Energetic costs of parasitism in the Cape ground squirrel Xerus inauris

Parasites have been suggested to influence many aspects of host behaviour. Some of these effects may be mediated via their impact on host energy budgets. This impact may include effects on both energy intake and absorption as well as components of expenditure, including resting metabolic rate (RMR) and activity (e.g. grooming). Despite their potential importance, the energy costs of parasitism have seldom been directly quantified in a field setting. Here we pharmacologically treated female Cape ground squirrels (Xerus inauris) with anti-parasite drugs and measured the change in body composition, the daily energy expenditure (DEE) using doubly labelled water, the RMR by respirometry and the proportions of time spent looking for food, feeding, moving and grooming. Post-treatment animals gained an average 19 g of fat or approximately 25 kJ d(-1). DEE averaged 382 kJ d-1 prior to and 375 kJ d-1 post treatment (p> 0.05). RMR averaged 174 kJ d-1 prior to and 217 kJ d-1 post treatment (p

Differential energy costs of winter acclimatized common spiny mice Acomys cahirinus from two adjacent habitats

The common spiny mouse Acomys cahirinus, of Ethiopian origin, has a widespread distribution across arid, semi-arid and Mediterranean parts of the Arabian sub-region. We compared the daily energy expenditure (DEE), water turnover NTTO) and sustained metabolic scope (SusMS = DEE/resting metabolic rate) of two adjacent populations during the winter. Mice were captured from North- and South- facing slopes (NFS and SFS) of the same valley, comprising mesic and xeric habitats, respectively. Both DEE and SusMS winter values were greater in NFS than SFS mice and were significantly greater than values previously measured in the summer for these two populations in the same environments. However, WTO values were consistent with previously established values and were not significantly different from allometric predictions for desert eutherians. We suggest that physiological plasticity in energy expenditure, which exists both temporally and spatially, combined with stable WTO, perhaps reflecting a xeric ancestry, has enabled A. cahirinus to invade a wide range of habitats. (C) 2003 Elsevier Inc. All rights reserved.

Costs, outputs and outcomes in school PFI contracts and the significance of project size

This article examines operational Private Finance Initiative (PFI) school projects and reports the experiences of UK headteachers. It considers the impact of project size on value for money (VFM). Headteachers involved in small projects are more satisfied with costs than those involved in large projects, but headteachers involved in larger projects are more satisfied with affordability. Generally, heads are more satisfied with the buildings than with the services. The authors question the government’s recent policy changes to increase the size of PFI projects.

Can the protein costs of bacterial resistance be offset by altered feeding behaviour?

1. Mounting an immune response is likely to be costly in terms of energy and nutrients, and so it is predicted that dietary intake should change in response to infection to offset these costs. The present study focuses on the interactions between a specialist grass-feeding caterpillar species, the African armyworm Spodoptera exempta, and an opportunist bacterium, Bacillus subtilis.
2. The main aims of the study were (i) to establish the macronutrient costs to the insect host of surviving a systemic bacterial infection, (ii) to determine the relative importance of dietary protein and carbohydrate to immune system functions, and (iii) to determine whether there is an adaptive change in the host's normal feeding behaviour in response to bacterial challenge, such that the nutritional costs of resisting infection are offset.
3. We show that the survival of bacterially infected larvae increased with increasing dietary protein-to-carbohydrate (P:C) ratio, suggesting a protein cost associated with bacterial resistance. As dietary protein levels increased, there was an increase in antibacterial activity, phenoloxidase (PO) activity and protein levels in the haemolymph, providing a potential source for this protein cost. However, there was also evidence for a physiological trade-off between antibacterial activity and phenoloxidase activity, as larvae whose antibacterial activity levels were elevated in response to immune activation had reduced PO activity.
4. When given a choice between two diets varying in their P:C ratios, larvae injected with a sub-lethal dose of bacteria increased their protein intake relative to control larvae whilst maintaining similar carbohydrate intake levels. These results are consistent with the notion that S. exempta larvae alter their feeding behaviour in response to bacterial infection in a manner that is likely to enhance the levels of protein available for producing the immune system components and other factors required to resist bacterial infections (‘self-medication’).

Costs of resistance: genetic correlations and potential trade-offs in an insect immune system

Theory predicts that natural selection will erode additive genetic variation in fitness-related traits. However, numerous studies have found considerable heritable variation in traits related to immune function, which should be closely linked to fitness. This could be due to trade-offs maintaining variation in these traits. We used the Egyptian cotton leafworm, Spodoptera littoralis, as a model system to examine the quantitative genetics of insect immune function. We estimated the heritabilities of several different measures of innate immunity and the genetic correlations between these immune traits and a number of life history traits. Our results provide the first evidence for a potential genetic trade-off within the insect immune system, with antibacterial activity (lysozyme-like) exhibiting a significant negative genetic correlation with haemocyte density, which itself is positively genetically correlated with both haemolymph phenoloxidase activity and cuticular melanization. We speculate on a potential trade-off between defence against parasites and predators, mediated by larval colour, and its role in maintaining genetic variation in traits under natural selection.

The costs of bearing arms and armour in the hermit crab Pagurus bernhardus

Hermit crabs use empty gastropod shells as protective armour and enlarged chelipeds as signals and weapons. However, carrying armour and arms may impose energy costs that result in increased lactate and hence potential fatigue and there may be consequent effects on general activity. We investigated whether variation in shell and cheliped size influences lactate levels in hermit crabs. Lactate was positively related to residual cheliped size for both sexes and was higher in males than females; when we controlled for body size, the former had larger chelipeds. Shell weight unexpectedly had no effect on lactate but crabs in small shells had high lactate, possibly because of reduced ability to maintain a respiratory current. The size of natural shells had no effect on activity but the addition of food odour increased locomotion. However, activity was not related to lactate. We conclude that possession of larger chelipeds than expected for body size imposes significant costs and may limit development of sexual dimorphism. (C) 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.