Acomys Russatus Research Articles

Defending body mass during food restriction inAcomys russatus: a desert rodent that does not store food

Golden spiny mice, which inhabit rocky deserts and do not store food, must therefore employ physiological means to cope with periods of food shortage. Here we studied the physiological means used by golden spiny mice for conserving energy during food restriction and refeeding and the mechanism by which food consumption may influence thermoregulatory mechanisms and metabolic rate. As comparison, we studied the response to food restriction of another rocky desert rodent, Wagner's gerbil, which accumulates large seed caches. Ten out of 12 food-restricted spiny mice (resistant) were able to defend their body mass after an initial decrease, as opposed to Wagner's gerbils (n = 6). Two of the spiny mice (nonresistant) kept losing weight, and their food restriction was halted. In four resistant and two nonresistant spiny mice, we measured heart rate, body temperature, and oxygen consumption during food restriction. The resistant spiny mice significantly (P < 0.05) reduced energy expenditure and entered daily torpor. The nonresistant spiny mice did not reduce their energy expenditure. The gerbils' response to food restriction was similar to that of the nonresistant spiny mice. Resistant spiny mice leptin levels dropped significantly (n = 6, P < 0.05) after 24 h of food restriction, and continued to decrease throughout food restriction, as did body fat. During refeeding, although the golden spiny mice gained fat, leptin levels were not correlated with body mass (r(2) = 0.014). It is possible that this low correlation allows them to continue eating and accumulate fat when food is plentiful.

Sex-biased parasitism, seasonality and sexual size dimorphism in desert rodents

We investigated seasonality of gender differences in the patterns of flea infestation in nine rodent species to test if sex-biased parasitism in terms of mean abundance, species richness, prevalence and the level of aggregation (a) varies among hosts and between seasons, and (b) is linked to sexual size dimorphism. Sexual size differences were significant in both summer and winter in Acomys cahirinus, Gerbillus pyramidum and Meriones crassus, and in winter only in Acomys russatus, Gerbillus dasyurus, Gerbillus nanus and Sekeetamys calurus. Sexual size dimorphism was male biased except for A. russatus in which it was female biased. Manifestation of sexual differences in flea infestation was different among hosts between seasons. A significant effect of sex on mean flea abundance was found in six hosts, on mean flea species richness in five hosts and on prevalence in two hosts. Male-biased parasitism was found in summer in one host only and in winter in five hosts. Female-biased parasitism occurred in winter in A. russatus. Gender differences in the slopes of the regressions of log-transformed variances against log-transformed mean abundances occurred in three hosts. No relationship was found between sexual size dimorphism and any parasitological parameter in any season using both conventional regressions and the method of independent contrasts. Our results suggest that sex-biased parasitism is a complicated phenomenon that involves several different mechanisms.

Adaptive mechanisms during food restriction in Acomys russatus: the use of torpor for desert survival

The golden spiny mouse (Acomys russatus) is an omnivorous desert rodent that does not store food, but can store large amounts of body fat. Thus, it provides a good animal model to study physiological and behavioural adaptations to changes in food availability. The aim of this study was to investigate the time course of metabolic and behavioural responses to prolonged food restriction. Spiny mice were kept at an ambient temperature of 27 degrees C and for 3 weeks their food was reduced individually to 30% of their previous ad libitum food intake. When fed ad libitum, their average metabolic rate was 82.77+/-3.72 ml O(2) h(-1) during the photophase and 111.19+/-4.30 ml O(2) h(-1) during the scotophase. During food restriction they displayed episodes of daily torpor when the minimal metabolic rate gradually decreased to 16.07+/-1.07 ml O(2) h(-1), i.e. a metabolic rate depression of approximately 83%. During the hypometabolic bouts the minimum average body temperature T(b), decreased gradually from 32.6+/-0.1 degrees C to 29.0+/-0.4 degrees C, with increasing duration of consecutive bouts. In parallel, the animals increased their activity during the remaining daytime. Torpor as well as hyperactivity was suppressed immediately by refeeding. Thus golden spiny mice used two simultaneous strategies to adapt to shortened food supply, namely energysaving torpor during their resting period and an increase in locomotor activity pattern during their activity period.

