Metabolizable energy intake and changes in body mass was measured in the desert gerbil Gerbillus dasyurus when parasitized by the¯ea Xenopsylla ramesis. We hypothesized that energy requirements for maintenance, or average daily metabolic rate, of parasitized gerbils would be higher than those of nonparasitized gerbils. We also hypothesized that the ef®ciency of utilization of energy for maintenance would be the same for parasitized and non-parasitized gerbils, as this measurement is dependent mainly on dietary quality. Fifty¯eas feeding on a gerbil consumed 3.68 1.19 mg blood, in total. This amounted to 34.3 1.8% of body mass of a starving¯ea and only about 0.17% of the blood volume of the host. The absolute amount of blood consumed by X. ramesis is the lowest reported for¯eas in other studies. This suggested that the pressure of parasitism of X. ramesis on G. dasyurus in terms of blood consumed was relatively low. Both our hypotheses were con®rmed. Average daily metabolic rate of the parasitized gerbils (7.75 kJ g 70.54 d 71 ) was 16% higher than that of non-parasitized gerbils (6.69 kJ g 70.54 d 71 ). In addition, at zero metabolizable energy intake, the parasitized gerbils lost body mass at a faster rate than the nonparasitized gerbils (4.34 vs 3.95% body mass d 71 ). The ef®ciency of utilization of energy in the parasitized and non-parasitized gerbils was similar.

BackgroundIn communal mammals the levels of social interaction among group members vary considerably. In recent years, biologists have realized that within-group interactions may affect survival of the group members. Several recent studies have demonstrated that the social integration of adult females is positively associated with infant survival, and female longevity is affected by the strength and stability of the individual social bonds. Our aim was to determine the social factors that influence adult longevity in social mammals.Methodology/Principal FindingsAs a model system, we studied the social rock hyrax (Procavia capensis), a plural breeder with low reproductive skew, whose groups are mainly composed of females. We applied network theory using 11 years of behavioral data to quantify the centrality of individuals within groups, and found adult longevity to be inversely correlated to the variance in centrality. In other words, animals in groups with more equal associations lived longer. Individual centrality was not correlated with longevity, implying that social tension may affect all group members and not only the weakest or less connected ones.Conclusions/SignificanceOur novel findings support previous studies emphasizing the adaptive value of social associations and the consequences of inequality among adults within social groups. However, contrary to previous studies, we suggest that it is not the number or strength of associations that an adult individual has (i.e. centrality) that is important, but the overall configuration of social relationships within the group (i.e. centrality SD) that is a key factor in influencing longevity.

Mating with close kin can lead to inbreeding depression through the expression of recessive deleterious alleles and loss of heterozygosity. Mate selection may be affected by kin encounter rate, and inbreeding avoidance may not be uniform but associated with age and social system. Specifically, selection for kin recognition and inbreeding avoidance may be more developed in species that live in family groups or breed cooperatively. To test this hypothesis, we compared kin encounter rate and the proportion of related breeding pairs in noninbred and highly inbred canid populations. The chance of randomly encountering a full sib ranged between 1-8% and 20-22% in noninbred and inbred canid populations, respectively. We show that regardless of encounter rate, outside natal groups mates were selected independent of relatedness. Within natal groups, there was a significant avoidance of mating with a relative. Lack of discrimination against mating with close relatives outside packs suggests that the rate of inbreeding in canids is related to the proximity of close relatives, which could explain the high degree of inbreeding depression observed in some populations. The idea that kin encounter rate and social organization can explain the lack of inbreeding avoidance in some species is intriguing and may have implications for the management of populations at risk.

