The origin of two cryptic species of African desert jerboas (Dipodidae: Jaculus)

The desert biota is exposed to extreme and variable conditions that shape its evolution and diversification processes. In this respect, the Jaculus jerboas have gained the attention of researchers as a result of their broad Saharan–Arabian distribution and their high and unexplained, morphological, anatomical, and molecular variation. In the present study, mitochondrial and nuclear genealogies where used to confirm monophyly of two cryptic species: Jaculus jaculus and Jaculus deserti. The reconstructed demography showed that the evolutionary histories of the species are markedly different and that the expansion into North‐West Africa by J. deserti was more recent than that of J. jaculus. The weak ecological separation between species and the signs of recent population growth and expansion of J. deserti suggest that its sympatric occurrence with J. jaculus is recent and that these species evolved in isolated populations, after diverging around the Pliocene–Pleistocene boundary. The importance of climate changes on the Sahara Desert biota is discussed in the context of genetic diversification. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 435–445.     

The effect of glucocorticoids on the diluting capacity of the kidney of a desert rodent: Gerbillus campestris]

The ability to excrete a water load was studied in Wistar rats and in gerbils (Gerbillus campestris). The rat excreted the entire water load in less than 2 h whereas Gerbillus campestris excreted less than 60% of the water load in 4 h. The gerbils which had received a dose of 15 micrograms/100 g body weight dexamethasone improved their rate of excretion which attained 92 +/- 6% in 2 h 30 min. The antidiuretic hormone (ADH) measured by radioimmunoassay at the time of maximum diuresis was undetectable in rats; in contrast, in gerbils the level of ADH remained relatively high (55.4 +/- 6.7 pg/ml). We conclude that the partial inability of the gerbil's kidney to excrete a water load is due to a high ADH level and probably to a low concentration of glucocorticoids.     

Phylogeography of two cryptic species of African desert jerboas (Dipodidae: Jaculus)

The lesser Egyptian jerboa Jaculus jaculus is a desert dwelling rodent that inhabits a broad Arabian–Saharan arid zone. Recently, two distant sympatric lineages were described in North‐West Africa, based on morphometric and molecular data, which may correspond to two cryptic species. In the current study, phylogenetic relationships and phylogeographical structure among those lineages and geographical populations from North Africa and the Middle East were investigated. The phylogeographical patterns and genetic diversity of the cytochrome b gene (1110 bp) were addressed on 111 jerboas from 41 localities. We found that the variation in Africa is partitioned into two divergent mitochondrial clades (10.5% divergence relating to 1.65–4.92 Mya) that corresponds to the two cryptic species: J. jaculus and J. deserti. Diversifications within those cryptic species/clades were dated to 0.23–1.13 Mya, suggesting that the Middle Pleistocene climatic change and its environmental consequences affected the evolutionary history of African jerboas. The third distant clade detected, found in the Middle East region, most likely represents a distinct evolutionary unit, independent of the two African lineages. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ??, ??–??.     

A Two-dimensional Model for Water Uptake by Desert Succulents: Implications of Root Distribution

Water uptake by Agave deserti and Ferocatus acanthodes was predictedusing a two-dimensional simulation model in which the soil arounda plant was divided into a series of layers and concentric cylindricalshells. Root lengths in 0.05 m thick soil layers were determinedfor both species in the field, where mean root depths were only0.11 m for A. deserti and 0.10 m for F. acanthodes. For a yearwith average precipitation (159 mm), 42 per cent of the annualprecipitation could be taken up by A. deserti and 25 per centby F. acanthodes. Predicted water uptake by both species wasgreater from the upper soil layers (above 0.15 m) for averageand dry years, but was greater from the deeper layers for awet year. The actual root distribution for both species ledto more water uptake than when all of the roots were in a singlelayer. The large number of days per year when the soil temperaturesexceeded 57 °C (the temperature for 50 per cent inhibitionof uptake of a vital stain by root cells) may exclude rootsfrom the 0.00–0.05 m soil layer, even though water uptakewhen all roots were located there was predicted to be maximal.Therefore, the observed root distribution of A. deserti andF. acanthodes may be limited near the soil surface by high temperaturesand at maximum depths by water availability for all but wetyears. Agave deserti, Ferocactus acanthodes, desert succulents, root system, root distribution, soil temperature, water uptake     

