Energetics reveals physiologically distinct castes in a eusocial mammal.

Eusociality, which occurs among mammals only in two species of African mole-rat, is characterized by division of labour between morphologically distinct 'castes'1. In Damaraland mole-rats (Cryptomys damarensis), colony labour is divided between 'infrequent worker' and 'frequent worker' castes2. Frequent workers are active year-round and together perform more than 95% of the total work of the colony, whereas infrequent workers typically perform less than 5% of the total work3. Anecdotal evidence suggests that infrequent workers may act as dispersers, with dispersal being limited to comparatively rare periods when the soil is softened by moisture4, 5. Here we show that infrequent workers and queens increase their daily energy expenditure after rainfall whereas frequent workers do not. Infrequent workers are also fatter than frequent workers. We suggest that infrequent workers constitute a physiologically distinct dispersing caste, the members of which, instead of contributing to the work of the colony and helping the queen to reproduce, build up their own body reserves in preparation for dispersal and reproduction when environmental conditions are suitable.

Relative energetics and structural properties of zirconia using a self-consistent tight-binding model

We describe an empirical, self-consistent, orthogonal tight-binding model for zirconia, which allows for the polarizability of the anions at dipole and quadrupole levels and for crystal field splitting of the cation d orbitals, This is achieved by mixing the orbitals of different symmetry on a site with coupling coefficients driven by the Coulomb potentials up to octapole level. The additional forces on atoms due to the self-consistency and polarizabilities are exactly obtained by straightforward electrostatics, by analogy with the Hellmann-Feynman theorem as applied in first-principles calculations. The model correctly orders the zero temperature energies of all zirconia polymorphs. The Zr-O matrix elements of the Hamiltonian, which measure covalency, make a greater contribution than the polarizability to the energy differences between phases. Results for elastic constants of the cubic and tetragonal phases and phonon frequencies of the cubic phase are also presented and compared with some experimental data and first-principles calculations. We suggest that the model will be useful for studying finite temperature effects by means of molecular dynamics.

The energetics of huddling in two species of mole-rat (Rodentia: Bathyergidae)

Small rodents with a large surf ace-area-to-volume ratio and a high thermal conductance are likely to experience conditions where they have to expend large: amounts of energy in order to maintain a constant body temperature at low ambient temperatures. The survival of small rodents is thus dependent on their ability to reduce heat loss and increase heat production at low ambient temperatures. Two such animals are the social subterranean rodents Cryptomys damarensis (the Damaraland mole-rat) and Cryptomys hottentotus natalensis (the Natal mole-rat). This study examined the energy savings associated with huddling as a behavioural thermoregulatory mechanism to conserve energy in both these species. Individual oxygen consumption (VO2) was measured in groups ranging in size from one to 15 huddling animals for both species at ambient temperatures of 14, 18, 22, 26 and 30 degrees C. Savings in energy (VO2) were then compared between the two species. Significant differences in VO2 (p

Seasonal energetics of the Hottentot golden mole at 1500m altitude

Winter is an energetically stressful period for small mammals as increasing demands for thermoregulation are often coupled with shortages of food supply. In sub-tropical savannah, Hottentot golden moles (Ambysomus hottentottus longiceps) forage throughout the year and for lone periods of each day. This may enable them to acquire sufficient resources from an insectivorous prey base that is both widely dispersed and energetically costly to obtain. However, they also inhabit much cooler regions; how their energy budgets are managed in these areas is unknown. We measured the daily energy expenditure (DEE), resting metabolic rate (RMR) and water turnover (WTO) of free-living golden moles during both winter and summer at high altitude (1500 m). We used measurements of deuterium dilution to estimate body fat during these two periods. DEE, WTO and body mass did not differ significantly between seasons. However, RMR values were higher during the winter than the summer and, in the latter case were also lower than allometric predictions. Body fat was also higher during the winter. Calculations show that during the winter they may restrict activity to shorter, more intense periods. This, together with an increase in thermal insulation, might enable them to survive the cold. (c) 2005 Elsevier Inc. All rights reserved.

