Gabriel E. Machovsky-Capuska

Nutritional ecology of obesity: from humans to companion animals

We apply nutritional geometry, a framework for modelling the interactive effects of nutrients on animals, to help understand the role of modern environments in the obesity pandemic. Evidence suggests that humans regulate the intake of protein energy (PE) more strongly than non-protein energy (nPE), and consequently will over- and under-ingest nPE on diets with low or high PE, respectively. This pattern of macronutrient regulation has led to the protein leverage hypothesis, which proposes that the rise in obesity has been caused partly by a shift towards diets with reduced PE:nPE ratios relative to the set point for protein regulation. We discuss potential causes of this mismatch, including environmentally induced reductions in the protein density of the human diet and factors that might increase the regulatory set point for protein and hence exacerbate protein leverage. Economics--the high price of protein compared with fats and carbohydrates--is one factor that might contribute to the reduction of dietary protein concentrations. The possibility that rising atmospheric CO₂ levels could also play a role through reducing the PE:nPE ratios in plants and animals in the human food chain is discussed. Factors that reduce protein efficiency, for example by increasing the use of ingested amino acids in energy metabolism (hepatic gluconeogenesis), are highlighted as potential drivers of increased set points for protein regulation. We recommend that a similar approach is taken to understand the rise of obesity in other species, and identify some key gaps in the understanding of nutrient regulation in companion animals.

The Multidimensional Nutritional Niche

The dietary generalist-specialist distinction plays a pivotal role in theoretical and applied ecology, conservation, invasion biology, and evolution and yet the concept remains poorly characterised. Diets, which are commonly used to define niche breadth, are almost exclusively considered in terms of foods, with little regard for the mixtures of nutrients and other compounds they contain. We use nutritional geometry (NG) to integrate nutrition with food-level approaches to the dietary niche and illustrate the application of our framework in the important context of invasion biology. We use an example that involves a model with four hypothetical nonexclusive scenarios. We additionally show how this approach can provide fresh theoretical insight into the ways nutrition and food choices impact trait evolution and trophic interactions.

Geometry of nutrition in field studies: an illustration using wild primates

Nutritional geometry has shown the benefits of viewing nutrition in a multidimensional context, in which foraging is viewed as a process of balancing the intake and use of multiple nutrients. New insights into nutrient regulation have been generated in studies performed in a laboratory context, where accurate measures of amounts (e.g. eaten, converted to body mass, excreted) can be made and analysed using amounts-based nutritional geometry. In most field situations, however, proportional compositions (e.g. of foods, diets, faeces) are the only measures readily available, and in some cases are more relevant to the problem at hand. For this reason, a complementary geometric method was recently introduced for analysing multi-dimensional data on proportional compositions in nutritional studies, called the right-angled mixture triangle (RMT). We use literature data from field studies of primates to demonstrate how the RMT can provide insight into a variety of important concepts in nutritional ecology. We first compare the compositions of foods, using as an example primate milks collected in both the wild and the laboratory. We next compare the diets of different species of primates from the same habitat and of the same species (mountain gorillas) from two distinct forests. Subsequently, we model the relationships between the composition of gorilla diets in these two habitats and the foods that comprise these diets, showing how such analyses can provide evidence for active nutrient-specific regulation in a field context. We provide a framework to relate concepts developed in laboratory studies with field-based studies of nutrition.

Coupling bio-logging with nutritional geometry to reveal novel insights into the foraging behaviour of a plunge-diving marine predator

ABSTRACT It is widely believed that predators maximise their energy intake while foraging and consume prey that are nutritionally similar. We combined GPS data loggers, miniaturised cameras, dietary sampling and nutritional geometry to examine the nutritional variability in the prey and selected diet, and foraging performance, of the masked booby (Sula dactylatra tasmani), a wild carnivore and marine top predator. Data loggers also revealed no significant differences between sexes in the foraging performance of chick-rearing adults. Females provided more food to their chicks than the males and, regardless of the nutritional variability of prey consumed, both sexes showed similar amounts of protein and lipid in their diets. Miniaturised cameras combined with nutritional analysis of prey provided, for the first time, fine-scale detail of the amounts of macronutrients consumed in each plunge dive and the overall foraging trip. Our methodology could be considered for future studies that aim to contribute to the general understanding of the behavioural and physiological mechanisms and ecological and evolutionary significance of animal foraging (e.g. energy expenditure budgets and prey selection for self- and offspring-feeding that could lead to sex-specific foraging strategies).

