The structure of mast cell secretory granules in the blind mole rat (Spalax ehrenbergi)

Eosinophils, basophils, and mast cells produce and secrete active substances whose role is to attack invading parasites and protect the host. In this study we use morphometric methods to study mast cells in the blind mole rat (Spalax ehrenbergi). The subterranean and solitary way of life of this species has led to the evolutionary development of special anatomical, morphological, behavioral, and physiological adaptations. Because of its particular lifestyle, the mole rat is less exposed to parasites than other rodents. This could provide a unique model for research into the pathobiology of mast cells. The paracrystalline structure of the mast cell granule content is composed of parallel plates. Diffraction analysis of electron micrographs of thin sections of araldite-embedded tissues indicated that each crystal line plate is a periodic array of parallelograms. The crystal unit cell volume is approximately 930 nm(3), suggesting that each unit cell is composed of one heparin molecule and one to three additional adsorbed proteins. Morphometric data show that characteristics of the secretory granules of mast cells of the blind mole rat resemble those of other rodents. The mast cell unit granule volume in the present study was calculated to be 0.055 microm(3), similar to that of rat peritoneal mast cells.     

Aggression patterns in three chromosome forms of the mole rat, Spalax ehrenbergi.

Three chromosome forms of the mole rat, Spalax ehrenbergi, 2n = 52, 2n = 58 and 2n = 60 were studied in an especially designed apparatus which simulated a natural territorial situation by permitting the animal free movement into and out of its home cage. Observed were variables representing agonistic, conflict and territorial behaviour. The data were analysed by means of a Smallest Space Analysis, SSA-II, which gave a graphic portrayal of the interrelations of behaviour categories where differences between means of single traits had been of no significance. 2n = 52 animals were found to be 'losers' in encounters. 'Lose', 'win' and 'draw' could be characterized by specific behaviour patterns: each outcome of encounter was surrounded by a cluster of behaviour categories consisting of agonistic, conflict and territorial activities that characterized its region of the SSA space.     

The amino-acid sequence of pancreatic ribonuclease from the mole rat Spalax ehrenbergi, chromosomal species 2n = 60

The amino-acid sequence of pancreatic ribonuclease from the chromosomal species of Spalax ehrenbergi with karyotype 2n = 60 was determined. From the comparison of the sequence with other mammalian sequences we found that Spalax diverged from the myomorph rodent branch before the divergence of the Muridae and the Cricetidae. All myomorph rodent sequences evolved faster than those of other mammals, an effect being most pronounced for the rat sequence. Spalax ribonuclease shares several amino-acid residues with other myomorph rodent species. These are not or only rarely observed outside this rodent suborder. However, there are 6 amino-acid replacements not observed earlier in pancreatic ribonucleases, and 2 other replacements and an insertion of one residue in the variable loop 15-24 are only observed in the enzyme from turtle pancreas.     

Hypoxic survival differs between two mole rat species (Spalax ehrenbergi) of humid and arid habitats.

1. Two chromosomal species, 2n = 52 and 2n = 60 of the mole rat superspecies (Spalax ehrenbergi), occupy humid (2n = 52) and arid (2n = 60) habitats in Israel. 2. Gas conductivity of the soil of the 2n = 52 mole rat is lower than that of the 2n = 60 mole rat, and the 2n = 52 mole rat is better adapted to hypoxia. 3. The hypothesis that the 2n = 52 mole rat can survive to a lower pO2 than the 2n = 60 mole rat was tested. 4. Terminal pO2 (Torr) of four females 2n = 52 was lower, 18.0 +/- 2.9 (SD), than the terminal pO2 of five females 2n = 60, 28.2 +/- 5.1 (SD). 5. The hypoxic survival of the 2n = 52 mole rat as compared to that of the 2n = 60 mole rat correlates with other physiological traits: breathing and heart frequencies, blood hemoglobin and tissue gas tensions.     

