Macronutrient regulation in nymphs of the two-spotted cricket, Gryllus bimaculatus (Orthoptera: Gryllidae)

Crickets have been extensively studied in recent insect nutritional research, but it remains largely unexplored how they balance the intake of multiple nutrients. Here, we used the nutritional geometry framework to examine the behavioural and physiological regulation of dietary protein and carbohydrate in nymphs of the two-spotted cricket, Gryllus bimaculatus (Orthoptera: Gryllidae). Growth, intake, utilization efficiencies, and body composition were measured from the eighth instar nymphs that received either food pairs or single foods with differing protein and carbohydrate content. When food choices were available, crickets preferentially selected a carbohydrate-biased protein:carbohydrate (P:C) ratio of 1:1.74. During this nutrient selection, carbohydrate intake was more tightly regulated than protein intake. When confined to nutritionally imbalanced foods, crickets adopted a nutrient balancing strategy that maximized the nutrient intake regardless of the nutrient imbalance, reflecting their omnivorous feeding habit. Intake was significantly reduced when crickets were confined to the most carbohydrate-biased food (P:C = 1:5). When nutrients were ingested in excess of the requirements, the post-ingestive utilization efficiencies of these nutrients were down-regulated, thereby buffering the impacts of nutrient imbalances on body nutrient composition. Crickets reared on the most carbohydrate-biased food (P:C = 1:5) suffered delayed development and reduced growth. Our data provide the most accurate description of nutrient regulation in G. bimaculatus and lay the foundation for further nutritional research in this omnivorous insect.

Land-based foraging by polar bears reveals sexual conflict outside mating season

According to sexual selection theory, the sexes are faced with opposing evolutionary goals. Male fitness benefits from access to females, whereas female fitness is constrained by food resources and safety for themselves and their offspring. Particularly in large solitary carnivores, such as polar bears (Ursus maritimus), these divergent goals can potentially lead to conflict between the sexes. Outside the mating season, when polar bears are on the move across vast distances, the consequences of such conflict can become apparent when individuals arrive at the same food source. To investigate interrelationships between the sexes, we observed successive polar bears visiting a bird breeding colony to feed on clutches of eggs. We found that males succeeded females more frequently and more closely than expected by chance. Moreover, when males were closer to conspecifics, they walked faster, spent less time in the colony and ingested less food. In contrast, female foraging performance was not associated with proximity to other bears. Irrespective of proximity, females generally spent short periods in the colony and ingested fewer clutches than males. Our results suggest that in polar bears, there is a trade-off between the benefits of food intake and the opportunities (in males) and risks (in females) posed by encountering conspecifics.

Optimum ratio of dietary protein and carbohydrate that maximises lifespan is shared among related insect species

Animals often regulate the intake and quantity of nutrients to maximise fitness through life-history traits such as lifespan, but we still lack a proper understanding of how specific nutrients influence these traits. Here, I developed an algorithm which allowed me to create a nutrient-specific database from literature data, and investigated how the requirements of protein (P) and carbohydrate (C) needed to maximise lifespan evolved across nine insect species. I found moderate evidence of a phylogenetic signal on the optimal ratio of protein to carbohydrate ratio (PC ratio) that maximised lifespan, suggesting that optimal PC ratio for lifespan could have evolved non-independently among related species. I also found evidence for weak-to-strong sex-specific optimal PC ratios for lifespan, suggesting that sex-specific nutritional needs to maximise lifespan can emerge and persist in some species. Although limited in the number of species, the approach adopted here is portable to experiments withn number of nutrients and, thus, can be used in complex comparative precision nutrition studies for insights into the evolution of animal nutrition.

