has the genetic potential to exist in either phase, changing between them within a lifetime and epigenetically across generations. Our aim was to compare final-instar nymphs of the two phases with respect to key nutritional variables, including (i) points of regulated intake (the 'intake target') for protein and carbohydrate, (ii) the nature of trade-offs between over-eating nutrients in excess and under-eating those in deficit when fed nutritionally unbalanced foods, (iii) diet-related patterns of nutrient utilisation, and (iv) the performance consequences of eating nutritionally unbalanced diets. When provided with pairs of nutritionally unbalanced but complementary foods, both phases regulated their intake of protein and carbohydrate to a similar point. However, when confined to foods that were of unbalanced protein to carbohydrate ratio, gregarious nymphs ate more than solitarious insects. Both phases regulated protein growth, but gregarious insects did so to a lower adult body protein content and converted ingested protein to growth less efficiently. When fed a food high in carbohydrate and low in protein, gregarious nymphs deposited more body lipid and survived less well than did solitarious insects. Solitarious nymphs developed more quickly than gregarious nymphs except on the two most extremely unbalanced diets, on which development time was similar. The results are discussed with respect to the different nutritional ecologies of the two phases and used to develop the hypothesis that animals have evolved to trade-off the cost of eating excess of a nutritionally unbalanced diet against the probability of encountering foods of complementary composition in the future.

Animal Nutritional Physiological Phenomena↗
PubMed2001

Nutritional regulation in nymphs of the German cockroach, Blattella germanica.

Synthetic foods varying in protein-carbohydrate ratio and total nutrient concentration were used in food selection experiments to investigate the ingestive and post-ingestive regulation of macronutrients by male and female nymphs of the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae). For both nutrient imbalance and food dilution, food ingestion varied between treatments with the effect that nutrient ingestion was regulated. However, this mechanism was insufficient to compensate for some food dilution treatments. In those cases, the regulation of protein intake was prioritised over that of carbohydrate intake, and two additional regulatory responses were seen. Firstly, cellulose digestion supplemented shortfalls in dietary soluble carbohydrates, and secondly the feeding period within the stadium was prolonged. These ingestive, post-ingestive and developmental responses were orchestrated in such a way that, in all treatments, nutrient gain approached similar levels, despite the variation in food properties.

Journal Article↗
PubMed2000

Sex-specific differences in nitrogen intake and investment by feral and laboratory-cultured cockroaches.

We compared nutrient selection in a laboratory culture of the American cockroach (Periplaneta americana: Insecta, Blattodea) and a feral population which was founded by escapees from the culture approximately 14 generations prior to the study. In a first experiment, adult male and female cockroaches were provided with two nutritionally complementary synthetic foods, and thus allowed to select the protein and carbohydrate components of their diet independently. There were no differences in the amounts of carbohydrate eaten by the two populations. However, feral males ingested more protein than cultured males. In a second experiment, the construction of nitrogen budgets showed that the additional nitrogen ingested by feral males was allocated preferentially to accessory sex glands, rather than somatic tissue or excretion via the faeces. This suggests a possible role for sexual selection in the dietary difference between the strains. By contrast with males, there was no statistically significant difference in the amount of protein eaten by females of the two populations. However, feral females were found to have a higher density of bacterial endosymbionts than cultured females. Since these symbionts are involved in the synthesis of essential amino acids, this might account for greater reproductive output observed in a previous study in the feral compared with the culture females.

Journal Article↗
PubMed1999

Assuaging nutritional complexity: a geometrical approach.