Extreme temperatures and thermal tolerances for seedlings of desert succulents

Summary Extreme temperatures near the soil surface, which can reach 70°C at the main study site in the northwestern Sonoran Desert, markedly affect seedling survival. Computer simulations indicated that for the rather spherical barrel cactus Ferocactus acanthodes (Lem.) Britt. & Rose the maximum surface temperature decreased 8°C and the minimum temperature increased 3°C as the seedling height was increased from 1 mm up to 50 mm. Simulated changes in shortwave and longwave irradiation alone showed that shading could decrease the maximum temperature by about 5°C for the common desert agave, Agave deserti Engelm., and raise the minimum 1°C. Actual field measurements on seedlings of both species, where shading would affect local air temperatures and wind speeds in addition to irradiation, indicated that shading decreased the average maximum surface temperature by 11°C in the summer and raised the minimum temperature by 3°C in winter.Seedlings grown at day/iight air temperatures of 30°C/20°C tolerated low temperatures of about -7°C and high temperatures of about 56°C, as measured by the temperature where stain uptake by chlorenchyma cells was reduced 50%. Seedling tolerance to high temperatures increased slightly with age, and F. acanthodes was more tolerant than A. deserti. Even taking the acclimation of high temperature tolerance into account (2.7°C increase per 10°C increase in temperature), seedlings of A. deserti would not be expected to withstand the high temperatures at exposed sites, consistent with previous observations that these seedlings occur only in protected microhabitats. Based primarily on greater high temperature acclimation (4.3°C per 10°C), seedlings of F. acanthodes have a greater high temperature tolerance and can just barely survive in exposed sites. Wide ranges in photoperiod had little effect on the thermal sensitivities of either species. When drought increased the chlorenchyma osmotic pressure from about 0.5 MPa to 1.3 MPa, seedlings of both species became about 2°C less tolerant of high temperatures, which would be nonadaptive in a desert environment, and 2°C more tolerant of low temperatures, which also occurs for other species.In conclusion, seedlings of A. deserti and F. acanthodes could tolerate tissue temperatures over 60°C when acclimated to high temperatures and below -8°C when acclimated to low temperatures. However, the extreme environment adjacent to desert soil requires sheltered microhabitats to protect the plants from high temperature damage and also to protect them from low temperature damage at their upper elevational limits.     

Influences of root distribution and growth on predicted water uptake and interspecific competition

Summary Root distribution and growth measured in the field were incorporated into a water uptake model for the CAM succulent Agave deserti and its nurse plant Hilaria rigida, a common desert bunchgrass. Agave deserti responds to the infrequent rainfalls of the Sonoran Desert by extending its existing established roots and by producing new roots. Most of such root growth was completed within one month after soil rewetting, total root length of A. deserti increasing by 84% for a seedling and by 58% for a mediumsized plant in the summer. Root growth in the winter with its lower soil temperatures was approximately half as much as in the summer. For a 15-year period, predicted annual root growth of A. deserti varied more than 18-fold because of annual variations in rainfall amount and pattern as well as seasonal variation in soil temperature. Predicted annual water uptake varied 47-fold over the same period. The nurse plant, which is crucial for establishment of A. deserti seedlings, reduced seedling water uptake by 38% during an average rainfall year. Lowering the location of the root system of a medium-sized A. deserti by 0.24 m reduced its simulated annual water uptake by about 25%, reflecting the importance of shallow roots for this desert succulent. Lowering the root system of a medium-sized H. rigida by 0.28 m increased the simulated annual water uptake of an associated A. deserti seedling by 17%, further indicating the influence of root overlap on competition for water.     

