Desmodillus Research Articles

A geometric morphometric analysis of geographic variation in the Cape Short-eared gerbil, Desmodillus auricularis (Rodentia: Gerbillinae)

Abstract The genus Desmodillus is monospecific, consisting of only the Cape short-eared gerbil (Desmodillus auricularis). Despite being widely distributed across southern Africa, previous studies did not find evidence of intraspecific phenotypic geographic differentiation. The objectives of this study is to use geometric morphometrics to investigate if and how the skull of D. auricularis varies spatially. It examines the covariation of skull morphology with broad spatial (latitude and longitude) and climatic variables, based on a sample of 580 specimens from southern Africa (Botswana, Namibia, and South Africa). The results did not support the differentiation of D. auricularis populations into distinct geographically isolated phenotypic groups. However, there is strong evidence for clinal variation in skull morphology; the most prominent pattern being a decrease in size from the west (closest to the South Atlantic coast) to the east (towards the continent’s interior). Shape variation was not localized in any skull region and seem to be driven mostly by size (allometry), although it also covaried significantly with latitude and longitude. Statistically significant skull shape sexual dimorphism was also detected, with males having larger crania than females. Spatial clinal variation in skull morphology was mostly associated with differences in the aridity of the habitats relative to their distance from the coast as evidenced by precipitation-related bioclimatic variables—annual precipitation (BIO12), precipitation of driest month (BIO14), and precipitation of driest quarter (BIO17)—covarying the most with skull morphology. This could be driven by either the climate influencing local resources available to populations or by the climate directly instigating phenotypic climatic adaptations.

Implications of potential biome boundary shifts for small mammal assemblages in the arid zone of South Africa

AbstractDesertification deteriorates the landscape functionality of rangelands, affecting the resilience of biome boundaries and this has a cascading effect on vegetation and animal communities. This study aimed to assess landscape functionality along the biome boundary of two arid biomes and its relationship to small mammal assemblages. The study further aimed to provide a landscape perspective of the current desertification process and projected expansion of the Desert biome in South Africa. Three Desert biome, ecotone and Succulent Karoo biome sites were selected to assess landscape functionality and small mammal assemblages over a one‐year period. The difference in landscape functionality between the three areas was assessed to determine the resilience of the biome boundary to desertification. Our results showed that the vegetation of the ecotone had higher desert‐like affinities while the soils seemed resilient and remained closely related to the Succulent Karoo biome. High livestock grazing pressure, as evident in the pastoral rangeland, may further deteriorate vegetation parameters and expose the soil to erosion, thereby advancing desertification. During both winter and summer, small mammal surveys using live Sherman traps were conducted and over the total 3204 trapping nights, 119 small mammal captures were recorded from three species. Desmodillus auricularis, Elephantulus rupestris and Gerbillurus paeba all had significantly higher densities in the Succulent Karoo biome. Our study supports the view that G. paeba would be the only species able to thrive in the less diverse Desert biome. This might have implications for the ecosystem services provided by the other two small mammal species in the landscape. As the trajectory for projected desertification appears to be on track, concerted efforts in improving rangeland management are required to maintain landscape functionality and stabilise small mammal assemblages.

Faunal Remains from Holocene Deposits, Excavation 1, Wonderwerk Cave, South Africa

Ungulate and small mammalian fauna have been recovered from Holocene deposits at Wonderwerk Cave, in the interior of South Africa, in the area of excavation 1. Statistical analyses of relative abundances of rodents and insectivores indicate that conditions were warm (between 19.1 and 19.3 °C) and very dry in the early Holocene in the Wonderwerk palaeo-environment, becoming moister in the mid-Holocene and still moister in the late Holocene. Temperatures in the late Holocene appear to have been about 1 °C lower than conditions in the early to mid-Holocene. In terms of habitats reflected by rodents, the early Holocene is associated with an abundance of the arid-indicator species, Desmodillus auricularis. The degree of aridity subsequently decreases, associated with an increase in a woodland savanna species, Saccostomus campestris. A later increase in abundance of Mystromus albicaudatus reflects an increase in open grassland in the Late Holocene. Equids (zebras) and alcelaphines (including wildebeest and hartebeest) dominate the ungulate assemblages. Two extinct species are represented in the early Holocene, namely Equus capensis (the giant zebra) and Megalotragus priscus (a large alcelaphine). Possible causes of their extinction may include both environmental and cultural factors. Homo sapiens was probably the main agent of accumulation of the Holocene deposits at Wonderwerk, although leopards (Panthera pardus) may have temporarily used the cave in the mid-Holocene at a time when wind-blown Kalahari sands were introduced.