We have introduced a framework that enables the identification of the important elements in complex nutritional systems, and the quantification of the interactions among them. These interactions include those among the multiple constituents of the ingesta, as well as between behavioural (ingestive) and physiological (post-ingestive) components of nutritional homeostasis. The resulting descriptions provide a powerful means to generate and test hypotheses concerning the mechanisms, ecology and evolution of nutritional systems. We provide an overview of the key concepts involved in our scheme, and then introduce four examples in which the framework is used to develop and test hypotheses. In the first example we use comparative methods based on a data set of 117 insect species to test a prediction about the relationship between evolving an association with bacterial endosymbionts and the composition of the optimal diet. Second, using two species of locusts (a grass specialist and a generalist), we consider the relationship between an animal's diet breadth and the decision rules employed when feeding on foods containing suboptimal protein: carbohydrate values. Third, we introduce a mathematical model that predicts the dose-response properties of gustatory systems in the context of nutritional homeostasis. Finally, we consider the interaction between tannic acid and macronutrient balance in the diet of locusts.

Animal Nutritional Physiological Phenomena↗
PubMed1997

Associative learning by locusts: pairing of visual cues with consumption of protein and carbohydrate

We investigated whether fifth instar African migratory locusts, Locusta migratoria could learn to associate visual cues with the macronutrient content of synthetic foods. During a 48-h training period, the insects had ad libitum access to two synthetic foods which were identical in all respects except that one lacked protein and the other lacked digestible carbohydrate. One food was placed at the end of a transparent Perspex cylinder which had been tinted green, and the other at the end of a yellow-tinted cylinder which was similar in all other respects. To obtain a balanced diet, the insects were thus forced to ingest the two macronutrients in visually different environments. Following this training period, they were then made selectively deficient in either protein or carbohydrate, before being tested for their tendency to enter, and the depth of entry into, yellow- or green-tinted cylinders that did not contain food. Locusts entered significantly more frequently the colour of cylinder that had previously been paired with the deficient nutrient (henceforth termed the 'training colour'). This was true irrespective of whether the nutrient was protein or carbohydrate, and whether the training colour was green or yellow. There was no effect of training on the average depth of entry into the cylinders. However, protein-deprived locusts penetrated significantly more deeply than carbohydrate-deprived locusts into both green and yellow cylinders, irrespective of the training colour. A separate experiment demonstrated that naive locusts entered more frequently into the yellow than the green side-arm, but there was no influence of colour on the depth of entry by naive locusts.Copyright 1997 The Association for the Study of Animal BehaviourCopyright 1997The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1997

Geometric analysis of macronutrient selection in the rat.

A conceptual framework is introduced which has been derived from work on insects. The scheme is intended to integrate studies of diet selection, regulation of amounts eaten, nutrient utilization, body composition and animal performance. Aspects of framework are illustrated with published data on macronutrient selection in the rat. An animal is viewed as moving through a multidimensional nutrient space, which is bounded by axes representing each required nutrient and within which lie optimal points of intake and nutrient allocation ("targets"). The aim is first to estimate the location of these functional optima experimentally, and then to interpret the responses of animals which are constrained from reaching them ("decisions of best compromise"). The framework can then be used to interpret data from animals reared under differing environmental conditions and to compare animals of differing developmental stage, genotype or nutritional state.

Animals↗
PubMed1997

The functional significance of switching interval in food mixing by Locusta migratoria.

To investigate the consequences of different patterns of switching between nutritionally complementary foods, nymphs of Locusta migratoria L. (Orthoptera: Acrididae) were forced to alternate between pairs of artificial foods differing only in their protein and carbohydrate content at one of several fixed intervals. Total food and nutrient intake over 6days were very similar in all groups despite the considerable variation in temporal patterns of nutrient intake. The effects of these treatments were determined using measurements of growth, stadium duration and carcass composition. Those given a low variance food pairing showed little effect in any of the measures while those given a high variance pairing showed no differences in dry weight growth or stadium duration but did differ in protein and lipid content. There was little evidence from our measurements that an ad-libitum alternation time of 4h previously observed in a laboratory experiment was physiologically optimal, suggesting that ecological factors may underlie such behaviour. Possible compensatory mechanisms used by L. migratoria are suggested.

Journal Article↗