Synaptonemal complex analysis of mole rats (Spalax ehrenbergi): unusual polymorphisms of chromosome 1

Two unusual structural polymorphisms in the largest chromosomal pair of the Israeli mole rat, Spalax ehrenbergi, were analyzed from surface-spread and silver-stained preparations of synaptonemal complexes. A C-band negative polymorphism for the length of the 1p arm was visible as axial length differences during late zygonema and early pachynema. This region underwent synaptic adjustment resulting in a fully paired, mid-pachytene synaptonemal complex with equalized axial lengths. The somatically variable and nonargentophilic secondary constriction in the 1q arm was evident as a distinct silver-stained thickening along the synaptonemal complex. Presence of this structure on the synaptonemal complex varied both among individuals and among cells within individuals. The intraindividual variation of this region is hypothesized to represent differential biochemical activity with its cellular visualization being regulated in a manner similar to that of nucleolus organizer regions.     

Adaptive variation of pelage color within and between species of the subterranean mole rat (Spalax ehrenbergi) in Israel

Summary Color notations of dorsal pelage were analyzed in 451 adult subterranean mole rats, comprising 19 populations and 4 chromosomal species (2n=52, 54, 58 and 60) of the Spalax ehrenbergi superspecies in Israel. In addition, the color notations of soil samples from the collection sites were measured. In an attempt to evaluate the degree of correlation between pelage color of mole rats and the local soil color, each color was compared both macro- and microgeographically. The macrogeographic comparisons were among populations of the 4 chromosomal species, and the microgeographic comparisons were among pairs of geographically neighboring subpopulations which occur under similar climatic conditions but differ in soil type and color. The results indicate that 1. no differences in pelage color notation exist between the sexes; 2. pelage of mole rats is generally characterized by an over-all grayish color, but its shades vary regionally and locally in accordance with varying soil color; 3. a positive correlation was found between pelage and local soil colors in the macrogeographic analysis and this correlation was verified in a microgeographic comparison; 4. specimens from populations of the northern chromosomal species (2n=52, 54) mainly inhabit terra rossa and basalt soils, respectively, with reddish brown tones, and they tend to have a more reddish shade, whereas animals from the central species (2n=58), which inhabits mainly dark soils including alluvial clays, terra rossa and brown rendzina and the souther species 2n=60, which occurs mainly in light soil types such as pale rendzina, sandy loams and loess, tend to have a more yellowish shade. The general appearance of specimens from 2n=58 was dark gray while that of 2n=60 specimens was light gray; 5. mole rats living in xeric environments (particularly 2n=60, but also 2n=54) are lighter than those which live in mesic environments (2n=52, 58). The results support the conclusion that pelage color of strictly subterranean mole rats is subject to selection pressures of overground predation of disharmonious types with their background soil color. The possibility that the pelage color variation and patterns also contributes to better thermoregulation while mole rats are above ground is discussed.     

Mole rat hemoglobin: primary structure and evolutionary aspects in a second karyotype of Spalax ehrenbergi, Rodentia, (2n = 52)

The hemoglobins of the four karyotypes of Spalax ehrenbergi (2n = 52, 54, 58, 60) did not show any differences in their electrophoretic pattern and in high performance liquid chromatography. The complete amino-acid sequence of mole rat hemoglobin (Spalax ehrenbergi), chromosome species 2n = 52, is presented. It was elucidated by automatic Edman degradation of the chains, the tryptic peptides, and the C-terminal peptide obtained by acid hydrolysis of the Asp-Pro bond in beta-chains. The alpha- and beta-chains are identical with those of the chromosome species 2n = 60. A comparison of the hemoglobins of mole rat, mouse, and other rodents shows homology but no indication of adaptation to subterranean life. In all probability alpha 11(A9)Arg and alpha 120(H3)Gly, unique in mole rat among all mammalian hemoglobins, are not involved in high oxygen affinity. The construction of a phylogenetic tree by the maximum parsimony method, based on hemoglobin sequences, made it possible to show that Rodentia originated as a monophyletic clade, and to find the phylogenetic relationship of Spalacidae to other Rodentia (Mus, Rattus, Ondatra, Mesocricetus, Citellus, and Cavia). Among all rodents the slowest rate of nucleotide replacements occurred in the lineage to Spalax (20%) and the fastest in the lineage to Cavia (59%).     