Comparative aspects of the thermal biology of the short-tailed gerbil, Desmodillus auricularis, and the bushveld gerbil, Tatera leucogaster

1. 1. The response of oxygen consumption (VO 2), thermal conductance ( C d and C min, body temperature ( T b), and evaporative water loss (EWL) of Tatera leucogaster and Desmodillus auricularis were measured over the range of ambient temperatures ( T a) from 5–35°C. 2. 2. Basal metabolic rate (BMR) of T. leucogaster was 0.841 ± 0.049 ml O 2 g −1 h −1 and lower than predicted, while that of D. auricularis was similar to the expected value (1.220 ± 0.058 ml O 2 g −1 h −1). D. auricularis had a high, narrow thermoneutral zone (TNZ) typical of nocturnal, xerophilic, burrowing rodents. 3. 3. D. auricularis and T. leucogaster regulated T b over the range T a = 5–35°C and kept EWL and dry thermal conductance at a minimum below the TNZ. However, the EWL of T. leucogaster increased rapidly above T a = 30°C. 4. 4. After comparison with data from other species, it was concluded that there is an optimum size for xeric, nocturnal, burrowing rodents.

Behavioural Divergence in Allopatric and Sympatric Gerbil Species (Rodentia: Gerbillinae)

AbstractSouthern African gerbils comprise 3 genera, each genus represented by morphologically‐ and ecologically‐similar species. All species are monomorphic, with social systems varying from asocial (Desmodillus auricularis) to colonial (Tatera species).This study compares the behaviour patterns of an allopatric species, T. afra, 2 sympatric species, T. leucogaster and T. brantsii, and a species of a different genus, D. auricularis which is sympatric with T. leucogaster and T. brantsii.Interactions between males and females of the same species were staged and quantified in terms of the frequencies of each of 23 behavioural acts. D. auricularis performed 2 acts, namely “sidle” and “fight” which have not been identified in Gerbillurus or Tatera interactions. Sequences of behaviour were similar in all species, and involved females moving away from males, which followed, sniffed the anogenital region and attempted to mount the females. Females responded by presenting, if receptive, or agonistic behaviour such as aggressive or upright postures. Exploration of the terrarium accounted for a large proportion of the behaviour during the 20 min encounter, and watching the opponent also occurred frequently.Discriminant function analysis successfully separated all 4 species on the basis of behaviour frequencies. Individuals were assigned to the correct species with an accuracy of 80%, indicating that each species exhibits species‐specific patterns of behaviour. D. auricularis displayed more agonistic and sexual behaviour and less huddling behaviour than any of the Tatera species.The sympatric species‐pair, T. leucogaster and T. brantsii, exhibited more significant difference in behaviour than either of the allopatric species‐pairs, T. afra and T. brantsii, and T. afra and T. leucogaster. Divergence in behaviour patterns has occurred in allopatric species, but divergence is more marked in species which are sympatric. It is not known whether divergence between T. leucogaster and T. brantsii occurred during a period of allopatry, or whether divergence has occurred due to selection against hybrids in sympatry.

Small mammal seed consumption in the Karoo, South Africa: further evidence for divergence in desert biotic processes

Annual seed consumption by a small mammal community in the semi-arid Karoo, South Africa, was calculated using population, biomass and dietary estimates and published estimates of field metabolic rate. The community comprised a macroscelid elephant shrew Macroscelides proboscideus, and two rodents Gerbillurus paeba and Desmodillus auricularis. Only G. paeba consumed seed during the study, and then in low amounts (annual mean = 0.4% of diet, insects = 53%, herbage = 47%), with M. proboscideus and D. auriocularis consuming mainly insects (88%) and herbage (90%), respectively. Energy requirements for the G. paeba population averaged 568 kJ ha-1 day-1. Total seed consumption was estimated to be ≈ 140 g ha-1, or 155 000 seeds ha-1 which represents ≈0.5% of the annual seed production for this site. These levels of granivory by small mammals are significantly lower than those recorded for North American deserts, and raises the question as to why granivory varies between these systems. These findings also refute the hypothesis that as a result of the harshness and similarity of physical conditions in deserts, the properties of desert communities are convergent.