TEMPORAL PARTITIONING: AN EXPERIMENT WITH TWO SPECIES OF SPINY MICE

We studied temporal partitioning between two spiny mouse species that coexist in hot rocky deserts in the Middle East: nocturnal common spiny mice (Acomys cahirinus) and diurnally active golden spiny mice (A. russatus). Although A. russatus is diurnally active, it retains the physical activity and body temperature rhythms of nocturnal mammals. We studied the two species in four 1000-m 2 enclosures at Ein Gedi, Israel: two experimental enclosures with A. russatus kept alone, and two controls with individuals of both species kept together. We monitored activity with Sherman traps and by studying foraging microhabitat use and efficiency using giving-up densities (GUDs) in food trays. The trays contained broken sunflower seeds mixed in local soil and placed in three micro- habitats: under boulders, between boulders, and in the open. Trapping revealed that, in the absence of A. cahirinus, the usually diurnal A. russatus was active both day and night. However, during the day A. russatus still foraged in significantly more patches and to significantly lower GUDs than during the night. Both species, but in particular A. russatus, preferred to forage in the boulder habitat. Spiny mice foraged in the same number of trays in the under- and between-boulder microhabitats, but to lower GUDs in the under-boulder microhabitat, both during the day (A. russatus) and during the night (both species). The nocturnal A. cahirinus exploited more patches with greater efficiency than did A. russatus either during the day or during the night. This result suggests that foraging trade-offs that give each species a competitive advantage along some portion of the resource axis cannot be a mechanism of nocturnal coexistence between the two species. Perhaps this is why A. russatus resorts to diurnal activity in this hot rocky desert and why the otherwise rare mechanism of temporal partitioning occurs for these species.

Diet salinity and vasopressin as reproduction modulators in the desert-dwelling golden spiny mouse ( Acomys russatus)

The time for reproduction in mammals largely depends on the availability of water and food in their habitat. Therefore, in regions where rains are limited to definite seasons of the year, mammals presumably will restrict their breeding correspondingly. But while mammals living in predictable ecosystems would benefit by timing their season to an ultimate predictable cue, such as photoperiod, in unpredictable ecosystems (e.g., deserts) they will need to use a more proximate signal. We suggest a mechanism by which water shortage (low water content in plants) could act as a proximate cue for ending the reproductive season. The golden spiny mouse ( Acomys russatus), a diurnal rodent living in extreme deserts, may face an increased dietary salt content as the summer progresses and the vegetation becomes dry. Under laboratory conditions, increased diet salinity lead to reproductive hiatus in females, notable in imperforated vagina, and a significant decrease in the ovaries, uteri, and body masses. In females treated with vasopressin (VP), a hormone expressed during water stress, the uteri and body masses have decreased significantly, and the ovaries exhibited an increased number of atretic follicles. VP has also led to a significant decrease in relative medullary thickness (RMT) of the kidney. It is thus suggested that VP could act as a modulator linking the reproductive system with water economy in desert rodents, possibly through its act on the energetic pathways.

RETINAL STRUCTURE AND FORAGING MICROHABITAT USE OF THE GOLDEN SPINY MOUSE (ACOMYS RUSSATUS)

The golden spiny mouse (Acomys russatus), an inhabitant of rocky deserts, exhibits adaptations to diurnal activity, but also some characteristics that appear evolutionarily constrained to a nocturnal mode of life. This species is probably driven into diurnality by its congener, the common spiny mouse (A. cahirinus). We carried out a comparative study of the retinal morphology of A. russatus and A. cahirinus, in search of possible anatomical adaptations for diurnal activity in the eyes of golden spiny mice. The observed photoreceptors of both species had rod-pattern properties that characterize nocturnal mammals. We also carried out a field study of the foraging microhabitat use of golden spiny mice and of illumination levels in those microhabitats. Throughout the year, golden spiny mice preferred to forage between and particularly under boulders, where light intensities were lower than in the open. Thus, the retinal structure of golden spiny mice has not evolved to meet with their needs as a diurnal species, but the combination of the biochemical properties of their eyes, coupled with their foraging microhabitat selection, may enable them to withstand diurnal activity with nocturnally adapted retinas.

On the Use of the Time Axis for Ecological Separation: Diel Rhythms as an Evolutionary Constraint

On the Use of the Time Axis for Ecological Separation: Diel Rhythms as an Evolutionary Constraint

Effect of congeneric chemical signals of different ages on foraging response and food choice in the field by golden spiny mice (Acomys russatus).