Evolution of crystallins: expression of lens-specific proteins in the blind mammals mole (Talpa europaea) and mole rat (Spalax ehrenbergi)

The mole (Talpa europaea; Insectivora) and the mole rat (Spalax ehrenbergi; Rodentia) both have degenerated eyes as a convergent adaptation to subterranean life. The rudimentary eye lenses of these blind mammals no longer function in a visual process. The crystallin genes, which display a lens-specific expression pattern, were studied in these blind mammals and in related species with normal eyes by hybridizing their genomic DNAs with probes obtained from cDNA clones for alpha A-, alpha B-, and beta Bp-crystallins from calf and gamma 3- crystallin from the rat. For all crystallin genes examined, the hybridization signals of mole and mole rat genomic DNA were comparable, respectively, with those of shrew and of rat and mouse, normal-vision representatives of the orders Insectivora and Rodentia. The expression of the crystallins at the protein level was tested by using antiserum specific for alpha-crystallin in immunofluorescence reactions on lens sections of mole and mole rat eyes and by using antisera against the beta- and gamma-crystallins on sections of the mole eye. All antisera gave positive fluorescence reactions exclusively with lens tissue of these blind mammals, indicating that the crystallins are still normally expressed despite the fact that these lenses have had no function in a visual process in these mammals for at least many million years. These findings apparently imply that some unknown selective advantage has conserved the crystallin genes and their expression after the loss of normal function of the lenses.      

The pineal gland of the mole-rat (Spalax ehrenbergi,Nehring)

Summary A comparative investigation of the distribution of monoaminergic neurons in non-malacostracan crustaceans was performed with the histochemical fluorescence method of Falck-Hillarp.Two fluorophores were found: the more widespread of the two emits a green fluorescence; and the more sparsely distributed emits a yellow to brown-yellow fluorescence.Specific green fluorescent areas were shown to exist in the protocerebrum. The central body and the optic ganglia of the compound eye (where present) are always fluorescent. Moreover, the centre of the nauplius eye may have a green fluorophore, as in ostracods, and a neuropile area, here called the frontal area. These neuropile centres are known from ordinary histological studies of the nervous system. In addition, there are specific monoaminergic centres, such as the so-called dorsal area of phyllopods and anostracans as well as the copepod specific areas. Specific monoaminergic areas appear in the deutocerebrum and the suboesophageal ganglion where they are particularly well developed.Presumed sensory neurons in the cavity receptor organ of Artemia salina are shown to be monoaminergic. Monoaminergic sensory neurons have not been described previously in Arthropods.Presumed motor innervation of hind-gut and trunk muscles is also found, and it is concluded that in crustaceans neurons of every type (sensory, internuncial, motor) may be monoaminergic.We have enjoyed unrestricted laboratory facilities at the Department of Histology, Faculty of Medicine, and with great pleasure express our sincere thanks to Prof. Bengt Falck. — Grants from the Swedish Natural Science Research Council (2760-007), the Swedish Medical Research Council (04X-712), the Royal Swedish Academy of Science (Hierta-Retzius), the Royal Physiographic Society of Lund, and the University of Lund supported the work.     

Burrow patterns of the mole rat Spalax ehrenbergi in two soil types (terra-rossa and rendzina) in Mount Carmel, Israel