Are there two cryptic species of the lesser jerboa Jaculus jaculus (Rodentia: Dipodidae) in Tunisia? Evidence from molecular,morphometric, and cytogenetic data

Jerboas belonging to the genus Jaculus are widely distributed rodents inhabiting Palearctic desert and semi‐desert areas. Previous studies on the lesser Egyptian jerboa Jaculus jaculus showed the existence of various morphological forms of controversial taxonomic status. They were sometimes related to two different species, J. jaculus and Jaculus deserti, although this has not been recognized in recent taxonomic updates. To clarify the systematic status of J. jaculus in Tunisia, we performed molecular (phylogenetic analyses of cytochrome b sequences), morphological (multivariate analyses of 13 skull measurements) and karyotypic (standard preparations from bone marrow cells) analyses on a number of specimens collected from ten localities. Our analyses revealed two monophyletic, well differentiated clades, with a mean genetic divergence value (K2P = 10.9 ± 0.01%), which is within the range of distances generally observed between rodent species. Morphometric analyses clearly separated populations of the two genetic clades from each other. However, karyotypes of individuals from both clades appeared similar. Individuals from both molecular clades/morphometric groups were found in sympatry in most of the localities sampled. These results, as obtained from a restricted area of the total distribution, suggest that there are two separate species within the currently accepted J. jaculus in Tunisia. Alternative hypotheses such as the occurrence of a strong, ancient phylogeographic structure, or the presence of pseudogenes, are also considered to account for the results obtained. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 673–686.     

Genetic differentiation and relationship of the dipodidsAllactaga andJaculus (Mammalia, Rodentia) in Egypt based on protein variation

Genetic differentiation among 14 populations representing all Egyptian dipodid (jerboa) species and subspecies was examined at 25 structural loci and interspecific relationships are discussed. Of the 25 loci, only 3 were monomorphic, with the same allele fixed in all taxa, 9 loci were monomorphic, but demonstrated intertaxon variation, and only 13 loci were polymorphic. The overall mean number of alleles per locus (A) was 1.23 ± 0.02 and the average percentage of polymorphic loci per taxon (P) was 23%. The overall mean of observed heterozygosity (H _o) was found significantly higher than that of expected heterozygosity (He); the overall means per taxon were 0.25 ± 0.017 and 0.085 ± 0.007. Mean levels of genetic identity (I) were 0.970 ± 0.003 among geographic populations, 0.718 ± 0.022 between subspecies, 0.590 ± 0.030 between congeneric species, and 0.368 ± 0.020 between genera. Phenetic analysis of genetic distance matrix produced a phenogram indicating a close association ofJaculus orientalis Erxleben, 1777 toJaculus jaculus (Linnaeus, 1758), particularly to its subspeciesJaculus jaculus butleri (Thomas, 1922), and indicating a distinct affinity between these latter two species andAllactaga tetradactyla (Lichtenstein, 1823). Estimates of genetic divergence demonstrated that J. orientalis appears to have shared a more recent common ancestor withJ. jaculus thanA. tetradactyla. Divergence of these species would have occurred by Miocene (ca 9.6 to 18.7 million years ago). The pattern of relationships of the dipodid species indicated in this study was closely consistent with the hypotheses derived from morphological and chromosomal data.     

INFREQUENT ESTABLISHMENT OF SEEDLINGS OF AGAVE DESERTI (AGAVACEAE) IN THE NORTHWESTERN SONORAN DESERT

Survival of seedlings of the common desert succulent, Agave deserti, required unusually wet years and the protection afforded by nurse plants or other shelters. The characteristics of seed germination and of seedlings showed that water stress in the seedling stage may be the most important factor affecting establishment. Leaves wilted irreversibly at an osmotic potential of −1.6 MPa (–16 bars). Survival of seedlings required the generation of enough biomass during the first wet season to survive drought periods when the water potential of the soil was below −1.6 MPa. Lengths of individual growing seasons and subsequent droughts were obtained from rainfall records for 1961 through 1978 for a site in the western Colorado desert. The length of the first major drought following germination apparently limited establishment of Agave deserti to only one year in the last 17. The favorable year, 1967, was consistent with the estimated year of germination of the six smallest Agave deserti observed in 1,500 m² at the field site.     

