A. Allan Degen

Ecophysiology of Small Desert Mammals

Since small mammals have a large surface to mass ratio, one would expect them to quickly dehydrate and perish at high environmental temperatures. Nonetheless, a large number of small mammal species inhabit deserts. This fascinating phenomenon is investigated by Prof. A. Allan Degen in his book. The majority of small desert mammals are rodents, but shrews of several grams and small foxes of 1 kg are also present. Their survival is due mainly to behavioural adaptations and habitat selection, however, physiological adaptations also contribute to the success. Interestingly, many small mammals that live in different deserts of the world show similarities in their adaptive traits although they have different taxonomic affinities.

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.

Some problems in fiber determination of a tannin- rich forage (Acacia saligna leaves) and their implications in in vivo studies

The detergent method for determination of cell-wall constituents has several applications in nutritional studies and was used for Acacia saligna leaves, a tannin-rich material, and for fecal samples of sheep and goats fed these leaves as a sole feed. The samples were analysed by the standard method which uses a separate sample for neutral detergent fiber (NDF) and acid detergent fiber (ADF) determinations and by the sequential approach in which NDF is subjected to acid detergent solution to obtain ADF. In both cases, the acid detergent lignin (ADL) is determined from ADF. For A. saligna leaves, sequentially determined ADF and ADL were higher compared with the directly determined ADF or ADL, whereas a reverse trend was observed for the fecal samples of both sheep and goats, suggesting a different nature of fibers in feed and in fecal samples. The hemicellulose (HC) content (NDF-ADF) for the leaves was 14.8% and 1.5% respectively, depending on whether the direct or sequential method was applied. Similarly, there was a difference in the HC contents of fecal samples when the fiber was determined directly or sequentially (sheep 5.2% and 8.9% and goats 5.5% and 9.4% respectively). There was a comparatively large difference in the values for cellulose (ADF-ADL) determined by the direct and sequential method in the leaves (14.3% vs. 19.4%) as compared with that in sheep feces (14.9% vs. 14%) and goat feces (15.3% vs. 14.1%). In leaves, both protein and condensed tannins (CT) were much higher in the sequentially determined fiber as compared with those values obtained for the leaves by determining fibers directly, explaining higher ADF and ADL values obtained sequentially. Also, the fiber fractions of fecal samples had a substantial amount of both protein and CT. The in vivo digestibilities of fiber and fiber bound proteins varied substantially and were negative in most cases when using the fiber values obtained. The results suggest that detergent extraction techniques do not predict or determine the in vivo digestibility of cell-wall constituents accurately and that these techniques are not suitable for tannin-rich forages. Further studies are required to account for the artifacts arising due to tannins, proteins, and their complexes in the fiber fractions.

Immune response to fleas in a wild desert rodent: effect of parasite species, parasite burden, sex of host and host parasitological experience

SUMMARY We studied immune responses of the jird Meriones crassus to different flea species belonging to the same family. We used jirds maintained in an outdoor enclosure (enclosure; N=18) and parasitized by fleas Xenopsylla conformis mycerini and Xenopsylla ramesis, and also jirds born in the laboratory to previously parasitized mothers (laboratory animals; N=23). We asked (i) whether cross-immunity to different fleas occurs, (ii) whether there is a sex difference in immune responses to flea parasitism and (iii) whether the severity of the immune responses depends on parasite load. In the enclosure animals, immune response to antigen from the unfamiliar flea Synosternus cleopatrae pyramidis did not differ from those to antigens from the familiar fleas. In contrast, laboratory rodents demonstrated no difference in the immune response between S. c. pyramidis antigen and either the phytohemagglutinin treatment or controls, although their responses to antigens of fleas familiar to their mothers (X. c. mycerini and X. ramesis) were significantly higher than those to antigen of S. c. pyramidis and phytohemagglutinin. The results clearly demonstrated that (i) cross-reactivity in rodent responses to different flea species occurred for enclosure but not for laboratory jirds and (ii) immune-naïve animals whose mothers were parasitized by fleas had some degree of immunity against fleas. The only sex difference in immunological parameters was the higher level of circulating immune complexes in females than in males. Only phagocytic activity was affected by flea burden, decreasing with an increase in flea numbers.

Effect of cold stress on performance and immune responses of Bedouin and White Leghorn hens

1. Bedouin chickens are kept in deserts mainly for eggs and are well adapted to arid conditions. However, deserts are also characterised by relatively cold winter nights. As a consequence of cold stress there is an involution of lymphoid organs and a depression of immunological function. We compared the performance and immunological responses of Bedouin and White Leghorn hens kept in outdoor pens in the Negev Desert during the winter. 2. Initial mean body mass was similar for the two breeds: 1525 g for Bedouin hens and 1542 g for White Leghorn hens. White Leghorns lost 7.74 g/d, compared with 0.60 g/d for Bedouin hens and produced 0.36 eggs/d, compared with 0.54 eggs/day for Bedouin hens. 3. The heterophil/lymphocyte ratio for Bedouin hens was 0.28, which was lower than the 0.44 for White Leghorn hens. Phagocytic index was higher in Bedouin hens than in White Leghorns. Furthermore, wattle index measured 24, 48 and 72 h after PHA injections and anti-SRBC antibody titres determined 10 d after challenge were also higher in Bedouin hens than in White Leghorns. 4. We concluded that the Bedouin hens were less stressed by the cold than were the White Leghorn hens.

