Showing papers by "Catherine Hambly published in 2020"

Late lactation in small mammals is a critically sensitive window of vulnerability to elevated ambient temperature

Abstract: Predicted increases in global average temperature are physiologically trivial for most endotherms. However, heat waves will also increase in both frequency and severity, and these will be physiologically more important. Lactating small mammals are hypothesized to be limited by heat dissipation capacity, suggesting high temperatures may adversely impact lactation performance. We measured reproductive performance of mice and striped hamsters (Cricetulus barabensis), including milk energy output (MEO), at temperatures between 21 and 36 °C. In both species, there was a decline in MEO between 21 and 33 °C. In mice, milk production at 33 °C was only 18% of that at 21 °C. This led to reductions in pup growth by 20% but limited pup mortality (0.8%), because of a threefold increase in growth efficiency. In contrast, in hamsters, MEO at 33 °C was reduced to 78.1% of that at 21 °C, yet this led to significant pup mortality (possibly infanticide) and reduced pup growth by 12.7%. Hamster females were more able to sustain milk production as ambient temperature increased, but they and their pups were less capable of adjusting to the lower supply. In both species, exposure to 36 °C resulted in rapid catastrophic lactation failure and maternal mortality. Upper lethal temperature was lowered by 3 to 6 °C in late lactation, making it a critically sensitive window to high ambient temperatures. Our data suggest future heat wave events will impact breeding success of small rodents, but this is based on animals with a long history in captivity. More work should be performed on wild rodents to confirm these impacts.

Acceleration predicts energy expenditure in a fat, flightless, diving bird.

Abstract: Energy drives behaviour and life history decisions, yet it can be hard to measure at fine scales in free-moving animals. Accelerometry has proven a powerful tool to estimate energy expenditure, but requires calibration in the wild. This can be difficult in some environments, or for particular behaviours, and validations have produced equivocal results in some species, particularly air-breathing divers. It is, therefore, important to calibrate accelerometry across different behaviours to understand the most parsimonious way to estimate energy expenditure in free-living conditions. Here, we combine data from miniaturised acceleration loggers on 58 free-living Adelie penguins with doubly labelled water (DLW) measurements of their energy expenditure over several days. Across different behaviours, both in water and on land, dynamic body acceleration was a good predictor of independently measured DLW-derived energy expenditure (R2 = 0.72). The most parsimonious model suggested different calibration coefficients are required to predict behaviours on land versus foraging behaviour in water (R2 = 0.75). Our results show that accelerometry can be used to reliably estimate energy expenditure in penguins, and we provide calibration equations for estimating metabolic rate across several behaviours in the wild.

Associations of Food Outlet Densities with Obesity Measures Identify Fish and Chip Shops as a Uniquely Important Problem.

Abstract: Increases in the number of food outlets have been proposed as a key factor driving obesity. This study aimed to investigate the association between the densities of food establishments serving meals (excluding supermarkets and grocery stores), with body mass index (BMI), waist to hip ratio (WHR) and percentage of body fat among middle-aged adults in the UK. BMIs, WHR, %fat and socioeconomic factors were obtained from 456,079 individuals from the UK Biobank and averaged across 923 postcode districts (PD). The number of Fast-Food Restaurants (FFRs), Full-Service Restaurants (FSRs), delivery shops, takeaways, fish and chip shops, pubs and cafes were also obtained for each PD. We adjusted the obesity measures for deprivation level, education, employment, ethnicity, household size, household income and age. After adjustment, the density of fish and chip shops (per 1000 population) was positively associated with BMI and %fat for both sexes (males: BMI converted (exponentiated coefficient) β = 0.5, R2 = 4.14%, p < 0.0001; %fat converted β = 0.8, R2 = 3.32%, p < 0.0001; females: BMI converted β = 0.9, R2 = 5.31%, p < 0.0001; %fat converted β = 1.4 R2 = 4.65%, p < 0.0001). The densities of FFRs and delivery shops (per 1000 population) were not related to the adjusted obesity measures among males and females, except BMI in males where FFRs were significantly negatively associated. The densities (per 1000 population) of FSRs, pubs, cafes and total food outlets were all significantly inversely related to the obesity measures for both sexes. The number of fish and chip shops per 1000 individuals was significantly positively associated with obesity in middle-aged adults in the UK. A negative association between the other types of food outlet densities and the measures of obesity suggests access to such establishments is not a major driver of obesity. This is potentially because the food supplied at such establishments is not significantly less healthy than what is eaten elsewhere including at home (and may even be better). Paying attention only to fast food and/or full-service restaurants in intervention policy will likely not be effective. Policy intervention should potentially focus on the numbers of fish and chip shops and the deep-fried food served in such restaurants.