Nutrigonometry III: curvature, area and differences between performance landscapes

Nutrition is one of the underlying factors necessary for the expression of life-histories and fitness across the tree of life. In recent decades, the geometric framework (GF) has become a powerful framework to obtain biological insights through the construction of multidimensional performance landscapes. However, to date, many properties of these multidimensional landscapes have remained inaccessible due to our lack of mathematical and statistical frameworks for GF analysis. This has limited our ability to understand, describe and estimate parameters which may contain useful biological information from GF multidimensional performance landscapes. Here, we propose a new model to investigate the curvature of GF multidimensional landscapes by calculating the parameters from differential geometry known as Gaussian and mean curvatures. We also estimate the surface area of multidimensional performance landscapes as a way to measure landscape deviations from flat. We applied the models to a landmark dataset in the field, where we also validate the assumptions required for the calculations of curvature. In particular, we showed that linear models perform as well as other models used in GF data, enabling landscapes to be approximated by quadratic polynomials. We then introduced the Hausdorff distance as a metric to compare the similarity of multidimensional landscapes.

Ovarian apoptosis is regulated by carbohydrate intake but not by protein intake in speckled cockroaches

When the likelihood of reproducing successfully is low, any prior investment in developing oocytes may be wasted. One means of recouping this investment is oosorption - where ova are absorbed and resources salvaged so they can be re-allocated to other traits. Food-limited female speckled cockroaches (Nauphoeta cinerea) appear to use this strategy. However, it is unclear if total food intake or the availability of specific nutrients induces this process. Here, we used the geometric framework of nutrition to determine how protein, carbohydrate and energy intake affect levels of ovarian apoptosis and necrosis (controlled versus uncontrolled cell death) in the terminal oocytes of female N. cinerea. We then compare the effects of nutrient intake on apoptosis (a key step towards oosorption) and offspring production to better understand the relationship between diet, apoptosis and female fitness. We found that even when food was abundant, females experienced high levels of apoptosis if their diet lacked carbohydrate. Necrosis was reduced when energy intake was high, but largely irrespective of nutrient ratio. Offspring production peaked on a low protein, high carbohydrate nutrient ratio (1_P:7.96_C), similar to that which minimized apoptosis (1_P:7.34_C) but not in the region of nutrient space that minimized necrosis. Thus, females consuming an ideal nutrient blend for reproduction can invest heavily in their current brood without needing to salvage nutrients from developing ova. However, offspring production was more dependent on carbohydrate consumption than apoptosis was, suggesting that the importance of carbohydrate in reproduction goes beyond regulating oosorption. This reliance on carbohydrate for female reproduction may reflect the unusual reproductive and nutritional physiology of speckled cockroaches; attributes that make this species an exciting model for understanding how diet regulates reproduction.

Concerted evolution of metabolic rate, economics of mating, ecology, and pace of life across seed beetles

Coevolution between females and males has led to remarkable differences between the sexes but has taken very different routes, even in closely related animal species, for reasons that are not well understood. We studied the physiological processes that convert resources into offspring (metabolism) in males and females of several related beetle species. We found that ecological factors dictate metabolic rate, which, in turn, have predictable direct and indirect effects on male–female coevolution. Our findings suggest that a complete understanding of differences between the sexes requires an understanding of how ecology affects metabolic processes and how these differ in the sexes.

Male–female coevolution has taken different paths among closely related species, but our understanding of the factors that govern its direction is limited. While it is clear that ecological factors, life history, and the economics of reproduction are connected, the divergent links are often obscure. We propose that a complete understanding requires the conceptual integration of metabolic phenotypes. Metabolic rate, a nexus of life history evolution, is constrained by ecological factors and may exert important direct and indirect effects on the evolution of sexual dimorphism. We performed standardized experiments in 12 seed beetle species to gain a rich set of sex-specific measures of metabolic phenotypes, life history traits, and the economics of mating and analyzed our multivariate data using phylogenetic comparative methods. Resting metabolic rate (RMR) showed extensive evolution and evolved more rapidly in males than in females. The evolution of RMR was tightly coupled with a suite of life history traits, describing a pace-of-life syndrome (POLS), with indirect effects on the economics of mating. As predicted, high resource competition was associated with a low RMR and a slow POLS. The cost of mating showed sexually antagonistic coevolution, a hallmark of sexual conflict. The sex-specific costs and benefits of mating were predictably related to ecology, primarily through the evolution of male ejaculate size. Overall, our results support the tenet that resource competition affects metabolic processes that, in turn, have predictable effects on both life history evolution and reproduction, such that ecology shows both direct and indirect effects on male–female coevolution.