Complete burrow systems of the mole rat Spalax ehrenbergi (Rodentia; Spalacidae), from two sites on Mount Carmel in Israel, with different soil types (terra-rossa and rendzina), were excavated and described here for the first time.
A comparison was made of burrow structure patterns in the two soils and of the sexes, with special attention to the features of the feeding tunnels.
The pattern in the rendzina revealed longer burrows with a longer main tunnel and fewer branches per metre of the main tunnel, while the pattern in the terra-rossa revealed shorter burrows with a shorter main tunnel and a relatively higher number of branches. These differences can primarily be related to the different levels of food availability, which is higher in the terra-rossa. It is suggested that each of the patterns reflects the mole rat's ability to optimize foraging efficiency in accordance with its given food availability.
The average total length of the males' burrows was much greater than those of the females' burrows in the rendzina soil. It appears that food requirements determine different burrow features of the sexes rather than reproduction requirements.
Other tunnel features (e.g. structural complexity, depth and width, segment length and spatial arrangement) and the factors which may affect them, as well as burrow structure of young mole rats and evidence of the underground dispersion of young mole rats, were presented and discussed.
Many similarities were found in a comparison of S. ehrenbergi burrow features with those of other solitary subterranean rodents.     

Photoperiod perception in the blind mole rat (Spalax ehrenbergi, Nehring): involvement of the Harderian gland, atrophied eyes, and melatonin

The involvement of the Harderian gland, atrophied eyes, and melatonin in the perception of photoperiodic changes has been studied in the mole rat, a fossorial blind mammal the thermoregulatory capacity of which is photoperiod-dependent. When transferred from a long photoperiod to a short one, mole rats increase their resistance to cold, a perfectly reversible phenomenon. After 2 weeks under short photoperiod the thermoregulatory capacities of animals without Harderian glands are less than those of the controls. The Harderian gland appears thus to be implicated in the detection of photoperiodic changes. After 5 weeks, however, the Harderianectomized animals had perfectly integrated the photoperiodic change, so demonstrating that other photoreceptor organs exist. The atrophied eyes, which, under these conditions, do not seem to play an important role, are involved when the animals are transferred from short photoperiod to long photoperiod. Melatonin, but not 5-methoxytryptamine, appears to be a crucial compound in such a phenomenon. These results, which demonstrate that in mammals (at least in the mole rat, as in nonmammalian vertebrates), nonocular photoreceptors exist, suggest that the mechanism by which mammals integrate photoperiodic changes is not the same when the animals are transferred from long to short photoperiod as when transferred from short photoperiod to long photoperiod.     

Speciation and adaptive radiation of subterranean mole rats, Spalax ehrenbergi superspecies, in Jordan

The major initial mechanism of speciation in subterranean blind mole rats, Spalacidae, is chromosomal, primarily through Robertsonian rearrangements. Here we highlight another scenario of chromosomal rearrangement leading to ecological speciation and adaptive radiation apparently initiated by pericentric inversions and genie divergence to different ecologies in mole rats in Jordan. We analysed karyotype, allozyme, size and ecological diversity across the range of mole rats in Jordan from mesic Irbid in the north to xeric Wadi Musa (Petra region) in the south, a transect of 250 km. We examined mole rats for chromosome ( N =71), size ( N =76), and allozyme ( N =67) diversities, encoded by 32 loci, in 12 populations of the Spalax ehrenbetgi superspecies in Jordan. By a combination of chromosome morphology, genetic distance, body size and ecogeography, we identified four new putative biological species. All species (except two animals in Madaba) share 2 n = 60 but vary in chromosome morphology, caused by pericentric inversions and/or centromeric shifts. The 'north Moav' species is karyotypically polymorphic for 2 n (2 n = 60; including locally also two animals with 2 n = 62). The distribution of the four species is associated with ecogeographical different domains and climatic diversity. Genetic diversity indices were low, but like chromosome arms (NFa) were positively correlated with aridity stress. Discriminant analysis correctly classified 91% of the individuals into the four species utilizing combinatorially chromosome, allozyme and size diversities. It is hypothesized that mole rat evolution underground is intimately associated with climatic diversity stress above ground.     