A mesocosm experiment in ecological physiology: adaptive modulation of energy budget in a hibernating marsupial under chronic caloric restriction

Abstract: During the last sixty years, mammalian hibernation (i.e., seasonal torpor) has been interpreted as a physiological adaptation for energy economy. However -and crucially for validating this idea - direct field comparisons of energy expenditure in hibernating and active free-ranging animals are scarce. Using replicated mesocosms and a combination of energy budgeting approaches (i.e., doubly labelled water, rates of CO2 production and food intake), we experimentally manipulated energy availability and quantified net energy costs of hibernation in a marsupial. We hypothesized that, when facing chronic caloric restriction (CCR), a hibernator should maximize torpor use for compensating the energetic deficit, compared to ad libitum fed individuals (=controls). However, intensifying torpor duration at low temperatures could increase other burdens (e.g., cost of rewarming, freezing risk). In order to explore this trade-off, we followed the complete hibernation cycle of the relict marsupial Dromiciops gliroides, and estimated its total energy requirements, and compared this with a control condition. Our results revealed: (1) that energy restricted animals, instead of promoting heat conservation strategies during hibernation (e.g., social clustering and thermoregulation), maximized torpor use and saved just enough energy to cover the deficit, and (2) that hibernation represents a net energy saving of 51% compared with animals that remained active. This work provides compelling evidence of a fine-tuning use of hibernation in response to food availability and presents the first direct estimation of energy savings by hibernation encompassing the total hibernation cycle.

Exposure to hot temperatures during lactation in Swiss mice stunts offspring growth and decreases future reproductive performance of female offspring.

Abstract: Among the important aspects of climate change, exposure to high temperatures (heat waves) is rapidly emerging as an important issue, in particular for female mammals during lactation. High temperatures adversely impact ability to dissipate heat, which has negative effects on reproductive output. The cumulative effects on growth of F1 offspring after weaning and future reproductive performance of offspring remain uncertain. In this study, the F1 mice that weaned from mothers lactating at 21°C and 32.5°C were housed at 21°C from day 19 till 56 of age; during which food intake and body mass were measured. The F1 adult females that had been weaned at the two temperatures were bred and then both exposed to 32.5°C during lactation. Energy intake, milk output and litter size and mass were determined. The F1 adults weaned at 32.5°C consumed less food and had lower body mass than their counterparts weaned at 21°C. Several visceral organs or reproductive tissues were significantly lower in mass in F1 weaned at 32.5°C than at 21°C. The exposure to 32.5°C significantly decreased energy intake, milk output and litter mass in F1 adult females during lactation. The F1 adult females weaned at 32.5°C produced less milk and raised lighter pups than those previously weaned at 21°C. The data suggest that transient exposure to hot temperature during lactation has long-lasting impacts on the offspring, including stunted growth and decreases in future reproductive performance when adult. This indicates that the offspring of females previously experiencing hot temperatures have a significant fitness disadvantage.

Frequency of Restaurant, Delivery and Takeaway Usage Is Not Related to BMI among Adults in Scotland

Abstract: Background: The frequency of visits to restaurants has been suggested to contribute to the pandemic of obesity. However, few studies have examined how individual use of these restaurants is related to Body Mass Index (BMI). Aim: To investigate the association between the usage of different types of food outlets and BMI among adults in Scotland. Method: The study was cross-sectional. Participants completed an online survey for seven consecutive days where all food purchased at food outlets was reported each day. We explored the relationship between BMI and usage of these food outlets. Results: The total number of participants that completed the survey was 681. The BMI of both males and females was not related to frequency of use of Full-Service Restaurants (FSRs), Fast-Food Restaurants (FFRs), delivery or takeaways, when assessed individually or combined (TFOs = total food outlets). Conclusion: These cross-sectional data do not support the widespread belief that consumption of food out of the home at fast-food and full-service restaurants, combined with that derived from deliveries and takeaways, is a major driver of obesity in Scotland.

Limits to sustained energy intake. XXX. Constraint or restraint? Manipulations of food supply show peak food intake in lactation is constrained

Abstract: Lactating mice increase food intake 4- to 5-fold, reaching an asymptote in late lactation. A key question is whether this asymptote reflects a physiological constraint, or a maternal investment strategy (a 'restraint'). We exposed lactating mice to periods of food restriction, hypothesizing that if the limit reflected restraint, they would compensate by breaching the asymptote when refeeding. In contrast, if it was a constraint, they would by definition be unable to increase their intake on refeeding days. Using isotope methods, we found that during food restriction, the females shut down milk production, impacting offspring growth. During refeeding, food intake and milk production rose again, but not significantly above unrestricted controls. These data provide strong evidence that asymptotic intake in lactation reflects a physiological/physical constraint, rather than restraint. Because hypothalamic neuropeptide Y (Npy) was upregulated under both states of restriction, this suggests the constraint is not imposed by limits in the capacity to upregulate hunger signalling (the saturated neural capacity hypothesis). Understanding the genetic basis of the constraint will be a key future goal and will provide us additional information on the nature of the constraining factors on reproductive output, and their potential links to life history strategies.

Limits to sustained energy intake. XXXI. Effect of graded levels of dietary fat on lactation performance in Swiss mice.