Root Water Uptake, Leaf Water Storage and Gas Exchange of a Desert Succulent: Implications for Root System Redundancy

A technique used for hydroponics was adapted to measure instantaneousroot water uptake from the soil for a leaf succulent CAM species,Agave deserti. Comparisons were made to previously modelledwater fluxes for A. deserti and to Encelia farinosa, a non-succulentC₃species. Net CO₂uptake and transpiration forA. deserti underwell-watered conditions occurred primarily at night whereasroot water uptake was relatively constant over 24 h. Leaf thicknessdecreased when transpiration commenced and then increased whenrecharge from the stem and soil occurred, consistent with previousmodels. A drought of 90 d eliminated net CO₂uptake and transpirationand reduced the water content of leaves by 62%. Rewetting theentire root system for 7 d led to a full recovery of leaf waterstorage but only 56% of maximal net CO₂uptake. Root water uptakewas maximal immediately after rewetting, which replenished rootwater content, and decreased to a steady rate by 14 d. Whenonly the distal 50% of the root system was rewetted, the timefor net CO₂uptake and leaf water storage to recover increased,but by 30 d gas exchange and leaf water storage were similarto 100% rewetting. Rewetting 10 or 20% of the root system resultedin much less water uptake; these plants did not recover leafwater storage or gas exchange by 30 d after rewetting. A redundancyin the root system of A. deserti apparently exists for dailywater uptake requirements under wet conditions but the entireroot system is required for rapid recovery from drought.Copyright1999 Annals of Botany Company Agave deserti Engelm., desert, drought, gas exchange, rewetting, roots, succulent, water uptake.     

突尼斯非洲跳鼠(Jaculus jaculus)和埃及跳鼠(J.orientalis)群体的等位酶多态及遗传分化(英文)

运用16种酶蛋白编码的23个遗传座位对突尼斯非洲跳鼠(Jaculus jaculus)和埃及跳鼠(J. orientalis)自然群体的遗传变异和分化进行了电泳分析。结果表明,与其他啮齿动物等哺乳动物的相关数据比较,发现这两个种群体的遗传变异水平较低。非洲跳鼠群体的观测杂合度 (H_obs) 为0.08—0.19,多态座位百分比(P)为26.2%—45.2%,每个座位的平均等位基因数(A)为1.1—1.4;埃及跳鼠的H_obs为0.10—0.15,P为29.3%—44.1%,A为1.1—1.7。两个种群体各自的遗传分化程度较低(非洲跳鼠和埃及跳鼠的F_st分别为0.0017和0.0019)。而两个种群体间的F_st为0.607（P<0.05）,表明两个种之间高度的遗传分化。本研究支持这两个种分类地位的合法性,并强调了地理因素（环境类型和生物气候阶段）对两个种遗传结构的影响。     

Are cryptic species of the Lesser Egyptian Jerboa,Jaculus jaculus (Rodentia,Dipodidae), really cryptic? Re‐evaluation of their taxonomic status with new data from Israel and Sinai

Two clades of the lesser Egyptian jerboa Jaculus jaculus sensu lato were recently described in North Africa and considered as cryptic species. Members of both clades are also found in Israel, where they can be easily identified according to fur and tail colouration and morphology of the male external genitalia, but cannot be separated confidently using skull characters. Examination of type specimens demonstrated that the correct names for the two species are Jaculus jaculus (Linnaeus 1758) and Jaculus hirtipes (Lichtenstein, 1823). Comparisons of geographic and habitat differences of the two species revealed a high niche divergence between them, slightly higher in the sympatric North African populations than in the parapatric populations of Israel and Sinai. A low niche divergence was detected between North African and Middle Eastern populations of J. jaculus, and a low niche convergence between North African and Middle Eastern populations of J. hirtipes. The levels of niche differentiation coincide with those of genetic differences.     

Responses of atrial natriuretic peptide and other fluid regulating hormones to long distance swimming in the sea

The plasma hormonal response following a swimming competition in the sea (18 km) was evaluated in 12 top level male endurance swimmers. At the end of the effort, while plasma renin activity (PRA) and aldosterone concentration (ALDO) were unchanged, a significant increase in plasma atrial natriuretic peptide (ANP) and antidiuretic hormone (ADH) concentrations were recorded. These changes were associated with a decrease in haematocrit and an increase in Na⁺ and Cl^– plasma concentrations. The individual variations of ANP (difference between the final and initial concentrations) were inversely correlated with the corresponding individual variations of PRA and ADH. The results suggest that, during prolonged swimming, ANP may exert an inhibitory effect on the PRA-ALDO axis and have a modulatory role with regard to ADH secretion.     

