Hawkmoths use nectar sugar to reduce oxidative damage from flight

More than just sugar: allocation of nectar amino acids and fatty acids in a Lepidopteran

The ability to allocate resources, even when limited, is essential for survival and fitness. We examine how nutrients that occur in minute amounts are allocated among reproductive, somatic, and metabolic demands. In addition to sugar, flower nectars contain two macronutrients-amino acids and fatty acids. We created artificial nectars spiked with ¹³C-labelled amino acids and fatty acids and fed these to adult moths (Manduca sexta: Sphingidae) to understand how they allocate these nutrients among competing sinks (reproduction, somatic tissue, and metabolic fuel). We found that both essential and non-essential amino acids were allocated to eggs and flight muscles and were still detectable in early-instar larvae. Parental-derived essential amino acids were more conserved in the early-instars than non-essential amino acids. All amino acids were used as metabolic fuel, but the non-essential amino acids were oxidized at higher rates than essential amino acids. Surprisingly, the nectar fatty acids were not vertically transferred to offspring, but were readily used as a metabolic fuel by the moth, minimizing losses of endogenous nutrient stores. We conclude that the non-carbohydrate components of nectar may play important roles in both reproductive success and survival of these nectar-feeding animals.

A procession of metabolic alterations accompanying muscle senescence in Manduca sexta

Biological aging profoundly impairs muscle function, performance, and metabolism. Because the progression of metabolic alterations associated with aging muscle has not been chronicled, we tracked the metabolic profiles of flight muscle from middle to advanced age in Manduca sexta to identify key molecules during the progression of muscle aging, as well as to evaluate the utility of the M. sexta system for molecular dissection of muscle aging. We identified a number of differences between Diel Time, Sexes, and Muscle Ages, including changes in metabolites related to energetics, extracellular matrix turnover, and glutathione metabolism. Increased abundances of glycolytic metabolites suggest a shift toward increased glycolysis with advancing age, whereas decreased abundances in lysolipids and acylcarnitines reflect decreasing beta-oxidation. We also observed a shift towards decreased polyamine metabolism with age, which might result in an age-related decline in lipid metabolism possibly due to regulation of energy metabolism by polyamines. Collectively, our findings demonstrate the feasibility of our system and approach and provide a deeper understanding of lepidopteran aging. More importantly, the results identify the key altered metabolic pathways that collectively contribute to the muscle aging phenotype and thereby improve our understanding of muscle senescence.

Learning to starve: impacts of food limitation beyond the stress period

Starvation is common among wild animal populations, and many individuals experience repeated bouts of starvation over the course of their lives. Although much information has been gained through laboratory studies of acute starvation, little is known about how starvation affects an animal once food is again available (i.e. during the refeeding and recovery phases). Many animals exhibit a curious phenomenon – some seem to ‘get better’ at starving following exposure to one or more starvation events – by this we mean that they exhibit potentially adaptive responses, including reduced rates of mass loss, reduced metabolic rates, and lower costs of digestion. During subsequent refeedings they may also exhibit improved digestive efficiency and more rapid mass gain. Importantly, these responses can last until the next starvation bout or even be inherited and expressed in the subsequent generation. Currently, however, little is known about the molecular regulation and physiological mechanisms underlying these changes. Here, we identify areas of research that can fill in the most pressing knowledge gaps. In particular, we highlight how recently refined techniques (e.g. stable isotope tracers, quantitative magnetic resonance and thermal measurement) as well as next-generation sequencing approaches (e.g. RNA-seq, proteomics and holobiome sequencing) can address specific starvation-focused questions. We also describe outstanding unknowns ripe for future research regarding the timing and severity of starvation, and concerning the persistence of these responses and their interactions with other ecological stressors.

Gigaspora margarita with and without its endobacterium shows adaptive responses to oxidative stress

Arbuscular mycorrhizal (AM) fungi experience oxidative stress during the plant-fungal interaction, due to endogenous reactive oxygen species (ROS) produced by fungal metabolism and exogenous ROS produced by plant cells. Here, we examine the responses to H₂O₂ in Gigaspora margarita, an AM fungus containing the endobacterial symbiont Candidatus Glomeribacter gigasporarum (CaGg). Previous studies revealed that G. margarita with its endobacterium produces more ATP and has higher respiratory activity than a cured line that lacks the endobacterium. This higher bioenergetic potential leads to higher production of ROS and to a higher ROS-detoxifying capacity, suggesting a direct or indirect role of the endobacterium in modulating fungal antioxidant responses. To test the hypothesis that the fungal-endobacterial symbiosis may enhance the fitness of the AM fungus in the presence of oxidative stress, we treated the fungus with a sublethal concentration of H₂O₂ and performed RNA-seq analysis. Our results demonstrate that (i) irrespective of the endobacterium presence, G. margarita faces oxidative stress by activating multiple metabolic processes (methionine oxidation, sulfur uptake, the pentose phosphate pathway, activation of ROS-scavenger genes); (ii) in the presence of its endobacterium, G. margarita upregulates some metabolic pathways, like chromatin status modifications and iron metabolism; and (iii) contrary to our hypothesis, the cured line responds to H₂O₂ by activating the transcription of specific ROS scavengers. We confirmed the RNA-seq findings by measuring the glutathione and ascorbate concentration, which was the same in both lines after H₂O₂ treatment. We conclude that both fungal lines may face oxidative stress, but they activate alternative strategies.

Functional Classification of the Gut Microbiota: The Key to Cracking the Microbiota Composition Code: Functional classifications of the gut microbiota reveal previously hidden contributions of indigenous gut bacteria to human health and disease

The last decade has seen an explosion of research on the gut microbiota-the trillions of microorganisms that colonize the human gut. It is now clear that interindividual diversity in microbiota composition plays an important role in determining susceptibility to a wide variety of diseases. However, identifying the precise changes in microbiota composition that play causal roles has remained a largely unrealized goal. Here, we propose that functional classifications of microbes based on their interactions with and effects on the host-particularly the host immune system-will illuminate the role of the microbiota in shaping human physiology. We outline the benefits of "functional" classification compared to phylogenetic classifications, and review current efforts at functional classification of the microbiota. Finally, we outline a theoretical framework for classifying host-microbiota interactions. Future advances enabling broader functional classifications of the microbiota promise to revolutionize our understanding of the role of gut microbes in health and disease.

Sex differences in the utilization of essential and non-essential amino acids in Lepidoptera

The different reproductive strategies of males and females underlie differences in behavior that may also lead to differences in nutrient use between the two sexes. We studied sex differences in the utilization of two essential amino acids (EAAs) and one non-essential amino acid (NEAA) by the Carolina sphinx moth (Manduca sexta). On day one post-eclosion from the pupae, adult male moths oxidized greater amounts of larva-derived AAs than females, and more nectar-derived AAs after feeding. After 4 days of starvation, the opposite pattern was observed: adult females oxidized more larva-derived AAs than males. Adult males allocated comparatively small amounts of nectar-derived AAs to their first spermatophore, but this allocation increased substantially in the second and third spermatophores. Males allocated significantly more adult-derived AAs to their flight muscle than females. These outcomes indicate that adult male and female moths employ different strategies for allocation and oxidation of dietary AAs.