Macronutrient selection of free-ranging urban Australian white ibis (Threskiornis moluccus)

Lay SummaryWhen offered a choice of experimental foods high in protein, lipid or carbohydrate, urban Australian white ibis showed a preference for high-carbohydrate foods. This is in contrast to the typical composition of their natural prey, which are low in carbohydrates and higher in protein and lipids. Furthermore, the proportion of macronutrients selected by ibis was affected by competition and previous rainfall, giving further insight into the complexities of a native species foraging in urban environments.Twitter: @SeanCoogs

Sexual segregation in tropical seabirds: drivers of sex-specific foraging in the Brown Booby Sula leucogaster

Sexual segregation in the behaviour, morphology or physiology of breeding seabirds can be related to divergent parental roles, foraging niche partitioning or sex-specific nutritional requirements. Here, we combine GPS tracking, dietary and nutritional analysis to investigate sex-specific foraging of Brown Boobies breeding on Raine Island, Great Barrier Reef, Australia. We observed sex-specific segregation in: (1) foraging location: females undertook longer trips, foraging at more distant locations than males; (2) foraging time: male activity and foraging occurred throughout the day, while female activity and foraging increased from midday to an afternoon peak; and (3) prey type, females mostly consumed flying fish, whereas males consumed equal proportions of flying fish and squid. Brown Booby diets contained five tropical prey species that significantly differed in their nutritional composition (Protein, Lipid and Water, wet mass). Despite this variation we found no differences in the overall nutritional content of prey caught by each sex. The observed sex-specific differences in prey type, location and time of capture are likely driven by a combination of a division of labour, risk partitioning and competition. However, Brown Boobies breeding on Raine Island, and other populations, might flexibly partition foraging niches by sex in response to varying competitive and environmental pressures. In light of such potential foraging dynamism, our inconclusive exploration of nutritional segregation between sexes warrants further investigation in the species.ZusammenfassungSexuelle Segregation bei tropischen Seevögeln: Einflussfaktoren geschlechtsspezifischer Nahrungssuche bei WeißbauchtölpelnSula leucogaster Sexuelle Segregation in Verhalten, Morphologie oder Physiologie brütender Seevögel kann mit unterschiedlichen Elternrollen, Nahrungsnischendifferenzierung oder geschlechtsspezifischem Nährstoffbedarf zusammenhängen. Hier kombinieren wir GPS-Ortung mit Nahrungs- und Nährstoffanalysen, um die geschlechtsspezifische Nahrungssuche bei auf Raine Island im australischen Great Barrier Reef brütenden Weißbauchtölpeln zu untersuchen. Wir haben geschlechtsspezifische Segregation gefunden in Bezug auf (a) den Ort der Nahrungssuche: Weibchen unternahmen längere Suchflüge als Männchen, da sie an weiter entfernten Orten nach Nahrung suchten; (b) den Zeitpunkt der Nahrungssuche: Männchen waren den ganzen Tag über aktiv und suchten nach Nahrung, während bei Weibchen die Aktivität und Nahrungssuche von mittags an zunahmen und am Nachmittag ihren Höhepunkt erreichten; (c) Beutetyp: Weibchen fraßen hauptsächlich fliegende Fische, während Männchen zu gleichen Teilen fliegende Fische und Kalmare verzehrten. Die Weißbauchtölpel nutzten fünf tropische Beutearten, die sich signifikant in ihrer Nährstoffzusammensetzung (Proteine, Lipide und Wasser in der Feuchtmasse) unterschieden. Trotz dieser Variation fanden wir keine Unterschiede im Gesamtnährstoffgehalt der von männlichen und weiblichen Tölpeln gefangenen Beute. Die beobachteten geschlechtsspezifischen Unterschiede im Beutetyp sowie Ort und Zeitpunkt des Beutefangs kommen wahrscheinlich durch eine Kombination von Arbeitsteilung, Risikoaufteilung und Konkurrenz zustande. Bei den auf Raine Island sowie in anderen Populationen brütenden Weißbauchtölpeln könnten die Geschlechter die Nahrungsnische flexibel unter sich aufteilen, abhängig von wechselnden Konkurrenz- und Umweltdrücken. Angesichts von solchem potenziellen Nahrungsdynamismus rechtfertigt unsere nicht beweiskräftige Erforschung der geschlechtsspezifischen Nahrungssegregation weitere Untersuchungen an Weißbauchtölpeln.