The common spiny mice Acomys dimidiatus and golden spiny mice Acomys russatus coexist in the extreme warm and dry parts of the Rift Valley in Israel. However, they are temporally segregated in that the former is nocturnal, whereas the latter is diurnal. Daily rhythms of physiological and behavioral variables in A. russatus responded to semiochemical signals released by A. dimidiatus (in the urine and feces). Both species feed upon the same food items but at different times of the 24-hr cycle. The main aim of the present study was to test under field conditions the foraging response of A. russatus to odors of different ages released by A. dimidiatus. Various feeding and behavioral variables were compared in three groups of A. russatus. The results show that fresh semiochemical signals released by A. dimidiatus decrease the feeding efficiency and increase the rate of smelling from a distance in A. russatus. These results support the idea that temporal segregation between the two coexisting species is at least partly through semiochemicals present in the urine and feces.

HOW DEHYDRATION AFFECTS THE THERMOREGULATORY ANDOSMOREGULATORY ABILITIES OF THE GOLDEN SPINY MOUSEACOMYS RUSSATUS

The impact of increasing salinity in drinking water on resting metabolic rates(RMR) and non-shivering thermogenesis (NST) was studied in golden spinymice Acomys russatus. Mice were acclimated to an ambient temperature of27 C under a photoperiod regime of 12L:12D for three weeks. Salinity was increased gradually from 1 to 7% NaCl. Mice were kept for 14 days at each concentration. At the end of each acclimation to a given NaCl concentration, urine was collected and RMR and NST were determined. NST was measured as the maximal response of oxygen consumption (VO2NA) and body temperature (TbNA) to a noradrenaline (NA) injection. Results revealed that under 7% NaCl, urine volume decreased significantly while urine osmolarity increased significantly (p < 0.001 for both variables) compared to mice acclimated to 1% NaCl. Furthermore, body mass and RMR also decreased significantly (p < 0.05 for both variables) in 7%NaCl-acclimated mice compared to mice kept on 1% NaCl. However, NST capacity (the ratio of VO2NA to RM...

POPULATION BIOLOGY AND SPATIAL RELATIONSHIPS OF COEXISTING SPINY MICE (ACOMYS) IN ISRAEL

Nocturnally active Acomys cahirinus and diurnally active A. russatus cooccur in hot rocky deserts, and their temporal partitioning results from competition. We studied their population biology at Ein Gedi near the Dead Sea to determine their spatial relationships and gain insight into their ecological overlap. Individuals of both species were trapped repeatedly for almost 2 years. Mean body mass did not change seasonally, and A. russatus was significantly heavier than A. cahirinus. Density of A. russatus was significantly greater than that of A. cahirinus. Acomys russatus had a shorter reproductive peak that overlapped the longer reproductive season of A. cahirinus. Acomys russatus showed a significant preference for boulder habitat versus open habitat at all seasons, whereas A. cahirinus showed a preference for boulder habitat only half of the time. Sexes of both species overlapped in home range.

Assembly Rules: Desert Rodent Communities Are Structured at Scales from Local to Continental

Assembly Rules: Desert Rodent Communities Are Structured at Scales from Local to Continental

Environmental determinants of the composition of desert‐living rodent communities in the north‐east Badia region of Jordan

AbstractThe spatial and temporal compositions of rodent communities in habitats of the Badia region of north‐east Jordan were investigated between 1996 and 1997. Live grid‐trapping and spot‐lighting techniques were employed to estimate rodent densities. Sixteen environmental variables including soil content, vegetation cover and relief were recorded within the study sites. TWINSPAN was used to derive six habitat classes based on the similarity of their rodent communities. These were hammada, harrat, marab, wadi and two types of sand dunes. The derived classifications were similar to the original categorization of habitat types based on ground‐truthed observations of the sites selected from satellite imagery. Multivariate statistical analyses (TWINSPAN and DECORANA) revealed three major rodent groups in relation to local habitat types: (1) petrophiles: Gerbillus dasyurus, Acomys russatus and Meriones tristrami; (2) open hammada‐dwelling species: Jaculus jaculus, Gerbillus henleyi and Meriones crassus; (3) psammophiles: Meriones libycus, Gerbillus nanus and Gerbillus cheesmani. Species richness was highest in marabs and lowest in red sand dunes. Species diversity (Hill's index) was highest in sand dunes and lowest in red sand dunes. Rodent biomass was highest in sand dunes and lowest in wadis. CANOCO showed rodent community composition to be correlated with vegetation parameters and soil content. TWINSPAN grouping and DECORANA ordination of rodent species provides some evidence for habitat preference, size disparity and competition as mechanisms of resource partitioning facilitating coexistence.

