Michael Kam

Energy cost of ectoparasitism: the flea Xenopsylla ramesis on the desert gerbil Gerbillus dasyurus

Metabolizable energy intake and changes in body mass was measured in the desert gerbil Gerbillus dasyurus when parasitized by the flea 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 efficiency 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 fleas feeding on a gerbil consumed 3.68 a 1.19 mg blood, in total. This amounted to 34.3 a 1.8% of body mass of a starving flea 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 fleas 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 confirmed. 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 efficiency of utilization of energy in the parasitized and non-parasitized gerbils was similar.

Variance in Centrality within Rock Hyrax Social Networks Predicts Adult Longevity

Background In 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 Findings As 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/Significance Our 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.

Growth rate, total body water volume, dry-matter intake and water consumption of domesticated ostriches ( Struthio camelus )

Growth rate, total body water volume (TBW), dry-matter intake (DMI) and water consumption were determined in ostriches from hatching to 350 days at which time they weighed approximately 100 kg. A Gompertz equation was used to describe the sigmoidal growth curve; mature body mass (Mmb) wascalculated as 104·1 kg from this equation. Highest average daily gain (ADG) was 455 g/day which occurred between 70 days and 98 days. Time to reach 0·5 Mmb and to grow from 0·25 to 0·75 Mmb per Mmb025 were 46·8 days and 39·7 days, respectively. Maintenance energy requirements were 1·07 MJ/kg063per day and energy requirements for kg mb increase were 0·260 MJ/kg109: thes e values were derived from a non-linear regression model. TBW as a fraction of mb declined from 0·84 in 35-day-old chicks to 0·57 in 322-day-old birds, indicating a concomitant increase in the fraction of body lipid content. Mass specific DMI decreased from 0·061 g/g mb in chicks to 0·020 g/g mb in 322 to 350 day old birds, while mass specific water influx decreased from 0·21 ml/g mb to 0·046 ml/g mb during this time. The ratio of DMI to ADG increased steadily from 1·07 to 17·1; the ratio of water consumption to DMI remained relatively constant at approximately 2·3.

GRANIVORY AND PLANT SELECTION BY DESERT GERBILS OF DIFFERENT BODY SIZE

Plant selection, energy intake, and digestibility were studied in nonrepro- ducing Gerbillus henleyi (10 g; n = 9), Gerbillus dasyurus (24 g; n = 6), and Meriones crassus (90 g; n = 9). These gerbils coexist in the Negev Desert Highlands, have similar dietary habits (being primarily granivores), and do not require drinking water, but they differ greatly in body mass. Each species was offered different levels (0% and -40% and 80% of maintenance energy requirements) of millet seeds and ad libitum fresh vegetation consisting of Atriplex halimus, Moricandia nitens, Zygophyllum dumosum, Lycium shawii, Anabasis articulate, and Thymelaea hirsuta, the dominant plants in the area inhabited by the rodents. Drinking water was not available. We hypothesized that: (1) smaller animals would be more dependent than larger animals on highly digestible food items such as seeds, and (2) smaller animals would be more selective than larger animals for highly digestible and energy-rich plant parts. The minimum levels of millet seeds needed to maintain body mass were 97%, 94%, and 36% of maintenance energy requirements for G. henleyi, G. dasyurus, and M. crassus, respectively. Therefore, G. henleyi was the most dependent on seeds, and M. crassus the least, supporting hypothesis 1. At similar levels of seeds consumed, apparent digestibilities of dry matter (DMD) and energy of the total diet were highest for G. henleyi. In the absence of seeds, vegetation DMD averaged 88% in G. henleyi and 70% in M. crassus, yet G. henleyi lost body mass, as a percentage, twice as fast as M. crassus. The three rodent species were selective in consuming vegetation and made similar choices. A. halimus and M. nitens were preferred, comprising -48%, 64%, and 67% of total plant dry matter consumption in G. henleyi, G. dasyurus, and M. crassus, respectively. Plant species not selected were relatively low in water and protein contents and were high in phenolic compounds and condensed tannins compared to preferred species. Gross energy, ash, and fiber levels did not appear to affect selectivity. Selection of plant parts within each plant species, as indicated by the leaf: stem (L:S) ratio, differed among rodent species. The L:S ratio for A. halimus was 4.8, but the L:S ratios ingested were 1.7, 4.0, and 7.4 in G. henleyi, G. dasyurus, and M. crassus, respectively, indicating selection of stems by G. henleyi, selection of leaves by M. crassus, and basically no selection by G. dasyurus. The ratio of seed: green vegetation (S:G) intake was highest in G. henleyi and lowest in M. crassus. A similar inverse rela- tionship between body mass and S:G ratio within seasons was found in other Old World and New World free-living granivorous desert rodents.