A preliminary study to estimate contact rates between free-roaming domestic dogs using novel miniature cameras.

Information on contacts between individuals within a population is crucial to inform disease control strategies, via parameterisation of disease spread models. In this study we investigated the use of dog-borne video cameras–in conjunction with global positioning systems (GPS) loggers–to both characterise dog-to-dog contacts and to estimate contact rates. We customized miniaturised video cameras, enclosed within 3D-printed plastic cases, and attached these to nylon dog collars. Using two 3400 mAh NCR lithium Li-ion batteries, cameras could record a maximum of 22 hr of continuous video footage. Together with a GPS logger, collars were attached to six free roaming domestic dogs (FRDDs) in two remote Indigenous communities in northern Australia. We recorded a total of 97 hr of video footage, ranging from 4.5 to 22 hr (mean 19.1) per dog, and observed a wide range of social behaviours. The majority (69%) of all observed interactions between community dogs involved direct physical contact. Direct contact behaviours included sniffing, licking, mouthing and play fighting. No contacts appeared to be aggressive, however multiple teeth baring incidents were observed during play fights. We identified a total of 153 contacts–equating to 8 to 147 contacts per dog per 24 hr–from the videos of the five dogs with camera data that could be analysed. These contacts were attributed to 42 unique dogs (range 1 to 19 per video) which could be identified (based on colour patterns and markings). Most dog activity was observed in urban (houses and roads) environments, but contacts were more common in bushland and beach environments. A variety of foraging behaviours were observed, included scavenging through rubbish and rolling on dead animal carcasses. Identified food consumed included chicken, raw bones, animal carcasses, rubbish, grass and cheese. For characterising contacts between FRDD, several benefits of analysing videos compared to GPS fixes alone were identified in this study, including visualisation of the nature of the contact between two dogs; and inclusion of a greater number of dogs in the study (which do not need to be wearing video or GPS collars). Some limitations identified included visualisation of contacts only during daylight hours; the camera lens being obscured on occasion by the dog’s mandible or the dog resting on the camera; an insufficiently wide viewing angle (36°); battery life and robustness of the deployments; high costs of the deployment; and analysis of large volumes of often unsteady video footage. This study demonstrates that dog-borne video cameras, are a feasible technology for estimating and characterising contacts between FRDDs. Modifying camera specifications and developing new analytical methods will improve applicability of this technology for monitoring FRDD populations, providing insights into dog-to-dog contacts and therefore how disease might spread within these populations.

Corticosterone responses to capture and restraint in Australasian Gannets, Morus serrator, at Cape Kidnappers, New Zealand

Abstract Birds can respond to threats or potential threats in their immediate environment with increased secretion of the glucocorticoid hormone corticosterone. The size of a corticosterone response to capture reflects the sensitivity of a bird to stimuli from its immediate environment, and there is marked variation between individual birds in their corticosterone responses. Whilst corticosterone responses to capture have been described in many species of birds, there are few reports of corticosterone responses in Australasian seabirds, and the aim of the present study was to describe individual and mean corticosterone responses to capture and restraint in Australasian Gannets (Morus serrator) at Cape Kidnappers, New Zealand. Corticosterone concentrations were low initially, then increased after capture in all gannets, with mean concentrations 55.77 ± 4.72 ng mL−1 after 30 min of restraint. This is the first report of corticosterone responses in gannets. Mean corticosterone concentrations at 30 min were within the range of responses reported for the blue-footed booby, another species within the family Sulidae, suggesting that different species of Sulidae have similar sensitivities to their immediate environment. Further studies of corticosterone in gannets and other Australasian seabirds will be worthwhile to provide information about how these seabirds can respond to changes in their environment.