Trophic status of small mammals in the semi‐arid Karoo, South Africa

The feeding habits of a community of small mammals from the semi‐arid Karoo, South Africa were analysed by microscopic examination of the stomach contents of animals caught during a 13‐month snap‐trapping study. The community comprised eight rodent species (Gerbillurus paeba, Mus minutoides, Rhabdomys pumilio, Otomys unisulcatus, Saccostomus campestris, Desmodillus auricularis, Malacothrix typica, Mastomys natalensis) and a single macroscelid elephant shrew (Macroscelides proboscideus.) The rodents were all predominantly herbivorous, while the elephant shrew ate mainly insects. No granivores or omnivores were represented in this community. The results presented here (including the first analysis of the diet of M. typica) indicate a greater emphasis on herbivory than previously described for these species. Limited dietary overlap was recorded between these species, although some instances of potential dietary competition that deserve further study were identified. The paucity of granivorous small mammals in the semi‐arid Karoo contrasts the patterns of trophic specialization for North American and Israeli semi‐arid communities, but is similar to that of South American, Australian and other southern African semi‐arid communities.

Small mammals in the semi-arid Karoo, South Africa: biomass and energy requirements

Small mammal communities in the semi-arid Karoo, South Africa were investigated by means of seasonal live-trapping. Eleven species were recorded, including nine Rodentia (pygmy hairy-footed gerbil Gerbillurus paeba, short-tailed gerbil Desmodillus auricularis, striped field mouse Rhabdomys pumilio, pygmy mouse Mus minutoides, multimammate mouse Mastomys natalensis, Namaqua rock mouse Aethomys namaquensis, grey climbing mouse Dendromus melanotis, bush Karoo rat Otomys unisulcatus and whistling rat Parotomys brantsii) and two Macroscelidea (round-eared elephant shrew Macroscelides proboscideus and Cape elephant shrew Elephantulus edwardii). Species richness was low (S = 3·8) but comparable to other southern African communities. Marked seasonal fluctuations in numbers, biomass and species richness were observed. Biomass of small mammals (mean = 324 g ha−1) was low in relation to Savanna communities, reflecting the low productivity of the Karoo. Despite low biomasses, the energy requirements of these largely herbivorous small mammal communities averaged 15% (maximum = 43%) of that needed to support the recommended carrying capacities of agricultural stock for these sites. The energy demands of the small mammals are highest in winter when plant production is depressed. Small mammal energy requirements need to be taken into account in ecosystem models for the Karoo, and when evaluating the impact of livestock on vegetation.

Viremia and Antibody Response of Small African and Laboratory Animals to Crimean-Congo Hemorrhagic Fever Virus Infection

Eleven species of small African wild mammals, laboratory rabbits, guinea pigs, and Syrian hamsters were infected with Crimean-Congo hemorrhagic fever (CCHF) virus. Low-titered viremia followed by development of antibody was observed in scrub hares (Lepus saxatilis), Cape ground squirrels (Xerus inauris), red veld rats (Aethomys chrysophilus), white tailed rats (Mystromys albicaudatus), bushveld gerbils (Tatera leucogaster), striped mice (Rhabdomys pumilio), and guinea pigs. The maximum viremic titer in 4 scrub hares was 10(1.7-4.2) 50% mouse lethal doses/ml. Viremia was detected in 1/17 infected laboratory rabbits. Antibody response was only detected in South African hedgehogs (Atelerix frontalis), highveld gerbils (T. brantsii), Namaqua gerbils (Desmodillus auricularis), 2 species of multimammate mouse (Mastomys natalensis and M. coucha), and Syrian hamsters. The results of the study indicate that a proportion of infected scrub hares develop CCHF viremia of an intensity shown in the Soviet Union to be sufficient for infection of feeding immature ixodid ticks, but that South African hedgehogs and wild rodents are unlikely to be of importance as maintenance hosts of the virus in southern Africa.

Rates of protein, chromosome and morphological evolution in four genera of rhombomyine gerbils

Electrophoretic, G- and C-band chromosomal, and morphological characters were examined in relation to evolutionary change for Desmodillus auricularis, Psammomys obesus, Sekeetamys calurus, Meriones shawi, and M. unguiculatus. Chromosomal evolution in these genera was complex and comparable to that found in the previously studied genera Tatera and Gerbillurus. Examination of 33 isoenzyme loci assayed by starch gel electrophoresis showed only three monomorphic loci and alternate allelic fixation occurring primarily at the generic level. Morphological, chromosomal, and electrophoretic data sets were found to be concordant in a cladistic arrangement of genera. However, the rates of fixation of electrophoretic and chromosomal characters in each lineage were not equal. The specialized morphology of Sekeetamys calurus coupled with extensive chromosomal rearrangements apparently has not been accompanied by a correlated rate of protein (genetic) evolution. The numbers of measured protein substitutions as judged by electrophoresis since divergence from a common ancestor for this and three other genera of gerbils were not significantly different from equality. This suggests that different parameters affect chromosomal and protein evolution in gerbils or the magnitude of effect varies for these parameters.