Abstract: The heat dissipation limit theory predicts that lactating female mice consuming diets with lower specific dynamic action (SDA) should have enhanced lactation performance. Dietary fat has lower SDA than other macronutrients. Here we tested the effects of graded dietary fat levels on lactating Swiss mice. We fed females five diets varying in fat content from 8.3 to 66.6%. Offspring of mothers fed diets of 41.7% fat and above were heavier and fatter at weaning compared with those of 8.3 and 25% fat diets. Mice on dietary fat contents of 41.7% and above had greater metabolizable energy intake at peak lactation (8.3%: 229.4±39.6; 25%: 278.8±25.8; 41.7%: 359.6±51.5; 58.3%: 353.7±43.6; 66.6%: 346±44.7 kJ day−1), lower daily energy expenditure (8.3%: 128.5±16; 25%: 131.6±8.4; 41.7%: 124.4±10.8; 58.3%: 115.1±10.5; 66.6%: 111.2±11.5 kJ day−1) and thus delivered more milk energy to their offspring (8.3%: 100.8±27.3; 25%: 147.2±25.1; 41.7%: 225.1±49.6; 58.3%: 238.6±40.1; 66.6%: 234.8±41.1 kJ day−1). Milk fat content (%) was unrelated to dietary fat content, indicating that females on higher fat diets (>41.7%) produced more rather than richer milk. Mothers consuming diets with 41.7% fat or above enhanced their lactation performance compared with those on 25% or less, probably by diverting dietary fat directly into the milk, thereby avoiding the costs of lipogenesis. At dietary fat contents above 41.7% they were either unable to transfer more dietary fat to the milk, or they chose not to do so, potentially because of a lack of benefit to the offspring that were increasingly fatter as maternal dietary fat increased.

Limits to sustained energy intake. XXXII. Hot again: dorsal shaving increases energy intake and milk output in golden hamsters (Mesocricetus auratus).

Abstract: Golden hamsters have four times the body size of mice, raise very large litters and are required to produce large quantities of milk during the 18-day lactation period. We have previously proposed that they may be prone to being limited by their heat dissipation capacity. Studies where lactating females are shaved to elevate their heat dissipation capacity have yielded conflicting data so far. With their short pregnancy of ∼18 days, the large litters and the reported high skin temperatures, they may serve as an ideal model to elucidate the role of epilation for energy budgets in lactating mammals. We shaved one group of lactating females dorsally on the sixth day of lactation, and tested if the elevated heat dissipation capacity would enable them to have higher energy intakes and better food-to-milk conversion rates. Indeed, we observed that females from the shaved group had 6% higher body mass and 0.78°C lower skin temperature than control females during lactation. When focusing on the phase of peak lactation, we observed significantly higher (10%) gross energy intake of food and 23.4% more milk energy output in the shaved females, resulting in 3.3 g higher individual pup weights. We conclude that shaving off the females’ fur, even though restricted to the dorsal surface, had large consequences on female energy metabolism in lactation and improved milk production and pup growth in line with our previous work on heat dissipation limitation. Our new data from golden hamsters confirm heat dissipation as a limiting factor for sustained metabolic rate in lactation in some small mammals and emphasise the large effects of a relatively small manipulation such as fur removal on energy metabolism of lactating females.

Active travelling to school is not associated with increased total daily physical activity levels, or reduced obesity and cardiovascular/pulmonary health parameters in 10–12-year olds: a cross-sectional cohort study

Abstract: Childhood obesity has increased enormously. Several lifestyle factors have been implicated, including decreased physical activity, partially involving a decline in active travel to school. We aimed to establish the association between school transport mode and physical activity levels of primary 6 and 7 children (aged 10–12). Secondary outcomes were body mass index standard deviation scores, blood pressure levels and lung function. A cross-sectional study was conducted with a total number of 432 children from three primary schools in North East Scotland. Actigraph accelerometers were used to provide objective measures of physical activity. Ninety-two children in primary 6 and 90 children in primary 7 (40 in common) had adequate data. Modes of transport to school were assessed by a questionnaire. Two hundred and seventeen children in primary 6 and one hundred and sixty-five in primary 7 returned adequate questionnaires. Children who used active transport modes for >70% of their journeys to school over the week were coded as active travellers and <30% were coded as passive travellers. All children also had height, weight, blood pressure levels and lung function measured. Children who lived further away from school, and in more expensive properties were more likely to travel passively to school. Actively commuting children (70% walking) had significantly higher activity levels than passive commuters during the 30 min that encompassed their journey to and from school. However, there were no significant differences between active and passive school travellers in total daily physical activity, BMI SDS, and both systolic and diastolic blood pressure and lung function. There was no evidence that more days of active travel to school had a significant influence on total physical activity, obesity and related health parameters. Public health interventions promoting active travel to school may have limited success in quelling the childhood obesity epidemic.

Correction: Exposure to hot temperatures during lactation in Swiss mice stunts offspring growth and decreases future reproductive performance of female offspring.

Abstract: There was an error published in the online full-text and PDF versions of Journal of Experimental Biology (2020) 223, [jeb223560][1] ([doi:10.1242/jeb.223560][2]). The common name of the study organism was originally given as striped hamsters in the title of the article. The correct name appears in