Most ectotherms mature at a larger body size in colder conditions, a phenomenon known as the temperature-size rule. While a number of hypotheses have been proposed to explain this rule, little work has been done to understand it from a nutritional perspective. We have used the final-instar caterpillars of Spodoptera litura to investigate how dietary protein∶carbohydrate (P∶C) balance influences the relationship between temperature and body size. The strength and direction of the thermal reaction norm for body size were significantly altered by dietary P∶C balance. The slope of the reaction norm was nearly flat for caterpillars raised on a balanced food ([Formula: see text]) but was significantly negative for those on nutritionally imbalanced foods (1∶5 or 5∶1), especially when carbohydrates were in considerable excess. These nutrient-dependent effects of temperature on body size were caused mainly by corresponding changes in body lipid storage. When allowed to choose between imbalanced diets, caterpillars increased their preference for carbohydrates to meet high energy demands at higher temperatures. The slope of the thermal reaction norm for body size was substantially reduced by such a temperature-driven shift in nutrient preference, indicating that the impact of high temperature on body size was buffered by altered food selection. This study highlights the importance of macronutrient balance as a key factor modulating the relationship between temperature and body size in ectotherms and provides a novel approach for understanding the temperature-size rule.

Summary1. Food limitation is the most common environmental challenge faced by animals and the capacity of animals to survive prolonged periods of starvation is linked to their diet and nutritional status. The fruit flies of the genus Drosophila have been widely used to study the ecology and evolution of starvation resistance (SR), but the nutritional basis of their resistance to starvation has not yet been fully explored. 2. We have taken a nutritionally explicit approach to investigate the quantitative and qualitative effects of nutrition on SR in Drosophila melanogaster using state-space geometric models of nutrition. Experimental flies were given ad libitum access to artificial diets differing in concentrations and ratios of protein and carbohydrate for 5 days before they were assayed for starvation time, body composition and life-history parameters. The main objectives of this study were to determine the most critical nutritional factor of SR and to understand the utilization patterns of endogenous metabolic fuels during starvation in Drosophila. 3. Starvation resistance in Drosophila was greatly influenced by the dietary protein : carbohydrate (P : C) ratio, but neither by the caloric content of the diet nor by carbohydrate alone. SR was strongest at the lowest P : C ratio and decreased with rising P : C ratio. When fed on low P : C diets, Drosophila not only deposited more lipids, but also lowered the minimum body weight required for tolerating starvation. During starvation, Drosophila exhibited a dramatic transition in the utilization of endogenous fuels. In the early phase of starvation, Drosophila exclusively used nonlipid substrates, but switched to the late phase during which they mobilized lipids to maintain life under starvation. 4. Our results highlight the important role that nutrition plays in determining the phenotypic expression of SR in Drosophila and provide broad implications for understanding starvation responses in other species, including humans. This study introduces how the recent advances in nutritional physiology can offer new insights into the ecology and evolution of starvation responses.

Protein and carbohydrate are the two major macronutrients that exert profound influences over fitness in many organisms, including Our understanding of how these macronutrients shape the components of fitness in has been greatly enhanced by the use of nutritional geometry, but most nutritional geometric analyses on this species have been conducted using semi-synthetic diets that are not chemically well defined. Here, we combined the use of nutritional geometry and chemically defined diets to compare the patterns of larval and adult life-history traits expressed across 34 diets systematically varying in protein:carbohydrate (P:C) ratio and in protein plus carbohydrate (P+C) concentration. The shape of the response surfaces constructed for all larval and adult traits differed significantly from one another, with the nutritional optima being identified at P:C 1:4 for lifespan (P+C 120 g l), 1:2 for egg-to-adult viability (120 g l), 1:1 for female body mass at adult eclosion (240 g l) and lifetime fecundity (360 g l), 2:1 for larval developmental rate (60 g l) and 8:1 for egg production rate (120 g l). Such divergence in nutritional optima among life-history traits indicates that confined to a single diet cannot maximize the expression of these traits simultaneously and thus may face a life-history trade-off. Our data provide the most comprehensive and nutritionally explicit analysis of the impacts of macronutrients on life-history traits in and support the emerging notion that the fundamental trade-offs among life-history traits are mediated by macronutrients.

No abstract

The spiking neural network (SNN) is regarded as the third generation of an artificial neural network (ANN). In order to realize a high-performance SNN, an integrate-and-fire (I&F) neuron, one of the key elements in an SNN, must retain the overflow in its membrane after firing. This paper presents an analog CMOS I&F neuron circuit for overflow retaining. Compared with the conventional I&F neuron circuit, the basic operation of the proposed circuit is confirmed in a circuit-level simulation. Furthermore, a single-layer SNN simulation was also performed to demonstrate the effect of the proposed circuit on neural network applications by comparing the raster plots from the circuit-level simulation with those from a high-level simulation. These results demonstrate the potential of the I&F neuron circuit with overflow retaining characteristics to be utilized in upcoming high-performance hardware SNN systems.