New Mammal Records for the Karoo National Park, with Notes on Several Other Species

Five species of mammal are recorded for the first time in the Karoo National Park: Suncus varilla, Nycteris thebaica, Aethomys granti, Petromyscus collinus and Desmodillus auricularis. The presence of a golden mole, Chrysochloridae, is noted. Notes on three previously recorded species are presented.

Phylogenetic Studies of the Rodent Family Gerbillidae: I. Chromosomal Evolution in the Southern African Complex

Chromosomes of several southern African gerbils were examined and compared by G- and C-banding techniques: Desmodillus auricularis, Gerbillurus paeba, G. vallinus, Tatera afra, T. brantsii , and T. leucogastor . Intraspecific chromosomal variation involves an inversion and a euchromatic addition in G. paeba , and heterochromatic additions in G. vallinus and the Tatera species. Chromosomal evolution in the southern African gerbils has been characterized by a minimum of 7 centric fissions, 6 centric fusions, 1 tandem fusion, 7 inversions (one unfixed), 6 translocations, and numerous but individually variable constitutive heterochromatic additions. The close affinity of the genera Tatera and Gerbillurus is confirmed by cladistic analysis of chromosomal data. Gerbillurus paeba (2n = 36) and G. vallinus (2n = 60) evidently arose from a common ancestor that had a 2n = 44; events leading to the former were fusions, to the latter fissions. This illustrates the hazard of assuming either a general decrease or increase in diploid numbers for any group of mammals.

Experimental plague infection in South African wild rodents.

Susceptibility studies were undertaken to determine the response of some South African wild rodent species to experimental plague (Yersinia pestis) infection. A degree of plague resistance was found in three gerbil species captured in the plague enzootic region of the northern Cape Province, these being the Namaqua gerbil, Desmodillus auricularis, (LD50 1 X 10(6) organisms), the bushveld gerbil, Tatera leucogaster, (LD50 9.1 X 10(5)) and the highveld gerbil, T. brantsii (LD50 4 X 10(2)). Animals from a population of the four-striped mouse, Rhabdomys pumilio, captured in the plague area of Port Elizabeth, proved moderately resistant to experimental plague infection (LD50 1.3 X 10(4)) while those from another population of the same species captured in a plague-free area of the Orange Free State were extremely susceptible (LD50, 5 organisms). The response of both populations however was a heterogeneous one. Marked differences in susceptibility were also found between two populations of multimammate mice, Mastomys natalensis (2n = 32) although both originated from areas outwith the known distribution of plague in southern Africa. The 50% infectious dose was relatively high in T. leucogaster (3.2 X 10(2)) and D. auricularis (1.7 X 10(3)), but was low (2-16 organisms) in the other rodent species tested. The plague antibody response, determined by enzyme-linked immunosorbent assay (ELISA), was extremely short-lived in T. leucogaster, only 10% of inoculated animals remaining seropositive at low titres after 11 weeks. Antibodies persisted for only slightly longer in the sera of T. brantsii which were reinoculated with 2 X 10(3) plague organisms 6 weeks after initial challenge. The demonstration of the existence of both susceptible and resistant populations of R. pumilio and M. natalensis indicates that these species must be considered as potential plague reservoir hosts in parts of South Africa. The results suggest that resistance to plague infection in previously epizootic hosts in the northern Cape Province such as Tatera sp. and D. auricularis has arisen through continual selective pressure of the organism. If the findings are applicable to gerbil populations in other plague enzootic regions of South Africa it is probable that acquired plague resistance has been responsible for the absence of gerbil epizootics and consequently for the dramatic decline in human plague outbreaks in South Africa since 1950.