Assembly Rules: Desert Rodent Communities Are Structured at Scales from Local to Continental

Assembly Rules: Desert Rodent Communities Are Structured at Scales from Local to Continental

Foraging Behavior and Microhabitat Use by Spiny Mice, Acomys cahirinus and A. russatus, in the Presence of Blanford's Fox (Vulpes cana) Odor

We investigated the responses of common and golden spiny mice (Acomys cahirinus and A. russatus, respectively) to the fecal odor of Blanford's fox (Vulpes cana), a predator of Acomys, which overlaps in habitat use with the mice. Neither species of mouse showed a significant response to the presence of fox odor compared with the presence of the fecal odor of a local herbivore (Nubian ibex, Capra ibex nubia). One explanation is that the impact of predation from V. cana may be sufficiently low that the cost of avoidance, in terms of missed feeding opportunities, conveys little selective advantage. Alternatively, fecal odor may not provide a focused cue of immediate danger for spiny mice. The diurnal A. russatus showed a stronger (near significant) response than the nocturnal A. cahirinus to fecal odor of this nocturnal predator. This may be a legacy of the underlying nocturnal activity rhythm of A. russatus or may indicate a generally more cautious response to predator odors, as A. russatus has a much stronger preference for sheltered microhabitats than A. cahirinus.

Seasonal thermogenic acclimation of diurnally and nocturnally active desert spiny mice.

Diurnally active golden spiny mice (Acomys russatus) and nocturnal common spiny mice (Acomys cahirinus) coexist in hot rocky deserts of Israel. Diurnal and nocturnal activities expose these species to different climatic conditions. Nonshivering thermogenesis (NST) capacity of individuals of both species immediately upon removal from the field exhibited seasonal changes, with no significant interspecific difference. Colony-reared mice of either species transferred in the laboratory from long to short photoperiod increased NST capacity, though to a lesser extent than observed in the seasonal acclimatization. The underlying biochemical mechanisms of short photoperiod acclimation differed between the species. In both Cytochrome-c oxidase (Cox) activity was higher in short as compared to long photoperiod. In short-photoperiod-acclimated A. cahirinus uncoupling protein (UCP) content in brown adipose tissue (BAT) was significantly higher than in long photoperiod, while in A. russatus there was no significant change. In A. russatus there was a significant increase in lipoprotein lipase (LPL) activity in BAT in short-photoperiod-acclimated individuals, while in A. cahirinus LPL activity was high under both acclimations. The low LPL activity in brown adipose tissue of desert-adapted A. russatus may facilitate lipid uptake in white adipose tissue, an advantage in desert conditions where food is scarce and irregularly distributed in space and time.

The dietary basis for temporal partitioning: food habits of coexisting Acomys species.

Two rodent species of the genus Acomys coexist on rocky terrain in the southern deserts of Israel. The common spiny mouse (A. cahirinus) is nocturnally active whereas the golden spiny mouse (A. russatus) is diurnally active. An early removal study suggested that competition accounts for this pattern of temporal partitioning: the golden spiny mouse is forced into diurnal activity by its congener. Theoretically, temporal segregation should facilitate coexistence if the shared limiting resources differ at different times (primarily among predators whose prey populations have activity rhythms), or if they are renewed within the period of the temporal segregation. We studied food preferences of the two Acomys species in a controlled cafeteria experiment in order to assess resource overlap and the potential for competition for food between the two species. We found no significant difference in food preferences between species. The dietary items preferred by both were arthropods. We also carried out a seasonal study of the percentage and identity of arthropods taken in the field by individuals of the two species. Individuals of both species took on annual average a high percentage of arthropods in their diets. Seasonal diet shifts reflect seasonal abundance of arthropods at Ein Gedi during day and night. Diurnal activity may also reduce interspecific interference competition between A. russatus and A. cahirinus. However, the strong interspecific dietary overlap in food preference, the heavy reliance on arthropods in spiny mouse diets, and the seasonal and circadian differences in arthropod consumption suggest that prey partitioning may be a viable mechanism of coexistence in this system.