The nutritive value of Acacia saligna and Acacia salicina for goats and sheep

Acacia saligna and A. salicina phyllodes, harvested in autumn from young and mature trees, were fed as sole diets to goats (20·3 (s.d. 4·8) kg; no. = 16) and sheep (32·6 (s.d. 4·9) kg; no. = 16). Crude protein of phyllodes from mature trees was 111 g/kg dry matter (DM) and from young trees ranged between 121 and 132 g/kg DM. Condensed tannins and ash content were about twice as high in young trees as in old ones and gross energy was higher in old trees than in young ones. DM intakes by goats from both tree species were low: 24·8 and 13·7 g/kg M 0·75 per day for mature and young trees, respectively. Corresponding intakes by sheep were 20·4 and 11·5 g/kg M 0·75 per day. Metabolizable energy intakes were up to 125 and 99 kj/kg M 0·75 per day for goats and sheep, respectively and were higher for phyllodes from mature trees than for young trees. Goats lost up to 219 glday and sheep up to 346 g/day and both species were in negative nitrogen balance. DM, organic matter and energy apparent digestibilities were low for all diets but were generally higher for goats than sheep. It is concluded that neither A. saligna nor A. salicina could be used as a sole food for small ruminants because of low intakes and negative nitrogen balances. This appears to be due to high tannin content.

Larval interspecific competition in two flea species parasitic on the same rodent host

Abstract.  1. The fleas Xenopsylla conformis and Xenopsylla ramesis exploit the same rodent host, Meriones crassus, and replace each other between two different habitats situated at the opposite sides of a steep precipitation gradient. It was hypothesised that the reason for this paratopic distribution is competition between larvae of the two species for food resources.

Immune responses to fleas in two rodent species differing in natural prevalence of infestation and diversity of flea assemblages

We studied in vitro immune response to fleas in two gerbils, Gerbillus dasyurus and Gerbillus andersoni allenbyi, which differed in their natural species richness of flea assemblages and prevalence of infestation. G. dasyurus is parasitized naturally by several flea species, but the prevalence of infestation is low, whereas G. a. allenbyi is parasitized by a single flea species, with high prevalence of infestation. We hypothesized that immunological parameters and the cell-mediated specific immune response to an antigen from an unfamiliar flea species differ between the two gerbil species. Parasitized and control gerbils of both species demonstrated similar, relatively low levels of spontaneous glucose consumption. The same was true for the phytohemagglutinin treatment. Responses to antigen from unfamiliar flea species were higher than both spontaneous glucose consumption and response to phytohemagglutinin in parasitized and control G. a. allenbyi and parasitized G. dasyurus. However, no significant difference in the spontaneous blast transformation index and responses to both phytohemagglutinin and flea antigen was found in control G. dasyurus. The number of white blood cells was significantly lower in control than in parasitized G. dasyurus, whereas no difference in the number of white blood cells was found between control and parasitized G. a. allenbyi. The levels of circulating immune complexes and concentrations of immunoglobulins did not differ between parasitized and control individuals in both species. Phagocytic activity was significantly higher in males than in females of G. a. allenbyi but not of G. dasyurus. In addition, phagocytes of G. dasyurus appeared to be significantly more active than those of G. a. allenbyi.

Energy costs of blood digestion in a host-specific haematophagous parasite.

SUMMARY Fleas consume and digest blood from their hosts. We hypothesized that the energy costs of digestion of blood by fleas is dependent on the host species. To test this hypothesis, we studied CO2 emission, a measure of energy expenditure, during digestion of a blood meal taken by Parapulex chephrenis from a preferred (Acomys cahirinus) and a non-preferred (Gerbillus dasyurus) host. We predicted that the energy cost of digestion would be lower for A. cahirinus blood than that for G. dasyurus. Male and female fleas consumed similar amounts of blood per unit body mass, independent of host species. Our prediction was supported in that fleas expended significantly more energy digesting blood of G. dasyurus than blood of A. cahirinus. We also found CO2 emission rates of fed fleas were higher than those of unfed fleas and differed significantly among stages of blood digestion when a flea fed on G. dasyurus but not when it fed on A. cahirinus. When fed on G. dasyurus, fleas spent less energy during earlier than later stages of digestion.

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.