영양은 모든 생명활동의 근본이며, 생물의 진화적 적응도를 결정하는 가장 중요한 요인이다. 곤충영양학은 곤충생리학의 전통적인 연구영 역이며, 최근 산업곤충의 대량사육 필요성이 증가함에 따라 그 중요성이 부각되고 있다. 이러한 중요성에도 불구하고, 곤충의 영양현상을 정확히 이해하기란 어려운데, 이는 영양의 다변량적 특성, 영양소 간의 교호작용 등으로 설명되는 영양적 복잡성에 기인한다. 영양기하학(Nutritional Geometry)은 이러한 난점을 극복하기 위해 고안된 통합적이고 다차원적인 분석모형으로서, 최근 곤충영양학이 급격하게 발전할 수 있는 이론적 및 실험적 기반을 제공하였다. 본 종설은 영양기하학의 기본개념을 소개하고, 이러한 방법론이 어떻게 최근 곤충영양학의 급속한 학문적 진보를 가능케 하였는지, 그리고 영양이 어떻게 생리학, 생태학, 진화생물학을 통합하는 구심점이 될 수 있었는지를, 최신 연구사례를 중심으로 살펴볼 것이다. 또한 본 종설은 향후 영양기하학을 적용함으로써 발전할 가능성이 높은 연구분야를 고찰할 것이다.

Different laboratory strains of Drosophila melanogaster are reported to differ considerably in their physiology, behavior, and life-histories, due to their adaptations to different laboratory conditions. Recent advances in insect aging research have highlighted the importance of protein:carbohydrate (P:C) balance as a key dietary determinant of lifespan and other components of fitness, but it remains unexplored whether P:C balance affects the fitness-related traits of D. melanogaster in a strain-specific manner. The purpose of this study was to compare the life-history consequences of six different laboratory strains of D. melanogaster (three Canton-S substrains, w1118, yw, and Oregon-R) allocated to four synthetic diets differing in P:C ratio (1:16, 1:4, 1:1, or 4:1). Five components of fitness (lifespan, fecundity, larval viability, development time, and body mass) were recorded from flies maintained at 25oC under L:D 12:12 photoperiod. All strains exhibited qualitatively similar responses to dietary P:C balance, with the increase in P:C ratio being associated with shortened lifespan and improved egg production. In all strains, fly larvae confined to P:C 1:16 suffered high mortality, retarded growth, and reduced body size. As indicated by significant diet×strain interactions for all measured fitness components, the magnitude of such diet effect varied among different laboratory strains in D. melanogaster. Possible explanations for such strain differences are discussed.

Diet and temperature are the two most critical environmental factors affecting life-history traits in insects, but the combined effects of these factors have been rarely investigated. In this study, various life-history traits were recorded from adult and larval Drosophila melanogaster fed on one of eight synthetic diets differing in protein:carbohydrate ratio (P:C=1:16, 1:8, 1:4, 1:2, 1:1, 2:1, 4:1, or 8:1) under one of six ambient temperatures (13, 18, 23, 28, 31, or 33oC). The patterns of adult and larval life-history traits expressed across 48 diet-by-temperature combinations were visualized using thin-plate spline technique and the presence of any significant linear, quadratic, and correlational effects of diet and temperature on trait expressions was analyzed using a second-order polynomial multiple regression. Life-history traits exhibited qualitatively different responses to variations in both diet and temperature, with the maximal expression of each trait being achieved at a completely divergent region of the diet-temperature fitness landscape. In adult females, for example, lifespan was maximized at P:C 1:16 under 13oC, but fecundity was maximized at P:C 4:1 under 28oC. These results provide empirical support for the emerging notion that environmental factors, such as diet and temperature, can mediate life-history trade-offs in insects.