Structural balance in the social networks of a wild mammal

The social structure of a population is based on individual social associations, which can be described using network patterns (motifs). Our understanding of the forces stabilizing specific social structures in animals is limited. Structural balance theory was proposed for exploring social alliances and suggested that some network motifs are more stable than others in a society. The theory models the presence of specific triads in the network and their effect on the global population structure, based on the differential stability of specific triad configurations. While structural balance was shown in human social networks, the theory has never been tested in animal societies. Here we use empirical data from an animal social network to determine whether or not structural balance is present in a population of wild rock hyraxes, Procavia capensis. We confirm its presence and show the ability of structural balance to predict social changes resulting from local instability. We present evidence that new individuals entering the population introduce social instability, which counters the tendency of social relationships to seek balanced structures. Our findings imply that structural balance has a role in the evolution of animal social structure.

Seasonal Energy, Water, and Food Consumption of Negev Chukars and Sand Partridges

Chukars (Alectoris chukar) and Sand Partridges (Ammoperdix heyi), two ground-dwelling phasianids, are permanent residents of the Negev desert and are sympatric over much of their ranges. Sand Partridges (body mass = 150-250 g), however, inhabit only arid and very arid areas, whereas Chukars (mb = 350-600 g) are widely distributed and inhabit deserts only at the margins of their ranges. We compared some of the desert adaptations of these phasianids by measuring the seasonal field metabolic rates (FMR) and water influxes (using doubly labelled water), diet selection, and food requirements of free- living Chukars and Sand Partridges at a site where both species occurred. Both species showed adaptation in the form of low energy metabolism, which ranged from 43 to 81% of that expected for birds of similar body mass. During summer, Sand Partridges had lower energy expenditures (5.47 kJ g-0.61 d-1) and water influxes (72.3 mL kg-0.75 d- 1) than did Chukars (6.42 kJg-0.61 d-1 and 93.5 mL.kg-075d-l1, respectively), indicating more pro- nounced adjustments to arid conditions in the desert specialist. However, both species obtained more than half of their water influx in summer by drinking. Their summer diet was relatively dry, consisting mainly of seeds (80%) along with some green vegetation (18%) and, in Chukars, occasional arthropods. This situation changed abruptly after winter rains, which induced germination and reduced the availability of seeds. Chukars were unable to maintain energy balance in the face of low ambient temperatures and a diet (90% green vegetation) that contained much water but comparatively little energy, and they mobilized fat reserves to meet energy requirements. Most Sand Partridges left the study area after winter rains, apparently migrating to the lower elevation, warmer, and drier Arava (part of the Rift Valley). The winter rainy season appears to be the most stressful time of the year for both species. The adaptations to hot, dry conditions possessed by Sand Partridges may be accompanied by constraints on their abilities to cope with cool, wet conditions, and this may restrict them to arid and very arid habitats.