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Average daily metabolic rate (ADMR), the metabolizable energy intake required by a caged animal to maintain constant body energy content, includes the basal metabolic rate (BMR) and the heat increment of feeding for maintenance (HIF m ). Therefore, when an animal is in energy balance, ADMR can be expressed as:This is so since locomotory and thermoregulatory costs are negligible.In addition to evaluating the energy requirements of animals, ADMR measurements could also serve a useful purpose in determining the efficiency of utilization of energy. However, unlike BMR and, recently, field metabolic rate measurements, it has been largely ignored in studies of energy expenditure Average daily metabolic rate (ADMR) is the metabolizable energy intake required by a caged animal to maintain constant body energy content. Linear regression of standardized, phylogenetically independent contrasts was used to describe the allometric relationship between ADMR and body mass in rodents. It was predicted that desert species would have a lower ADMR than non-desert species and that granivores would have a lower ADMR than those of herbivores and omnivores. The efficiency of utilization of energy for maintenance was also determined in these species. Here, it was predicted that the efficiency in granivores would be higher than in both herbivores and omnivores and in desert species would be higher than in non-desert species.2. The regression of the phylogenetic contrasts of ADMR on body mass (m b ) for 53 independent data points based on 63 species of rodents was highly significant (P < 0·0001) with an allometric slope of 0·53. Independent comparisons of both basal metabolic rate (BMR) and ADMR showed significantly lower rates in desert than in non-desert species.There was a trend for granivores to have a lower ADMR per g 0.53 than either omnivores or herbivores, but this trend is not significant in independent comparisons between the categories. Thus, the predictions in regard to desert and non-desert habitats were confirmed, and there is a non-significant trend in the predicted direction with respect to diet. Herbivores and omnivores showed no significant difference in either BMR or ADMR. 3. In independent comparisons between categories, there was no evidence for trends in the efficiency of utilization of energy for maintenance (BMR:ADMR ratio or k m ) with either habitat or diet categories. Thus, these results are not in agreement with our predictions. Taking simple means, k m equals 0·47 ± 0·21, 0·37 ± 0·12 and 0·56 ± 0·11 for granivores, omnivores and herbivores, respectively, and 0·37 ± 0·12 and 0·55 ± 0·16 for desert and non-desert mammals, respectively. 4. It is recommended that conditions for ADMR measurements be standardized, as is common for basal metabolic rate measurements. This would allow more reliable comparisons among species measured in different laboratories and also provide more accurate estimates of efficiency of utilization of energy.Key-words: Average daily metabolic rate, dietary comparisons, efficiency of utiliz...

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Recently, a conservation strategy developed to restore populations of black-tailed prairie dog (Cynomys ludovicianus) suggested reintroducing animals into the Chihuahuan Desert grasslands of the southwestern United States. Rainfall in desert habitats is lower and more variable compared to rainfall near the center of the prairie dog's range. Additionally, peak rainfall comes months after prairie dogs reproduce in these desert systems. Thus, southwestern populations may be less prolific and fluctuate more than those found in northerly climes. Using mark-recapture and mark-resight techniques, we estimated reproduction and monthly survival from 577 individuals inhabiting 6 reintroduced colonies from 2003 to 2005 in the northern Chihuahuan Desert. During 2003 precipitation was 64% of the long-term average, whereas both 2004 and 2005 had near-average precipitation. Probability that a female became pregnant, number of juvenile prairie dogs emerging from maternity burrows, and date of emergence were all correlated to adult female body mass. Adult monthly survival decreased from .0.95 during spring to 0.70 in summer 2003, following a rapid loss in adult body mass that coincided with low precipitation. In 2003 monthly juvenile survival was near zero on 2 of the 3 largest colonies and growth rates of juveniles were half that of subsequent years. Estimated population size declined by 68% (range 5 18-91%) from 2003 to 2004, and 5 of 6 populations declined an average of 75% from their original introduction size. Prairie dog populations in desert environs may have a high risk of extirpation caused by weather patterns indicative of desert climates. Our results are important for those managers involved in the conservation of prairie dogs and we suggest that regional differences should be carefully considered prior to any reintroduction effort.

Summary1. Two immunological tactics, a constitutive response that is always present, and an induced response that is only employed after an invader has been recognized, have evolved in animals as a defence against parasites. 2. The energy requirements, body mass change and blood parameters of flea-parasitized and nonparasitized gerbils ( Gerbillus andersoni ) were measured and compared with published data for a close relative ( Gerbillus dasyurus ). G. andersoni possesses a constitutive immune response that could require additional maintenance costs, whereas G. dasyurus develops an immune response only after being attacked by fleas. We therefore predicted that G. andersoni has higher energy requirements than G. dasyurus when both species are parasite-free. However, we also predicted that the immunological 'readiness' of G. andersoni makes it less susceptible to flea infestation than G. dasyurus. 3. Energy requirements for maintenance were estimated by offering different levels of metabolizable energy to parasitized and nonparasitized animals and measuring changes in their body mass. At the end of the experiment, blood samples were taken from all rodents and haematological and biochemical analyses were done. 4. Adjusted energy requirements per unit body mass of nonparasitized G. andersoni were higher than those reported for G. dasyurus . Also, there was no difference between energy requirements, body mass change and blood parameters of parasitized and nonparasitized G. andersoni in contrast to the pronounced differences found for parasitized and nonparasitized G. dasyurus . However, parasitized G. andersoni did not have lower energy requirements than parasitized G. dasyurus as predicted from the second prediction. 5. The results illustrate the energy costs and benefits related to each immunological strategy and suggest that parasites can cause other nonenergetic costs to their hosts. The two strategies are most likely a reflection of interspecific differences in probability of flea attacks.