Diets influence lifespan and reproduction in insects, but little is known how temperature modulates the impacts of diet on these two key fitness components. Here we examined the interactive effects of temperature and nutrient balance on lifespan and egg production rate in Drosophila melanogaster. Newly emerged adult D. melanogaster were allowed to feed ad libitum on one of eight chemically defined diets differing in P:C ratio (1:16, 1:8, 1:4, 1:2, 1:1, 2:1, 4:1, or 8:1) under one of six ambient temperatures (13, 18, 23, 28, 31, or 33℃). For both males and females, lifespan was longest for D. melanogaster fed on P:C 1:16 diet at 13℃ and shortened as both temperature and P:C ratio increased. As indicated by a significant temperature-by-diet interaction for lifespan, the diet effects on lifespan were more pronounced at lower temperatures than at higher temperatures. Egg production rate was maximized on P:C 4:1 diet at 28℃.

Protein and carbohydrate are two major macronutrients that exert profound influences over fitness in many insects, including Drosophila melanogaster. Until recently, most studies examining the impacts of these macronutrients on various life-history traits in this species have used semi-synthetic diets that are not nutritionally well-defined. Here we used chemically defined diets to examine the patterns of larval and adult traits expressed across 34 diets systematically varying in the ratio and concentration of protein and carbohydrate. The shapes of the nutritional landscapes plotted for all larval and adult traits differed significantly from one another. Diverging nutritional optima identified for these landscapes suggest that D. melanogaster cannot maximize the expression of all life-history traits simultaneously, thus leading them to face a nutrient-dependent life-history trade-off.

Temperature can modulate how insects respond to environmental stressors, such as starvation. In this study, we examine whether and how the effects of temperature on starvation resistance depend on nutritional condition and developmental stages in Drosophila melanogaster. Starvation resistance decreased as the temperature exposed during starvation rose from 18 to 28 ̊C, which was mainly caused by warming-induced increase in energy expenditure. When exposed to warm temperatures during feeding, D. melanogaster accumulated more energy reserves and thus become more starvation resistant. The temperature experienced during the larval stage also had a significant effect on starvation resistance at adult stages, with those larvae raised at cold temperatures developing into adult phenotypes with reduced resistance to starvation. This study suggests that the effects of temperature on starvation resistance are highly complex and context dependent in D. melanogaster.

Temperature can affect the ability of insects to tolerate prolonged period of food deprivation through altering the amountof energy storage, the speed of energy expenditure, or the threshold energy storage for survival. In this study, we examinedthe mechanistic basis of the temperature-dependence of starvation resistance in Drosophila melanogaster. Starvation resistancedecreased as the temperature experienced during starvation rose from 18 to 28 ̊C. This warming-mediated decrease instarvation resistance was due to accelerated energy expenditure. However, the threshold energy storage for survival wasnot affected by starvation temperature. Exposure to warm temperatures during feeding led D. melanogaster to accumulatemore energy reserves and thus to become more starvation resistant. This study highlights the important role played bytemperature in shaping the phenotypic responses of insects to starvation.

Recent research has suggested that the dietary protein:carbohydrate (P:C) balance is a critical determinant of fitness in insects. In this study, we examined the effects of dietary P:C balance on life-time reproductive success in the mealworm beetle, Tenebrio molitor. Both males and females lived the longest when fed on P:C 1:1 diet. Throughout their adult lives, females fed on P:C 1:1 diet laid significantly more eggs than those on nutritionally imbalanced diets (P:C 1:5 or 5:1). When given a choice, beetles regulated their intake of protein and carbohydrate to a ratio close to 1:1. Taken together, our results indicate the balanced intake of protein and carbohydrate maximizes life-time reproductive success in this species.

Most ectotherms mature at a larger body size in colder conditions. This negative relationship between developmental temperature and final body size is termed the temperature-size rule. In this study, we investigated how dietary protein:carbohydrate (P:C) balance modulates the fundamental relationship between temperature and body size in the final-instar caterpillars of Spodoptera litura. The magnitude and sign of the thermal reaction norm for body size were altered by the dietary P:C balance of the food eaten by caterpillars. The slope of the reaction norm was flat for caterpillars raised on a nutritionally balanced food (P:C = 1:1) but was negative for those on imbalanced foods (1:5 or 5:1). When allowed to self-compose their preferred diet, caterpillars preferred carbohydrate-rich food at higher temperatures. The negative impact of high temperature on body size was mitigated by such a temperature-driven shift in nutrient preference. This study highlights the importance of macronutrient balance as a key factor modulating the relationship between temperature and body size in insects.