Ecological and histological aspects of tail loss in spiny mice (Rodentia: Muridae, Acomys) with a review of its occurrence in rodents

Many individual nocturnal common spiny mice Acomys cahirinus and diurnal golden spiny mice A. russatus in the field are found missing all or part of their tails. Possibly, this is a predator avoidance mechanism. A 25-month field study revealed that at Ein Gedi (Israel) percentage tail-loss is 63% in male and 44% in female golden spiny mice, and 12% in male and 25% in female common spiny mice. Tail loss is significantly more common in golden spiny mice than in common spiny mice, possibly reflecting differences in predation risk or predator efficiency between the different microhabitats used by these species and in their different activity times. However, inter- and intraspecific aggressive interactions may also account in part for this pattern. Few significant differences in longevity, body mass, or reproductive condition were found between tailed and tail-less spiny mice, suggesting an advantage to tail-less individuals. Histological sections revealed a plane separating the skin layer from the underlying muscles and vertebrae, facilitating loss of the skin with little bleeding. The remainder (muscles and bone) is later chewed off by the mouse. A survey of published cases of tail loss in rodents revealed that this phenomenon occurs in at least 35 species and has evolved separately in eight rodent families, with no clear pattern in systematics, geography, or habitat use.

Ecological and histological aspects of tail loss in spiny mice (Rodentia: Muridae, Acomys) with a review of its occurrence in rodents

AbstractMany individual nocturnal common spiny mice Acomys cahirinus and diurnal golden spiny mice A. russatus in the field are found missing all or part of their tails. Possibly, this is a predator avoidance mechanism. A 25‐month field study revealed that at Ein Gedi (Israel) percentage tail‐loss is 63% in male and 44% in female golden spiny mice, and 12% in male and 25% in female common spiny mice. Tail loss is significantly more common in golden spiny mice than in common spiny mice, possibly reflecting differences in predation risk or predator efficiency between the different microhabitats used by these species and in their different activity times. However, inter‐ and intraspecific aggressive interactions may also account in part for this pattern. Few significant differences in longevity, body mass, or reproductive condition were found between tailed and tail‐less spiny mice, suggesting an advantage to tail‐less individuals. Histological sections revealed a plane separating the skin layer from the underlying muscles and vertebrae, facilitating loss of the skin with little bleeding. The remainder (muscles and bone) is later chewed off by the mouse. A survey of published cases of tail loss in rodents revealed that this phenomenon occurs in at least 35 species and has evolved separately in eight rodent families, with no clear pattern in systematics, geography, or habitat use.

Telemetric field studies of body temperature and activity rhythms of Acomys russatus and A. cahirinus in the Judean Desert of Israel.

Two species of the genus Acomys coexist in arid zones of southern Israel. Acomys russatus is distributed in extremely arid areas, while A. cahirinus is common in both Mediterranean and arid regions. Individuals of both species from a rodent community in the Ein Gedi Nature Reserve were implanted with temperature-sensitive transmitters. Body temperature (T b) rhythms were recorded in free-ranging mice at four different seasons of the year. A. cahirinus (30-45 g) showed a nocturnal rhythm of T b throughout the year. In the activity phase during the night T b increased to 38.2°C. During the day T b decreased to 34°C. This species displayed this pattern in summer also when ambient temperatures rose above T b. The T b of A. russatus (45-65 g) varied between 34.8 and 41°C during the hot season, showing a bimodal temperature rhythm with maximal values in the morning and in the evening. Measurements of activity in this species showed inactivity during the hottest period of a summer day. In winter A. russatus showed no clearly detectable diurnal or ultradian rhythm in T b, which remained constant between narrow limits of 35.2 and 36.8°C.

Daily scheduling of the golden spiny mouse under photoperiodic and social cues.

A most important function of the circadian system is to ensure that behaviors and metabolism are appropriately timed with respect to the light/dark cycle and photoperiod. Ecological constraints can perturb the daily schedules; would they also impair photoperiodic adaptations? A natural model exists in the golden spiny mouse (Acomys russatus), which is nocturnal, but driven into diurnal activity when sharing the habitat with its congener, A. cahirinus. We show here that the presence of A. cahirinus alters the diurnal rhythms of body temperature and urine volume, delays excretion of the major melatonin metabolite, 6-sulfatoxymelatonin (6-SMT), and increases 2-deoxyglucose uptake by the suprachiasmatic nuclei in A. russatus. Nevertheless, a clear photoperiod effect on urine volume and 6-SMT rhythms was observed. These results indicate that the circadian system can adapt to major changes in daily scheduling without impairing daylength measurement, and consequently seasonal adaptation.