Evaluation by capacitance measurements of antidiuretic hormone induced membrane area changes in toad bladder

A technique for estimating effective transepithelial capacitance in vitro was used to investigate changes in epithelial cell membrane area in response to antidiuretic hormone (ADH) exposure in toad bladder. The results indicate that transepithelial capacitance increases by about 30% within 30 min after serosal ADH addition and decreases with ADH removal. This capacitance change is not blocked by amiloride and occurs whether or not there is a transepithelial osmotic gradient. It is blocked by methohexital, a drug which specifically inhibits the hydro-osmotic response of toad bladder to ADH. We conclude that the hydro-osmotic response of toad bladder to ADH is accompanied by addition of membrane to the plasmalemma of epithelial cells. This new membrane may contain channels that are permeable to water. Stimulation of Na⁺ transport by ADH is not related to membrane area changes, but appears to reflect activation of Na⁺ channels already present in the cell membrane before ADH challenge.     

Growth establishment and phenology of four woody Saharan species

Henophyton deserti, Calligonum polygonoides, Ephedra alata and Anthyllis henoniana may be suitable Saharan species for the rehabilitation of degraded lands. In this context, the phenology, excavation of root systems and seedling establishment of these species were investigated in the southern Tunisia. Our data suggest that phenological differences between the studied species may depend on the rooting depth. The mean seedling emergence rate was 73% in H. deserti, 66% in A. henoniana, 60% in C. polygonoides and 50% in E. alata. Statistical analyses of seedling establishment showed a highly significant difference among the four species in both seasons (F = 1595.15, P < 0.0001), species (F = 781.57, P < 0.0001) and species/season interaction (F = 61.84, P < 0.0001). After 3 years, seedling mortality ranged from 73% to 89%. Seedling mortality reached a maximum in the summer of the first year of study (P < 0.001). This study provided further understanding of the ecological tolerance, adaptive strategy and the low density of these species in nature. Henophyton deserti appears to be better adapted to the harsh desert environment. These findings explain the very high density observed in the Sahara compared with other studied species. This species has therefore proven to be an excellent candidate for the ecological restoration of degraded desert rangelands and can be introduced successfully in to rehabilitation programmes.     

Isolation and characterization of specialized regions of toad urinary bladder apical plasma membrane involved in the water permeability response to antidiuretic hormone

Summary Antidiuretic hormone (ADH) increases the apical (external facing) membrane water permeability of granular cells that line the toad urinary bladder. In response to ADH, cytoplasmic vesicles called aggrephores fuse with the apical plasma membrane and insert particle aggregates which are visualized by freeze-fracture electron microscopy. Aggrephores contain particle aggregates within their limiting membranes. It is generally accepted that particle aggregates are or are related to water channels. High rates of transepithelial water flow during ADH stimulation and subsequent hormone removal decrease water permeability and cause the endocytosis of apical membrane and aggrephores which retrieve particle aggregates. We loaded the particle aggregate-rich endocytic vesicles with horseradish peroxidase (HRP) during ADH stimulation and removal. Epithelial cells were isolated and homogenized, and a subcellular fraction was enriched for sequestered HRP obtained. The HRP-enriched membrane fraction was subjected to a density shifting maneuver (Courtoy et al.,J. Cell Biol. 98:870, 1984), which yielded a purified membrane fraction containing vesicles with entrapped HRP. The density shifted vesicles were composed of approximately 20 proteins including prominent species of 55, 17 and 7 kD. Proteins of these molecular weights appear on the apical surface of ADH-stimulated bladders, but not the apical surface of control bladders. Therefore, we believe these density shifted vesicles contain proteins involved in the ADH-stimulated water permeability response, possibly components of particle aggregates and/or water channels.     

Role of substance P in water homeostasis.

The effect of the naturally occurring peptide substance P on release of antidiuretic hormone (ADH) was studied in anesthetized dogs. Intravenous infusions of substance P in doses of 0.5, 5.0, and 50 ng/kg/min increased plasma concentrations of ADH in a dose-related fashion. At the two low doses, this increase occured in the absence of changes in urine volume, sodium excretion, free water clearance, and urinary cyclic AMP excretion. In addition, when substance P was administered in a concentration of 0.5 ng/kg/min, plasma levels of ADH were increased even though blood pressure did not change, suggesting that substance P may release antidiuretic hormone by a direct mechanism. Intrarenal infusions at a rate of 0.5 and 5 ng/kg/min caused dose-related decreases in free water clearance and significant increases in urinary cyclic AMP excretion. These data suggest that substabce P may play an important role in the regulation of water balance.     