Recent studies have shown that mating can alter starvation resistance in female D. melanogaster, but little is known about the behavioral and physiological mechanisms underlying such mating-mediated changes in starvation resistance. In the present study, we first investigated whether the effect of mating on starvation resistance is sex-specific in D. melanogaster. As indicated by a significant sex × mating status interaction, mating increased starvation resistance in females but not in males. In female D. melanogaster, post-mating increase in starvation resistance was mainly attributed to increases in food intake and in the level of lipid storage relative to lean body weight. We then performed quantitative genetic analysis to estimate the proportion of the total phenotypic variance attributable to genetic differences (i.e., heritability) for starvation resistance in mated male and female D. melanogaster. The narrow-sense heritability (h2) of starvation resistance was 0.235 and 0.155 for males and females, respectively. Mated females were generally more resistant to starvation than males, but the degree of such sexual dimorphism varied substantially among genotypes, as indicated by a significant sex × genotype interaction for starvation resistance. Cross-sex genetic correlation was greater than 0 but less than l for starvation resistance, implying that the genetic architecture of this trait was partially shared between the two sexes. For both sexes, starvation resistance was positively correlated with longevity and lipid storage at genetic level. The present study suggests that sex differences in starvation resistance depend on mating status and have a genetic basis in D. melanogaster.

Macronutrient balance has a strong influence on fitness in insects. Previous studies have revealed that altering the concentrations of yeast and sugar in the semi-synthetic diet has a profound impact on lifespan and fecundity in Drosophila melanogaster, indicating the role of dietary protein:carbohydrate (P:C) balance in determining these two key components of fitness. However, since yeast contains not only proteins but also other macro- and micronutrients, this lifespan-determining role of dietary P:C balance needs to be corroborated using a chemically defined diet. In this study, the effects of dietary P:C balance on lifespan and fecundity were investigated in female D. melanogaster flies on one of eight isocaloric synthetic diets differing in P:C ratio (0:1, 1:16, 1:8, 1:4, 1:2, 1:1, 2:1 or 4:1). Lifespan and dietary P:C ratio were related in a convex manner, with lifespan increasing to a peak at the two intermediate P:C ratios (1:2 and 1:4) and falling at the imbalanced ratios (0:1 and 4:1). Ingesting nutritionally imbalanced diets caused flies to start ageing earlier and senesce faster. Egg production increased progressively as the dietary P:C ratio rose from 0:1 to 4:1. Long-lived flies at the intermediate P:C ratios(1:2 and 1:4) stored a greater amount of lipids than those short-lived ones at the two imbalanced ratios (0:1 and 4:1). These findings provide a strong support to the notion that dietary P:C balance is a critical determinant of lifespan and fecundity in D. melanogaster.

Mating elicits a dramatic changes in physiology, behavior, and life-history traits in insects, but little is known about the relationship between mating and the capacity of insects to resist environmental stressors. Starvation is one of the most ubiquitous forms of environmental stress faced by all insects under natural conditions. Previous studies using Drosophila melanogaster flies has shown that mated females lived longer under starvation than did virgin females, but the mechanistic basis for such post-mating increase in starvation resistance remains largely unexplored. The objective of this study was to investigate the behavioral and physiological mechanisms of mating-induced alteration in starvation resistance and its heritable genetic variations in D. melanogaster. In the first experiment (Experiment 1), we compared starvation resistance (measured as starving time before death), body compositions, and food intake between mated and unmated flies of both sexes using a large outbred population. In the second experiment (Experiment 2), starvation resistance and body composition were quantified for mated male and female flies derived from each of 19 highly inbred genetic lines. Results from Experiment 1 showed that mated females were better able to resist starvation than virgin females and males because they ate more and thus laid down more fats in their body. Results from Experiment 2 revealed a significant heritable genetic variation in starvation resistance and its correlated body composition parameters for both sexes. Overall, females had a higher starvation resistance than males, but the magnitude of such intersexual difference varied among genetic lines, as suggested by a significant sex-by-line interaction. Cross-sex genetic correlations were highly significant and positive for starvation resistance, indicating that the genetic factors controlling the starvation resistance in D. melanogaster are shared between the two sexes.