Plague in South African rodents 1972–1981

Sera from 3012 rodents of 24 species captured in South Africa during the period 1972–1981 were tested for antibody to the Fraction 1 antigen of Yersinia pestis by passive haemagglutination. Antibodies were found in seven (0·23%) rodents of three species. These were Desmodillus auricularis and Tatera brantsii in the northern Cape Province and Rhabdomys pumilio in the eastern Cape Province. Rodents were found positive in 1972, 1974, 1975 and 1979, indicating that plague continues to circulate in rodent populations apparently without causing human cases. The significance of the results is discussed in relation to plague outbreaks in neighbouring countries and to the 1982 outbreak in South Africa.

Comparative Demography of Three Namib Desert Rodents: Responses to the Provision of Supplementary Water

This study was designed to test the hypothesis that increased dietary water intake is a critical factor in desert rodent reproduction. Populations of three Namib Desert rodent species ( Desmodillus auricularis, Gerbillurus paeba , and Rhabdomys pumilio ) were monitored by mark-and-recapture live-trapping on two study areas, one of which served as a control. On the other, rodents were continuously provided with sources of drinking water. Populations of G. paeba and R. pumilio grew rapidly following rains in early 1974, and reached peak population sizes in September or October 1974. Reproduction in both of these species on the control area showed marked declines during the hot, dry months of September to December, January, or February. Both G. paeba and R. pumilio showed marked responses to the increased availability of water on the experimental area, as evidenced by a greater number of pregnancies and higher proportions of lactating females, and an extension of the breeding season longer into the hot, dry portions of the year. The effect of increased water availability on these species was most pronounced during times of the year when water stress might be expected to be greatest. Population growth in D. auricularis proceeded in a much less seasonally restricted manner than in the other two species, and peak population sizes were not reached until February or March 1975. Breeding intensity in this species on the control area declined only slightly during portions of the year when R. pumilio and G. paeba were relatively inactive reproductively. On the experimental area, D. auricularis showed no consistent reproductive or numerical response to increased water availability. The relationship between response to the experimental provision of water in these species and the seasonality of demographic patterns is discussed.

Physiological Correlates of Demographic Patterns in Three Sympatric Namib Desert Rodents

Water metabolism in three sympatric Namib Desert rodents (Gerbillurus paeba, Desmodillus auricularis, and Rhabdomys pumilio) was measured using a complete water-balance methodology, with the objective of relating physiological characteristics to population-level properties in these species. Desmodillus auricularis was found to be capable of maintaining water balance on a diet of considerably lower water content than that needed by the other two species. Physiological differences among these species are correlated with differences in (a) their reproductive response to the provision of drinking water in an earlier field experiment; (b) the seasonality of their demographic patterns; and (c) particular features of their life histories. An argument is presented that the water-conserving abilities of these species are intimately related to population processes: G. paeba and R. pumilio, with relatively high water needs, are restricted to breeding during brief periods of high water availability, and their lifehis...

Notes on early Post-Natal development of the Namaqua Gerbil <i>Desmodillus Auricularis</i>

Early post-natal development is discussed of fivelitters of Desmodillus auricularis born in captivity. Litter sizeranged from one to three, with a mean of two. Nipple-clingingwas absent and young developed slowly, with eyes opening onday 22 and weaning occurring on day 33.

Behaviour and Breeding in Captivity of the Namaqua Gerbil Desmodillus Auricularis (Cricetidae: Gerbillinae)

Desmodillus auricularis was kept in observation cages and subjected to an increased number of light-hours. The animal is nocturnal and its activity rhythm was adjusted using a red light to simulate darkness during the day. Three litters were produced from one pair and observations were made on twelve other litters born in the laboratory from pregnant field-trapped specimens. The breeding season appears to be all year. Litter size varied from one to five with a mean of 3,25. The gestation period was twenty-one days and gestation of a post-partum pregnancy was thirty-five days. The young were not attached to the nipple except when suckling. Behaviour is discussed with special reference to individual behaviour and parent-young relationship. Much of the general behaviour-pattern appears to be typical of most desert-adapted rodents. Hoarding and sandbathing were exhibited.

A note on the smaller mammals of the Mountain Zebra National Park

Collecting in April 1971 yielded 74 specimens of 16 species. Of these, seven species (Elephantulus rupestris, Lepus saxatilis, Pronolagus crassicaudatus, Graphiurus murinus, Aethomys namaquensis, Desmodillus auricularis and Gerbillurus paeba) are new records for the park. Distribution in habitat-types for each species known to occur are described.

Burrow systems of Desmodillus Auricularis in the Kalahari Gemsbok National Park

Burrow systems of Desmodillus Auricularis in the Kalahari Gemsbok National Park