Influence of season on plasma antidiuretic hormone, angiotensin II, aldosterone and plasma renin activity in young volunteers

We investigated seasonal changes in hormonal and thermoregulatory responses. Eight volunteers were subjected to the experiment at four times of the year: around the vernal and autumnal equinoxes, and at the summer and winter solstices at latitude 35° N. Plasma antidiuretic hormone (ADH), angiotensin II (ANG II), aldosterone (ALD) and plasma renin activity (PRA) were analyzed before and after water immersion. Seasonal changes in thermoregulatory responses were assessed by measuring core temperature and sweat rate during immersion of the leg in hot water (at 42°C) for 30 min in a room maintained at 26°C. The concentration of plasma ADH and ALD before water immersion was significantly higher in summer than in other seasons. The concentrations of ANG II and PRA did not show seasonal variations. Changes in tympanic temperature during water immersion showed significant differences between seasons, and were higher in winter than in other seasons. The sweat rate was significantly higher in summer than in other seasons. In summary, ADH and ALD concentrations displayed a seasonal rhythm with marked elevation in summer; this may be a compensative mechanism to prevent dehydration from increased sweat loss during summer due to heat acclimatization.     

The comparative gastrointestinal morphology of Jaculus jaculus (Rodentia) and Paraechinus aethiopicus (Erinaceomorpha)

Jaculus jaculus (Lesser Egyptian jerboa) and Paraechinus aethiopicus (Desert hedgehog) are small mammals which thrive in desert conditions and are found, among others, in the Arabian Peninsula. Jaculus jaculus is omnivorous while P. aethiopicus is described as being insectivorous. The study aims to describe the gastrointestinal tract (GIT) morphology of these animals which differ in diet and phylogeny. The GITs of J. jaculus (n = 8) and P. aethiopicus (n = 7) were weighed, photographed, and the length, basal surface areas, and luminal surface areas of each of the anatomically distinct gastrointestinal segments were determined. The internal aspects of each area were examined and photographed while representative histological sections of each area were processed to wax and stained using haematoxylin and eosin. Both species had a simple unilocular stomach which was confirmed as wholly glandular on histology sections. Paraechinus aethiopicus had a relatively simple GIT which lacked a caecum. The caecum of J. jaculus was elongated, terminating in a narrow cecal appendix which contained lymphoid tissue on histological examination. The internal aspect of the proximal colon of J. jaculus revealed distinct V‐shaped folds. Stomach content analysis of J. jaculus revealed mostly plant and seed material and some insects, whereas P. aethiopicus samples showed plant material in addition to insects, indicating omnivorous feeding tendencies in areas where insects may be scarce. J. Morphol. 277:671–679, 2016. © 2016 Wiley Periodicals, Inc.     

Quantitative analysis of the structural events associated with antidiuretic hormone-induced volume reabsorption in the rabbit cortical collecting tubule

Summary We quantitatively examined the influence of antidiuretic hormone (ADH)-dependent volume reabsorption on the morphology of the rabbit cortical collecting tubule. Estimates of cell volume and the geometry of the lateral intercellular spaces were extracted from differential interference contrast images of perfused nephron segments using the morphometric procedures described in the preceding paper (K.L. Kirk, D.R. DiBona and J.A. Schafer,J. Membrane Biol. 79:53–64, 1984). The results indicate that ADH addition in the presence, but not absence, of a lumen-to-bath osmotic gradient (130 to 290 mOsm) stimulated transepithelial volume flow and simultaneously increased the volumes of both the cells (+28%) and the lateral intercellular spaces (+78%). In addition, the formation of cytoplasmic vacuoles could be observed during the latter stages of the swelling response, and vacuole formation continued well after new steadystate values for transepithelial water flow and cell volume had been reached. Two main conclusions can be drawn from these results. First, the cytoplasmic vacuoles comprise a slowly filling compartment that lies in parallel to the transepithelial pathway for ADH-stimulated volume reabsorption. Second, from the magnitude of the cell volume increase, we estimate that the hydraulic conductivities of the opposing cell membranes are nearly equal during maximal ADH stimulation.