Starvation resistance is an important fitness trait that is controlled by both environmental and heritable factors. The main objective of this study is to explore the genotype-by-nutrient interactions for starvation resistance and its correlating physiological traits in Drosophila melanogaster. In this study, we conducted a split-family quantitative genetic experiment, in which female adults of Drosophila from 19 isofemale genetic lines were allowed to ingest one of two synthetic diets that differed in protein-to-carbohydrate ratio (P:C = 4:1 or 1:16 with the P+C concentration of 120 g L-1) before they were assayed for starvation time and lipid storage. In all genetic lines, Drosophila flies that had fed carbohydrate-rich diet (P:C=1:16) resisted starvation better and stored more lipids than did those that had fed protein-rich diet (4:1). Importantly, the extent to which both starvation resistance and lipid reserves were affected by dietary P:C ratio varied greatly among different genetic lines of Drosophila, as indicated by significant genotypeby-nutrient interactions for these two traits. When the patterns of the bivariate reaction norm for body lipid and starvation resistance were compared across the genotypes, we found strong evidence for genetic variations in the pattern of energy storage and usage associated with maintaining survival under starvation in Drosophila.

The nutritional quality of host plant is critically important for insect herbivores to maximize their fitness, but it is relatively unexplored whether the ingestion of a specific host plant will have the same effects on insects under different thermal conditions. We have used a multi-factorial experimental design to investigate how the nutritional quality of host plant and temperature interact to affect life-history traits in a generalist caterpillar Hyphantria cunea (Lepidoptera: Arctiidae) feeding on five different host plants. Caterpillars raised on Platanus occidentalis, Sophora japonica and Prunus x yedoensis exhibited substantially higher survival, faster growth and heavier mass at pupation than those on Cornus kousa and Betula platyphylla. Caterpillars developed more quickly and attained a smaller final body mass at higher temperatures, but the way that these traits responded to temperature differed by host plant. Caterpillars on P.occidentalis displayed a monotonic decrease in development time with increasing temperature, but the development time of those on P. x yedoensis declined with temperature in a biphasic manner. Furthermore, the rate at which pupal mass increased with decreasing temperature was much greater for caterpillars on P.occidentalis than those on P. x yedoensis.

Nutritional conditions experienced during early growth have important implications for the lifetime fitness of herbivores. We investigated how the early life effects of imbalanced nutrient intake can be overcome in a generalist caterpillar, Spodoptera litura (Lepidoptera: Noctuidae). Over the fifth larval instar, caterpillars were pretreated on one of three diets that varied in protein: carbohydrate balance (p35:c7, p21:c21 or p7:c35). After molting to the sixth instar, they were transferred to one of three no-choice diets (p35:c7 ,p21:c21 or p7:c35) or a food choice where they received two nutritionally complementary diets (p35:c7 versus p7:c35). Approximately 80% of caterpillars that had been protein-deprived (p7:c35) during the fifth instar molted to the seventh instar. The threshold body mass for pupal metamorphosis was 144 mg at the start of the sixth instar. When given a choice, caterpillars pretreated on the low-protein diet (p7:c35) selected significantly more protein than those from other diets (p35:c7,p21:c21). Our results suggest that caterpillars are not only capable of switching their developmental program to reduce the deleterious effects of a nearly deficiency of protein, but also flexible at adjusting nutrient preference store dress specific nutritional imbalances experienced early in life.

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 objective of this study is to investigate the effects of nutrition on starvation resistance in Drosophila melanogaster. 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. 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 dietary carbohydrate alone. Starvation resistance was strongest at the lowest P:C ratio and declined with rising P:C ratio. While starving, Drosophila underwent a dramatic transition in the utilization of physiological fuels, switching from the early phase characterized by preferential consumption of non-lipid substrates to the next phase in which they began to mobilize lipids as fuels for enduring starvation. Our results highlight the importance of nutrition as a key factor determining starvation responses of Drosophila.