Energetics and water economy of common spiny mice Acomys cahirinus from north- and south-facing slopes of a Mediterranean valley

1. A comparison was made of the daily energy expenditure (DEE), resting metabolic rate (RMR) and water turnover (WTO) of two populations of Common Spiny Mice Acomys cahirinus from north- and south-facing slopes (NFS and SFS) of the same valley, which represented 'Mediterranean' and 'desert' habitats, respectively.

The energetics of lactation in cooperatively breeding meerkats Suricata suricatta

Species may become obligate cooperative breeders when parents are unable to raise their offspring unassisted. We measured the daily energy expenditure of mothers, helpers and offspring during peak lactation in cooperatively breeding meerkats Suricata suricatta using the doubly labelled water technique. Lactating mothers expended more energy per day than allo-lactating subordinate females, non-lactating females or suckling offspring. Metabolizable energy intakes of lactating mothers were calculated from isotope-based estimates of offspring milk energy intake, and were not significantly different from the previously suggested maximal limit for mammals. Allo-lactating females were the only category of animals that lost weight during the period of study, probably because they spent more time babysitting than non-lactating females. Daily energy expenditure (DEE) of lactating mothers increased with litter size but decreased with the number of helpers. Calculations show that for every 10 helpers, even in the absence of allo-lactators, mothers are able to reduce their DEE during peak lactation by an amount equivalent to the energy cost of one pup. These results indicate that helpers have beneficial energetic consequences for lactating mothers in an obligate cooperatively breeding mammal.

Energetics and litter size variation in domestic dog Canis familiaris breeds of two sizes

We measured resting metabolic rate (RMR), daily energy expenditure (DEE) and metabolisable energy intake (MEI) in two breeds of dog during peak lactation to test whether litter size differences were a likely consequence of allometric variation in energetics. RMR of Labrador retrievers (30 kg, n = 12) and miniature Schnauzers (6 kg, n = 4) averaged 3437 and 1062 kJ/day, respectively. DEE of Labradors (n = 6) and Schnauzers (n = 4) averaged 9808 and 2619 kJ/day, respectively. MEI of Labradors (n = 12) was 22448 kJ/day and of Schnauzers (a = 7) was 5382 kJ/day. DEE of Labrador pups (2.13 kg, n = 19) was 974 kJ/day and Schnauzers (0.89 kg, n = 7) were 490 kJ/day. Although Labradors had higher MEIs than Schnauzers during peak lactation, there was no difference in mass-specific energy expenditure between the two breeds. Hence, it is unlikely that litter size variation is a likely consequence of differences in maternal energy expenditure. Individual offspring were relatively more costly for mothers of the smaller breed to produce. Therefore, litter size variations were consistent with the expectation that smaller offspring should be more costly for mothers, but not that smaller mothers should per se invest more resources in reproduction. (C) 2001 Elsevier Science Inc. All rights reserved.

The energetics of tetrahydrocarbazole aromatization over Pd(111): A computational analysis

The carbazole moiety is a component of many important pharmaceuticals including anticancer and anti-HIV agents and is commonly utilized in the production of modern polymeric materials with novel photophysical and electronic properties. Simple carbazoles are generally produced via the aromatization of the respective tetrahydrocarbazole (THCZ). In this work, density functional theory calculations are used to model the reaction pathway of tetrahydrocarbazole aromatization over Pd(111). The geometry of each of the intermediate surface species has been determined and how each structure interacts with the metal surface addressed. The reaction energies and barriers of each of the elementary surface reactions have also been calculated, and a detailed analysis of the energetic trends performed. Our calculations have shown that the surface intermediates remain fixed to the surface via the aromatic ring in a manner similar to that of THCZ. Moreover, the aliphatic ring becomes progressively more planer with the dissociation of each subsequent hydrogen atom. Analysis of the reaction energy profile has revealed that the trend in reaction barriers is determined by the two factors: (i) the strength of the dissociating ring-H bond and (ii) the subsequent gain in energy due to the geometric relaxation of the aliphatic ring. (c) 2008 American Institute of Physics.