ENERGY REQUIREMENTS DURING REPRODUCTION IN FEMALE COMMON SPINY MICE (ACOMYS CAHIRINUS)

Abstract We hypothesized that energy intake of lactating females is the main factor determining growth of the young and that use of maternal energy reserves is less important when food is available in abundance. We studied reproducing female common spiny mouse (Acomys cahirinus) offered millet seeds and water ad libitum. Females gave birth to 1 or 2 young, and growth rate was similar between litters of 1 infant and 2 infants combined. In addition, energy intake of the 2 groups of females was similar. Lactating females increased energy intake by 45% (per g0.75) over that of nonreproducing females. Energy intake and change in body mass of the lactating female each explained about 50% of the variance in infant growth and, therefore, our hypothesis was not supported. Energy intake and change in body mass of the lactating female together explained approximately 76% of the variance in growth of young.

Time-activity budget of ostriches (Struthio camelus) offered concentrate feed and maintained in outdoor pens

The time-activity budget of 5–6-month-old growing ostriches (mean body mass = 57.4±14.5 kg; n = 8) that were offered only concentrate feed and were maintained on packed ground in four outdoor pens (3×6 m each) was studied. They were kept in pairs matched for age and weight. The ostriches were active for ∼ 12 h during the day and sat for 12 h at night. They spent 20.4±14.0% of the 12-h active day sitting, 61.5±12.5% walking, 5.5±3.2% standing, 6.6±3.6% eating concentrate feed, 5.0±1.7% foraging (pecking the ground) and 1.1±0.4% drinking. Each pair of ostriches usually behaved in synchrony, i.e., ate together, drank together, etc. Sitting was mostly done with their necks straight up and their legs folded under their bodies, and on occasion with their necks and heads prone on the ground. The ostriches spent most of their time walking with their necks straight up and sometimes with their heads in an S-shape more or less parallel or close to the ground. They usually walked at a rate of ∼ 1 m/s−1 along the edges of their pens. Each ostrich consumed 1911±266 g dry matter (DM) feed day−1; this figure was based on the intake of each pair of birds. They spent 46.4±25.3 min eating this feed and pecked at their feed 2830±394 times; therefore they consumed 41.2±5.7 g DM min−1 feeding and 0.7±0.1 g DM per peck. They also consumed 129.2±25.4 g DM earth, spent 35.3±13.3 min day−1 foraging and pecked at the ground 1957±737 times day−1; therefore they consumed 3.7±1.4 g DM earth min−1 foraging and 0.1±0.0 g DM per peck. Total water influx, which was determined using tritiated water, was 10.1±3.4 l day−1. Furthermore, it was estimated that 1.0±0.1 l day−1 were obtained from preformed and metabolic water from feed and 9.1±3.1 l day−1 from drinking. They spent 8.2±3.3 min day−1 drinking, during which time they took 315±106 sips.

Scaling of field metabolic rate to basal metabolic rate ratio in homeotherms

Abstract:Linear regression analyses were used to describe the allometric relationships of basal metabolic rate (BMR), field metabolic rate (FMR) and FMR:BMR ratio on body mass in non-reproducing individuals of bird, marsupial and eutherian mammal species. Measurements of FMR were made by the double labelled water method and of BMR by indirect calorimetry using O2 consumption. All regressions were significant, including FMR:BMR ratio on body mass. In addition, the slope of BMR on body mass was significantly higher than that of FMR on body mass for each group of animals. This shows that the FMR:BMR ratio is not constant within each group and is greater for smaller than for larger animals. We propose that this difference is due mainly to thermoregulatory costs. The use of a constant FMR:BMR ratio to estimate FMR from BMR, as is commonly done, could result in erronoeus results. However, the ratio found in the allometric relationships between FMR:BMR ratio and body mass for the three groups of homeotherms coul...

Daily energy expenditure and water flux of free-living Blanford's foxes (Vulpes cana), a small desert carnivore

The Blanfords fox, Vulpes cana (Blanford 1877) is a small canid (mean body mass = 956 g) that inhabits rocky mountains and canyons in the deserts of Israel, where it feeds mainly on invertebrates and fruits. We hypothesized that the energy expenditure of Blanfords foxes would be higher than that of a small canid that inhabits flat terrain, all else being equal. To test this hypothesis, we measured daily energy expenditure and water intake of freeliving Blanfords foxes and compared the results with those of the kit fox, Vulpes macrotis (Say 1823)