Effect of photoperiod variation on testes and accessory sex organs in the male blind mole rat Spalax ehrenbergi

The blind mole rat is a seasonally breeding fossorial rodent that is perceptionally blind. This study examines the effect of photoperiod on the morphology and histology of the male mole rat reproductive system, three groups of male mole rats were maintained in the laboratory under short day (SD) conditions (9L: 15D); long day (LD) conditions (15L:9D); and constant darkness (CD), and compared to animals trapped in the field (FL). It was found that the field animals revealed higher testes and prostate gland weights, higher prostate tubuli volume (v*) and lower testes tubuli volume (v*) compared to the other three groups. Distribution of the tubuli in the testes (Vv) was low in the FL group compared to the SD and LD groups but still higher than in the CD group. Distribution of lumen in the testes (Vv) was higher in the CD group in comparison to the other three groups. Distribution of interstitial tissue in the testes (Vv) was higher in the FL group than in the other three groups. Electrolytes and elements secreted from the prostate gland did not differ among the four groups. In the FL group distribution of the tubuli (Vv) in the prostate gland was low and lumen ratio (Vv) was high compared to the other three groups. Distribution of connective tissue in the prostate gland did not differ among all four groups. Testosterone levels and total sperm count was highest in the FL group. Sperm production was noted in all groups; however spermatid and spermatozoa cell production was higher in the FL group. This study shows that photoperiod could be important in initiating timing in the breeding season but that certain other conditions which are absent in the laboratory appear to be responsible for successful breeding in the field.     

Adaptive hypoxic tolerance in the subterranean mole rat Spalax ehrenbergi: the role of vascular endothelial growth factor.

Spalax ehrenbergi has evolved adaptations that allow it to survive and carry out normal activities in a highly hypoxic environment. A key component of this adaptation is a higher capillary density in some Spalax tissues resulting in a shorter diffusion distance for oxygen. Vascular endothelial growth factor (VEGF) is an angiogenic factor that is critical for angiogenesis during development and in response to tissue ischemia. We demonstrate here that VEGF expression is markedly increased in those Spalax tissues with a higher capillary density relative to the normal laboratory rat Rattus norvegicus. Upregulation of VEGF thus appears to be an additional mechanism by which Spalax has adapted to its hypoxic environment.     

The myoglobin of rodents:Lagostomus maximus (viscacha) andSpalax ehrenbergi (mole rat)

The primary sequences of the myoglobins of two rodents (the South American viscacha and the Mediterranean mole rat) have been determined. Both myoglobins exhibit one polymorphism. The two rodent sequences have been compared with each other and with other known myoglobins. The myoglobin of the viscacha is similar to those of the diving mammals and penguin in having a high arginine content. Among mammalian sequences, the arginines at positions 77 (in one of the viscacha myoglobins) and 79 have been found only in the myoglobin from viscacha. Mole rat myoglobin has a lysine at position 31, where arginine or serine is found in all other known vertebrate myoglobins.     

DNA sequence variation in the mitochondrial control region of subterranean mole rats,Spalax ehrenbergi superspecies,in Israel

The complete mitochondrial control region was sequenced for 60 individuals representing different populations for each of the four species of the subterranean mole rat Spalax ehrenbergi superspecies in Israel: Spalax galili (2n = 52), S. golani (2n = 54), S. carmeli (2n = 58), and S. judaei (2n = 60). The control region of all species and populations is very similar both in length (979 to 983 bp) and in base composition. As in agreement with previous surveys on mitochondrial control regions on mammals, the mole rat control region can be divided into a central domain and two flanking domains, ETAS (extended termination associated sequences) and CSB (conserved sequence blocks). Along with the common conserved blocks found in these domains (ETAS1, ETAS2, CSB1, CSB2, and CSB3), we have also detected in all individuals an ETAS1-like and a CSB1-like element, both in the ETAS domain. The most conserved region was the central domain, followed by the CSB and ETAS domains, showing important differences in the four species analyzed. Phylogenetic analysis supported the existence of two clades. One clade contained individuals belonging to Spalax galili (2n = 52) and S. golani (2n = 54), separated in two different branches depending on the species. The other clade contained individuals belonging to S. carmeli (2n = 58) and S. judaei (2n = 60) mixed together, suggesting a more recent event of speciation. Within species we have observed a southward trend of increasing variability. These results have been explained as a consequence of the adaptation of the species to ecological factors such as aridity and temperature stresses.